SP2209E Datasheet, PDF (9/17 Pages) Sipex Corporation – High ESD Dual Port RS-232 Transceiver

One receiver in each RS-232 port can be
kept active by a low current, +3.3V to +5V
power supply while the rest of the channels
are powered down. This allows the SP2209E
device to monitor peripheral devices while
the rest of the system is in a power-saving
standby mode. The SP2209E device can
be implemented as a power management
device to wake up the entire system when
any communication is initiated in peripheral
devices. The SP2209E device has a low
standby current of 100µA.
Since receiver input is usually from a trans-
mission line where long cable lengths and
system interference can degrade the signal,
the inputs have a typical hysteresis margin
of 300mV. This ensures that the receiver is
virtually immune to noisy transmission lines
and inputs with slow transition times.
Charge Pump
DESCRIPTION
The charge pump is an Exar-patended
design (U.S. 5,306,954) and uses a unique
approach compared to older less-efficient
designs. The charge pump requires two
external capacitors using a two-phase volt-
age shifting technique with a 200kHz internal
oscillator to attain a -9V power supply. Refer
to Figure 7 for the internal charge pump
circuit. The internal power supply consists
of a charge pump that provides output volt-
ages of at least +/-5V regardless of the input
voltage (V_DD). This is important to maintain
compliant RS-232 levels regardless of power
supply fluctuations. A description of each
phase follows.
Figure 7. Charge Pump Circuit
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP2209E_100_071612