L6924U Datasheet by STMicroelectronics

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This is information on a product in full production.
January 2019 DocID14716 Rev 4 1/41
L6924U
USB compatible battery charger system
with integrated power switch for Li-Ion/Li-Polymer
Datasheet
-
production data
Features
Fully integrated solution, with power MOSFET,
reverse blocking diode, sense resistor, and
thermal protection
Charges single-cell Li-Ion batteries from
selectable AC adapter or USB input
Programmable charge current up to 1 A in AC
adapter mode
Programmable charging current in USB mode
for both high-power and low-power inputs
4.2 V output voltage with ± 1% accuracy
Linear or quasi-pulse operating mode
Closed-loop thermal control
Programmable end-of-charge current
Programmable charge timer
(NTC) or (PTC) thermistor interface for battery
temperature monitoring and protection
Status outputs to drive LEDs or to interface
with a host processor
Small VFQFPN 16-lead package (3x3 mm)
Applications
GPS and MP3 players
USB-powered devices
Digital still cameras
Standalone chargers
Wireless appliances
VFQFPN16
Table 1. Device summary
Order code Package Packing
L6924UTR VFQFPN16 Tape and reel
www.st.com
Contents L6924U
2/41 DocID14716 Rev 4
Contents
1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6 Operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Linear mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2 Quasi-pulse mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7 Application information: charging process . . . . . . . . . . . . . . . . . . . . . 17
7.1 Pre-charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2 AC or USB mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.3 Fast charge phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.4 End-of-charge current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.5 Recharge flow chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.6 Recharge threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.7 Maximum charging time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8 Application information: monitoring and protection . . . . . . . . . . . . . . 23
8.1 NTC thermistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.2 Battery absence detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.3 Status pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.4 Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
9 Additional application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.1 Selecting the input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
9.2 Selecting the output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
DocID14716 Rev 4 3/41
L6924U Contents
41
9.3 Battery floating voltage setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.3.1 Battery floating voltage: V
FLOAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.4 Layout guidelines and demonstration board . . . . . . . . . . . . . . . . . . . . . . 32
10 Application idea: dual input management with AC priority . . . . . . . . 36
11 Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1 VFQFPN16 package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
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Description L6924U
4/41 DocID14716 Rev 4
1 Description
The L6924U is a fully monolithic battery charger that safely charges single-cell Li-
Ion/Polymer battery from either a USB power source or an AC adapter. In USB mode, the
L6924U supports both low-power and high-power mode. Alternatively the device can charge
from an AC wall adapter. The ideal solution for space-limited portable products integrates
the power MOSFET, reverse blocking diode, sense resistor and thermal protection into a
compact VFQFPN16 package. When an external voltage regulated adapter or USB port is
used, the L6924U works in linear mode, and charges the battery in a constant current
constant voltage (CC/CV) profile. Moreover, when a current-limited adapter is used, the
device can operate in quasi-pulse mode, dramatically reducing the power dissipation.
Regardless of the charging approach, a closed-loop thermal control avoids device
overheating. The device has an operating input voltage ranging from 2.5 V to 12 V and it
allows the user to program many parameters, such as fast-charge current, end-of-charge
current threshold, and charge timer. The L6924U offers two open collector outputs for
diagnostic purposes, which can be used to either drive two external LEDs or communicate
with a host microcontroller. Finally, the L6924U also provides other features like gas gauge
function, checks for battery presence, and monitors and protects the battery from unsafe
thermal conditions.
Figure 2. Basic application schematic
Figure 1. Minimum size application board
VIst STZ STl IAC IUSB MODE IEN‘D UUUU JUUL- fl flflflfl TPRC GND SD TH REF VOUT VOSNS ISEL
DocID14716 Rev 4 5/41
L6924U Pin description
41
2 Pin description
Figure 3. Pin connections (top view)
2.1 Pin description
Table 2. Pin functions
Pin I/O Name Pin description
1IV
IN
Input pin of the power stage.
2IV
INSNS
Supply voltage pin of the signal circuitry.
The operating input voltage ranges from 2.5 V to 12 V, and the
start-up threshold is 4 V.
3 - 4 O ST
2
-ST
1
Open-collector status pins.
5IT
PRG
Maximum charging time program pin.
It must be connected with a capacitor to GND to fix the maximum
charging time, see Section 7.7: Maximum charging time.
6 - GND Ground pin.
7ISD
Shutdown pin.
When connected to GND enables the device; when floating
disables the device.
8ITH
Temperature monitor pin.
It must be connected to a resistor divider including an NTC or PTC
resistor. The charge process is disabled if the battery temperature
(sensed through the NTC or PTC) is out of the programmable
temperature window see Section 8.1: NTC thermistor.
Pin description L6924U
6/41 DocID14716 Rev 4
Pin I/O Name Pin description
9 I ISEL
Switches between high power USB (I
USB
up to 500 mA) and low
power USB (I
USB/5
) in USB mode. A low level sets the L6924U in
low power mode and a high level sets the L6924U in high power
mode. When the AC mode is selected, the ISEL pin must be
connected to ground or left floating.
10 I V
OSNS
Output voltage sense pin.
It senses the battery voltage to control the voltage regulation loop.
11 O V
OUT
Output pin. (connected to the battery)
12 O V
REF
External reference voltage pin. (reference voltage is 1.8 V ± 2%)
13 I/O I
END
Charge termination pin.
