7 Detailed Description

7.1 Overview

The MAX3243 device consists of three line drivers, five line receivers, and a dual charge-pump circuit with

±15kV ESD (HBM) protection pin to pin (serial- port connection pins, including GND). The device meets the

requirements of TIA/EIA-232-F and provides the electrical interface between an asynchronous communication

controller and the serial-port connector. This combination of drivers and receivers matches that needed for the

typical serial port used in an IBM PC/AT, or compatible. The charge pump and four small external capacitors

allow operation from a single 3V to 5.5V supply. In addition, the device includes an always-active noninverting

output (ROUT2B), which allows applications using the ring indicator to transmit data while the device is powered

down. Flexible control options for power management are available. when the serial port is inactive. The auto-

power-down feature functions when FORCEON is low and FORCEOFF is high. During this mode of operation, if

the device does not sense a valid RS-232 signal, the driver outputs are disabled. If FORCEOFF is set low, both

drivers and receivers (except ROUT2B) are shut off, and the supply current is reduced to 1µA. Disconnecting the

serial port or turning off the peripheral drivers causes the auto-powerdown condition to occur. Auto-powerdown

can be disabled when FORCEON and FORCEOFF are high and should be done when driving a serial mouse.

With auto-powerdown enabled, the device is activated automatically when a valid signal is applied to any

receiver input. The INVALID output is used to notify the user if an RS-232 signal is present at any receiver

input. INVALID is high (valid data) if any receiver input voltage is greater than 2.7V or less than –2.7V or has

been between –0.3V and 0.3V for less than 30µs. INVALID is low (invalid data) if all receiver input voltages are

between –0.3V and 0.3V for more than 30µs.

7.2 Functional Block Diagram

DIN3

DIN2

DIN1

DOUT3

DOUT2

DOUT1

Auto-powerdown

INVALID

RIN1

RIN2

RIN3

RIN4

RIN5

FORCEOFF

FORCEON

ROUT1

ROUT2B

ROUT2

ROUT3

ROUT4

ROUT5

14

13

12

22

23

19

20

18

17

16

15

9

10

11

21

4

5

6

7

8

5 k

5 k

5 k

5 k

5 k

W

W

W

W

W

MAX3243

SLLS350Q – APRIL 1999 – REVISED AUGUST 2024

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