4 A052804
Low Voltage, Buck Boost, High Brightness LED Driver
Introduction
The Supertex HV9910DB4 demo board is a
complete high current, high brightness (HB) LED
power driver to supply a string of LEDs using the
HV9910 IC from a low DC voltage. The demo board
can be used to test the performance of the HV9910
as a constant current driver to power LEDs.
HV9910DB4 can drive LED strings whose voltage is
less or more than the input voltage.
HV9910DB3 can supply a maximum output current
of 350mA to drive LED strings having a maximum
string voltage of 22V. HV9910DB4 is ideally suited
to drive a string of 5 or 6 high brightness LEDs at
high efficiencies (typically greater than 85%).
The power conversion stage of HV9910DB4
consists of a current-controlled buck-boost converter
operating at a switching frequency of 80kHz. The
nominal output current of the demo board can be
adjusted to any value less than 350mA using the on-
board trimming potentiometer. PWM dimming can be
achieved by applying a pulse-width-modulated
square wave signal between the PWMD and GND
pins.
Specifications
Input 8VDC – 24VDC
(replacing C1 and C2 with 35V capacitors will
increase the maximum input voltage rating to 30V)
Load Current 350mA maximum
(see instructions)
LED String Voltage 22V maximum
Switching Frequency 80kHz
Efficiency >85% (typ.)
Board Layout and Connections
HV9910DB4
Supertex, Inc.
• 1235 Bordeaux Drive, Sunnyvale, CA 94089 • Tel: (408) 222-8888 • FAX: (408) 222-4895 • www.supertex.com
B042204
A052804
8-30VDC
PWMDimming
(optional)
Enable
Connection
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2
Instructions
VIN+: Connect the positive terminal of the DC input
source to this pin.
VIN-: Connect the negative terminal of the DC input
source to this pin.
LED+: Connect the Anode of the LED string to this
pin.
LED-: Connect the Cathode of the LED string to this
pin.
VDD: This pin is connected to the VDD pin of the
HV9910. The typical voltage on the pin is 7.6V.
This voltage can be used to drive any additional
circuitry required. Please see the datasheet
regarding the output current capability at the VDD
pin.
GND: This pin is connected to the Ground
connection of the buck converter.
PWMD: This terminal can be used to either
enable/disable the converter or to apply a PWM
dimming signal.
To just enable the converter, connect the PWMD pin
to the VDD pin. Disconnecting the PWMD pin will
cause the circuit to stop.
PWM dimming of the LED light can be achieved by
turning on and off the converter with low frequency
50Hz to 1000Hz TTL logic level signal. Changing the
Duty Ratio of the signal changes the effective
average current via the LEDs, changing the light
emission.
Note: In the case of PWM dimming, the PWMD pin
should not be connected to the VDD pin!
Setting the Output Current
The output current of the HV9910DB4 depends on
the LED string voltage. The power conversion circuit
of the HV9910DB4 behaves as a constant power
converter. Thus, given a fixed output voltage (as in
the case of LEDs, it translates to a fixed output
current. The small variation in the LED voltages
among different batches of LEDs will cause a small,
but usually not significant, change in the LED
current. However, changing the number of LEDs or
changing the type of LED will alter the preset output
current and the potentiometer has to be used to
adjust the LED current. However, this circuit will
reject any input voltage changes and will maintain
the same output current over a large input voltage
range.
The output current can be set using the following
equation:
×
×××
=o
LD
sense
s
oV
V
R
fL
I2
2
200
η
where
o
I: output current (350mA)
L
: inductor value (15µH)
s
f: switching frequency (80kHz)
: estimated efficiency % (85%)
sense
R: sense resistor value (0.05Ω)
LD
V: voltage at the dimming pin
o
V: output voltage (22V)
The values in brackets indicate the values for the
HV9910DB4.
For this particular demo board, the equation for the
output current is
×= o
LD
oV
V
I2
204 (in Amperes)
Testing HV9910DB4
Connect the LED string to the output terminals.