A resistor connected from this pin to GND sets the charge
termination current threshold I
ENDTH
: if I
CHG
< I
ENDTH
, the charge
process ends. The voltage across the resistor is proportional to the
current delivered to the battery (gas gauge function).
14 I MODE
Selects pin AC adapter or USB port input modes. A high level sets
the L6924U in USB mode while a low level sets the L6924U in the
AC adapter mode. When the AC adapter input is selected, the ISEL
pin status does not affect the current set.
15 I I
USB
Charge current program pin in USB mode: a resistor connected
from this pin to ground sets the fast charge current value (I
USB
up
to 500 mA) with an accuracy of 7%. The USB high power/low
power mode is selected with the ISEL pin.
16 I I
AC
Charge current program pin in AC mode: a resistor connected from
this pin to GND sets the fast charge current value (I
AC
up to 1 A)
with an accuracy of 7%.
Table 2. Pin functions (continued)
DocID14716 Rev 4 7/41
L6924U Maximum ratings
41
3 Maximum ratings
Stressing the device above the rating listed in the “absolute maximum ratings” table may
cause permanent damage to the device. These are stress ratings only and operation of the
device at these or any other conditions above those indicated in the operating sections of
this specification is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability. Refer also to the STMicroelectronics sure
program and other relevant quality documents.
Table 3. Absolute maximum ratings
Symbol Parameter Value Unit
V
IN
Input voltage -0.3 to 16 V
V
INSNS
, SD Input voltage -0.3 to V
IN
V
V
OUT
, V
OSNS
Output voltage -0.3 to 5 V
ISEL, MODE Input voltage -0.3 to 6 V
ST1, ST2 Output voltage -0.3 to V
IN
V
Output current 30 mA
V
REF
, TH, I
END
,
I
AC
, I
USB
,
T
PRG
,
GND -0.3 to 4 V
All pins Maximum withstanding voltage range test condition:
CDFAEC-Q100-002- “human body model”
acceptance criteria: “normal performance’ ± 2 kV
Table 4. Thermal data
Symbol Parameter Value Unit
R
thJA
Thermal resistance junction to ambient
(1)
1. Device mounted on demonstration board
75 °C/W
T
STG
Storage temperature range - 55 to 150 °C
T
J
Junction temperature range - 40 to 125 °C
P
TOT
Power dissipation at T = 70 °C 0.67 W
Electrical characteristics L6924U
8/41 DocID14716 Rev 4
4 Electrical characteristics
T
J
= 25 °C, V
IN
= 5 V, unless otherwise specified.
Table 5. Electrical characteristics
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
IN
(1)
Operating input voltage 2.5 12 V
Start up threshold 4.1 V
I
IN
(1)
Supply current Charging mode (R
PRG
= 24 kΩ)1.82.5mA
Shutdown mode (R
PRG
= 24 kΩ)6080µA
I
SINK
Current flowing from V
OUT
Shutdown mode (R
PRG
= 24 kΩ)500nA
Stand by mode (R
PRG
= 24 kΩ)
(V
IN
= 2.5 V < V
BATTERY
)500 nA
V
OUT
(1)
Battery regulated voltage 4.16 4.2 4.24 V
I
AC
Charge current with AC
adapter input
MODE at GND, R
PRG
= 24 kΩ450 490 525 mA
MODE at GND, R
PRG
= 12 kΩ905 975 1045 mA
I
USB
Charge current with USB
input
MODE at HIGH, ISEL at HIGH,
R
PRG-USB
= 24 kΩ450 490 525
mA
MODE at HIGH, ISEL at LOW,
R
PRG-USB
= 2 4 kΩ86 96 105
I
PRE_AC
Pre-charge current with AC
input
MODE at GND,
R
AC
= 24 kΩ41 49 56 mA
I
PRE_USB
Pre-charge current with USB
input (high power mode)
MODE at HIGH, ISEL at HIGH
R
USB
= 24 kΩ41 49 56 mA
Pre-charge current with USB
input (low power mode)
MODE at HIGH, ISEL at LOW
R
USB
= 24 kΩ7.6 9.6 11.4 mA
V
PRETH
Pre-charge voltage threshold 2.9 3.0 3.1 V
I
ENDTH
Termination current R
END
= 3.3 kΩ12 16 20 mA
T
MAXCH (2)
Maximum charging time C
TPRG
= 10 nF
R[I
PRG
] = 24 kΩ3hours
T
MAXCH (2)
Maximum charging time
accuracy C
TPRG
= 5.6n F
R
PRG
= 24 kΩ10 %
SD
TH
Shutdown threshold high 2 V
Shutdown threshold low 0.4 V
ST1,2 Output status sink current Status on 10 mA
MODE
TH
MODE threshold high 1.3 V
MODE threshold low 0.4 V
ISEL
TH
ISEL threshold high 1.3 V
ISEL threshold low 0.4 V
DocID14716 Rev 4 9/41
L6924U Electrical characteristics
41
Symbol Parameter Test condition Min. Typ. Max. Unit
R
DS(on)
Power MOSFET resistance
(3)
Charge current = 500 mA 280 380 mΩ
TH
NTC pin hot threshold
voltage 10 12.5 15 %V
REF
NTC pin cold threshold
voltage 40 50 60 %V
REF
1. T
J
from -40 °C to 125 °C
2. Guaranteed by design
3. Device working in quasi pulse mode
Table 5. Electrical characteristics (continued)
vms sn m: LDGI msa
Block diagram L6924U
10/41 DocID14716 Rev 4
5 Block diagram
Figure 4. Block diagram
OSC
BG
ANALOG
PRE.
