ICL3221, ICL3222, ICL3223, ICL3232, ICL3241, ICL3243

4. Application Information

FN4805 Rev.23.00

Page 16 of 36

Apr.26.19

4.5.2 INVALID Output

The INVALID output always indicates whether a valid RS-232 signal is present at any of the receiver inputs (See

Table 5), giving you a way to determine when the interface block should power down. In the case of a

disconnected interface cable where all the receiver inputs are floating (but pulled to GND by the internal receiver

pull down resistors), the INVALID logic detects the invalid levels and drives the output low. The power

management logic then uses this indicator to power down the interface block. Reconnecting the cable restores

valid levels at the receiver inputs, INVALID switches high, and the power management logic wakes up the

interface block. INVALID can also be used to indicate the DTR or RING INDICATOR signal as long as the other

receiver inputs are floating or driven to GND (as in the case of a powered down driver). Connecting FORCEOFF

and FORCEON together disables the automatic powerdown feature, enabling them to function as a manual

SHUTDOWN input (See Figure 10).

N.A.

H

N.A.

H

Active

High-Z

Active

N.A.

Normal Operation w/Rcvr.

Disabled

ICL3221, ICL3223

No

H

H

L

Active

Active

N.A.

L

Normal Operation

(Auto Powerdown Disabled)

No

H

H

H

Active

High-Z

N.A.

L

Yes

H

L

L

Active

Active

N.A.

H

Normal Operation

(Auto Powerdown Enabled)

Yes

H

L

H

Active

High-Z

N.A.

H

No

H

L

L

High-Z

Active

N.A.

L

Powerdown Due to Auto

Power-Down Logic

No

H

L

H

High-Z

High-Z

N.A.

L

Yes

L

X

L

High-Z

Active

N.A.

H

Manual Powerdown

Yes

L

X

H

High-Z

High-Z

N.A.

H

Manual Powerdown w/Rcvr.

Disabled

No

L

X

L

High-Z

Active

N.A.

L

Manual Powerdown

No

L

X

H

High-Z

High-Z

N.A.

L

Manual Powerdown w/Rcvr.

Disabled

ICL3243

No

H

H

N.A.

Active

Active

Active

L

Normal Operation

(Auto Powerdown Disabled)

Yes

H

L

N.A.

Active

Active

Active

H

Normal Operation

(Auto Powerdown Enabled)

No

H

L

N.A.

High-Z

Active

Active

L

Powerdown Due to Auto

Power-Down Logic

Yes

L

X

N.A.

High-Z

High-Z

Active

H

Manual Powerdown

No

L

X

N.A.

High-Z

High-Z

Active

L

Manual Powerdown

Note:

6. Applies only to the ICL3241 and ICL3243.

Table 5.

Powerdown and Enable Logic Truth Table (Continued)

RS-232

Signal Present at

Receiver Input?

FORCEOFF

or SHDN

Input

FORCEON

Input

EN

Input

Transmitter

Outputs

Receiver

Outputs

ROUTB

Outputs

(Note 6)

INVALID

Output

Mode of Operation

ICL3222, ICL3241