SP3244E Datasheet, PDF (10/22 Pages) Sipex Corporation – 3.0V to 5.5V RS-232 Transceivers with Auto On-Line® Plus

The SP3244E and SP3245E are 3-driver/5-re-
ceiver devices ideal for serial ports in battery-
powered, portable, or handheld applications
such as notebook or handheld computers.
SP3244E/3245E transceivers meet the EIA/
TIA-232 and ITU-T V.28/V.24 communication
protocols for reliable serial communication.
The SP3244E/3245E devices feature Sipex’s
proprietary and patented (U.S. 5,306,954)
on-board charge pump circuitry that generates
±5.5V RS-232 voltage levels from a single
+3.0V to +5.5V power supply.
The SP3244E/3245E is an ideal choice
for power sensitive designs. With the Auto
On-line^® Plus enabled the SP3244E/3245E
reduces power consumption to a 1µA supply
current whenever the transceivers are idle. In
shutdown, the internal charge pump and the
drivers will shut down. Receivers remain active
unless the device is put into manual shutdown
using the SHUTDOWN pin. This feature allows
design engineers to address power saving
concerns without major design changes.
Theory Of Operation
The SP3244E/3245E is made up of four basic
circuit blocks:
1. Drivers, 2. Receivers, 3. the Sipex propri-
etary charge pump, and 4. Auto On-line^® Plus
circuitry.
Drivers
The drivers are inverting level transmitters that
convert TTL or CMOS logic levels to 5.0V EIA/
TIA-232 levels with an inverted sense relative
to the input logic levels. Typically, the RS-232
output voltage swing is +5.4V with no load and
+5V minimum fully loaded. The driver outputs
are protected against infinite short circuits to
ground without degradation in reliability. These
drivers comply with the EIA/TIA-232-F and
all previous RS-232 versions. Unused driver
inputs should be connected to GND or VCC.
The SP3244E/3245E devices operate at this
typical data rate when fully loaded. The drivers
can guarantee output data rates fully loaded
with 3KΩ in parallel with 1000pF (SP3244E), or
250pF (SP3245E) ensuring compatibility with
popular PC-to-PC communication software.
The slew rate of the driver output on the
SP3244E is internally limited to a maximum
of 30V/µs in order to meet the EIA standards
DESCRIPTION
(EIA RS-232D 2.1.7, Paragraph 5). The slew
rate of SP3245E is not limited to enable higher
speed data transfers. The transition of the
loaded output from HIGH to LOW also meets
the monotonic signal transition requirements of
the standard.
Receivers
The receivers convert EIA/TIA-232 signal
levels to TTL or CMOS logic output levels. Re-
ceivers remain active unless the device is put
into manual shutdown using the SHUTDOWN
pin. The non-inverted output of Receiver
2 (R2OUT) will continue to be active in all
modes, including shutdown.
Since receiver input is usually from a transmis-
sion line where long cable lengths and system
interference can degrade the signal, the inputs
have a typical hysteresis margin of 500mV.
This ensures that the receiver is virtually im-
mune to noisy transmission lines. Should an
input be left unconnected, an internal 5KΩ pull-
down resistor to ground will commit the output
of the receiver to a HIGH state.
Highly Efficient Charge Pump
The charge pump is used to generate positive
and negative signal voltages for the RS-232
drivers. This enables fully compliant RS-232
and V.28 signals from a single 3.0 or 5.5V
power supply.
The charge pumps use four external capaci-
tors to hold and transfer electrical charge. The
Sipex patented design (US Patent #5,306,954)
uses a unique approach compared to older less
efficient designs. The pumps use a four–phase
voltage shifting technique to attain symmetrical
V+ and V- power supplies. An intelligent control
oscillator regulates the operation of the charge
pump to maintain the proper voltages at maxi-
mum efficiency.
Phase 1
VSS charge store and double. The positive
terminals of capacitors C1 and C2 are charged
from VCC with their negative terminals initially
connected to ground. C1+ is then connected
to ground and the stored charge from C1– is
superimposed onto C2– . Since C2+ is still
connected to VCC the voltage potential across
capacitor C2 is now 2 x VCC.
Rev M 10/9/06
SP3244E-SP3245E, 3.0V to 5.5V RS-232 Transceivers with Auto On-Line^® Plus
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© Copyright 2006 Sipex Corporation