SP333 Datasheet, PDF (7/13 Pages) Sipex Corporation – +5V Only RS-232/AppleTalk Programmable Transceiver

signals up to ±15V. The input resistance of the
single-ended inverting receiver is typically 5kΩ
(3kΩ to 7kΩ). The GPI receiver can operate up
to 10Mbps.
SINGLE ENDED DRIVERS/RECEIVERS...
RS-232 (V.28) Drivers...
The single-ended drivers and receivers comply
the with the RS-232E and V.28 standards. The
drivers are inverting transmitters which accept
either TTL or CMOS inputs and output the RS-
232 signals with an inverted sense relative to the
input logic levels. Typically, the RS-232 driver
output voltage swing is ±9V with no load and is
guaranteed to be greater than ±5V under full
load. The drivers rely on the V+ and V- voltages
generated by the on-chip charge pump to main-
tain proper RS-232 output levels. With worst
case load conditions of 3kΩ and 2500pF, the
four RS-232 drivers can still maintain ±5V
output levels. The drivers can operate over
400kbps; the propagation delay from input to
output is typically 1.5µs. During shutdown, the
driver outputs will be put into a high impedance
tri-state mode.
RS-232 (V.28) Receivers...
The RS-232 receivers convert RS-232 input
signals to inverted TTL signals. Each of the four
V_CC = +5V
+
C_{1 –}
+10V
+
C_{2 –}
C₄
+ – _{VDD Storage Capacitor}
– + _{VSS Storage Capacitor}
C₃
receivers features 500mV of hysteresis margin
to minimize the affects of noisy tranmission
lines. The inputs also have a 5kΩ resistor to
ground, in an open circuit situation the input of
the receiver will be forced low, committing the
output to a logic HIGH state. The input resis-
tance will maintain 3kΩ-7kΩ over a ±15V range.
The maximum operating voltage range for the
receiver is ±30V, under these conditions the
input current to the receiver must be limited to
less than 100mA. Due to the on-chip ESD pro-
tection circuitry, the receiver inputs will be
clamped to ±15V levels; this should not affect
operation at ±30Volts. The RS-232 receivers
can operate over 400kbps.
CHARGE PUMP...
The charge pump is a Sipex-patented design
(5,306,954) and uses a unique approach com-
pared to older less-efficient designs. The charge
pump still requires four external capacitors, but
uses a four-phase voltage shifting technique to
attain symmetrical 10V power supplies. The
capacitor values of the SP333 can be as low as
0.1µF. Figure 11a shows the waveform found
on the positive side of capacitor C2, and Figure
11b shows the negative side of capacitor C2.
There is a free-running oscillator that controls
the four phases of the voltage shifting. A de-
scription of each phase follows.
V_CC = +5V
+
C_{1 –}
–5V
+5V
+
C_{2 –}
–5V
C₄
+ – _{VDD Storage Capacitor}
– + _{VSS Storage Capacitor}
C₃
Figure 7. Charge Pump Phase 1
Figure 8. Charge Pump Phase 2
V_CC = +5V
+
C_{1 –}
+
C_{2 –}
–10V
C₄
+ – _{VDD Storage Capacitor}
– + _{VSS Storage Capacitor}
C₃
V_CC = +5V
+
C_{1 –}
–5V
+5V
+
C_{2 –}
–5V
C₄
+ – _{VDD Storage Capacitor}
– + _{VSS Storage Capacitor}
C₃
Figure 9. Charge Pump Phase 3
Figure 10. Charge Pump Phase 4
TGoddard/SP333/9617R0
SP333 RS-232/AppleTalk Programmable Transceiver
7
© Copyright 2000 Sipex Corporation