Features • • • • Few External Components Low Power Consumption Microcomputer Compatible Insensitive to Ambient Light and Other Continuous Interferences Applications IR Receiver for Data Communication • Keyless Entry Systems • Remote Control • Wireless Data Transfer up to 4 kbit/s Description The IC U2538B is a complete IR receiver for data communication. The useful input signals are separated by a special input circuit and amplified by a gain-controlled amplifier. The bandpass filter suppresses the off-band signals. The signal detector, consisting of a demodulator, an integrator and a Schmitt trigger, forms the input signal to an output pulse that can be interfaced to a microcomputer. The AGC and the ATC circuit control the receiver's sensitivity, making it insensitive to ambient light sources. U2538B Figure 1. Block Diagram with Typical Circuit VS U2538B Input Amplifier and filter Detector mC AGC/ATC Modulated IR signal carrier frequency 20 to 60 kHz minimum 6 pulses/burst Rev. 4717A–IRRC–05/03 1 Block Diagram VS RF0 VS RF BIAS + BPF IN CGA AGND TIA CGA BPF AGC Transimpedance amplifier Controlled gain amplifier Bandpass filter Automatic gain control 2 U2538B ATC AGC CAGC DEM 100 kW OUT Vth + - TIA Comp 1 & dt Comp 2 INT ST DGND CAGC ATC DEM INT ST Automatic threshold control Demodulator Integrator Schmitt trigger 4717A–IRRC–05/03 U2538B Pin Configuration Figure 2. Pinning SO8 NC RF AGND IN 8 7 6 5 U2538B 1 2 3 4 VS CAGC OUT DGND Pin Description Pin Symbol Function 1 VS Supply voltage 2 CAGC AGC capacitor 3 OUT 4 DGND Data output 5 IN Input pin diode 6 AGND GND amplifier GND - DEM/INT/ST 7 RF Frequency determination 8 NC Not connected 3 4717A–IRRC–05/03 Functional Description Input Stage (TIA) The input stage provides the necessary bias voltage for the photo diode and ensures decoupling of the useful signal. This involves processing the DC and AC portions in separate parts of the circuit: the bias voltage (BIAS) and the transimpedance amplifier circuit (TIA). The bias voltage circuit operates like a load resistor with respect to the photo diode, the value of which is low for DC and low-frequency signals (3 to 100 kW), but as high as possible for the operating frequency (100 kHz to 1 MHz) depending on the input current). The ac portion of the input signal feeds an inverted amplifier with a sufficiently low input resistance (Zi < 10 kW). If the input resistance is too high, the useful signal will be lost due to the junction capacitance of the photodiode. Controlled Gain Amplifier (CGA) The controlled gain amplifier accounts for the greatest part of the voltage gain and can be controlled via the voltage at CAGC (Pin 2). Gain control is needed to support the interference suppression of the detector. High-pass behaviour results from the capacitive coupling of the individual stages. The cut-off frequency is approximately 20 kHz. Bandpass Filter (BPF) The bandpass filter basically consists of integrated components. An external resistor determines the mid-frequency. The filter quality is about 7 and is practically independent of the selected mid-frequency (see Figure 3). The following formula can be used for calculating the resistor, Rf0: 8855 R fO (kW ) = ------------------- – 13 f0 (kHz) where: 20 kHz < f0 < 60 kHz Figure 3. Characteristic of the Bandpass Filter 120 100 Grel 80 60 40 20 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 f/f0 4 U2538B 4717A–IRRC–05/03 U2538B Automatic Threshold Control (ATC) During the reception of an incoming telegram, the ATC reduces the sensitivity of the demodulator to establish the highest possible signal-to-noise ratio according to the signal strength. This prevents interferences which may arise during transmission from affecting the output. The advantage of the circuit is achieved if its output voltage exceeds VTh (Comp 1). That is the case when the input signal strength is more than twice as much as the minimum detectable signal intensity. Automatic Gain Control (AGC) The automatic gaincontrol improves the circuit's resistance to interference by adapting the amplification of the gain-controlled amplifier to the relevant existing interference level. In order to prevent the