AT9933DB1 User Guide

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.
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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.
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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)
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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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(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
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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.
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AT9933DB1
PCB Top Layer
PCB Bottom Layer
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Appendix – Conducted EMI Test Results
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Appendix – Conducted EMI Test Results (cont.)
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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.
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1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
www.supertex.com
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