+3.0V to+5.5V, 1µA, RS-232/RS-485/422

Multiprotocol Transceivers

18

______________________________________________________________________________________

ceivers to be connected in parallel on one communica-

tion line. The MAX3161/MAX3162 have a 1/8-unit load

receiver input impedance (96k

Ω), allowing up to 256

transceivers to be connected in parallel on one com-

munication line. Any combination of these devices

and/or other RS-485 transceivers with a total of 32-unit

loads or fewer can be connected to the line.

The MAX3160/MAX3161/MAX3162 RS-485 driver out-

puts are 1/8-unit load when disabled This impedance

may be reduced if the D1 pin is toggled at a high fre-

485 transmitter output impedances typically go to 1/2-

unit load on the MAX3161/MAX3162, and to one-unit

load on the MAX3160.

Driver Output Protection

Two mechanisms prevent excessive output current and

power dissipation caused by faults or by bus con-

tention. The first, a foldback current limit on the output

stage, provides immediate protection against short cir-

cuits over the whole common-mode voltage range (see

Typical Operating Characteristics). The second, a ther-

mal shutdown circuit, forces the driver outputs into a

high-impedance state if the die temperature becomes

excessive.

Protection Against Wiring Faults

EIA/TIA-485 standards require a common input voltage

range of -7V to +12V to prevent damage to the device.

The MAX3160/MAX3161/MAX3162 inputs are protected

to RS-232 levels of ±25V for the receiver inputs and

±13.2V for the transmitter/driver outputs. This provides

additional protection for the RS-485 transceivers

against ground differential or faults due to miswiring.

RS-485/422 Reduced EMI and Reflections

The MAX3160/MAX3161/MAX3162 can be configured

for slew-rate limiting by pulling FAST low. This minimizes

EMI and reduces reflections caused by improperly ter-

minated cables. Operation in slew-rate limited mode

reduces the amplitudes of high-frequency harmonics.

SUPPLY VOLTAGE

(V)

C1 (µF)

(µF)

+3.0 TO +3.6

0.1

0.1

+4.5 TO +5.5

0.047

0.33

+3.0 TO +5.5

0.1

0.47

Table 13. Required Minimum Capacitance

Values

INPUTS

OUTPUT

RS485/RS232

SHDN

HDPLX

A - B

Y(A) - Z(B)

RO/R2OUT

1

0

X

X

X

110

≥-50mV

X

1

110

≤-200mV

X

0

1

1

0

Floating

X

1

111

X

≥-50mV

1

111

X

≤-200mV

0

1

1

1

X

Floating

1

0

X

X

X

X

RS-232 Mode

Table 11. MAX3161

INPUTS

OUTPUT

SHDN

RE485

A - B

RO

0

X

X

High-Z

X

1

X

High-Z

10

≥-50mV

1

10

≤-200mV

0

1

0

Inputs Open

1

Table 12. MAX3162

Truth Tables (continued)