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19-1390; Rev 0; 10/98
Low-Profile, 3V, 120A, IrDA Infrared Transceiver
General Description
The MAX3120 IrDA 1.2-compatible infrared transceiver is optimized for battery-powered, space-constrained applications. It consumes only 120A while supporting data rates up to 115kbps over a wide 3V to 5.5V operating range, and features a 10nA shutdown mode to further extend battery life. The MAX3120 reduces the space required for IrDA applications by requiring a minimum of external components: photodiode, infrared LED, and current-setting resistor. Optical components are external to allow maximum flexibility in PC board design. The MAX3120 is available in 8-pin MAX and SO packages. The MAX package consumes half the board space of an 8-pin SO.
Features
o IrDA 1.2 Compatible: 2.4kbps to 115.2kbps o +3V to +5.5V Single-Supply Operation o Flexible Optics Selection and Layout o 120A Supply Current o 10nA Shutdown Supply Current o 200mA, High-Current Infrared LED Drive
MAX3120
Ordering Information
PART MAX3120CUA MAX3120CSA MAX3120EUA MAX3120ESA TEMP. RANGE 0C to +70C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE 8 MAX 8 SO 8 MAX 8 SO
Applications
IrDA Applications Personal Digital Assistants (PDAs) Palmtop Computers Cell Phones Hand-Held Equipment Peripherals
Typical Operating Circuit
+3.3V
Pin Configuration
TOP VIEW
CS SCLK DIN DOUT
VCC
VCC
SHDN LED
TX
TXD
LEDC
MAX3100
RX
MAX3120
RXD PINC
TXD VCC GND PINC
1 2 3 4
8
RXD LEDC PGND SHDN
GND GND PGND PIN DIODE
MAX3120
7 6 5
MAX/SO
________________________________________________________________ Maxim Integrated Products
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver MAX3120
ABSOLUTE MAXIMUM RATINGS
(Referred to GND) VCC ...........................................................................-0.3V to +6V TXD, SHDN, LEDC ...................................................-0.3V to +6V RXD ............................................................-0.3V to (VCC + 0.3V) PGND ....................................................................-0.1V to +0.1V PINC....................................................................................10mA Continuous LEDC Current.................................................200mA Repetitive Pulsed LEDC Current (<90s, duty cycle <20%) ..........................................500mA Continuous Power Dissipation (TA = +70C) MAX (derate 4.1mW/C above +70C) ....................330mW SO (derate 5.88mW/C above +70C) .......................471mW Operating Temperature Ranges MAX3120C_A....................................................0C to +70C MAX3120E_A.................................................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C and VCC = +3.3V.) PARAMETER DC CHARACTERISTICS Supply Current Shutdown Supply Current LOGIC INPUTS (TXD, SHDN) Input Logic Threshold Low Input Logic Threshold High Input Leakage Current Input Capacitance LOGIC OUTPUT (RXD) VOL Output Voltage Output Rise and Fall Time IR RECEIVER Supported Data Rates Equivalent Input Noise Current Input Current Sensitivity Ambient DC Current Rejection Shutdown Time Shutdown Disable Time IR Receiver Output Pulse Width VOH tr, tf ISINK = 200A ISOURCE = 100A CLOAD = 50pF 2.4 INOISE (Note 2) (Note 3) VCC = 3.3V VCC = 5.0V Delay until ICC < 1A Delay until maximum IR receiver data rate is valid Data rate = 2.4kbps Data rate = 115.2kbps 1 1 10 0.0002 100 375 10 300 90 8 6 VCC 0.5 0.1 VCC 0.05 50 115.2 0.4 V ns kbps nARMS mA A s s s VIL VIH ILEAK CIN VCC = 3.3V VCC = 5.0V 2.0 2.4 -1 2 1 0.8 V V A pF ICC TA = +25C, SHDN = VCC (Note 1) 120 0.01 200 1.0 A A ICC(SHDN) TA = +25C, SHDN = GND (Note 1) SYMBOL CONDITIONS MIN TYP MAX UNITS
