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AT9933DB1 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 supertexs 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. board layout high bright led driver ic meeting automotive requirements speci? cations parameter value input voltage (steady state): 9.0vdc - 16vdc input voltage (transient): 42vdc output led string voltage: 28v max output current: 350ma +/-5% output current ripple: 5% typical switching frequency: 300khz (9.0v input) 430khz (13.5v input) 500khz (16.0v input) ef? ciency: 80% (at 13.5v input) open led protection: included; clamps output voltage at 33v output short circuit protection: included; limits current at 350ma reverse polarity protection: -20v max input current limit: 1.9a pwm dimming frequency: up to 1.0khz conducted emi: meets sae j1113 conducted emi standards 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. 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 actual size: 2.25 x 1.25
2 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. connect- ing an ammeter in series with the leds will allow measure- ment of the led current. the current will be 350ma +/- 5%. open led test: connect a voltmeter across the output ter- minals 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 volt- age 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 discon- nected, apply a ttl compatible, push-pull square wave sig- nal 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 typical results fig.1 shows the ef? ciency plot for the AT9933DB1 over the input voltage range. the converter has ef? ciencies 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 speci? cations for the automo- tive industry. fig.3 shows the output current variation over the input volt- age 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 C 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 out- put 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 brie? y 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 dur- ing 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.
3 AT9933DB1 fig. 1. efficiency vs. input voltage 70 72 74 76 78 80 82 84 8 1012141618 input voltage (v) efficiency (%) 300 350 400 450 500 81012141618 input voltage (v) switching frequency (khz) fig.2. switching frequency vs. input voltage 348 348.5 349 349.5 350 350.5 81012141618 input voltage (v) output current (ma) fig. 3. output current vs. input voltage
4 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
5 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) (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 short circuit (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)
6 AT9933DB1 fig. 9. pwm dimming rise and fall times channel 1 (blue): pwm dimming input signal (2v/div) channel 4 (green): led current (100ma/div) (a): rise time (b): fall time 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 ? lters (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 C c1 C d3). table 1 details the conducted emi limit as per sae j1113 and the maximum conducted emi obtained from measure- 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 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. frequency range conducted emi limit for class 3 conducted emi by AT9933DB1 class as per sae j1113 150khz - 300khz 70 dbv (narrowband) 40 dbv class 5 530khz - 2.0mhz 50 dbv (narrowband) 48 dbv class 3 5.9mhz - 6.2mhz 45 dbv (narrowband) 29 dbv class 5 30mhz - 54mhz 65 dbv (broadband) 54 dbv class 4 70mhz - 108mhz 49 dbv (broadband) 47 dbv class 3 table 1. conducted emi measurements
7 AT9933DB1 circuit schematic: r e f r 1 0 . 4 7 , 1 /2 w c 5 4 . 7 u f , 5 0 v r 5 1 0 r e f r 1 1 1 0 k r 4 4 . 4 2 k r 7 1 0 k c 1 0 . 1 u f , 5 0 v r e f c 2 4.7uf, 25v r 8 1 . 6 9 , 1 / 4 w c 6 4.7uf, 25v d 3 b 2 1 0 0 - 1 3 d 4 1 n 4 1 4 8 q 1 f d s 3 6 9 2 r 3 0 . 4 7 , 1 / 2 w r 1 0 5 . 4 9 k c 3 4.7uf, 25v q 2 2 n 3 9 0 7 a c 4 4.7uf, 25v d 1 b 2 2 0 - 1 3 1 j 1 a 2 j 1 b 1 j 2 a 2 j 2 b r 2 4 .7 , 1 / 2 w 2 j 3 b 3 j 3 c 1 j 3 a v in 1 g a t e 4 gnd 3 r e f 8 c s 1 2 c s 2 7 p w m d 5 v dd 6 at9933 u 1 c 1 0 0 . 1 u f , 5 0 v d 2 3 3 v , 3 5 0 m w r 9 1 0 0 c 9 2 . 2 u f , 1 6 v 1 2 l 1 d r 1 2 5 - 8 2 0 1 2 l 2 d r 7 4 - 1 5 1 c 8 1 u f , 1 6 v
8 AT9933DB1 pcb top layer pcb bottom layer
9 AT9933DB1 appendix C conducted emi test results ref. level = 70db v ref. level = 50db v ref. level = 45db v
10 AT9933DB1 appendix C conducted emi test results (cont.) ref. level = 65db v ref. level = 49db v
11 nr120706 AT9933DB1 item # quantity refdes description package manufacturer manufacturers part # 1 1 c1 0.22f, 50v x7r ceramic capacitor smd1210 kemet c1210c224k5ractu 23 c2, c3, c4, c6 4.7f, 25v x5r ceramic capacitor smd1210 panasonic ecj-4yb1e475k 3 1 c5 4.7f, 50v x7r ceramic capacitor smd1210 murata grm32er71h475ka88l 4 1 c8 1f, 16v x7r ceramic capacitor smd0805 kemet c0805c105k4ractu 5 1 c9 2.2f, 16v x7r ceramic capacitor smd0805 tdk corp. c2012x7r1c225k 6 1 c10 0.1f, 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 82h, 2a rms, 2.4a sat inductor smt coiltronics dr125-820 14 1 l2 150h, 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 0.47, 1/2w, 5% chip resistor smd2010 panasonic erj-12zqjr47u 18 1 r2 8.2, 1/2w, 5% chip resistor smd2010 panasonic erj-12zyj8r2u 19 1 r4 4.42k, 1/8w, 1% chip resistor smd0805 yageo 9c08052a4421fkhft 20 1 r5 10, 1/8w, 1% chip resistor smd0805 yageo 9c08052a10r0fkhft 21 2 r7, r11 10k, 1/8w, 1% chip resistor smd0805 yageo 9c08052a1002fkhft 22 1 r8 1.69, 1/4w, 1% chip resistor smd1206 yageo 9c12063a1r69fghft 23 1 r9 100, 1/8w, 1% chip resistor smd0805 yageo 9c08052a1000fkhft 24 1 r10 5.49k, 1/8w, 1% chip resistor smd0805 yageo 9c08052a5491fkhft 25 1 u1 boost-buck led driver so-8 supertex at9933lg-g

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