SP3222EH_06 Datasheet, PDF (8/19 Pages) Sipex Corporation – 3.3V, 460 Kbps RS-232 Transceivers

DESCRIPTION
The SP3222EH and SP3232EH are 2-driver/
2-receiver devices ideal for portable or hand-held
applications. The SP3222EH features a 1µA
shutdown mode that reduces power consumption
and extends battery life in portable systems.
Its receivers remain active in shutdown mode,
allowing external devices such as modems to be
monitored using only 1µA supply current.
The SP3222EH/3232EH transceivers meet the
EIA/TIA-232 and V.28/V.24 communication
protocols. They feature Sipex's proprietary
on-board charge pump circuitry that generates
2 x V_CC for RS-232 voltage levels from a single
+3.0V to +5.5V power supply. The SP3222EH/
3232EH drivers operate at a minimum data
rate of 460Kbps.
THEORY OF OPERATION
The SP3222EH/3232EH are made up of three
basic circuit blocks: 1. Drivers, 2. Receivers, and 3.
the Sipex proprietary charge pump.
Drivers
The drivers are inverting level transmitters that
convert TTL or CMOS logic levels to +5.0V
EIA/TIA-232 levels inverted relative to the input
logic levels. Typically, the RS-232 output voltage
swing is +5.5V with no load and at least +5V
minimum fully loaded. The driver outputs are
protected against infinite short-circuits to ground
without degradation in reliability. Driver outputs
will meet EIA/TIA-562 levels of +3.7V with
supply voltages as low as 2.7V.
The drivers have a minimum data rate of
460Kbps fully loaded with 3KΩ in parallel with
1000pF, ensuring compatibility with PC-to-PC
communication software.
The slew rate of the driver output is internally
limited to a maximum of 30V/µs in order to meet
the EIA standards (EIA RS-232D 2.1.7,
Paragraph 5). The transition of the loaded output
from HIGH to LOW also meets the monotonicity
requirements of the standard.
Figure 8 shows a loopback circuit used to test the
RS-232 drivers. Figure 9 shows the test results
of the loopback circuit with all drivers active at
120Kbps and RS-232 loads in parallel with
1000pF capacitors. Figure 10 shows the test
results where one driver is active at 460Kbps and
all drivers are loaded with an RS-232 receiver
in parallel with a 1000pF capacitor.
The SP3222EH driver's output stages are
tri-stated in shutdown mode. When the power is
off, the SP3222EH device permits the outputs to
be driven up to +12V. Because the driver's
inputs do not have pull-up resistors, unused
inputs should be connected to V_CCor GND.
In the shutdown mode, the supply current is less
than 1µA, where SHDN = LOW. When the
SP3222EH device is shut down, the device's
driver outputs are disabled (tri-stated) and the
charge pumps are turned off with V+ pulled
down to V and V- pulled to GND. The time
CC
required to exit shutdown is typically 100µs.
SHDN is connected to V_CC if the shutdown mode
is not used. SHDN has no effect on RxOUT or
RxOUTB. As they become active, the two driver
outputs go to opposite RS-232 levels: one driver
input is HIGH and the other LOW. Note that the
drivers are enabled only when the magnitude of
V- exceeds approximately 3V.
Date: 1/18/06
SP3222EH/3232EH 3.3V, 460 Kbps RS-232 Transceivers
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© Copyright 2006 Sipex Corporation