NTC/PTC
MANAG.
VDD
VDD
VDD
VOSNS
VREF
4.2V
VREF
Logic
SD
VIN
VINS
ST1
ST2TPRG
TH
VPRE
VREF
VDD
LOGIC
BODY
CONTROL
Logic
VBG
IAC
IUSB
POWER MOS
Mos
Driver
Charge
Control CA-VA-TA
REG
UVLO
THERMAL
CONTROL
GND
Logic
IEND
Logic
VOUT
Logic Logic
I FAULT I DETECT
Gas Gauge
ISEL
MODE
DocID14716 Rev 4 11/41
L6924U Operation description
41
6 Operation description
The L6924U is a fully integrated battery charger that allows a very compact battery
management system for space limited applications. It integrates in a small package all the
power elements: power MOSFET, reverse blocking diode and the sense resistor.
It normally works as a linear charger when powered from an external voltage regulated
adapter or USB port.
However, thanks to its very low minimum input voltage (down to 2.5 V) the L6924U can also
work as a quasi-pulse charger when powered from a current limited adapter. To work in this
condition, it is enough to set the device’s charging current higher than the adapter’s one
(Section 6.2: Quasi-pulse mode). The advantage of the linear charging approach is that the
device has a direct control of the charging current and so the designer needn’t to rely on
power source. However, the advantage of the quasi-pulse approach is that the power
dissipated inside the portable equipment is dramatically reduced.
The L6924U charges the battery in three phases:
Pre-charge constant current: in this phase (active when the battery is deeply
discharged) the battery is charged with a low current (internally set to 10 % of the fast-
charge current).
Fast-charge constant current: in this phase the device charges the battery with the
maximum current (I
AC
for AC adapter mode, I
USB
for USB mode).
Constant voltage: when the battery voltage reaches the selected output voltage, the
device starts to reduce the current, until the charge termination is done.
The full flexibility is provided by:
Programmable fast-charging current (I
AC
or I
USB
) (Section 7.3: Fast charge phase).
Programmable end of charge current threshold (I
ENDTH
) (Section 7.4: End-of-charge
current).
Programmable end of charge timer (T
MAXCH
) (Section 7.7: Maximum charging time).
If a PTC or NTC resistor is used, the device can monitor the battery temperature in order to
protect the battery from operating under unsafe thermal conditions.
Beside the good thermal behavior guaranteed by low thermal resistance of the package,
additional safety is provided by the built-in temperature control loop. The IC monitors
continuously its junction temperature. When the temperature reaches approximately 120 °C,
the thermal control loop starts working, and reduces the charging current, in order to keep
the IC junction temperature at 120 °C.
Two open collector outputs are available for diagnostic purpose (status pins ST1 and ST2).
They can be also used to drive external LEDs or to interface with a microcontroller. The
voltage across the resistor connected between I
END
and GND gives information about the
actual charging current (working as a gas gauge), and it can be easily fed into a
microcontroller ADC.
Battery disconnection control is provided thanks to the differentiated sensing and forcing
output pins. A small current is sunk and forced through V
OUT
. If V
OSNS
doesn’t detect the
battery, the IC goes into a standby mode.
Figure 5 on page 12 shows the real charging profile of a Li-Ion battery, with a fast charge
current of 450 mA (R
1
or R
2
= 26 kΩ).
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Operation description L6924U
12/41 DocID14716 Rev 4
Figure 5. Li-Ion charging profile
6.1 Linear mode
When operating in linear mode, the device works in a way similar to a linear regulator with a
constant current limit protection.
It charges the battery in three phases:
Pre-charging current ("pre-charge" phase).
Constant current ("fast-charge" phase).
Constant voltage ("voltage regulation" phase).
V
ADP
is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage
of the L6924U. If the battery voltage is lower than the default pre-charge voltage (V
PRETH
),
the pre-charge phase takes place. The battery is pre-charged with a low current, internally
set to 10 % of the fast charge current.
When the battery voltage goes higher than V
PRETH
, the battery is charged with the fast
charge current (I
USB
or I
AC
according to the selection of the MODE pin).
Finally, when the battery voltage is close to the regulated output voltage (4.2 V), the voltage
regulation phase takes place and the charging current is reduced. The charging process
ends when the charging current reaches the programmed value (I
ENDTH
) or when the
charging timer expires.
Figure 6 shows the different phases.
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0.500
0 200 400 600 800 1000 1200
Charging time (sec)
Ichg (A)
0.000
0.500
1.000
1.500
2.000
2.500
3.000
3.500
4.000
4.500
Vbatt (V)
Ichg
Vbatt
DocID14716 Rev 4 13/41
L6924U Operation description
41
Figure 6. Typical charge curves in linear mode
The worst case in power dissipation occurs when the device starts the fast-charge phase. In
fact, the battery voltage is at its minimum value. In this case, there is the maximum
difference between the adapter voltage and battery voltage, and the charge current is at its
maximum value.
The power dissipated is given by the following equation:
Equation 1
The higher the adapter voltage is, the higher the power dissipated is. The maximum power
dissipated depends on the thermal impedance of the device mounted on board.
End
Charge
Voltage-Regulation
Phase
Power dissipation
Pre-Charge
Phase Fast-Charge
Phase
I
PRETH
I
CHG
V
OPRGTH
Battery Voltage
Charge Current
Adapter Voltage
V
ADP
V
PRETH
CHGBATADPDIS
IVVP ×= )(
Operation description L6924U
14/41 DocID14716 Rev 4
6.2 Quasi-pulse mode
The quasi-pulse mode can be used when the system can rely on the current limit of the
upstream adapter to charge the battery. In this case, the fast charge current must be set
higher than the current limit of the adapter. In this mode, the L6924U charges the battery
with the same three phases as in Linear Mode, but the power dissipation is greatly reduced
as shown in Figure 7.