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C and VCC = +3.3V.) PARAMETER IR TRANSMITTER Transmitter Rise Time Transmitter Fall Time Transmitter Output Resistance Off-Leakage Current SYMBOL tr tf CONDITIONS 10% to 90% of 200mA drive current 90% to 10% of 200mA drive current VCC = 3.3V IOUT = 200mA VCC = 5.0V MIN TYP 20 20 1.15 0.9 0.01 MAX 600 600 2.0 1.6 10 UNITS ns ns A
MAX3120
Note 1: All supply current measurements are made under the following conditions: no load at all outputs, input voltages at GND or VCC, no PIN diode input current. Note 2: Equivalent input current noise is calculated by dividing the output noise of the transimpedance amplifier by the midband transimpedance gain. Note 3: Sensitivity is measured with an IrDA-compliant input signal, where the data rate is within the Supported Data Rate, rise/fall times are less than 600ns, and pulse widths are between 1.41s and 3/16 of the baud rate.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
LED DRIVER ON-RESISTANCE vs. TEMPERATURE
MAX3120 TOC01
SUPPLY CURRENT vs. TEMPERATURE
MAX3120 TOC02
1.6 ILEDC = 100mA 1.4 VCC = 3.3V
140
130 SUPPLY CURRENT (A) VCC = 5V 120
RLEDC ()
1.2
1.0 VCC = 5V
110
VCC = 3V
0.8
100
0.6 -40 -15 10 35 60 85 TEMPERATURE (C)
90 -40 -15 10 35 60 85 TEMPERATURE (C)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX3120 TOC03
LEDC VOLTAGE vs. LEDC CURRENT
PULSED AT 20% DUTY CYCLE
MAX3120 toc04
135 130 SUPPLY CURRENT (A) 125
600 500 400 VLEDC (mV) VCC = 3.3V 300 200 VCC = 5V 100 0
120 115 110 105 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
100
150
200
250
300
350
400
LEDC CURRENT (mA)
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver MAX3120
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
AMBIENT PHOTODIODE CURRENT REJECTION vs. SUPPLY VOLTAGE
MAX3120 TOC05
RXD OUTPUT PULSE WIDTH vs. DISTANCE
TRANSMITTER POWER = 200mW/sr INPUT PULSE WIDTH = 78s TEMIC BPV22NF VCC = 3.3V
MAX3120 TOC06
RXD OUTPUT PULSE WIDTH vs. DISTANCE
MAX3120 TOC07
450 400 CURRENT REJECTION (A) 350 300 250 200 150 100 50 0 3.0 3.5 4.0 4.5 5.0
100
4.0 3.5 RXD PULSE WIDTH (s) 3.0 2.5 2.0 1.5 1.0 TRANSMITTER POWER = 200mW/sr INPUT PULSE WIDTH = 1.63s TEMIC BPV22NF VCC = 3.3V 0 20 40 60 80
80 RXD PULSE WIDTH (s)
60
40
20
0 5.5 0 20 40 60 80 100 SUPPLY VOLTAGE (V) DISTANCE (cm)
100
DISTANCE (cm)
RXD OUTPUT vs. INFRARED INPUT
MAX3120 toc08
RXD OUTPUT vs. INFRARED INPUT
MAX3120 toc09
2V/div
RXD OUTPUT
2V/div
RXD OUTPUT
2V/div
INFRARED INPUT
2V/div
INFRARED INPUT
2s/div VCC = 3.3V, 115.2kbps AT 1cm DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
100s/div VCC = 3.3V, 2400bps AT 1cm DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
RXD OUTPUT vs. INFRARED INPUT
MAX3120 toc10
RXD OUTPUT vs. INFRARED INPUT
MAX3120 toc11
2V/div
RXD OUTPUT
2V/div
RXD OUTPUT
2V/div
INFRARED INPUT
2V/div
INFRARED INPUT
2s/div VCC = 3.3V, 115.2kbps AT 10cm DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
100s/div VCC = 3.3V, 2400bps AT 10cm DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
RXD OUTPUT vs. INFRARED INPUT RXD OUTPUT vs. INFRARED INPUT
MAX3120
MAX3120 toc12
MAX3120 toc13
2V/div
RXD OUTPUT
2V/div
RXD OUTPUT
2V/div
INFRARED INPUT
2V/div
INFRARED INPUT
2s/div VCC = 3.3V, 115.2kbps AT 1m DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
100s/div VCC = 3.3V, 2400bps AT 1m DISTANCE, TERMIC BPV22NF, TRANSMIT POWER 200mW/sr
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME TXD VCC GND PINC SHDN PGND LEDC RXD Supply Voltage Ground. Connect anode of PIN diode to GND. Connect GND to PGND. PIN Diode Cathode Input. Connect cathode of PIN diode to PINC. Shutdown Input. Active low. Power Ground. Ground for IR LED driver. Connect PGND to GND. LED Driver Output. Connect cathode of IR-emitting LED to LEDC. IR Receiver TTL/CMOS Data Output. Pulses low for IR input pulse. FUNCTION IR Transmitter TTL/CMOS Data Input. High = LED on.
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 resulting 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).