circuit from responding to transmitted data signals, it gradually reduces the sensitivity, but only if the duty cycle exceeds a specific value (see Figure 4). When using telegrams with higher duty cycles than this value, the capacitor, CAGC , maintains the sensitivity for a certain time period. A higher capacitance enables a longer transmission time. A capacitance of C1 = 22 nF is adequate for most known telegrams. A typical value for the maximum duty cycle (DC) can be calculated by the following formula: N DC max = ------------------------------------14.2 + 1.1 ´ N Figure 4. Duty Cycle Transmitted Burst (N cycles) t pl = N f DC = T Detector t pl T N ³ 6; f = 20 kHz to 60 kHz The output signal of the bandpass filter is compared to a fixed reference (Comp 1) and to a reference generated by the ATC circuit (Comp 2). The output of the comparator with the higher threshold voltage controls the integrator. Using the integrator keeps the output free of short-time interference. The integrator drives the output stage after being processed through a Schmitt trigger. The internal pull-up resistor can replace an external resistor in some applications. 5 4717A–IRRC–05/03 Absolute Maximum Ratings Parameters Symbol Value Unit Supply voltage Pin 1 VS -0.3 to +6.0 V Input voltages Pin 2, 3, and 5 Pin 7 VIN -0.3 to VS -0.3 to +1.5 V Input current Pin 7 IIN 0 to 0.1 mA Ptot 110 mW Junction temperature Tj 125 °C Ambient temperature Tamb -40 to +105 °C Storage temperature Tstg -40 to +125 °C Power dissipation Tamb = 105°C Thermal Resistance Parameters Symbol Value Unit RthJA 180 K/W Junction ambient Electrical Characteristics Tamb = 25°C, VS = 5 V Parameters Test Conditions Symbol Min. Typ. Max. Unit Supply voltage Pin 1 VS 4.5 5.5 V Supply current Pin 1 IS 0.35 0.65 mA Maximum input current VIN = 0 Pin 5 IIN 0.6 Output voltage low: IOL = 2 mA Pin 3 VOL Internal pull-up resistor Pin 3 RL 75 Center frequency of bandpass RF = 240 k f0 33.3 Q factor Q Freqency range f AGC current source sink Pin 2 AGC slope Pin 2 mA 0.2 V 100 125 kW 35 36.7 kHz 60 kHz 155 140 nA nA 7 20 90 70 120 100 20 Number of pulses required dB/V 6 Sensitivity Pin 5 0.7 nA(rms) Switch-on delay, iIN = 0.7 nA (rms) Pin 3, see Figure 5 tdon 3 7.5 Period Switch-off delay, iIN = 0.7 nA (rms) Pin 3, see Figure 5 Pulse width, iIN = 0.7 nA (rms), 6 pulse bursts tdoff 5 10 Period Pin 3, see Figure 5 tpo 4.5 10 Period 8855 - – 13 k W RfO (k W ) = -----------------f0 (kHz) 6 U2538B 4717A–IRRC–05/03 U2538B Figure 5. Switch On/Off Delay VIN Burst, X pulses Repetition rate = 10 ms VOUT tpo tdon tdoff Figure 6. Application Circuit C1 R1 10 m 16 V 220 3 C2 RfO 100 n C3 VBatt 1 VS NC 8 2 CAGC RF 7 AGND 6 10 n R2 > 10 k (1) U2538B 2 OUT 470 p(1) 1 GND feedback reduction (1) C4 3 OUT 4 DGND (1) IN D1 (1) D2 (1) D3 (1) 5 optional 7 4717A–IRRC–05/03 Ordering Information Extended Type Number Package Remarks U2538B-MFP SO8 Tube U2538B-MFPG3 SO8 Taped and reeled Package Information Package SO8 Dimensions in mm 5.2 4.8 5.00 4.85 3.7 1.4 0.25 0.10 0.4 1.27 6.15 5.85 3.81 8 0.2 3.8 5 technical drawings according to DIN specifications 1 8 4 U2538B 4717A–IRRC–05/03 Atmel Headquarters Atmel Operations Corporate Headquarters Memory 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 487-2600 Europe Atmel Sarl Route des Arsenaux 41 Case Postale 80 CH-1705 Fribourg Switzerland TEL (41) 26-426-5555 FAX (41) 26-426-5500 Asia Room 1219 Chinachem Golden Plaza 77 Mody Road Tsimhatsui East Kowloon Hong Kong TEL (852) 2721-9778 FAX (852) 2722-1369 Japan 9F, Tonetsu Shinkawa Bldg. 1-24-8 Shinkawa Chuo-ku, Tokyo 104-0033 Japan TEL (81) 3-3523-3551 FAX (81) 3-3523-7581 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 436-4314 Microcontrollers 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 436-4314 La Chantrerie BP 70602 44306 Nantes Cedex 3, France TEL (33) 2-40-18-18-18 FAX (33) 2-40-18-19-60 ASIC/ASSP/Smart Cards Zone Industrielle 13106 Rousset Cedex, France TEL (33) 4-42-53-60-00 FAX (33) 4-42-53-60-01 RF/Automotive Theresienstrasse 2 Postfach 3535 74025 Heilbronn, Germany TEL (49) 71-31-67-0 FAX (49) 71-31-67-2340 1150 East Cheyenne Mtn. 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