Supertex inc. AT9933DB1 High Bright LED Driver IC Demoboard Meeting Automotive Requirements General Description Specifications The AT9933DB1 is an LED driver capable of driving up to 7 1-watt LEDs in series from an automotive input of 9 - 16V DC. The demoboard uses Supertex’s AT9933 in a boost-buck topology. The converter operates at frequencies in excess of 300kHz and has excellent output current regulation over the input voltage range. It can also withstand transients up to 42V and operate down to 6V input. The converter is also protected against open LED and output short circuit conditions. Protection against reverse polarity up to 20V is also included. Parameter Board Layout Input voltage (steady state): Input voltage (transient): Output LED string voltage: Output current: Value 9.0 - 16VDC 42VDC 28V max 350mA +/-5% Output current ripple: 5% typical Switching frequency: 300kHz (9.0V input) 430kHz (13.5V input) 500kHz (16.0V input) Efficiency: 80% (at 13.5V input) Open LED protection: Output short circuit protection: Reverse polarity protection: Input current limit: PWM dimming frequency: Conducted EMI: Included; clamps output voltage at 33V Included; limits current at 350mA -20V max 1.9A Up to 1.0kHz Meets SAE J1113 conducted EMI standards Actual Size: 2.25” x 1.25” Connections: Input: The input is connected between the terminals of connector J1 as shown in the Connection Diagram. Output: The output is connected between the terminals of connector J2 as shown. Note: During PWM dimming, pin 2 of connector J3 should be left open. Also, the PWM signal must have the proper polarity with the positive connected to pin 1 of J3. Note that pin 3 of J3 is internally connected to the return path of the input voltage Enable/PWM Dimming: To just enable the board, short pins 1 and 2 of connector J3 as shown. For PWM dimming, connect the external push-pull square wave source between terminals 1 and 3 of connector J3 as shown by the dotted lines. Doc.# DSDB-AT9933DB1 A032713 Supertex inc. www.supertex.com AT9933DB1 Testing the Demoboard The waveforms in Fig.4 show the drain voltage of the FET (channel 1 (blue); 10V/div) and the LED current (channel 4 (green); 100mA/div) at three different operating conditions – 9V in, 13.5V in and 16V in. Normal Operation: Connect the input source and the output LEDs as shown in the Connection Diagram and enable the board. The LEDs will glow with a steady intensity. Connecting an Ammeter in series with the LEDs will allow measurement of the LED current. The current will be 350mA +/- 5%. Fig. 5 shows the operation of the converter during cold crank conditions as the input voltage decreases from 13.5 to 6V and increases back to 13.5V. In these cases, the input current reaches the limit set and the output current drops correspondingly. Thus, the LEDs continue to glow, but with reduced intensity. Once the voltage ramps back up, the output current goes back to its normal value and the converter comes out of the input current limit. Open LED test: Connect a voltmeter across the output terminals of the AT9933DB1. Start the demoboard normally and once the LED current reaches steady state, unplug one end of the LED string from the demoboard. The output voltage will rise to about 33V and stabilize. Short Circuit Test: When the AT9933DB1 is operating in steady state, connect a jumper across the terminals of the LED string. Notice that the switching frequency drops, but the average output current remains the same. Fig.6 shows the LED current during an input step change from 13.5 to 42V and back to 13.5V (similar to a clamped load dump). It can be seen that the LED current drops briefly when the input voltage jumps, but there are no overshoots. PWM Dimming: With the input voltage to the board disconnected, apply a TTL compatible, push-pull square wave signal between PWMD and GND terminals of connector J3 as shown in the Connection Diagram. Turn the input voltage back on and adjust the duty cycle and / or