Figure 7. Typical charge curves in quasi pulse mode
The big difference is due to the fact that the charge current is higher than the current limit of
the adapter. During the fast-charge phase, the output voltage of the adapter drops and goes
down to the battery voltage plus the voltage drop across the power MOSFET of the charger,
as shown in the following equation:
Equation 2
Adapter Voltage
Charge Current
Power dissipation
Battery Voltage
End
Charge
Voltage Regulation
Phase
Pre-Charge
Phase Fast-Charge
Phase
I
LIM
Ilim x Rdson
I
PRETH
I
CHG
V
PRETH
V
OPRGTH
V
ADP
MOSBATADPIN
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DocID14716 Rev 4 15/41
L6924U Operation description
41
Where ΔV
MOS
is given by:
Equation 3
Where,
I
LIM
= current limit of the wall adapter, and R
DS(on)
= resistance of the power MOSFET.
The difference between the programmed charge current and the adapter limit should be
high enough to minimize the R
DS(on)
value (and the power dissipation). This makes the
control loop completely unbalanced and the power element is fully turned on.
Figure 8 shows the R
DS(on)
values for different output voltages and charging currents for an
adapter current limit of 500 mA.
Figure 8. R
DS(on)
curves vs. charging current and output voltage
Neglecting the voltage drop across the charger (ΔV
MOS
) when the device operates in this
condition, its input voltage is equal to the battery one, and so a very low operating input
voltage (down to 2.5 V) is required. The power dissipated by the device during this phase is:
Equation 4
IRV
LIM)ON(DSMOS
×=
Δ
Operation description L6924U
16/41 DocID14716 Rev 4
When the battery voltage approaches the final value, the charger gets back the control of
the current, reducing it. Due to this, the upstream adapter exits the current limit condition
and its output goes up to the regulated voltage V
ADP
. This is the worst case in power
dissipation:
Equation 5
In conclusion, the advantage of the linear charging approach is that the designer has direct
control of the charge current, and consequently the application can be very simple. The
drawback is the high power dissipation.
The advantage of the quasi-pulse charging method is that the power dissipated is
dramatically reduced. The drawback is that a dedicated upstream adapter is required.
LIMBATADPDIS
I)VV(P ×=
DocID14716 Rev 4 17/41
L6924U Application information: charging process
41
7 Application information: charging process
Figure 9. Charging process flow chart
7.1 Pre-charge phase
The L6924U allows pre-charging the battery with a low current when the battery is deeply
discharged.
Application information: charging process L6924U
18/41 DocID14716 Rev 4
The battery is considered deeply discharged when its voltage is lower than a threshold
(V
PRETH
), internally set to 3 V.
During the pre-charge phase, the current (I
PRECH
) has a default value equal to 10 % of the
fast-charge current.
A safety timer is also present. If the battery voltage does not rise over V
PRETH
within this
time, a fault is given (Section 7.7: Maximum charging time).
If at the beginning of the charge process, the battery voltage is higher than the V
PRETH
, the
pre-charge phase is skipped.
7.2 AC or USB mode
The L6924U can charge batteries from both an AC adapter and USB inputs.
The power supply type can be chosen by driving the MODE pin.
A low level sets the L6924U in AC mode. The fast charge current is determined by the
resistor connected to the I
AC
pin (Section 7.3: Fast charge phase), regardless of the resistor
connected to I
USB
.
On the other hand, a high level at the MODE pin sets the L6924U in USB mode. The fast
charge current is determined by the resistor connected to the I
USB
pin (Section 7.3: Fast
charge phase), regardless of the resistor connected to I
AC
.
Figure 10. MODE pin selection
7.3 Fast charge phase
When the battery voltage reaches the pre-charge voltage threshold (V
PRETH
), the L6924U
enters the fast-charge phase.
In this phase the device charges the battery with a constant current, whose value can be set
by external resistors connected to I
AC
pin (AC adapter mode selected) or to I
USB
pin (USB
mode) with an accuracy of 7%.
In AC adapter mode (MODE pin low), the resistor R
AC
can be calculated as:
I
AC
R
AC
L6924U
MODE
AC adapter mode
R
USB
I
AC
R
AC
L6924U
MODE
USB mode
R
USB
I
USB
V
IN
I
USB
Sets the fast charge current Sets the fast charge current
I
AC
R
AC
L6924U
MODE
AC adapter mode
R
USB
I
AC
R
AC
L6924U
MODE
USB mode
R
USB
I
USB
V
IN
I
USB
Sets the fast charge current Sets the fast charge current
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DocID14716 Rev 4 19/41
L6924U Application information: charging process
41
Equation 6
Where V
BG
is the internal reference equal to 1.23 V, whereas K
PRG
is a constant equal to
9500.
Figure 11. I
AC
pin connection
In USB mode (MODE pin high), the R
USB
resistor can be selected as:
Equation 7
Where V
BG
and K
PRG
have the same meaning and value above mentioned.
The charge current in USB mode depends on R
USB
as well as the state of the ISEL pin.
When this pin is high, the “high-power” USB mode is selected and the charge current is
determined by the equation 7.
