8

FN4878.8

February 27, 2006

Powerdown Functionality

This 3V family of RS-232 interface devices requires a

nominal supply current of 0.3mA during normal operation

(not in powerdown mode). This is considerably less than the

5mA to 11mA current required of 5V RS-232 devices. The

already low current requirement drops significantly when the

device enters powerdown mode. In powerdown, supply

current drops to 1

µA, because the on-chip charge pump

the transmitter outputs three-state. Inverting receiver outputs

may or may not disable in powerdown; refer to Table 2 for

details. This micro-power mode makes these devices ideal

for battery powered and portable applications.

Software Controlled (Manual) Powerdown

These three devices allow the user to force the IC into the

low power, standby state, and utilize 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. To switch between

active and powerdown modes, under logic or software

control, only the FORCEOFF input need be driven. The

FORCEON state isn’t critical, as FORCEOFF dominates

over FORCEON. Nevertheless, if strictly manual control over

powerdown is desired, the user must strap FORCEON high

to disable the enhanced automatic powerdown circuitry.

ICL3245 inverting (standard) receiver outputs also disable

when the device is in powerdown, thereby eliminating the

possible current path through a shutdown peripheral’s input

protection diode (see Figures 2 and 3).

Connecting FORCEOFF and FORCEON together disables

the enhanced automatic powerdown feature, enabling them

to function as a manual SHUTDOWN input (see Figure 4).

TABLE 2. POWERDOWN LOGIC TRUTH TABLE

RCVR OR

XMTR

EDGE

WITHIN

30s?

FORCEOFF

INPUT

FORCEON

INPUT

TRANSMITTER

OUTPUTS

RECEIVER

OUTPUTS

(NOTE 4)

OUTPUTS

RS-232

LEVEL

PRESENT

AT

RECEIVER

INPUT?

INVALID

OUTPUT

MODE OF OPERATION

ICL3225

NO

H

H

Active

Active

N.A.

No

L

Normal Operation (Enhanced

Auto Powerdown Disabled)

NO

H

H

Active

Active

N.A.

Yes

H

YES

H

L

Active

Active

N.A.

No

L

Normal Operation (Enhanced

Auto Powerdown Enabled)

YES

H

L

Active

Active

N.A.

Yes

H

NO

H

L

High-Z

Active

N.A.

No

L

Powerdown Due to Enhanced

Auto Powerdown Logic

NO

H

L

High-Z

Active

N.A.

Yes

H

X

L

X

High-Z

Active

N.A.

No

L

Manual Powerdown

X

L

X

High-Z

Active

N.A.

Yes

H

ICL322X - INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)

X

NOTE 5

NOTE 5

Active

Active

N.A.

Yes

H

Normal Operation

X

NOTE 5

NOTE 5

High-Z

Active

N.A.

No

L

Forced Auto Powerdown

ICL3245

NO

H

H

Active

Active

Active

No

L

Normal Operation (Enhanced

Auto Powerdown Disabled)

NO

H

H

Active

Active

Active

Yes

H

YES

H

L

Active

Active

Active

No

L

Normal Operation (Enhanced

Auto Powerdown Enabled)

YES

H

L

Active

Active

Active

Yes

H

NO

H

L

High-Z

Active

Active

No

L

Powerdown Due to Enhanced

Auto Powerdown Logic

NO

H

L

High-Z

Active

Active

Yes

H

X

L

X

High-Z

High-Z

Active

No

L

Manual Powerdown

X

L

X

High-Z

High-Z

Active

Yes

H

ICL3245 - INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWERDOWN)

X

NOTE 5

NOTE 5

Active

Active

Active

Yes

H

Normal Operation

X

NOTE 5

NOTE 5

High-Z

High-Z

Active

No

L

Forced Auto Powerdown

NOTES:

4. Applies only to the ICL3245.

5. Input is connected to INVALID Output.

ICL3225, ICL3245