Keep communications cables short to minimize capaci-

tive loading. Lowering the capacitive loading on the

transmitter outputs reduces the MAX3218’s power con-

sumption. Using short, low-capacitance cable also

helps transmission at the highest data rates.

EIA/TIA-232E and

_____________EIA/TIA-562 Standards

RS-232 circuits consume much of their power because

the EIA/TIA-232E standard demands that the transmit-

ters deliver at least 5V to receivers with impedances

that can be as low as 3k

Ω. For applications where

power consumption is critical, the EIA/TIA-562 standard

provides an alternative.

EIA/TIA-562 transmitter output voltage levels need only

reach ±3.7V, and because they have to drive the same

3k

Ω receiver loads, the total power consumption is con-

siderably reduced. Since the EIA/TIA-232E and

EIA/TIA-562 receiver input voltage thresholds are the

same, interoperability between EIA/TIA-232E and

EIA/TIA-562 devices is guaranteed. Maxim’s MAX560

and MAX561 are EIA/TIA-562 transceivers that operate

on a single supply from 3.0V to 3.6V, and the MAX562

transceiver operates from 2.7V to 5.25V while produc-

ing EIA/TIA-562 levels.

1µA Supply Current, 1.8V to 4.25V-Powered

RS-232 Transceiver with AutoShutdown™

_______________________________________________________________________________________

9

TRANSMITTERS ENABLED, INVALID HIGH

AUTOSHUTDOWN, TRANSMITTERS DISABLED,

1

µA SUPPLY CURRENT, INVALID LOW

TRANSMITTERS ENABLED, INVALID HIGH

-2.8V

-0.3V

+2.8V

+0.3V

(a)

(b)

0V

INDETERMINATE

INDETERMINATE

V-

0V

V+

0

INVALID

REGION

RECEIVER

INPUT

VOLTAGE

(V)

INVALID

OUTPUT

(V)

Figure 4. AutoShutdown Trip Levels

Figure 5. AutoShutdown with Initial Turn-On to Wake Up a

System

FORCEON

MASTER SHDN LINE

0.1µF

1M

FORCEOFF

MAX3218

POWER

MANAGEMENT

UNIT