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SP3282 Datasheet, PDF (7/15 Pages) Sipex Corporation – Intelligent +2.35V to +5.5V RS-232 Transceivers | |||
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VCC
+
C5 0.1µF
+
C1 0.1µF
+
C2 0.1µF
VCC
C1+
V+
C1-
C2+ SP3282EB V-
C2-
LOGIC
INPUTS
TxIN
TxOUT
LOGIC
OUTPUTS
VCC
RxOUT
ONLINE
SHUTDOWN
RxIN
5kâ¦
GND
+
C3 0.1µF
C4 0.1µF
+
1000pF
Figure 6. Loopback Test Circuit for RS-232 Driver Data
Transmission Rates
Since receiver input is usually from a transmission
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. Should an input be left
unconnected, an internal 5k⦠pulldown resistor to
ground will commit the output of the receiver to a
HIGH state.
Charge Pump
The charge pump is a Sipexâpatented design
(U.S. #5,306,954) and uses a unique approach
compared to older lessâefficient designs. The
charge pump uses a fourâphase voltage
shifting technique to attain symmetrical ±5.5V
power supplies. The internal power supply con-
sists of a regulated dual charge pump that provides
output voltages ±5.5V regardless of the input
voltage (VCC) over the +3.3V to +5.5V range.
This is important to maintain compliant RS-232
levels regardless of power supply
fluctuations. The charge pump will provide out-
put voltage levels of ±4.0V when the input voltage
(VCC) is from +3.1V to +2.35V.
The charge pump operates in a discontinuous
mode using an internal oscillator. If the output
voltages are less than a magnitude of 5.5V ( VCC
> 3.3V ) and 4.0V (VCC < 3.1V), the charge pump
is enabled. If the output voltages exceed a
magnitude of 5.5V (VCC > 3.3V) and 4.0V (VCC <
3.1V), the charge pump is disabled. This oscilla-
tor controls the four phases of the voltage shifting
(Figure 10).
A description of each phase follows.
Phase 1 (Figure 11)
Figure 7. Loopback Test Circuit Result at 120kbps
(All Drivers Fully Loaded)
a) C2+
1
2
2
[
T
T
]
+6V
0V
0V
b) C2-
T
-6V
Ch1 2.00V Ch2 2.00V M 1.00µs Ch1 1.96V
Figure 8. Loopback Test Circuit result at 250kbps
(All Drivers Fully Loaded)
Figure 10. Charge Pump Waveforms
Date: 02/24/05
SP3282EB Intelligent +2.35V to +5.5V RS-232 Transceivers
7
© Copyright 2005 Sipex Corporation
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