ICL232

FN3020 Rev 8.00

Page 5 of 8

October 15, 2014

Detailed Description

The ICL232 is a dual RS-232 transmitter/receiver powered by a

single +5V power supply which meets all ElA RS232C

specifications and features low power consumption. Figure 1

illustrates the major elements of the ICL232. The circuit is divided

into three sections: a voltage doubler/inverter, dual transmitters,

and dual receivers.

Voltage Converter

An equivalent circuit of the dual charge pump is illustrated in

Figure 6.

The voltage quadrupler contains two charge pumps which use two

phases of an internally generated clock to generate +10V and

-10V. The nominal clock frequency is 16kHz. During phase one of

then during phase one, it is inverted with respect to ground to

accepts input voltages up to 5.5V. The output impedance of the

doubler (V+) is approximately 200Ω, and the output impedance of

the inverter (V-) is approximately 450Ω . Typical graphs are

presented which show the voltage converters output vs input

voltage and output voltages vs load characteristics. The test circuit

(Figure 2) uses 1µF capacitors for C1 to C4, however, the value is

not critical. Increasing the values of C1 and C2 will lower the

output impedance of the voltage doubler and inverter, and

increasing the values of the reservoir capacitors, C3 and C4,

lowers the ripple on the V+ and V- supplies.

Transmitters

The transmitters are TTL/CMOS compatible inverters which

translate the inputs to RS-232 outputs. The input logic threshold is

results in a voltage of between -5V and V- at the output, and a logic

0 results in a voltage between +5V and (V+ - 0.6V). Each

transmitter input has an internal 400kΩ pullup resistor so any

unused input can be left unconnected and its output remains in its

low state. The output voltage swing meets the RS-232C

specification of

5V minimum with the worst case conditions of:

both transmitters driving 3kΩ minimum load impedance,

transmitters have an internally limited output slew rate which is

less than 30V/µs. The outputs are short circuit protected and can

be shorted to ground indefinitely. The powered down output

impedance is a minimum of 300Ω with

2V applied to the outputs

Receivers

The receiver inputs accept up to

30V while presenting the

required 3kΩ to 7kΩ input impedance even it the power is off

which is within the

3V limits, known as the transition region, of

output will be low whenever the input is greater than 2.4V and

high whenever the input is floating or driven between +0.8V and

-30V. The receivers feature 0.5V hysteresis to improve noise

rejection.

Applications

The ICL232 may be used for all RS-232 data terminal and

communication links. It is particularly useful in applications

where

12V power supplies are not available for conventional

RS-232 interface circuits. The applications presented represent

typical interface configurations.

A simple duplex RS-232 port with CTS/RTS handshaking is

illustrated in Figure 11. Fixed output signals such as DTR (data

terminal ready) and DSRS (data signaling rate select) is

generated by driving them through a 5kΩ resistor connected to V+.

90%

10%

Instantaneous

Slew Rate (SR) =

or

FIGURE 7. SLEW RATE DEFINITION

300Ω

400kΩ

V-

V+

FIGURE 8. TRANSMITTER

5kΩ

GND

FIGURE 9. RECEIVER

Average Propagation Delay =

2

OR

OR

FIGURE 10. PROPAGATION DELAY DEFINITION