5

FN3020.7

July 28, 2005

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. The

functional diagram 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 5.

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

it is inverted with respect to ground to produce a signal across

voltages up to 5.5V. The output impedance of the doubler (V+)

is approximately 200

Ω, and the output impedance of the

inverter (V-) is approximately 450

Ω. Typical graphs are

presented which show the voltage converters output vs input

voltage and output voltages vs load characteristics. The test

circuit (Figure 3) uses 1

µF capacitors for C1-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

1 at the input 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 400k

Ω 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 3k

Ω

allowable operating temperature. The 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

9

9

R2out

Receiver 2 TTL/CMOS output.

10

10

11

11

12

12

Receiver 1 TTL/CMOS output.

13

13

RS-232 Receiver 1 input, with internal 5K pulldown resistor to GND.

14

14

RS-232 Transmitter 1 output

±10V (typical).

15

15

GND

Supply Ground.

16

16

Positive Power Supply +5V

±10%

PDIP, CERDIP

SOIC

PIN NAME

DESCRIPTION

+

-

C1

+

-

C3

+

-

C2

+

-

C4

S1

S2

S5

S6

S3

S4

S7

S8

GND

RC

OSCILLATOR

GND

GND

V- = -(V+)

C1

-

C2

-

VOLTAGE INVERTER

VOLTAGE DOUBLER

FIGURE 5. DUAL CHARGE PUMP

90%

10%

Instantaneous

Slew Rate (SR)

=

or

FIGURE 6. SLEW RATE DEFINITION

ICL232

ICL232