Supertex inc.
HV9910BDB3
Low Voltage, High Current,
LED Driver Demoboard
General Description
Specifications
The HV9910BDB3 demoboard is a high current LED driver
designed to drive one LED or two LEDs in series at currents
up to 1.0A from a 10 – 30VDC input. The demoboard uses
Supertex’s HV9910B Universal LED driver IC to drive a
buck converter.
Parameter
Output voltage constant frequency mode
2.0 - 4.5V
The HV9910BDB3 can be configured to operate in either a
constant frequency mode (for driving a single LED) or in a
constant off-time mode (for driving two LEDs).
Output voltage constant off-time mode
4.0 - 8.0V
The output current can be adjusted in two ways – either
with linear dimming using the onboard potentiometer or
with PWM dimming by applying a TTL – compatible square
wave signal at the PWMD terminal. Using linear dimming,
the output current of the HV9910DB1 can be lowered to
about 0.01A (note: zero output current can be obtained
only by PWM dimming).
Input voltage
Maximum output current
Output current ripple (typ)
Efficiency (@ 12V input)
Open LED protection
Output short circuit protection
Dimensions
Value
10 - 30VDC
1.0A ± 10%
20% (peak-peak)
86% (for one LED)
93% (for two LEDs)
yes
no
48.2mm X 29.0mm
Connection Diagram
+
-
+
Short for
constant off-time mode
Connections
1. Input Connection - Connect the input DC voltage
between VIN and GND terminals of connector J1 as shown
in the connection diagram.
2. Output Connection - Connect the LEDs between
LED+ (anode of LED string) and LED- (cathode of LED
string) of connector J2.
a. If the load is one LED, short the RT and FREQ
terminals of connector J4 using a jumper.
Short for constant
frequency mode
3. PWM Dimming Connection
a. If no PWM dimming is required, short PWMD and
VDD terminals of connector J3.
b. If PWM dimming is required, connect the TTLcompatible PWM sourc between PWMD and GND
terminals of connector J3. The recommended PWM
dimming frequency is ≤ 1.0kHz.
b. If the load is two LEDs, short the RT and OFFT
terminals of connector J4 using a jumper.
Doc.# DSDB-HV9910BDB3
A032813
Supertex inc.
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HV9910BDB3
Frequently Asked Questions
1. Why does the demoboard have two operating
modes?
2. If the minimum input voltage in my application is higher (say 20V), does that mean I can drive a 9V LED string
in the constant frequency mode or an 16V LED string in
the constant off-time mode using the demoboard?
Constant frequency mode limits the maximum output
voltage to less then 50% of the minimum input voltage.
So, in this case, if we use only the constant frequency
mode, the maximum output voltage will have to be less
than 5V. Constant off-time mode removes this limitation and allows the output voltage become higher. However, in order to achieve reasonable noise immunity and
to limit the switching frequency variation over the input
voltage range, it is not recommended to operate the
HV9910DB3 with the output voltage exceeding 80% of
the input voltage, even in the constant off-time mode.
Please refer to application note AN-H50 on the Supertex
website for more details.
Although a larger LED string can be driven using the
demoboard in these conditions, the demoboard will not
be able to drive the LED at 1A.
The HV9910B is a constant peak current controller. The
average LED current is equal to the peak current set
(using the sense resistor) minus one-half of the ripple
current in the inductor.
Higher output voltages lead to larger ripple current values, which will reduce the maximum LED current the
board can deliver.
3. How can I compute the maximum LED current the
demoboard can deliver if I use a higher input voltage
and a higher LED string voltage?
See table below:
Parameters
Minimum input voltage
= VIN,MIN
Maximum LED string voltage
= VO,MAX
Switching frequency (constant frequency mode)
= fS
(100kHz)
Off-Time (constant off-time mode)
= TOFF
(5.1μs)
HV9910B CS threshold voltage
= VCS
(0.25V)
Sense Resistor
= RCS
(0.22Ω)
Inductor
=L
(220μH)
Constant Off-Time Mode
Δl =
Constant Frequency Mode
VO,MAX • TOFF
L
VO,MAX •
ILED =
VCS
RCS
–
Δl
2
Maximum Switching Frequency =
Doc.# DSDB-HV9910BDB3
A032813
Δl =
{
1–
VO, MAX
VIN,MIN
{
ILED =
{
1–
VO, MAX
VIN,MIN
{
L • fS
VCS
RCS
–
Δl
2
TOFF
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HV9910BDB3
Frequently Asked Questions (cont.)
Conduction losses are dependent on the duty cycle.
Since the voltage drop on the FET is smaller than the
voltage drop on the diode (the on-resistance of the FET
is very small), the higher the duty cycle, the smaller is
the conduction loss. Please note that we are ignoring
the losses in the inductor, which will be identical in both
cases.
4. If the constant off-time mode allows a wider LED voltage range, why not use that mode exclusively? Why do
we need the constant frequency mode?
