Detailed Description

The MAX3160/MAX3161/MAX3162 3V/5V, multiprotocol

transceivers can be pin configured in a number of RS-

232 and RS-485/422 interface combinations. These cir-

cuit configurations are ideal for the design of RS-232 to

RS-485 converters, multiprotocol buses, or any applica-

tion that requires both RS-232 and RS-485 transceivers.

The slew rate of these devices is on-the-fly pin pro-

grammable, allowing reduced EMI data rates, or up to

10Mbps RS-485 communications. Power consumption

can be reduced to 1µA by using the shutdown function,

but the RS-232 receivers remain active allowing other

devices to query the interface controller. A flow-through

pinout and the space-saving SSOP packages (avail-

able in the commercial and extended temperature

ranges) facilitate board layout.

Device Selection

The MAX3160/MAX3161/MAX3162 contain RS-232

transceivers and an RS-485/422 transceiver. The pri-

mary difference between the devices is the multiplexing

of the I/O pins.

The MAX3160 has common transmitter outputs and

receiver inputs for its RS-232 and RS-485/422 trans-

ceivers, and common digital I/O pins. The MAX3160 is

optimized for multiprotocol operation on a single inter-

face bus and comes in a 20-pin SSOP.

The MAX3161 has separate transmitter outputs and

receiver inputs for its RS-232 and RS-485/422 trans-

ceivers, and common digital I/O pins. The MAX3161 is

optimized for multiplexing a single UART across two

interface buses and comes in a 24-pin SSOP.

The MAX3162 has separate transmitter outputs and

receiver inputs for its RS-232 and RS-485/422 trans-

ceivers, and separate digital I/O pins. The MAX3162 is

optimized for protocol translation between two interface

buses and comes in a 28-pin SSOP.

See Tables 1–12,

Functional Diagrams, and the follow-

ing descriptions for details on each device.

MAX3160

The MAX3160 is a 2TX/2RX RS-232 transceiver in RS-

232 mode, capable of RS-232-compliant communica-

tion. Assertion of RS-485/RS-232 converts the device to

a single RS-485 transceiver by multiplexing the RS-232

I/O pins to an RS-485 driver and receiver pair. The

logic inputs now control the driver input and the driver

enable. One logic output carries the RS-485 receiver

output, and the other is three-stated. The receiver input

impedance is dependent on the device mode and is

1/4-unit load for RS-485 operation and 5k

Ω for RS-232

operation.

MAX3161

The MAX3161 is a 2TX/2RX RS-232 transceiver in RS-

232 mode or a single RS-485/422 transceiver in RS-485

mode. When in RS-485 mode, the unused RS-232

transmitter and receiver output pins are disabled. When

in RS-232 mode, the RS-485 transmitter outputs are

disabled and the RS-232 receiver inputs are 5k

Ω to

GND. The RS-485 receiver inputs are always 1/8-unit

load. Logic lines are shared between the two protocols

and are used for signal inputs and as an RS-485 driver

enable.

MAX3162

The MAX3162 is a 2TX/2RX RS-232 transceiver and a

single RS-485/422 transceiver simultaneously. All dri-

vers, receivers, and transmitters can be enabled or dis-

abled by pin configuration. All outputs are high-Z when

not activated. RS-232 receiver inputs are 5k

Ω when

enabled, and RS-485 receiver inputs are 1/8-unit load.

FAST Mode operation

The FAST control pin is used to select the slew-rate lim-

iting of the RS-232 transmitters and the RS-485/422 dri-

vers. With FAST unasserted, the RS-232 transmitters

and the RS-485/422 driver are slew-rate limited to

reduce EMI. RS-232 data rates up to 1Mbps and RS-

485/422 data rates up to 10Mbps are possible when

FAST is asserted. FAST can be changed during opera-

tion without interrupting data communications.

Half-Duplex RS-485/422 Operation

Asserting HDPLX places the MAX3160/MAX3161 in

half-duplex mode. The RS-485 receiver inputs are inter-

nally connected to the driver outputs. The RS-485 dri-

ver outputs can be disabled by pulling DE485 low.

HDPLX has no affect on RS-232 operation.

Low-Power Shutdown

The MAX3160/MAX3161/MAX3162 have an active-low

shutdown control input, SHDN. When driven low, the

charge pump and transmitters are shut down and sup-

ply current is reduced to 1µA. The RS-232 receiver out-

puts remain active if in RS-232 mode. The charge-

pump capacitors must be recharged when coming out

of shutdown before resuming operation in either RS-232

or RS-485/422 mode (Figure 10).

Dual Charge-Pump Voltage Converter

The MAX3160/MAX3161/MAX3162s’ internal power

supply consists of a regulated dual charge pump that

provides output voltages of +5.5V (doubling charge

pump) and -5.5V (inverting charge pump) for input volt-

pumps operate in a discontinuous mode: if the magni-

tude of either output voltage is less than 5.5V, the

+3.0V to+5.5V, 1µA, RS-232/RS-485/422

Multiprotocol Transceivers

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