The charge current in USB mode should be set in accordance with the typical USB current
capability (up to 500 mA). If ISEL is low, the “low-power” USB mode is selected and the
charge current is a fifth of the high-power USB mode charge current (up to 100 mA)
During low power USB mode operation, since the charge current is reduced by one fifth, the
maximum charging time is proportionally increased (Section 7.7: Maximum charging time).
Figure 12. I
USB
pin connection
Regardless of the operation mode (AC adapter or USB), during the fast-charge phase the
battery voltage increases until it reaches the programmed output voltage (4.2 V). A safety
timer is also present. If the Fast-charge phase does not finish within the programmed time
(see Chapter 7.7: Maximum charging time on page 22), a fault is given.
PRG
AC
BG
AC
K
I
V
R
=
PRG
USB
BG
USB
K
I
V
R
=
END L6924U
Application information: charging process L6924U
20/41 DocID14716 Rev 4
7.4 End-of-charge current
When the charge voltage approaches the battery regulated voltage (internally set to 4.2 V),
the voltage regulation phase takes place. The charge current starts to decrease until it goes
below a programmable termination current, I
ENDTH
. This current can be selected by an
external resistor connected between the I
END
pin and GND Figure 13, whose value can be
calculated as:
Equation 8
Figure 13. I
END
pin connection
Where K
END
is 1050 and V
MIN
is 50 mV.
When the charge current goes below I
ENDTH
, after a deglitch time, the status pins notify the
end of charge and the charge process ends.
This de-glitch time is expressed as:
Equation 9
where T
MAXCH
is the maximum charging time. (Chapter 7.7 on page 22)
I
END
pin is also used to monitor the charge current, because the current injected in R
END
is
proportional to the charge current. The voltage across R
END
can be used by a
microcontroller to check the charge status like a gas gauge.
×=
ENDTH
END
MINEND
I
K
VR
E
220
MAXCH
DEGLITCH
T
T=
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DocID14716 Rev 4 21/41
L6924U Application information: charging process
41
7.5 Recharge flow chart
Figure 14. Recharge flow chart
7.6 Recharge threshold
When, from an end-of-charge condition, the battery voltage goes below the recharging
threshold (V
RCH
), the device goes back in charging state. The value of the recharge
threshold is 4.05 V.
PRG £69240 TYRG I CTPRG De \
Application information: charging process L6924U
22/41 DocID14716 Rev 4
7.7 Maximum charging time
To avoid the charging of a dead battery for a long time, the L6924U has the possibility to set
a maximum charging time starting from the beginning of the fast-charge phase. This timer
can be set through a capacitor, connected between the T
PRG
pin and GND. C
TPRG
is the
external capacitor (in nF) and is given by the following equation:
Equation 10
Note: The maximum recommended C
TPRG
value must be less than 50 nF.
Figure 15. T
PRG
pin connection
Where,
R
PRG
= resistor which sets the current (R
USB
or R
AC
)
V
REF
= 1.8 V,
K
T
= 279 x 10
5
,
V
BG
= 1.23 V, and
T
MAXCH
is the charging time given in seconds.
If the battery does not reach the end-of-charge condition before the timer expires, a fault is
issued.
Also during the pre-charge phase there is a safety timer, given by:
Equation 11
If this timer expires and the battery voltage is still lower than V
PRETH
, a fault signal is
generated, and the charge process finishes.
Note: When the device is charged in low power USB mode, in order to take into account the
reduced charge current, the maximum charging time is proportionally increased (five times
the maximum charging time calculated with R
USB
).
9
10×
×
=
REF
PRG
BG
T
MAXCH
TPRG
V
R
V
K
T
C
E
MAXCHMAXPRECH
TT ×=
8
1
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DocID14716 Rev 4 23/41
L6924U Application information: monitoring and protection
41
8 Application information: monitoring and protection
The L6924U uses a VFQFPN (3 x 3 mm) 16-pin package with an exposed pad that allows
the user to have a compact application and good thermal behavior at the same time. The
L6924U has a low thermal resistance because of the exposed pad (approximately
75 °C/W, depending on the board characteristics). Moreover, a built-in thermal protection
feature prevents the L6924U from having thermal issues typically present in a linear
charger.
Thermal control is implemented with a thermal loop that reduces the charge current
automatically when the junction temperature reaches approximately 120 °C. This avoids
further temperature rise and keeps the junction temperature constant. This simplifies the
thermal design of the application as well as protects the device against over-temperature
damage.
Figure 16 shows how the thermal loop acts (dotted lines), when the junction temperature
reaches 120 °C.
8.1 NTC thermistor
The device allows designers to monitor the battery temperature by measuring the voltage
across an NTC or PTC resistor. Li-Ion batteries have a narrow range of operating
temperature, usually from 0 °C to 50 °C. This window is programmable by an external
divider which is comprised of an NTC thermistor connected to GND and a resistor
connected to V
REF
. When the voltage on the TH pin exceeds the minimum or maximum
Figure 16. Power dissipation in both linear and quasi pulse modes with thermal loop
was was: 0x when m. Emery mmpeumn mm wD mm “R“ cums smv mm mm so on mm we magma comm. pxuczss now mat TH Lam” NTC
Application information: monitoring and protection L6924U
24/41 DocID14716 Rev 4
voltage threshold (internal window comparator), the device stops the charge process, and
indicates a fault condition through the status pin.
When the voltage (and thus, the temperature), returns to the window range, the device re-
starts the charging process. Moreover, there is a hysteresis for both the upper and lower
thresholds, as shown in Figure 18.