Although the constant off-time mode allows the
demoboard to operate at a higher output voltage, the
LED ripple current is directly proportional to the output
voltage in this mode. This makes it difficult to get a good
load regulation of the LED current in the constant offtime mode with a wide variation in the LED string voltage
(in this case it will be a 1:4 variation). At lower LED voltage values, the ripple will be lower and the LED current
would be higher.
Also, efficiency = POUT / PIN = POUT / (POUT + losses) = 1/ (1
+ losses/POUT), where POUT is the output power and PIN
is the input power. So, if the output power is higher, the
fixed switching losses are a smaller fraction of the output
power and thereby the efficiency is higher.
Comparing the operation of the converter in both modes
at 12V input for this particular demoboard, the following are the differences:
a. Output power is higher with 2 LEDs as the load
b. Switching frequency in the constant off-time
mode is 55kHz, whereas it is 100kHz in the constant
frequency mode
c. Duty cycle of operation is about higher in the constant off-time mode by a factor of 2 than in the constant frequency mode
By switching between the two modes depending on the
load, we can get a better current accuracy without having to adjust the LD voltage or the sense resistor.
Load Regulation (@ VIN = 12V)
10
Change in current (%)
Constant off-time mode
8
All the above factors favor the higher load voltage and thus
the demoboard has a higher efficiency when the load is larger.
With mode change
6
4
Constant Off-time Mode
Constant Frequency Mode
6. Why are the LED current rise and fall times during
PWM dimming different when the load changes from one LED to two LEDs?
2
0
2
4
Load Voltage (V)
6
The LED current rise time is directly proportional to VIN
- VOUT and the fall time is proportional to VOUT (where VIN
is the input voltage and VOUT is the output voltage). Since
VOUT is higher with two LEDs, the rise time will be larger
and the fall time will be smaller.
8
Constant Off-Time Mode
5. Why is the efficiency of the demoboard higher with a
load of two LEDs compared to a single LED load?
Losses in the HV9910BDB3 occur due mainly due to
two factors:
a. Conduction losses in the FET and diode
b. Switching losses in the FET
Switching losses are dependent on the switching frequency, input voltage and total parasitic capacitance at
the node. At higher switching frequencies, the switching
losses are higher.
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HV9910BDB3
Typical Results
Constant Frequency Mode:
this mode, the line regulation of the LED current is less
than 2% and full-load efficiency greater than 80%.
The HV9910BDB3 is designed to be operated in the constant frequency mode when the load is a single LED. In
Efficiency vs. Input Voltage (@VO = 4V)
86
84
82
12
16
20
24
28
0
-1
-2
32
8
12
16
20
24
28
32
Input Voltage (V)
Input Voltage (V)
Fig. 1. Efficiency vs. Input Voltage Plot
Fig. 2. Line Regulation of LED Current Plot
Efficiency vs. Load Voltage (@ VIN = 12V)
80
2
3
4
Load Regulation (@ VIN = 12V)
3
85
75
1
Change in current (%)
Efficiency (%)
90
8
Line Regulation (@VO = 4V)
2
Change in current (%)
Efficiency (%)
88
2
1
0
5
2
3
4
5
Load Voltage (V)
Load Voltage (V)
Fig. 3. Efficiency vs. Load Voltage Plot
Fig. 4. Load Regulation of LED Current Plot
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HV9910BDB3
Typical Results (cont.)
Constant Off-Time Mode:
In this mode, the line regulation of the LED current is less
than 2% and the efficiency greater than 80%.
The HV9910BDB3 is designed to be operated in the constant off-time mode when the load is two LEDs in series.
Efficiency vs. Input Voltage (@VO = 7.8V)
95
Change in current (%)
Efficiency (%)
94
93
92
91
90
1
0
-1
-2
8
12
16
20
24
28
Line Regulation (@ VO = 7.8V)
2
32
8
Fig. 5 . Efficiency vs. Input Voltage Plot
Efficiency vs. Load Voltage (@VIN = 12V)
Change in current (%)
Efficiency (%)
80
4
6
28
32
Load Voltage (V)
8
6
4
2
0
8
Fig. 7 . Efficiency vs. Load Voltage Plot
Doc.# DSDB-HV9910BDB3
A032813
24
Load Regulation (@ VIN = 12V)
10
85
2
20
Fig. 6. Line Regulation of LED Current Plot
90
75
16
Input Voltage (V)
Input Voltage (V)
95
12
2
4
6
Load Voltage (V)
8
Fig. 8. Load Regulation of LED Current Plot
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HV9910BDB3
Typical Results (cont.)
The variation in the switching frequency, when the
HV9910BDB3 is operated in the constant off-time mode, is
Switching Frequency vs. Input Voltage
(@VO = 7.8V)
140
120
100
80
60
40
20
8
12
16
20
24
28
Switching Frequency vs. Load Voltage
(@VIN = 12V)
140
Switching Frequency (kHz)
Switching Frequency (kHz)
shown in Figs. 9 and 10.
