1µA Supply-Current, True +3V to +5.5V

RS-232 Transceivers with AutoShutdown

6

_______________________________________________________________________________________

RS-232 Receivers

The MAX3221/MAX3223/MAX3243’s receivers convert

RS-232 signals to CMOS-logic output levels. All

receivers have one inverting three-state output. In shut-

down (FORCEOFF = low) or in AutoShutdown, the

MAX3221/MAX3223’s receivers are active (Table 1).

Driving EN high places the receiver(s) in a high-imped-

ance state. The MAX3243’s receivers are high imped-

ance when the part is shut down.

The MAX3243 has an always-active complementary

output (R2OUTB). R2OUTB is an extra output that mon-

itors receiver activity while the other receivers are high

impedance. This allows Ring Indicator to be monitored

without forward biasing other devices connected to the

set to 0V in shutdown to accommodate peripherals,

such as UARTs (Figure 2).

MAX3243

I/O

CHIP

WITH

UART

CPU

RS-232

POWER

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

FORCEOFF

FORCEON

INVALID

MAX3243

T1OUT

R2OUTB

Tx

5kΩ

UART

T1IN

THREE-STATED

LOGIC

TRANSITION

DETECTOR

R2IN

PROTECTION

DIODE

R2OUT

FORCEOFF = GND

TO

µP

Rx

PREVIOUS

RS-232

Tx

UART

SHDN = GND

GND

Rx

5kΩ

RECEIVER OUTPUT IN SHUTDOWN.

DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT PATH

THROUGH THE UART'S PROTECTION DIODE.

GND

PROTECTION

DIODE

I

I

Figure 1. Interface Under Control of PMU

Figure 2. The MAX3243 detects RS-232 activity when the

UART and interface are shut down.