Note: T
BAT
= OK when the battery temperature is between 0 °C and 50 °C
Figure 17. Battery temperature control flow chart
Figure 18. Voltage window with hysteresis on TH
Figure 19. Pin connection
V
MINTH
V
MAXTH
V
MINTH_HYS
V
MAXTH_HYS
900mV
780mV
225mV
248mV
Voltage
Variation on TH pin Charge disable
Charge enable
DocID14716 Rev 4 25/41
L6924U Application information: monitoring and protection
41
When the TH pin voltage rises and exceeds the V
MINTH
= 50% of V
REF
(900 mV typ.), the
L6924U stops the charge, and indicates a fault by the status pins. The device re-starts to
charge the battery, only when the voltage at the TH pin goes under V
MINTH_HYS
= 780 mV
(typ).
For what concerns the high temperature limit, when the TH pin voltage falls under the
V
MAXTH
= 12.5% of V
REF
(225 mV typ.), the L6924U stops the charge until the TH pin
voltage reaches the V
MAXTH_HYS
= 248 mV (typ.).
When the battery is at the low temperature limit, the TH pin voltage is 900 mV. The correct
resistance ratio to set the low temperature limit at 0 °C can be found with the following
equation:
Equation 12
Where R
UP
is the pull-up resistor, V
REF
is equal to 1.8 V, and R
NTC0°C
is the value of the
NTC at 0 °C. Since at the low temperature limit V
MINTH
= 900 mV:
Equation 13
It follows that:
Equation 14
Similarly, when the battery is at the high temperature limit, the TH pin voltage is 225 mV.
The correct resistance ratio to set the high temperature limit at 50 °C can be found with the
following equation:
Equation 15
Where R
NTC50°C
is the value of the NTC at 50 °C. Considering V
MAXTH
= 225 mV it follows
that:
Equation 16
Consequently:
CNTCUP
CNTC
REFMINTH
RR
R
VV
°
°
+
×=
0
0
CNTCUP
CNTC
RR
R
°
°
+
×=
0
0
8.19.0
UPCNTC
RR =
°0
CNTCUP
CNTC
REFMAXTH
RR
R
VV
°
°
+
×=
50
50
CNTCUP
CNTC
RR
R
°
°
+
×=
50
50
8.1225.0
225 X0.039 °C °C
Application information: monitoring and protection L6924U
26/41 DocID14716 Rev 4
Equation 17
Based on Equation 14 and Equation 17, it derives that:
Equation 18
The temperature hysteresis can be estimated by the equation:
Equation 19
Where V
TH
is the pin voltage threshold on the rising edge, V
TH_HYS
is the pin voltage
threshold on the falling edge, and NTC
T
(-%/°C) is the negative temperature coefficient of
the NTC at temperature (T) expressed in% resistance change per °C. For NTC
T
values, see
the characteristics of the NTC manufacturers (e.g. the 2322615 series by VISHAY). At low
temperature, the hysteresis is approximately:
Equation 20
Obviously at high temperature hysteresis is:
Equation 21
Considering typical values for NTC
0°C
and NTC
50°C
, the hysteresis is:
Equation 22
And:
Equation 23
7
50 UP
CNTC
R
R=
°
7
50
0
=
°
°
CNTC
CNTC
R
R
TTH
HYSTHTH
HYS
NTCV
VV
T×
=
_
C
N
T
C
mV
mVmV
T
CHYS
°×
=
°
0
900
780900
0
C
N
T
C
mV
mVmV
T
CHYS
°×
=
°
50
225
248225
50
C
mV
mVmV
T
CHYS
ο
5.2
051
.
0
900
780900
0
×
=
°
C
mV
mVmV
T
CHYS
ο
5.2
039
.
0
225
248225
50
×
=
°
DocID14716 Rev 4 27/41
L6924U Application information: monitoring and protection
41
If a PTC connected to GND is used, the selection is the same as above, the only difference
is when the battery temperature increases, the voltage on the TH pin increases, and vice
versa. For applications that do not need a monitor of the battery temperature, the NTC can
be replaced with a simple resistor whose value is one half of the pull-up resistor R
UP
.
In this case, the voltage at the TH pin is always inside the voltage window, and the charge is
always enabled.
8.2 Battery absence detection
This feature provides a battery absent detection scheme to detect the removal or the
insertion of the battery. If the battery is removed, the charge current falls below the I
ENDTH
.
At the end of the de-glitch time, a detection current I
DETECT
, equal to 1 mA, is sunk from the
output for a time of T
DETECT
. The device checks the voltage at the output. If it is below the
V
PRETH
, a current equal to I
DETECT
is injected in the output capacitor for a T
DETECT
, and it is
checked to see if the voltage on the output goes higher than V
RCH
(4.05 V). If the battery
voltage changes from V
PRETH
to V
RCH
and vice versa in a T
DETECT
time, it means that no
battery is connected to the charger. The T
DETECT
is expressed by:
Equation 24
3
10
54
×
=
MAXCH
DETECT
T
T
BATTERY ABSENT V Deleu Low Ahmm \m \m m NO V Dawn ngh Abwm FAST CHARGE I’RE CHARGE L 6924U 3T2 ST1
Application information: monitoring and protection L6924U
28/41 DocID14716 Rev 4
8.3 Status pins
To indicate various charger status conditions, there are two open-collector output pins, ST1
and ST2. These status pins can be used either to drive status LEDs, connected with an
external power source, by a resistor, or to communicate to a host processor.
