ICL3221EM, ICL3221EF

4. Application Information

FN7552 Rev.2.00

Page 9 of 22

May.29.19

4.

Application Information

ICL3221EM and ICL3221EF interface ICs operate from a single +3V 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.

4.1

Charge Pump

The ICL3221EM and ICL3221EF use 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” on page 14 and Table 6 on page 15 for capacitor

recommendations for other operating conditions. The charge pumps operate discontinuously (they turn off as

soon as the V+ and V- supplies are pumped up to the nominal values), and provides significant power savings.

4.1.1 Charge Pump Abs Max 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 (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

5.80

6.56

-5.60

-5.88

L

5.80

6.56

-5.60

-5.88

2.4kbps

5.80

6.56

-5.60

-5.88

3kΩ // 1000pF

H

5.88

6.60

-5.56

-5.92

L

5.76

6.36

-5.56

-5.76

2.4kbps

6.00

6.64

-5.64

-5.96

0.047

0.33

Open

H

5.68

6.00

-5.60

-5.60

L

5.68

6.00

-5.60

-5.60

2.4kbps

5.68

6.00

-5.60

-5.60

3kΩ // 1000pF

H

5.76

6.08

-5.64

-5.64

L

5.68

6.04

-5.60

-5.60

2.4kbps

5.84

6.16

-5.64

-5.72

1

1

Open

H

5.88

6.24

-5.60

-5.60

L

5.88

6.28

-5.60

-5.64

2.4kbps

5.80

6.20

-5.60

-5.60

3kΩ // 1000pF

H

5.88

6.44

-5.64

-5.72

L

5.88

6.04

-5.64

-5.64

2.4kbps

5.92

6.40

-5.64

-5.64

Table 3.

V+ and V- Values for VCC = 4.5V to 5.5V

C1 (μF)

C2, C3, C4 (μF)

Load

T1IN

(Logic State)

V+ (V)

V- (V)

VCC = 4.5V

VCC = 5.5V

VCC = 4.5V

VCC = 5.5V