Check the polarity of the LED connection, anode
end of the string should be connected to the positive
output, cathode should be connected to the negative
output. Connect the DC input to the input terminals
(check the polarity). Short the PWMD pin to VDD.
Apply a DC voltage at the input terminals and the
LED string should start to glow.
An ammeter can be connected in series with the
LED(s) to measure the output current. The current
level can then be changed by adjusting the trimming
potentiometer.
HV9910DB4
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3
Open LED Condition:
This power stage cannot be run under open LED
condition. A no-load at the output will cause
excessive voltages at the output and will damage
the demo board. Make sure that the LEDs are
connected at the output before powering up the
circuit.
Linear Dimming Test:
Gradual change of current via LED(s) is possible by
using the trimming potentiometer placed on the
demo board. The HV9910 has a preset voltage
reference level of 250mV when the voltage at the LD
pin of the IC is above 250mV. The external resistor
divider consisting of R2, R3 and potentiometer R5
can change that level by pulling down the pin LD
below 250mV, reducing the LED string current in
linear fashion.
The maximum recommended output current of the
HV9910DB4 is 350mA.
PWM Dimming Test:
During normal demo board operation, by applying a
PWM TTL level signal to pin PWMD, the output
current through the LEDs can be changed in PWM
fashion in a 0 to 100% range. In this dimming mode,
the output current has normally two levels – zero
and nominal current, except at very low duty ratios
where inductor current cannot ramp up to the
nominal value within the short time.
HV9910DB4
4 A052804
Vin 1
LD
7
PWMD
5
Gnd
3
CS 2
Gate 4
Rosc 8
Vdd
6
HV9910
U1
R2
147K
1
2
L1
15uH
D1
B260A-13
C3
10uF, 25V
Q1
IRFL014
R5
0.05
C5
2.2uF, 16V
VIN+
VIN-
VDD
PWMD
LED+
LED-
GND
C2
10uF, 25V
C1
10uF, 25V
R1
267K
C6
0.1uF, 25V
R3
5K
HV9910DB4 – Bill of Materials
HV9910DB4
Schematic Diagram
Quantity
RefDes
Description
Manufacturer
Manufacturer's Part Number
3C1,C2,C3 10uF, 25V SMD 1206 Multilayer Ceramic Chip capacitors Panasonic ECJ-3YB1E106M
1C5 2.2uF, 25V SMD 0805 Ceramic Capacitor Panasonic ECJ-3YB1E106M
1C6 0.1uF, 25V SMD 0805 Ceramic Capacitor Panasonic ECJ-2VF1E104Z
1D1 B260A-13
1VIN-,VIN+,VDD,PWMD,LED-, 7 Position Breakaway Header Molex/ Waldom 22-28-4070
LED+,GND
1 L1 15uH, 4.5A inductor Coilcraft MSS1278-153MXB
1Q1 55V, 1.9A SOT-223 N-channel Mosfet IR IRFL014N
1R1 267K, 1/10W, 1% SMD 0805 chip resistor Panasonic ERJ-6ENF2673V
1R2 147K, 1/10W, 1% SMD 0805 chip resistor Panasonic ERJ-6ENF1473V
1R3 5K vertical mount trim pot BC components CT-94W-502
1R5 0.05 ohm, 1/4W, 1% SMD 1210 chip resistor Panasonic ERJ-L14KF50MU
1U1 Universal LED Driver Supertex HV9910LG
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Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unle
ss it receives an
adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of
devices determined to be defective due to workmanship.
No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change
without notice. For the latest product specifications, refer to the Supertex website: http://www.supertex.com. For complete liability in
formation on all Supertex products, refer to the
most current databook or to the Legal/Disclaimer page on the Supertex website.
2004 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 222-8888 / FAX: (408) 222-
4895
www.supertex.com
HV9910DB4 – Top layer
HV9910DB4 – Bottom Layer
HV9910DB4
A052804