Datasheet
MAX3120
Low-Profile, 3V, 120µA,
IrDA Infrared Transceiver
_______________________________________________________________________________________
5
2V/div
2V/div
RXD OUTPUT
vs. INFRARED INPUT
MAX3120 toc12
2µs/div
RXD
OUTPUT
INFRARED
INPUT
V
CC
= 3.3V, 115.2kbps AT 1m DISTANCE,
TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
2V/div
2V/div
RXD OUTPUT
vs. INFRARED INPUT
MAX3120 toc13
100µs/div
RXD
OUTPUT
INFRARED
INPUT
V
CC
= 3.3V, 2400bps AT 1m DISTANCE,
TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
Pin Description
NAME FUNCTION
1 TXD IR Transmitter TTL/CMOS Data Input. High = LED on.
2 V
CC
Supply Voltage
PIN
3 GND Ground. Connect anode of PIN diode to GND. Connect GND to PGND.
4 PINC PIN Diode Cathode Input. Connect cathode of PIN diode to PINC.
8 RXD IR Receiver TTL/CMOS Data Output. Pulses low for IR input pulse.
7 LEDC LED Driver Output. Connect cathode of IR-emitting LED to LEDC.
6 PGND Power Ground. Ground for IR LED driver. Connect PGND to GND.
5
SHDN
Shutdown Input. Active low.
Detailed Description
The MAX3120 is an IrDA 1.2-compatible infrared (IR)
transceiver. By selecting appropriate external optical
components (see
IR LED and PIN Photodiode Selection
section), the MAX3120 will operate at data rates of
2.4kbps to 115kbps at distances from 1cm to 1m.
Because of its low-noise design, the MAX3120
achieves a bit error rate (BER) below 10
-8
at maximum
data rates when used with the appropriate external
components. On-chip filtering rejects out-of-band
ambient light signals that would otherwise interfere with
IR communication. Also included in the MAX3120 is
a high-power LED driver capable of sinking 200mA. It
can drive most available IR LEDs at IrDA speeds of
2.4kbps to 115kbps.
Receiver
The MAX3120’s IR receiver amplifier reverse biases the
PIN diode by approximately 1.2V, and the PIN diode
converts pulses of IR light into pulses of current. The
input transimpedance (current-to-voltage) amplifier
then converts these current pulses into voltage pulses
of a useful magnitude. The MAX3120 filters the result-
ing output voltage pulses to remove low-frequency
ambient light interference and high-frequency circuit
noise. Finally, a high-speed comparator translates
these voltage pulses into usable CMOS output levels
(Figure 1).