120
100
80
60
40
32
2
4
6
8
Input Voltage (V)
Load Voltage (V)
Fig. 9. Switching Frequency vs. Input Voltage Plot
Fig. 10. Switching Frequency vs. Load Voltage Plot
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HV9910BDB3
Waveforms
Constant Frequency mode (LED Voltage = 3.3V):
LED Current
LED Current
Drain Voltage
Drain Voltage
(a) 10V Input
(b) 12V Input
LED Current
LED Current
Drain Voltage
Drain Voltage
(d) 30V Input
(c) 24V Input
Fig. 13. Steady State Waveforms in Constant Frequency Mode
C1 (Yellow)
:
Drain Voltage (10V/div)
C4 (Green)
:
LED Current (200mA/div)
Time Base
:
10μs/div
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HV9910BDB3
Waveforms (cont.)
PWM
Dimming
Input
LED Current
(a) PWM Dimming Performance
Time Scale
:
500μs/div
LED Current
PWM Dimming Input
PWM Dimming Input
LED Current
(b) PWM Dimming Rise Time
Time Scale
:
10μs/div
(c) PWM Dimming Fall Time
Time Scale
:
10μs/div
Fig. 12. PWM Dimming Performance in Constant Frequency Mode
C1 (Yellow)
:
PWMD Input Voltage (2V/div)
C4 (Green)
:
LED Current (200mA/div)
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HV9910BDB3
Waveforms (cont.)
Constant Off-time mode (LED Voltage = 6.4V):
LED Current
LED Current
Drain Voltage
Drain Voltage
(a) 10V Input
(b) 12V Input
LED Current
LED Current
Drain Voltage
Drain Voltage
(d) 30V Input
(c) 24V Input
Fig. 13. Steady State Waveforms in Constant Frequency Mode
C1 (Yellow)
:
Drain Voltage (10V/div)
C4 (Green)
:
LED Current (200mA/div)
Time Base
:
10μs/div
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A032813
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HV9910BDB3
Waveforms (cont.)
PWM
Dimming
Input
LED Current
(a) PWM Dimming Performance
Time Scale
:
500μs/div
PWM Dimming Input
PWM Dimming Input
LED Current
LED Current
(b) PWM Dimming Rise Time
Time Scale
:
10μs/div
(c) PWM Dimming Fall Time
Time Scale
:
10μs/div
Fig. 14. PWM Dimming Performance in Constant Frequency Mode
C1 (Yellow)
:
PWMD Input Voltage (2V/div)
C4 (Green)
:
LED Current (200mA/div)
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Doc.# DSDB-HV9910BDB3
A032813
C6
2.2µF
16V
11
R6
5k
R2
147k
2
1
J1
3
J3
C5
1.0µF
16V
C1
100µF
35V
1
2
5
R3
1.0k
7
6
C2
100µF
35V
EN
HD
1
VIN
1
ROsc
3
GND
CS
GATE
HV9910B
VDD
U2
R5
226k
1
J4
2
4
8
2
R7
105k
3
C3
2.2µF
50V
R4
0.22
220µH
L1
Q1
Si2318DS
1
D1
B140-13
2
C4
2.2µF
50V
1
2
J2
HV9910BDB3
Schematic Diagram
Supertex inc.
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HV9910BDB3
Bill of Materials
Package
Manufacturer
Manufacturer’s Part
Number
SMT
Panasonic
EEV-FK1V101P
2.2µF, 50V, X7R ceramic chip
capacitor
SMD1206
Murata
GRM31CR71H225KA88L
C5
0.1µF, 16V X7R ceramic chip
capacitor
SMD0805
Panasonic
ECJ-2VB1C104K
1
C6
2.2µF, 16V X7R ceramic chip
capacitor
SMD0805
TDK Corp
C2012X7R1C225K
5
1
D1
40V, 1A schottky diode
SMA
Diodes Inc
B140-13
6
2
J1,J2
2 position, 5mm pitch, vertical
header
Thru-Hole
On Shore
Tech
EDSTL130/02
7
2
J3,J4
3 position, 0.100” pitch, vertical
header
Thru-Hole
Molex
22-03-2031
8
1
L1
220uH, 1.3A rms, 2.4A sat inductor
SMT
Coiltronics
DR127-221-R
9
1
Q1
40V, 45mΩ, 10nC N-channel FET
SOT-23
Vishay
Si2318DS
10
1
R2
147KΩ, 1/8W, 1% chip resistor
SMD0805
-
-
11
1
R3
1kΩ, 1/8W, 1% chip resistor
SMD0805
-
-
12
1
R4
0.22Ω, 1/4W, 1% chip resistor
SMD1206
-
-
13
1
R5
226kΩ, 1/8W, 1% chip resistor
SMD0805
-
-
14
1
R6
5KΩ top adjust trimpot
SMT
Bourns Inc
3361P-1-502G
15
1
R7
105kΩ, 1/8W, 1% chip resistor
SMD0805
-
-
16
1
U1
Universal LED Driver
SO-8
Supertex
HV9910BLG-G
#
Quan
Ref Des Description
1
2
C1,C2
100µF, 35V, electrolytic capacitor
2
2
C3,C4
3
1
4
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.
©2014 Supertex inc. All rights reserved. Unauthorized use or reproduction is prohibited.
Doc.# DSDB-HV9910BDB3
A032813
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1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
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