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver MAX3120
RXD TXD LEDC
IPIN = (4W/cm2 )(0.075cm2 )(1.8)(0.95)2 (0.6A/W) = 291nA
PGND
BANDPASS FILTER
+
PINC
GND
BIAS
MAX3120
SHDN VCC
1.2V
The first term (4W/cm2) is the minimum guaranteed irradiance in the 15 angular range. The second term (0.075cm2) is the effective sensitive area of the PIN diode. The factor of 1.8 accounts for the efficiency increase due to the spherical lens. The first 0.95 factor normalizes the sensitivity to the 875nm wavelength, while the second 0.95 factor adjusts for decreased receiver efficiency at 15 off-axis. The last term, 0.6A/W, is the sensitivity of the PIN diode. In this example, the Temic BPV22NF is an appropriate selection. The final important factor in selecting a PIN diode is effective diode capacitance. It is important to keep this capacitance below 70pF at 1.2V reverse bias. Higher input capacitance can compromise system noise performance by increasing the noise gain of the input transimpedance amplifier.
Figure 1. Functional Diagram
Transmitter
The MAX3120's IR transmitter consists of a high-power MOS switch, capable of quickly switching 200mA with less than 2 of on-resistance. Internal buffering keeps the input capacitance of the TXD pin extremely low to ease the input drive requirement. Connect an IR LED in series with a current-setting resistor to select the appropriate IR output power (see the Powering the IR LED section). Note that the transmitter does not have an automatic shutoff circuit, so pay special attention to component power dissipation in high-duty-cycle transmit schemes.
Powering the IR LED
Set the current in the IR LED using an external resistor. Consult the IR LED manufacturer's data sheet to select a forward current that will meet IrDA specifications discussed in the IR LED and PIN Photodiode Selection section. Look up the drop across the LED (VLED) and the drop across the MAX3120 LED driver (see Typical Operating Characteristics - VLEDC) and choose the current-setting resistor based on the following equation: RSET = VCC - VLED - VLEDC ISET
Applications Information
IR LED and PIN Photodiode Selection
The IrDA specification calls for an IR transmitter with a peak wavelength between 850nm and 900nm. Within a 15 half-cone-angle, the output intensity of the IR LED must be between 40mW/sr and 500mW/sr. Outside a 30 half-cone-angle, the output intensity of the IR LED must fall below 40mW/sr. The optical rise and fall times of the IR LED must be less than 600ns. Based on these system requirements, the Hewlett Packard HSDL-4220 or the Temic TSHF5400 IR LEDs are two appropriate choices. Appropriate PIN photodiode selection is extremely important to system performance. The PIN diode must generate at least 200nA (minimum sensitivity of the MAX3120) of current when aimed 15 off-axis with an incident irradiance of 4W/cm2. Use the following equation to determine if the Temic BPV22NF meets these requirements:
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Using the Hewlett Packard HSDL-4220 IR LED as an example, VCC = 5V, ISET = 100mA, and VLED = 1.67V, therefore: VLEDC = 0.08V RSET = 32.5
Low-Profile, 3V, 120A, IrDA Infrared Transceiver
Power-dissipation requirements of the MAX3120, IR LED, and RSET must be met based on maximum duty cycle and output current requirements. MAX3120 Power Dissipation = ISET * VLEDC * Duty Cycle IR LED Power Dissipation = ISET * VLED * Duty Cycle RSET Power Dissipation = ISET2 * RSET * Duty Cycle
Layout Considerations
The MAX3120 requires careful layout techniques to minimize parasitic signal coupling to the PINC input. Keep the lead length between the photodiode and PINC as short as possible. Be sure to keep PC board traces to the PIN diode separate from other noisy traces. To minimize coupling, run the AGND trace adjacent to the PINC trace on both sides. To prevent oscillation, avoid routing the RXD signal near the PINC signal. Connect the anode of the PIN diode, the GND pin, and the supply bypass capacitor pin in a star-ground connection. Connect PGND and GND together. Reduce the output trace length from RXD as much as possible to minimize coupling back to the input via parasitic capacitance.
MAX3120
Power-Supply Noise Rejection
Because of the extremely sensitive nature of photodiode amplifiers, it is important to maintain a quiet supply voltage. Use a separate analog supply voltage where possible. Place a 1F ceramic bypass capacitor as close to the VCC pin as possible. In especially noisy systems, connect a small (10) resistor in series with VCC, in addition to the normal bypass capacitor.
Chip Information
TRANSISTOR COUNT: 256
Package Information
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Low-Profile, 3V, 120A, IrDA Infrared Transceiver MAX3120
Package Information (continued)
SOICN.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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