3V to 5.5V, IrDA Infrared Transceiver with
Integrated RS-232 Interface
MAX3130/MAX3131
MAX3130 Function Table
MAX3130
CONTROL INPUTS
RSSD
X
X
0
0
1
1
IRMODE
0
0
1
1
1
1
IRSD
0
1
0
1
0
1
LOGIC INPUTS
T1IN
RS-232
Input
RS-232
Input
T2IN
IrDA
Input
IrDA
Input
T1OUT
High-Z
High-Z
High-Z
High-Z
RS-232 I/O
T2OUT
High-Z
High-Z
High-Z
High-Z
RS-232
Output
RS-232
Output
R1IN
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
R2IN
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
RS-232
Input
LOGIC OUTPUTS
R1OUT
RS-232
Output
RS-232
Output
RS-232
Output
RS-232
Output
RS-232
Output
RS-232
Output
R2OUT
IrDA
Output
IrDA
Output
RS-232
Output
RS-232
Output
RS-232
Output
RS-232
Output
IrDA
OUTPUT
LEDC
Enabled
Enabled
Disabled
Disabled
Disabled
Disabled
IrDA
INPUT
PINC
Disabled
Enabled
Disabled
Enabled
Disabled
Enabled
RS-232 RS-232
Input
Input
RS-232 RS-232
Input
Input
RS-232 RS-232 RS-232
Input
Input
Output
RS-232 RS-232 RS-232
Input
Input
Output
X = Don’t care
MAX3131 Operational Modes Table
RSSD
0
0
1
1
IRSD
0
1
0
1
T_OUT
High-Z
High-Z
Enabled
Enabled
R_IN
Enabled
Enabled
Enabled
Enabled
LEDC
Enabled
Enabled
Enabled
Enabled
RXD
Logic High
IrDA Output
Logic High
IrDA Output
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
below 10
-8
at maximum data rates. On-chip filtering
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.
8
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).
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