SEMICDNDUCTDR
http://www.union-ic.com Rev.01 Oct.2017 7/27
UM207/208/211/213
Detailed Description
The UM207/208/211/213 consists of three sections: charge-pump voltage converters, drivers, and
receivers. These E versions provide extra protection against ESD. They survive ±15kV discharges to
the RS-232 inputs and outputs, tested using the Human Body Model. When tested according to
IEC61000-4-2, they survive ±8kV contact-discharges and ±15kV air-gap discharges. The rugged E
versions are intended for use in harsh environments or applications where the RS-232 connection is
frequently changed.
RS-232 Drivers
The drivers are inverting transmitters, which accept TTL or CMOS inputs and output RS-232 signals
with an inverted sense relative to the input logic levels. Typically the RS-232 output voltage swing is
±6V. Even under worst case loading conditions of 3kΩ and 2500pF, the output is guaranteed to be
±5V, which is consistent with the RS-232 standard specifications. The transmitter outputs are
protected against infinite short-circuits to ground without degradation in reliability. The instantaneous
slew rate of the transmitter output is internally limited to a maximum of 30V/μs in order to meet the
RS-232 standard. The smooth transition of the loaded output from VOL to VOH clearly meets the
monotonicity requirements of the RS-232 standard.
RS-232 Receivers
The receivers convert RS-232 input signals to inverted TTL signals. The input thresholds are 0.8V
minimum and 2.4V maximum, again well within the 3V RS-232 requirements. The receiver inputs are
also protected against voltage up to 30V. A 5kΩ pull down resistor to ground will commit the output
of the receiver to a high state when the pin is float. In actual system applications, it is quite possible
for signals to be applied to the receiver inputs before power is applied the receiver circuitry. This
occurs, for example, when a PC user attempts to print, only to realize the printer wasn’t turned on. In
this case an RS-232 signal from the PC will appear on the receiver input at the printer. When the
printer power is turned on, the receiver will operate normally. All of these enhanced devices are fully
protected.
Shutdown and Enable Control
In shutdown mode, the UM211/213 charges pumps are turned off, V+ is pulled down to VCC, V- is
pulled to ground, and the transmitter outputs are disabled. This reduces supply current typically to
1µA. The time required to exit shutdown is 1ms.
All receivers except R4 and R5 on the UM213 are put into a high-impedance state in shutdown mode.
The UM213’s R4 and R5 receivers still function in shutdown mode. These two receivers are useful for
monitoring external activity while maintaining minimal power consumption.
The enable control is used to put the receiver outputs into a high-impedance state, so that the receivers
can be connected directly to a three-state bus. It has no effect on the RS-232 drivers or on the charge
pumps.
UM213 Receiver Operation in Shutdown
During normal operation, the UM213’s receiver propagation delay is typically 1μs. When entering
shutdown with receivers active, R4 and R5 are not valid until 80μs after SHDN
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is driven low. In
shutdown mode, propagation delays increase to 4μs for a high-to-low or a low-to-high transition.
When exiting shutdown, all receiver outputs are invalid until the charge pumps reach nominal
values(<2ms when using 0.1μF capacitors).