ICL3221EM, ICL3221EF

4. Application Information

FN7552 Rev.2.00

Page 11 of 22

May.29.19

4.4

Low Power Operation

These 3V devices require a nominal supply current of 0.3mA, during normal operation (not in powerdown mode),

which is considerably less than the 5mA to 11mA current required by comparable 5V RS-232 devices, allowing

you to reduce system power simply by switching to this new family.

4.5

Powerdown Functionality

The already low current requirement drops significantly when the device enters powerdown mode. In

power-down, supply current drops to 1µA, because the on-chip charge pump turns off (V+ collapses to VCC, V-

collapses to GND), and the transmitter outputs three-state. Inverting receiver outputs can disable in powerdown;

see Table 5 for details. This micro-power mode makes these devices ideal for battery powered and portable

applications.

4.5.1 Software Controlled (Manual) Powerdown

The ICL3221EM and ICL3221EF devices provide a pin that allows you to force the IC into the low power, standby

state. Driving this pin high enables normal operation, and driving it low forces the IC into its powerdown state.

Connect FORCEOFF to VCC if the powerdown function is not needed. Note: All the receiver outputs remain

enabled during shutdown (see Table 5). For the lowest power consumption during powerdown, the receivers

should also be disabled by driving the EN input high (see Figures 6 and 7).

The ICL3221EM and ICL3221EF use a two pin approach where the FORCEON and FORCEOFF inputs

determine the IC’s mode. For always enabled operation, FORCEON and FORCEOFF are both strapped high.

Under logic or software control, only the FORCEOFF input needs to be driven to switch between active and

powerdown modes. The FORCEON state is not critical because FORCEOFF overrides FORCEON. However, if

strictly manual control over powerdown is needed, you must strap FORCEON high to disable the automatic

powerdown circuitry.

Figure 5. Inverting Receiver Connections

Table 5.

Powerdown and Enable Logic Truth Table

RS-232 SIgnal

Present at

Receiver Input?

FORCEOFF

Input

FORCEON

Input

EN

Input

Transmitter

Outputs

Receiver

Outputs

INVALID

Output

Mode of Operation

ICL3221EM and ICL3221EF

No

H

H

L

Active

Active

L

Normal Operation

(Auto Powerdown Disabled)

No

H

H

H

Active

High-Z

L

Yes

H

L

L

Active

Active

H

Normal Operation

(Auto Powerdown Enabled)

Yes

H

L

H

Active

High-Z

H

No

H

L

L

High-Z

Active

L

Powerdown Due to Auto

Power-Down Logic

No

H

L

H

High-Z

High-Z

L

Yes

L

X

L

High-Z

Active

H

Manual Powerdown

Yes

L

X

H

High-Z

High-Z

H

Manual Powerdown with

Receiver Disabled

No

L

X

L

High-Z

Active

L

Manual Powerdown

No

L

X

H

High-Z

High-Z

L

Manual Powerdown with

Receiver Disabled

RXOUT

GND ≤ VROUT ≤ VCC

5kΩ

RXIN

-25V ≤ VRIN ≤ +25V

GND

VCC