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AT9933DB1 High Bright LED Driver IC Meeting Automotive Requirements
General Description
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 demo board 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.
Specifications
Parameter Input voltage (steady state): Input voltage (transient): Output LED string voltage: Output current: Output current ripple: Switching frequency: Value 9.0VDC - 16VDC 42VDC 28V max 350mA +/-5% 5% typical 300kHz (9.0V input) 430kHz (13.5V input) 500kHz (16.0V input) 80% (at 13.5V input) 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
Board Layout
Efficiency: Open LED protection: Output short circuit protection: Reverse polarity protection: Input current limit: PWM dimming frequency: Conducted EMI:
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.
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. 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
Output:
The output is connected between the terminals of connector J2 as shown.
AT9933DB1
Testing the Demo Board
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%. 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. 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 1kHz PWM dimming frequency, the best PWM dimming ratios can be obtained at lower frequencies like 100 or 200Hz 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. 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. Fig. 5 shows the operation of the converter during cold crank conditions as the input voltage decreases from 13.5V 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. Fig.6 shows the LED current during an input step change from 13.5V 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. 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%. 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 25s. 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.
Typical Results
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 0.3W - 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 150kHz 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.
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AT9933DB1
84 82 80 78 76 74 72 70 8 10 12 14 16 18
Efficiency (%)
Input Voltage (V)
Fig. 1. Efficiency vs. Input Voltage
Switching Frequency (kHz)
500 450 400 350 300 8 10 12 14 16 18
Input Voltage (V)
Fig.2. Switching Frequency vs. Input Voltage
Output Current (mA)
350.5 350 349.5 349 348.5 348 8 10 12 14 16 18
Input Voltage (V)
Fig. 3. Output Current vs. Input Voltage
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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
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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)
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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 demo board, 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). Table 1 details the conducted EMI limit as per SAE J1113 and the maximum conducted EMI obtained from measurements 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 HV9930DB1 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. Conducted EMI Measurements
Frequency Range 150kHz - 300kHz 530kHz - 2.0MHz 5.9MHz - 6.2MHz 30MHz - 54MHz 70MHz - 108MHz Conducted EMI Limit for Class 3 70 dBV (narrowband) 50 dBV (narrowband) 45 dbV (narrowband) 65 dbV (broadband) 49 dbV (broadband) Conducted EMI by AT9933DB1 40 dBV 48 dBV 29 dBV 54 dBV 47 dBV Class as per SAE J1113 Class 5 Class 3 Class 5 Class 4 Class 3
6
J1A 1 2 DR125-820 B220-13 R2 R3 4.7, 1/2W 4.7uF, 50V C5 D2 33V, 350mW C1 0.1uF, 50V DR74-151 1 2
4.7uF, 25V 4.7uF, 25V
D1 L1 L2
1 C6 R1 0.47, 1/2W 0.47, 1/2W R5 FDS3692 10 R7 Q2 2N3907A D4 10k 1N4148 1.69, 1/4W R9 100 R8 Q1 D3 B2100-13
J2A 1
Circuit Schematic:
4.7uF, 25V
4.7uF, 25V
C2
C3
C4
J1B
2
J3C R4 4.42k
3
C10 0.1uF, 50V
J2B 2
REF
2 U1
VIN
C9 6 2.2uF, 16V 2 CS1 Gate
GND
1
3
7
VDD REF 4 8 C8 1uF, 16V REF
J3B R10 5.49k
AT9933
7
J3A 5 PWMD CS2
R11
1
REF
10k
AT9933DB1
AT9933DB1
PCB Top Layer
PCB Bottom Layer
8
AT9933DB1
Appendix - Conducted EMI Test Results
Ref. Level = 70dBV
Ref. Level = 50dBV
Ref. Level = 45dBV
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AT9933DB1
Appendix - Conducted EMI Test Results (cont.)
Ref. Level = 65dBV
Ref. Level = 49dBV
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AT9933DB1
Item # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Quantity 1 3 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 2 1 1 1 1 RefDes C1 C2, C3, C4, C6 C5 C8 C9 C10 D1 D2 D3 D4 J1, J2 J3 L1 L2 Q1 Q2 R1, R3 R2 R4 R5 R7, R11 R8 R9 R10 U1 Description 0.22F, 50V X7R ceramic capacitor 4.7F, 25V X5R ceramic capacitor 4.7F, 50V X7R ceramic capacitor 1F, 16V X7R ceramic capacitor 2.2F, 16V X7R ceramic capacitor 0.1F, 50V X7R ceramic capacitor 20V, 2A schottky diode 33V, 350mW zener diode 75V, 400mW switching diode 100V, 2A schottky diode 2 pin, 2.5mm pitch right angle connector 3 pin, 2.5mm pitch right angle connector 82H, 2A rms, 2.4A sat inductor 150H, 0.86A rms, 1A sat inductor 100V, 4.5A N-channel MOSFET -60V, 600mA PNP transistor 0.47, 1/2W, 5% chip resistor 8.2, 1/2W, 5% chip resistor 4.42k, 1/8W, 1% chip resistor 10, 1/8W, 1% chip resistor 10k, 1/8W, 1% chip resistor 1.69, 1/4W, 1% chip resistor 100, 1/8W, 1% chip resistor 5.49k, 1/8W, 1% chip resistor Boost-Buck LED Driver Package SMD1210 SMD1210 SMD1210 SMD0805 SMD0805 SMD0805 SMB SOT-23 SOD123 SMB Thru-Hole Thru-Hole SMT SMT SO-8 SOT-23 SMD2010 SMD2010 SMD0805 SMD0805 SMD0805 SMD1206 SMD0805 SMD0805 SO-8 Manufacturer Kemet Panasonic Murata Kemet TDK Corp. Yageo Diodes Inc. Zetex Inc. Diodes Inc. Diodes Inc. JST Sales Amer. JST Sales Amer. Coiltronics Coiltronics Fairchild Semi Zetex Inc. Panasonic Panasonic Yageo Yageo Yageo Yageo Yageo Yageo Supertex Manufacturer's Part # C1210C224K5RACTU ECJ-4YB1E475K GRM32ER71H475KA88L C0805C105K4RACTU C2012X7R1C225K 08052R104K9B20D B220-13 BZX84C33-7 1N4148W-7 B2100-13 S2B-EH S3B-EH DR125-820 DR74-151 FDS3692 FMMT2907ATA ERJ-12ZQJR47U ERJ-12ZYJ8R2U 9C08052A4421FKHFT 9C08052A10R0FKHFT 9C08052A1002FKHFT 9C12063A1R69FGHFT 9C08052A1000FKHFT 9C08052A5491FKHFT AT9933LG-G
NR120706
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