MAX3221 Просмотр технического описания (PDF) - Maxim Integrated

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MAX3221

1µA Supply-Current, True +3V to +5.5V RS-232 Transceivers with AutoShutdown

Maxim Integrated 

1µA Supply-Current, True +3V to +5.5V

RS-232 Transceivers with AutoShutdown

POWER

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

FORCEOFF

FORCEON

INVALID

MAX3243

I/O

CPU

CHIP

WITH

UART

VCC

RS-232

PROTECTION

DIODE

VCC

Rx

I

UART

Tx

GND

SHDN = GND

PREVIOUS

RS-232

5kΩ

(a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE

RECEIVER OUTPUT IN SHUTDOWN.

Figure 1. Interface Under Control of PMU

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

receiver outputs. This is ideal for systems where VCC is

set to 0V in shutdown to accommodate peripherals,

such as UARTs (Figure 2).

VCC

TO LOGIC

µP TRANSITION

DETECTOR

PROTECTION

DIODE

I

R2OUTB

VCC

Rx

UART

R2OUT

THREE-STATED

Tx

GND

T1IN

FORCEOFF = GND

MAX3243

R2IN

5kΩ

T1OUT

(b) NEW MAX3243: IN SHUTDOWN, R2OUTB IS USED TO MONITOR EXTERNAL

DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT PATH

THROUGH THE UART'S PROTECTION DIODE.

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

UART and interface are shut down.

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