Supertex HV9910DB3v.3 User manual

1
General Description
The Supertex HV9910DB3v.3 demo board is a complete
high current, High-Brightness LED power driver to supply a
string of LED(s) 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.
The HV9910DB3v.2 (constant frequency HV9910
demoboard) was not capable of driving LED strings whose
voltage was greater than one-half the input voltage. The
HV9910DB3v.3 rectifies this drawback by operating in a
constant off-time mode as compared to a constant frequency
mode. The constant off-time mode enables regulation of the
LED current even when the LED voltage string is greater than
one half the input voltage. (Please refer to the application
note AN-H50 on the Supertex website for more information
on the constant off-time mode of operation.)
The HV9910DB3v.3 can supply a maximum output current
of 900mA to drive LED strings from a 9VDC to 30VDC
input. It achieves an overall efficiency above 85%. The
HV9910DB3v.3 is ideally suited to drive two 1Watt or 3Watt
LEDs from a 12V or 24V input voltage.
The power conversion stage of the HV9910DB3v.3 consists
of a current-controlled buck converter operating at an off-
time of about 5.8µs. The nominal output current of the demo
board can be adjusted to any value less than 900mA 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.
Board Layout and Connections
HV9910DB3v3
Low Voltage, High Brightness
LED Driver Demo Board
Specifications
Input Voltage: 8V – 30V DC
LED string voltage: See instructions
Load current: 900mA maximum
Switching Frequency: variable
Efficiency: >85%
Dimensions: 82mm X 28mm
8
to
30V
DC
PWM Dimming
(opti onal )
Enable
Connection
321
(Board Size: 53mm x 18mm)

2
HV9910DB3v.3
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(s) to this pin.
LED-: Connect the Cathode of the LED(s) to this pin.
VDD:This pin is connected to the VDD pin of the HV9910/
HV9910B. 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
the converter on and off with a low frequency 50Hz to 1000Hz
TTL logic level signal. Changing the Duty Ratio of the signal
changes the effective average current via the LEDs, thus
changing the light emission.
Note: In the case of PWM dimming, the PWMD pin should
not be connected to the VDD pin!
J1: The three pins in J1 are used to set the current level of
the output. The HV9910DB3v.3 has two current levels:
Pin 2 connected to Pin 1: Output Current is 900mA
Pin 2 connected to Pin 3: Output current can be adjusted
using the potentiometer
LED STRING VOLTAGE
In a constant-off time buck converter, the relationship
between the output current ripple ΔI0, the LED string voltage
V0, the inductance value L, and the programmed off time toff
is given by:
From the above equation, it can be seen that for a given value
of Land toff, the output current ripple is directly proportional
to the output voltage. A plot of the current ripple vs. the
output voltage is given below:
In cases where the current ripple is too high (as a percentage
of the average LED current), it may be necessary to add
a small ceramic capacitor between the output terminals to
reduce the LED current ripple.
Testing the HV9910DB3v.3
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.
Open LED test:
After the initial test of functionality, the demo board can be
tested at open LED string. The test is non-destructive and
not time restricted. Disconnect one end of the LEDs and
power up the demo. There will be no light emission and the
AC current withdrawn from the line will be very low. There is
no switching at the switching node.
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 and potentiometer
R6 can change that level by pulling down the pin LD below
250mV, reducing the LED string current in linear fashion.
The maximum output current of the HV9910DB3v.3 is about
900mA.
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.
Instructions:
VL
I
t
o
off
0=⋅
∆
0
100
200
300
400
2468
Output Voltage (V)
Current Ripple (mA)

3
HV9910DB3v.3
Schematic Diagram
D1
B140-13
Q1
VN3205
12
L1
220μH
C3
2.2μF, 10V
V
IN
+
V
IN
-V
DD
PWMD
LED+
LED-
GND
R2
147KΩ
R4
0.27Ω
C2
10μF, 35V
C1
10μF, 35V
R5
124kΩ
C4
0.1μF, 10V
R6
5KΩ
1
7
5
3
2
4
86
HV9910
U1
V
IN
LD
PWMD
GND
CS
GATE
R
T
V
DD
Bill of Materials
Quantity RefDes Description Manufacturer Manufacturer’s Part
Number
2 C1,C2 10μF, 35V SMD 1812 Multilayer Ceramic Chip
Capacitors Panasonic ECJ-5YF1V106Z
1 C3 2.2uF, 16V X7R Ceramic Capacitor TDK Corp. C2012X7R1C225K
1 C4 0.1uF, 16V X5R Ceramic Chip Capacitor Panasonic ECJ-2VB1C104K
1 D1 40V, 1A SMA Schottky Diode Diodes, Inc. B140-13
1 L1 220μH, 1A Shielded Power Inductor Coilcraft MSS1278-224KXB
1 Q1 50V, 1.5A SOT-89 Power MOSFET Supertex VN3205N8
1 R2 147KΩ, 1/10W, 1% SMD 0805 Chip Resistor Panasonic ERJ-6ENF1473V
1 R4 0.27Ω, 1/4W, 1% SMD 1206 Chip Resistor Panasonic ERJ-8RQFR27V
1 R5 124K, 1/10W, 1% SMD 0805 Chip Resistor Panasonic ERJ-6ENF1243V
1 R6 5KΩ Surface Mount Trim Pot Murata PVG3A502A01R00
1 U1 Universal LED Driver Supertex HV9910LG/HV9910BLG

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A043007
HV9910DB3v.3
Top Layer
Bottom Layer
Silk Screen