7

TGoddard/SP333/9617R0

SP333 RS-232/AppleTalk Programmable Transceiver

© Copyright 2000 Sipex Corporation

receivers features 500mV of hysteresis margin

to minimize the affects of noisy tranmission

lines. The inputs also have a 5k

Ω 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 3k

Ω-7kΩovera±15Vrange.

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

0.1

µF. 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.

signals up to

±15V. The input resistance of the

single-ended inverting receiver is typically 5k

Ω

(3k

Ω 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 3k

Ω 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 1.5

µs. 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

Figure 7. Charge Pump Phase 1

Figure 8. Charge Pump Phase 2

Figure 9. Charge Pump Phase 3

Figure 10. Charge Pump Phase 4

+10V

+

+

++

–

–

–

–

–5V

–5V

+5V

+

+

++

–

–

–

–

–10V

+

+

++

–

–

–

–

–5V

+5V

–5V

+

+

++

–

–

–

–