3V to 5.5V, IrDA Infrared Transceiver with

Integrated RS-232 Interface

8

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Detailed Description

The MAX3130/MAX3131 are IrDA 1.2 compatible,

infrared transceivers with an integrated RS-232 inter-

face. By selecting appropriate external optical compo-

nents, these devices support IrDA 1.2 data rates from

2.4kbps to 115kbps at distances from 1cm to 1m. A

low-noise design allows them to achieve a bit-error rate

rejects out-of-band ambient light signals that interfere

with infrared communication. Both devices include a

high-power LED driver capable of sinking 200mA.

The MAX3130 and MAX3131 contain two RS-232 drivers

and two RS-232 receivers that support data rates up to

120kbps. The RS-232 transceiver is powered by a high-

efficiency, dual charge-pump power supply that oper-

ates with input supply voltages from +3.0V to +5.5V.

The MAX3130 is optimized for applications using a sin-

gle UART for both infrared and RS-232 communication.

The infrared transmitter input and infrared receiver out-

put are multiplexed with one RS-232 transmitter input

and one RS-232 receiver output, respectively. The

MAX3131 IrDA and RS-232 transceivers are indepen-

dent of each other for use in simultaneous multiprotocol

transceiver applications.

IR Receivers

The receiver amplifier reverse biases the PIN diode

with approximately 1.2V, and the PIN diode converts

pulses of IR light into pulses of current. The input trans-

impedance (current-to-voltage) amplifier converts and

amplifies these current pulses into voltage pulses. The

MAX3130/MAX3131 incorporate filters that remove low-

frequency ambient light interference and high-frequency

circuit noise from these voltage pulses. A high-speed

comparator then translates these voltage pulses into

CMOS output levels. Figures 1 and 2 show system

functional diagrams.

The RXD pin is the output of the infrared receiver for

the MAX3131. The R2OUT pin is the output of the

infrared receiver for the MAX3130 (IRMODE = low).

With the ENDEC disabled, the infrared receiver output

pulses low upon each incoming infrared pulse. The

pulse width of the receiver output depends on many

factors, including transmitter distance and power, PIN

photodiode efficiency and area, and incoming data

rate. Under all circumstances the output pulse is less

than one baud period. To communicate with UARTs

that are not IrDA compatible, enable the ENDEC (see

the

IrDA Encoder/Decoder (ENDEC) section).

MAX3131 Operational Modes Table

RSSD

IRSD

T_OUT

R_IN

LEDC

RXD

0

0

High-Z

Enabled

Enabled

Logic High

0

1

High-Z

Enabled

Enabled

IrDA Output

1

0

Enabled

Enabled

Enabled

Logic High

1

1

Enabled

Enabled

Enabled

IrDA Output

MAX3130 Function Table

RSSD

X

X

0

0

IRMODE

MAX3130

CONTROL INPUTS

IRSD

0

1

RS-232

Input

RS-232

Input

T1IN

LOGIC INPUTS

IrDA

Input

IrDA

Input

T2IN

Enabled

High-Z

High-Z

T1OUT

RS-232 I/O

High-Z

High-Z

T2OUT

Disabled

RS-232

Input

RS-232

Input

R1IN

PINC

RS-232

Input

RS-232

Input

R2IN

IrDA

INPUT

RS-232

Output

RS-232

Output

R1OUT

LOGIC OUTPUTS

IrDA

Output

IrDA

Output

R2OUT

Disabled

Enabled

Enabled

LEDC

IrDA

OUTPUT

0

1

0

RS-232

Input

RS-232

Input

High-Z

High-Z

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

Disabled

0

1

1

RS-232

Input

RS-232

Input

High-Z

High-Z

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

Disabled

Enabled

Disabled

Enabled

1

1

0

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

Disabled

1

1

1

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

RS-232

Input

RS-232

Input

RS-232

Output

RS-232

Output

Disabled

X = Don’t care