Figure 20. Battery absence detection flow chart
BATTERY
ABSENT
Detect Low Absent
V
BAT
>
V
PRETH
FAST CHARGE
Detect High Absent
V
BAT
>
V
RCH
PRE CHARGE
NO
YES
YES
NO
DETECT LOW ABSENT
= a I
SINK
is sunk for a T
DET
from the battery
DETECT HIGH ABSENT = a I
INJ
is injected for a T
DET
in the battery
T
DET
= 100ms (Typ.)
I
SINK
= I
INJ
= 1mA (Typ.)
Figure 21. ST1 and ST2 connection with LEDs or microcontroller
DocID14716 Rev 4 29/41
L6924U Application information: monitoring and protection
41
8.4 Shutdown
The L6924U has a shutdown pin; when the pin is connected to GND, the device is
operating. When the pin is left floating, the device enters the shutdown mode, the
consumption from the input is dramatically reduced to 60 µA (typ.). In this condition, V
REF
is
turned OFF.
Table 6. Status LEDs Indications
Charge condition Description ST1 ST2
Charge in progress When the device is in pre-charge or fast-
charge status ON OFF
Charge done When the charging current goes below the
I
ENDTH
OFF ON
Stand by mode When the input voltage goes under
V
BAT
+ 50 mV OFF OFF
Bad battery temperature When the voltage on the TH pin is out of
the programmable window, in accordance
with the NTC or PTC thermistor ON ON
Battery absent When the battery pack is removed ON ON
Over time When T
MAXCH
or T
MAXPRECH
expires ON ON
Additional application information L6924U
30/41 DocID14716 Rev 4
9 Additional application information
9.1 Selecting the input capacitor
In most applications, a 1 µF ceramic capacitor, placed close to the V
IN
and V
INSN
pins can
be used to filter the high frequency noise.
9.2 Selecting the output capacitor
Typically, a 4.7 µF ceramic capacitor placed close to the V
OUT
and V
OUTSN
pin is enough to
keep voltage control loop stable. This ensures proper operation of battery absent detection
in removable battery pack applications.
DocID14716 Rev 4 31/41
L6924U Additional application information
41
9.3 Battery floating voltage setup
The L6924U has been evaluated with the following application schematic.
Figure 22. Application schematic
Table 7. External component values for the L6924U
Name Value Description Note
R6, R5 1 kPull-up resistor
C1 1 µF Input supply voltage capacitor
C3 10 nF Maximum charging time capacitor
Rosns 7500 V
FLOAT
programming resistor
C2 1 µF Output battery capacitor
R4 1 kNTC supply resistor
RT1 470 NTC tuning parallel resistor
C4 1 µF V
REF
filter capacitor
R1 12 kFast-charge current programming resistor AC mode I
FAST
= 975 mA
R2 48.6 kFast-charge current programming resistor USB mode I
FAST
= 240 mA
R3 2.2 kSet standard I
END
= 10% I
FAST
I
END
~ 24 mA
VFLOAT +0 +3900 +7500 49a7654321395765422129375 4333333333422222212241111 444444444 444444444 4444 E umm=o> MES: ruzmm 7500 3900 Rosns [Q]
Additional application information L6924U
32/41 DocID14716 Rev 4
9.3.1 Battery floating voltage: V
FLOAT
The battery floating voltage can be set to a value higher than 4.2 V by using the following
formula:
V
FLOAT
= 4.2 V + Rosns * 19.5 µA = 4.346 V
As an example, with Rosns = 7.5 k the battery floating voltage (V
FLOAT
) is set to be
V
FLOAT
= 4.346 V.
Figure 23. V
FLOAT
vs. Rosns
The L6924U works with the selected external components. The test results confirm that their
behavior is in line with the design.
9.4 Layout guidelines and demonstration board
The thermal loop keeps the device at a constant temperature of approximately 120 °C which
in turn, reduces I
CHG
. However, in order to maximize the current capability, it is important to
ensure a good thermal path. Therefore, the exposed pad must be properly soldered to the
board and connected to the other layer through thermal vias. The recommended copper
thickness of the layers is 70 μm or more.
The exposed pad must be electrically connected to GND. Figure 24 shows the thermal
image of the board with the power dissipation of 1 W. In this instance, the temperature of the
case is 89 °C, but the junction temperature of the device is given by the following equation:
Equation 25
Where the R
thJA
of the device mounted on board is 75 °C/W, the power dissipated is 1 W,
and the ambient temperature is 25 °C.
AMBDISSATHJJ
TPRT +×=
98 8 ‘C B? 2 77.5 87 9 58 3 48 7 39 1 234 199 - _.._ . (BATT. 'EVAL L6924U'
DocID14716 Rev 4 33/41
L6924U Additional application information
41
In this case the junction temperature is:
Equation 26
The V
OSNS
pin can be used as a remote sense; it should be therefore connected as closely
as possible to the battery. The demonstration board layout and schematic are shown in
Figure 25, Figure 26 and Figure 27.
