ICL3221EM, ICL3221EF

4. Application Information

FN7552 Rev.2.00

Page 10 of 22

May.29.19

The resulting new maximum voltages at V+ and V- are listed in Table 4.

4.2

Transmitters

The transmitters are proprietary, low dropout, inverting drivers that translate TTL/CMOS inputs to EIA/TIA-232

output levels. These transmitters are coupled with the on-chip ±5.5V supplies and deliver true RS-232 levels

across a wide range of single supply system voltages.

The transmitter output disables and assumes a high impedance state when the device enters the powerdown

mode (see Table 5 on page 11). These outputs can be driven to ±12V when disabled.

All devices ensure a 250kbps data rate for full load conditions (3kΩ and 1000pF), VCC ≥ 3.0V, with one transmitter

operating at full speed. Under more typical conditions of VCC ≥ 3.3V, RL = 3kΩ, and CL = 250pF, one transmitter

easily operates at 900kbps.

Transmitter inputs float if left unconnected, and can cause ICC increases. Connect unused inputs to GND for best

performance.

4.3

Receivers

The ICL3221EM and ICL3221EF devices contain standard inverting receivers that three-state using the EN or

FORCEOFF control lines. The receivers convert RS-232 signals to CMOS output levels and accept inputs up to

±25V while presenting the required 3kΩ to 7kΩ input impedance (see Figure 5 on page 11) even if the power is off

(VCC = 0V). The receivers’ Schmitt trigger input stage uses hysteresis to increase noise immunity and decrease

errors due to slow input signal transitions.

The ICL3221EM’s and ICL3221EF’s inverting receivers are disabled only when EN is driven high (see Table 5).

Standard receivers driving powered down peripherals must be disabled to prevent current flow through the

peripheral’s protection diodes (see Figures 6 and 7 on page 12). When disabled, the receivers cannot be used for

wake up functions, but the corresponding monitor receiver can be dedicated to this task as shown in Figure 7.

0.1

0.1

Open

H

7.44

8.48

-6.16

-6.40

L

7.44

8.48

-6.16

-6.44

2.4kbps

7.44

8.48

-6.17

-6.44

3kΩ // 1000pF

H

7.76

8.88

-6.36

-6.72

L

7.08

8.00

-5.76

-5.76

2.4kbps

7.76

8.84

-6.40

-6.64

0.047

0.33

Open

H

6.44

6.88

-5.80

-5.88

L

6.48

6.88

-5.84

-5.88

2.4kbps

6.44

6.88

-5.80

-5.88

3kΩ // 1000pF

H

6.64

7.28

-5.92

-6.04

L

6.24

6.60

-5.52

-5.52

2.4kbps

6.72

7.16

-5.92

-5.96

1

1

Open

H

6.84

7.60

-5.76

-5.76

L

6.88

7.60

-5.76

-5.76

2.4kbps

6.92

7.56

-5.72

-5.76

3kΩ // 1000pF

H

7.28

8.16

-5.80

-5.92

L

6.44

6.84

-5.64

-6.84

2.4kbps

7.08

7.76

-5.80

-5.80

Table 4.

New Measured Withstanding Voltages

V+, V- to Ground

±13V

V+ to V-

20V

Table 3.

V+ and V- Values for VCC = 4.5V to 5.5V (Continued)