MAX3221/MAX3223/MAX3243

+3V to +5.5V RS-232 Transceivers

with AutoShutdown

Maxim Integrated | 7

www.maximintegrated.com

AutoShutdown

A 1µA supply current is achieved with Maxim’s new

AutoShutdown feature, which operates when

FORCEON is low and FORCEOFF is high. When the

MAX3221/MAX3223/MAX3243 sense no valid signal

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

power supply and drivers are shut off, reducing supply

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

connected or the connected peripheral transmitters are

turned off. The system 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. When using AutoShutdown,

the INVALID output is high when the device is on and

low when the device is shut down. Because INVALID

indicates the receiver inputs’ condition, it can be used

in any mode (Figure 3).

Table 2 and Figure 3c summarize the MAX3221/

MAX3223/MAX3243 operating modes. FORCEON and

FORCEOFF override the automatic circuitry and force

the transceiver into its normal operating state or into its

low-power standby state. When neither control is assert-

ed, the IC selects between these states automatically

based on receiver input levels. Figures 3a, 3b, and 5a

depict valid and invalid RS-232 receiver levels.

A mouse or other system with AutoShutdown may need

time to wake up. Figure 4 shows a circuit that forces the

transmitters on for 100ms, allowing enough time for the

other system to realize that the MAX3221/MAX3223/

Table 1a. MAX3221/MAX3223 F

FO

OR

RC

CE

EO

OF

FF

F and

Enable Control Truth Table

Table 1b. MAX3243 F

FO

OR

RC

CE

EO

OF

FF

F Control

Truth Table

Active*

1

1

Active*

0

1

F

FO

OR

RC

CE

EO

OF

FF

F

High-Z

1

0

High-Z

0

0

T_OUT

E

EN

N

High-Z

Active

High-Z

Active

R_OUT

+0.3V

-0.3V

INVALID

TO MAX32_ _

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

Active*

1

High-Z

0

T_OUT

F

FO

OR

RC

CE

EO

OF

FF

F

Active*

High-Z

R_OUT

Active

Active

R2OUTB

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

AutoShutdown

FORCEON = GND), it is shut down if no valid RS-232

levels are present on all receiver inputs.

FORCEON

MASTER SHDN LINE

0.1

μF1MΩ

FORCEOFF

MAX3221

MAX3223

MAX3243

POWER

MANAGEMENT

UNIT

Figure 4. AutoShutdown with Initial Turn-On to Wake Up a

Mouse or Another System

+2.7V

-2.7V

INVALID

TO MAX32_ _

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_ _ with Transmitters Enabled Using

AutoShutdown

FORCEOFF

POWER DOWN

INVALID

FORCEON

INVALID IS AN INTERNALLY GENERATED SIGNAL

THAT IS USED BY THE AUTOSHUTDOWN LOGIC

AND APPEARS AS AN OUTPUT OF THE DEVICE.

POWER DOWN IS ONLY AN INTERNAL SIGNAL.

IT CONTROLS THE OPERATIONAL STATUS OF

THE TRANSMITTERS AND THE POWER SUPPLIES.

Figure 3c. AutoShutdown Logic