±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,

RS-232 Transceivers with AutoShutdown

8

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Table 1. Output Control Truth Table

+0.3V

-0.3V

INVALID

TO MAX32_ _E

POWER SUPPLY

AND TRANSMITTERS

R_IN

* TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1

µA IF

ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30

µs.

30µs

COUNTER

R

Figure 3a. MAX32_ _E Entering 1µA Supply Mode via

AutoShutdown

+2.7V

-2.7V

INVALID

TO MAX32_ _E

POWER SUPPLY

R_IN

* TRANSMITTERS ARE ENABLED IF:

ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V.

ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30

µs.

30µs

COUNTER

R

Figure 3b. MAX32__E with Transmitters Enabled Using

AutoShutdown

X = Don’t Care

The MAX3221E/MAX3223E/MAX3243E feature an

INVALID output that is enabled low when no valid RS-232

signal levels have been detected on all receiver inputs.

INVALID is functional in any mode (Figures 3 and 5).

AutoShutdown

The MAX3221E/MAX3223E/MAX3243E achieve a 1µA

supply current with Maxim’s new AutoShutdown fea-

ture, which operates when FORCEON is low and

FORCEOFF is high. When these devices sense no valid

signal levels on all receiver inputs for 30µs, the on-

board charge pump and drivers are shut off, reducing

supply current to 1µA. This occurs if the RS-232 cable

is disconnected or the connected peripheral transmit-

ters are turned off. The device turns on again when a

valid level is applied to any RS-232 receiver input. As a

result, the system saves power without changes to the

existing BIOS or operating system.

0

0

0

1

X

1

FORCEON

X

Active

Active

Active

R2OUTB

(MAX3243E)

Active

Active

Active

Active

Active

Active

High-Z

R_OUT

(MAX3221E/

MAX3223E)

Active

Active

High-Z

High-Z

1

1

1

1

0

1

FORCEOFF

0

Active

High-Z

Active

T_OUT

High-Z

Active

Active

High-Z

Active

High-Z

Active

R_OUT

(MAX3243E)

High-Z

Active

Active

High-Z

0

0

Yes

No

Normal Operation

(AutoShutdown)

Yes

0

X

Normal Operation

(Forced On)

X

Shutdown

(Forced Off)

X

EN

(MAX3221E/

MAX3223E)

VALID

RECEIVER

LEVEL

0

X

OPERATION

STATUS

1

1

1

0

Active

High-Z

1

High-Z

High-Z

Shutdown

(AutoShutdown)

No

1