ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243

4. Application Information

FN4805 Rev.23.00

Page 13 of 36

Apr.26.19

4.

Application Information

The ICL32xx interface ICs operate from a single +3V to +5.5V supply, ensure a 250kbps minimum data rate,

require only four small external 0.1µF capacitors, feature low-power consumption, and meet all ElA RS-232C and

V.28 specifications. The circuit is divided into three sections:

• Charge-pump

• Transmitters

• Receivers

4.1

Charge Pump

The ICL32xx family uses regulated on-chip dual charge pumps as voltage doublers, and voltage inverters to

generate ±5.5V transmitter supplies from a VCC supply as low as 3.0V, which allows these devices to maintain

RS-232 compliant output levels over the ±10% tolerance range of 3.3V powered systems. The efficient on-chip

power supplies require only four small, external 0.1µF capacitors for the voltage doubler and inverter functions at

VCC = 3.3V. See Capacitor Selection and Table 6 on page 19 for capacitor recommendations for other operating

conditions. The charge pumps operate discontinuously (for example, they turn off as soon as the V+ and V-

supplies are pumped up to the nominal values), resulting in significant power savings.

4.1.1 Charge Pump Absolute Maximum Ratings

These 3V to 5V RS-232 transceivers have been fully characterized for 3.0V to 3.6V operation, and at critical

points for 4.5V to 5.5V operation. Furthermore, load conditions were favorable using static logic states only.

The specified maximum values for V+ and V- are +7V and -7V, respectively. These limits apply for VCC values set

to 3.0V and 3.6V (see Table 2). For VCC values set to 4.5V and 5.5V, the maximum values for V+ and V- can

approach +9V and -7V respectively (see Table 3). The breakdown characteristics for V+ and V- were measured

with ±13V.

Table 2.

V+ and V- Values for VCC = 3.0V to 3.6V

C1 (μF)

C2, C3, C4 (μF)

Load

T1IN (Logic

State)

V+ (V)

V- (V)

VCC = 3.0V

VCC = 3.6V

VCC = 3.0V

VCC = 3.6V

0.1

0.1

Open

H

5.8

6.56

-5.6

-5.88

L

5.8

6.56

-5.6

-5.88

2.4kbps

5.8

6.56

-5.6

-5.88

3kΩ // 1000pF

H

5.88

6.6

-5.56

-5.92

L

5.76

6.36

-5.56

-5.76

2.4kbps

6

6.64

-5.64

-5.96

0.047

0.33

Open

H

5.68

6

-5.6

-5.6

L

5.68

6

-5.6

-5.6

2.4kbps

5.68

6

-5.6

-5.6

3kΩ // 1000pF

H

5.76

6.08

-5.64

-5.64

L

5.68

6.04

-5.6

-5.6

2.4kbps

5.84

6.16

-5.64

-5.72

1

1

Open

H

5.88

6.24

-5.6

-5.6

L

5.88

6.28

-5.6

-5.64

2.4kbps

5.8

6.2

-5.6

-5.6

3kΩ // 1000pF

H

5.88

6.44

-5.64

-5.72

L

5.88

6.04

-5.64

-5.64

2.4kbps

5.92

6.4

-5.64

-5.64