8-52

Detailed Description

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

a single +5V power supply which meets all ElA RS232C spec-

ifications and features low power consumption. The functional

diagram illustrates the major elements of the ICL232. The cir-

cuit 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 thresh-

the input results in a voltage of between -5V and V- at the out-

put, 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 mini-

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 indef-

initely. The powered down output impedance is a minimum of

300

Receivers

The receiver inputs accept up to

±30V while presenting the

required 3k

Ω to 7kΩ input impedance even it the power is off

1.3V which is within the

±3V limits, known as the transition

region, of the RS-232 specification. The receiver output 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.

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

300

Ω

400k

Ω

V-

V+

FIGURE 7. TRANSMITTER

ICL232