frequency of the PWM dimming signal. The output current will track the PWM dimming signal. Note that although the converter operates perfectly well at 1.0kHz PWM dimming frequency, the best PWM dimming ratios can be obtained at lower frequencies like 100 or 200Hz Fig. 7a shows the operation of the converter during an Open LED condition and Fig. 7b shows the operation during output short circuit condition. In both cases, it can be seen that the AT9933DB1 can easily withstand faults and come back into normal operation almost instantly. Fig. 8 shows the PWM dimming performance of the AT9933DB1 with a 100Hz, 3.3V square wave signal. The converter can easily operate at PWM dimming duty cycles from 1 - 99%. Typical Results Fig. 9 shows the rise and fall times of the output current during PWM dimming. The converter has nearly symmetric rise and fall times of about 25µs. These rise and fall times can be reduced (if desired) by reducing the output capacitance C10. However, this will lead to increased ripple in the output current. Fig.1 shows the efficiency plot for the AT9933DB1 over the input voltage range. The converter has efficiencies greater than 80% over 13V input. Note that these measurements so not include the 0.3 - 0.5W loss in the reverse blocking diode. Fig.2 shows the variation of the switching frequency over the input votage range. The frequency varies from 300kHz to 500kHz over the entire input voltage range and avoids the restricted frequency band of 150 to 300kHz and the AM band greater than 530kHz. This makes it easier to meet the conducted and radiated EMI specifications for the automotive industry. Fig.3 shows the output current variation over the input voltage range. The LED current has a variation of about 2mA over the entire voltage range. Doc.# DSDB-AT9933DB1 A032713 2 Supertex inc. www.supertex.com AT9933DB1 Fig. 1. Efficiency vs. Input Voltage 84 Efficiency (%) 82 80 78 76 74 72 70 8.0 10 12 14 16 18 Input Voltage (V) Fig.2. Switching Frequency vs. Input Voltage Switching Frequency (kHz) 500 450 400 350 300 8.0 10 12 14 16 18 Input Voltage (V) Output Current (mA) 350.5 Fig. 3. Output Current vs. Input Voltage 350.0 349.5 349.0 348.5 348.0 8.0 10 12 14 16 18 Input Voltage (V) Doc.# DSDB-AT9933DB1 A032713 3 Supertex inc. www.supertex.com AT9933DB1 (a) (b) (c) Fig. 4. Steady State Waveforms (a): 9V in; (b): 13.5V in; (c): 16V in Fig. 5. Cold Crank Operation Channel 1 (blue): Input Voltage (10V/div) Channel 3 (pink): Input Current (1A/div) Channel 4 (green): LED current; 100mA/div Doc.# DSDB-AT9933DB1 A032713 4 Supertex inc. www.supertex.com AT9933DB1 Fig. 6. LED current during step changes in the input voltage Channel 1(blue): Input Voltage (10V/div) Channel 4 (green): LED current (100mA/div) Short Circuit (a): Open LED Condition (b): Output Short Circuit Fig. 7. HV9930DB1 during output fault conditions FET drain Voltage (20V/div) (Channel 1 in (a); Channel 2 in (b) Channel 4 (green): LED current (a) (b) (c) Fig. 8. PWM Dimming at 100Hz Channel 1 (blue): PWM Dimming Input Signal (2V/div) Channel 4 (Green): LED current (100mA/div) Doc.# DSDB-AT9933DB1 A032713 5 Supertex inc. www.supertex.com AT9933DB1 (a): rise time (b): fall time Fig. 9. PWM Dimming rise and fall times Channel 1 (blue): PWM Dimming Input Signal (2V/div) Channel 4 (Green): LED current (100mA/div) Conducted EMI Tests on the AT9933DB1 In preliminary tests conducted on the demoboard, the board meets SAE J1113 Class 3 conducted EMI standards without the need for any input filters (other than the input capacitors already included). This is a result of the combination of the continuous input current and a localized switching loop (Q1 – C1 – D3). ments on the board. The table also lists the Class of the SAE standard the board meets in each frequency range. The conducted EMI plots for the AT9933DB1 obtained at an input voltage of 13.5V and an LED string voltage of 27V (output current is 350mA) are given in the Appendix. Table 1 details the conducted EMI limit as per SAE J1113 and the maximum conducted EMI obtained from measure- Table 1. Conducted EMI Measurements Frequency Range Conducted EMI Limit for Class 3 Conducted EMI by AT9933DB1 Class as per SAE J1113 150 - 300kHz 70 dBµV (narrowband) 40 dBµV Class 5 530 - 2.0MHz 50 dBµV (narrowband) 48 dBµV Class 3 5.9 - 6.2MHz 45 dbµV (narrowband) 29 dBµV Class 5 30 - 54MHz 65 dbµV (broadband) 54 dBµV Class 4 70 - 108MHz 49 dbµV (broadband) 47 dBµV Class 3 Doc.