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

RS-232 Transceivers with AutoShutdown

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7

RS-232 Receivers

The MAX3221E/MAX3223E/MAX3243E’s receivers con-

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

receivers have inverting three-state outputs and can be

active or inactive. In shutdown (FORCEOFF = low) or in

AutoShutdown, the MAX3221E/MAX3223E’s receivers

are active (Table 1). Drive EN high to place the receiv-

er(s) in a high-impedance state. The MAX3243E’s

receivers are high-impedance when the part is in shut-

down (FORCEOFF = low).

The MAX3243E features an extra, always-active com-

plementary output (R2OUTB). R2OUTB monitors

receiver activity while the other receivers are high-

impedance. This allows Ring Indicator to be monitored

without forward biasing other devices connected to the

drops to 0 in shutdown to accommodate peripherals

such as UARTs (Figure 2).

MAX3243E

I/O

CHIP

WITH

UART

CPU

RS-232

POWER-

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

FORCEOFF

FORCEON

INVALID

MAX3243E

T1OUT

R2OUTB

Tx

5k

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

5k

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 MAX3243E detects RS-232 activity when the

UART and interface are shut down.