MAX3387EEUG View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX3387EEUG

3V, ±15kV ESD-Protected, AutoShutdown Plus RS-232 Transceiver for PDAs and Cell Phones

Maxim Integrated 

3V, ±15kV ESD-Protected, AutoShutdown Plus

RS-232 Transceiver for PDAs and Cell Phones

Detailed Description

Dual Charge-Pump

Voltage Converter

The MAX3387E’s internal power supply consists of a

regulated dual charge pump that provides output volt-

ages of +5.5V (doubling charge pump) and -5.5V

(inverting charge pump), regardless of the input volt-

age (VCC) over a +3.0V to +5.5V range. The charge

pumps operate in a discontinuous mode: if the output

voltages are less than 5.5V, the charge pumps are

enabled; if the output voltages exceed 5.5V, the charge

pumps are disabled. Each charge pump requires a fly-

ing capacitor (C1, C2) and a reservoir capacitor (C3,

C4) to generate the V+ and V- supplies.

RS-232 Transmitters

The transmitters are inverting level translators that con-

vert CMOS-logic levels to 5.0V EIA/TIA-232 levels.

The MAX3387E transmitters guarantee a 250kbps data

rate with worst-case loads of 3kΩ in parallel with

1000pF, providing compatibility with PC-to-PC commu-

nication software (such as Laplink®). Transmitters can

be paralleled to drive multiple receivers or mice. Figure 1

shows a complete system connection.

POWER-

MANAGEMENT

UNIT OR

KEYBOARD

CONTROLLER

I/O CHIP

POWER SUPPLY

FORCEON

FORCEOFF

INVALID

VCC

VL

MAX3387E

These RS-232 output stages are turned off (high imped-

ance) when the device is in shutdown mode. When the

power is off, the MAX3387E permits the outputs to be

driven up to ±12V.

The transmitter inputs do not have pull-up resistors.

Connect unused inputs to GND or VL.

RS-232 Receivers

The receivers convert RS-232 signals to CMOS-logic

output levels. The MAX3387E’s receivers are always

active, even when the device is in shutdown.

The MAX3387E features an INVALID output that indi-

cates when no signal is present on any RS-232 receiver

inputs. INVALID is independent of other control logic

functions; it indicates the receiver input conditions only

(Figures 2 and 3).

+0.3V

R_IN

-0.3V

30μs

COUNTER

R

INVALID

TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1μA IF

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

Figure 2a. INVALID Function Diagram, INVALID = Low

+2.7V

I/O

CHIP

WITH

UART

CPU

RS-232

R_IN

30μs

COUNTER INVALID

-2.7V

R

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 30μs.

Figure 1. Interface Under Control of PMU

Figure 2b. INVALID Function Diagram, INVALID = High

Laplink is a registered trademark of Laplink Software, Inc.

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