# DSDB-AT9933DB1 A032713 6 Supertex inc. www.supertex.com Doc.# DSDB-AT9933DB1 A032713 7 1 2 3 2 1 J3A J3B J3C J1B J1A C2 4.7µF 25V C9 2.2µF 16V REF C3 4.7µF 25V 10k R7 C4 4.7µF 25V B220-13 5 2 6 VIN 1 REF PWMD CS1 3 GND CS2 GATE AT9933 VDD U1 D4 1N4148 R4 4.42k C6 4.7µF 25V D1 7 4 8 1 10 R5 0.47, 1/2W R3 0.47, 1/2W R1 DR125-820 L1 C8 1.0µF 16V Q2 2N3907A 2 REF Q1 FDS3692 4.7, 1/2W R2 4.7µF, 50V C5 0.1µF, 50V C1 R8 D3 B2100-13 D2 33V 350mW DR74-151 L2 R9 100 1.69, 1/4W 1 10k R11 R10 5.49k 2 REF 2 J2B C10 0.1µF 50V 1 J2A AT9933DB1 Circuit Schematic: Supertex inc. www.supertex.com AT9933DB1 PCB Top Layer PCB Bottom Layer Doc.# DSDB-AT9933DB1 A032713 8 Supertex inc. www.supertex.com AT9933DB1 Appendix – Conducted EMI Test Results Doc.# DSDB-AT9933DB1 A032713 9 Supertex inc. www.supertex.com AT9933DB1 Appendix – Conducted EMI Test Results (cont.) Doc.# DSDB-AT9933DB1 A032713 10 Supertex inc. www.supertex.com AT9933DB1 Bill of Materials Item Quan RefDes Description C1 0.22µF, 50V X7R ceramic capacitor Package Manufacturer Manufacturer’s Part # SMD1210 Kemet C1210C224K5RACTU SMD1210 Panasonic ECJ-4YB1E475K 1 1 2 3 3 1 C5 4.7µF, 50V X7R ceramic capacitor SMD1210 Murata GRM32ER71H475KA88L 4 1 C8 1µF, 16V X7R ceramic capacitor SMD0805 Kemet C0805C105K4RACTU 5 1 C9 2.2µF, 16V X7R ceramic capacitor SMD0805 TDK Corp. C2012X7R1C225K 6 1 C10 0.1µF, 50V X7R ceramic capacitor SMD0805 Yageo 08052R104K9B20D 7 1 D1 20V, 2A schottky diode SMB Diodes Inc. B220-13 8 1 D2 33V, 350mW zener diode SOT-23 Zetex Inc. BZX84C33-7 9 1 D3 75V, 400mW switching diode SOD123 Diodes Inc. 1N4148W-7 10 1 D4 100V, 2A schottky diode SMB Diodes Inc. B2100-13 11 2 J1, J2 2 pin, 2.5mm pitch right angle connector Thru-Hole JST Sales Amer. S2B-EH 12 1 J3 3 pin, 2.5mm pitch right angle connector Thru-Hole JST Sales Amer. S3B-EH 13 1 L1 82µH, 2A rms, 2.4A sat inductor SMT Coiltronics DR125-820 14 1 L2 150µH, 0.86A rms, 1A sat inductor SMT Coiltronics DR74-151 15 1 Q1 100V, 4.5A N-channel MOSFET SO-8 Fairchild Semi FDS3692 16 1 Q2 -60V, 600mA PNP transistor SOT-23 Zetex Inc. FMMT2907ATA 17 1 R1, R3 0.47Ω, 1/2W, 5% chip resistor SMD2010 Panasonic ERJ-12ZQJR47U 18 1 R2 8.2Ω, 1/2W, 5% chip resistor SMD2010 Panasonic ERJ-12ZYJ8R2U 19 1 R4 4.42kΩ, 1/8W, 1% chip resistor SMD0805 Yageo 9C08052A4421FKHFT 20 1 R5 10Ω, 1/8W, 1% chip resistor SMD0805 Yageo 9C08052A10R0FKHFT 21 2 R7, R11 10kΩ, 1/8W, 1% chip resistor SMD0805 Yageo 9C08052A1002FKHFT 22 1 R8 1.69Ω, 1/4W, 1% chip resistor SMD1206 Yageo 9C12063A1R69FGHFT 23 1 R9 100Ω, 1/8W, 1% chip resistor SMD0805 Yageo 9C08052A1000FKHFT 24 1 R10 5.49kΩ, 1/8W, 1% chip resistor SMD0805 Yageo 9C08052A5491FKHFT 25 1 U1 Boost-Buck LED Driver SO-8 Supertex AT9933LG-G C2, C3, 4.7µF, 25V X5R ceramic capacitor C4, C6 Supertex inc. does not recommend the use of its products in life support applications, and will not knowingly sell them for use in such applications unless it receives an adequate “product liability indemnification insurance agreement.” Supertex inc. does not assume responsibility for use of devices described, and limits its liability to the replacement of the devices determined defective due to workmanship. No responsibility is assumed for possible omissions and inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications refer to the Supertex inc. (website: http//www.supertex.com) Supertex inc. ©2013 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited. Doc.# DSDB-AT9933DB1 A032713 11 1235 Bordeaux Drive, Sunnyvale, CA 94089 Tel: 408-222-8888 www.supertex.com