Figure 24. Thermal image of the demonstration board
Figure 25. Demonstration board layout, top side
CT
J
ο
10025175
=+×=
- ' --GND- . “'15. .+BATT'~. I ac}. .‘ ].l2 . (BATT . AC ADAPIERnr Ilsa amm
Additional application information L6924U
34/41 DocID14716 Rev 4
Figure 27. Demonstration board schematic
Figure 26. Demonstration board layout, bottom side
Table 8. Demonstration board components description
Name Value Description
R1 24 kAC mode fast-charge current resistor. Used to set the charging current in AC mode
R2 24 kUSB mode fast-charge current resistor. Used to set the charging current in USB
mode
R3 3.3 kEnd of Charge current resistor. Used to set the termination current and, as a “gas
gauge” when measuring the voltage across on it
R4 1 kPull up resistor. Connected between VREF and TH pin
R5 1 kPull up resistor. To be used when the ST1 is connected to a LED
R6 1 kPull up resistor. To be used when the ST2 is connected to a LED
RT1 470 If a NTC is not used, a half value of R4 must be mounted to keep the TH voltage in
the correct window
C1 1 µF Input capacitor
C2 4.7 µF Output capacitor
C3 10 nF T
MAX
capacitor. Used to set the maximum charging time
DocID14716 Rev 4 35/41
L6924U Additional application information
41
C4 1 nF V
REF
filter capacitor
D1 GREEN ST1 LED
D2 RED ST2 LED
J1 ST2 jumper. Using to select the LED or the external microcontroller
J2 ST1 jumper. Using to select the LED or the external microcontroller
J3 SD jumper. If open, the device is in shutdown mode; when closed, the device starts
to work
J4 Low power/ high power USB mode selection jumper
J5 AC/USB mode selection jumper
Table 8. Demonstration board components description
Application idea: dual input management with AC priority L6924U
36/41 DocID14716 Rev 4
10 Application idea: dual input management with AC
priority
In some applications both AC adapter and USB power source may be available.
Figure 28 shows a possible schematic which provides the possibility to manage two power
sources (AC/USB) and gives the priority to AC adapter in case both sources are available at
the same time.
For simplicity, only the relevant pins of the L6924U for this application have been indicated.
If only the AC adapter is available, since the gates of Q1 and Q2 are connected to AC, both
MOSFETs are off. The AC adapter voltage is provided to the V
IN
pin through the diode D1.
The voltage at the V
IN
pin is:
A correct choice of this diode is important to limit V
diode
and keeping V
IN
as close as
possible to AC.
In this condition the MODE pin is low. This sets the L6924U in AC mode and the battery is
charged with the current programmed by R
AC
.
When only the USB power source is available, both Q1 and Q2 switch on and the pin V
IN
is
connected to USB.
The MODE pin is connected to the drains of Q1 and Q2 and is high. Therefore the USB
mode for the L6924U is selected and the battery is charged with a current in accordance
with the resistor connected to the pin I
USB
(R
USB
).
The voltage of the V
IN
pin is given by:
The voltage drop across the MOSFETs must be kept as low as possible to avoid reducing
too much the voltage of the V
IN
pin.
When both sources are present, this circuit gives the priority to the AC adapter. In fact, for
V
AC
5 V, surely both Q1 and Q2 are off and V
IN
is connected to the AC adapter through
D1. The MODE pin is kept low and L6924U is set to AC mode.
The use of two P-channel MOSFETs connected as shown in Figure 28 is particularly useful
in this case because they remove any path between the two power sources.
(
)
USB2Q_DSon1Q_DSonUSBIN
IRRVV +=
we" mm vm Inga I“ MODE RM Russ RM
DocID14716 Rev 4 37/41
L6924U Application idea: dual input management with AC priority
41
Figure 28. Dual input management
L6924U
V
IN
MODE
AC
USB
R
G
R
M
Q1 Q2
D1
I
AC
I
USB
R
AC
R
USB
V
OUT
Li-Ion
battery
L6924U
V
IN
MODE
AC
USB
R
G
R
M
Q1 Q2
D1
I
AC
I
USB
R
AC
R
USB
V
OUT
Li-Ion
battery
Package information L6924U
38/41 DocID14716 Rev 4
11 Package information
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK
®
packages, depending on their level of environmental compliance. ECOPACK
®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK
®
is an ST trademark.
SEAT‘NG o PLANE I E 2 < e="" \="" w:’="" 2="" :j="" d="" pw="" #1="" \d="" m="" r:ozo="" e="" 13="" 15="" 12="" k="" w="" m="" 7:="" +="" m="" g="" 3=""><3 4="" $="" w="" m="" 4‘="" 8g="" a="" 5,="" j="" d2="" bowom="" vwa="">
DocID14716 Rev 4 39/41
L6924U Package information
41
11.1 VFQFPN16 package information
Figure 29. VFQFPN16 (3x3 mm) package outline
Table 9. VFQFPN16 (3x3 mm) mechanical data
Dim. mm
Min. Typ. Max.
A 0.80 0.90 1.00
A1 0.02 0.05
A2 0.65 1.00
A3 0.20
b 0.18 0.25 0.30
D 2.85 3.00 3.15
D2 1.45 1.60 1.75
E 2.85 3.00 3.15
E2 1.45 1.60 1.75
e 0.45 0.50 0.55
L 0.30 0.40 0.50
Revision history L6924U
40/41 DocID14716 Rev 4
12 Revision history
Table 10. Document revision history
Date Revision Changes
20-May-2008 1 First release
22-Sep-2010 2 Modified: Table 9 and Figure 29 on page 39. Minor changes.
25-Sep-2017 3 Updated Applications and Table 1: Device summary
Added Section 9.3: Battery floating voltage setup
18-Jan-2019 4 Updated Figure 22.
DocID14716 Rev 4 41/41
L6924U
41
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acknowledgement.
Purchasers are solely responsible for the choice, selection, and use of ST products and ST assumes no liability for application assistance or
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© 2019 STMicroelectronics – All rights reserved

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