boost converter designed for driving Light Emitting
Diodes (LEDs) with constant current where the light
intensity is proportional to the current through them.
The input supply voltage range into the device (V
DD
)
is 2.6 to 4.6V. Operation of the driver at lower
voltages is possible as long as a 2.6–4.6V low-
current supply is available for the HV9903. The
device uses a single inductor and a minimum
number of passive components. The device can be
enabled/disabled via the SHDN pin.
The HV9903 has an internal oscillator. The oscillator
frequency is at fixed frequency of 1.2MHz that allows
use of small value inductors. The LED current can
be adjusted from 5 to 40mA by an external resistor
connected between the R
SET
and the GND pins. The
amount of current though the LED can also be
adjusted via DC voltage or a pulse width modulated
(PWM) signal to the R
SET
pin.
Soft-start is implemented on-chip, minimizing inrush
current to only 30% over steady state current.
An open LED circuit detects an open LED condition,
disables the driver, and sets the R
SET
pin high. The
driver is re-enabled by asserting SHDN low, then
high. If the open LED condition persists, the driver
will again latch off.
Applications
❑
❑
❑
❑
❑
❑
Color LCD Backlighting
Cell phones, smart phones
PDAs, pocket PCs
Organizers
Digital Cameras
MP3 Players
Typical Application
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 unless 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 information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer
page on the Supertex website.
HV9903
HV9903
Ordering Information
Device
HV9903
Package Option
MLP (3mm x 3mm)
Demo Kit
HV9903DB1
HV9903K6*
*Product supplied on 3000 piece carrier tape reels
Absolute Maximum Ratings
V
DD
V
SW
, SW Voltage
V
SHDN
I
Rset
V
Rset
Storage Temperature
Operating Temperature
6V
+35V
-0.5V to 6V
10mA
V
DD
+ 0.5V
-65ºC to +150ºC
-40ºC to +85ºC
Recommended Operating Conditions
Symbol
V
DD
I
SW(pk)
T
AMB
I
LED
Parameter
Supply voltage
Peak switch current
Operating temperature
LED current
-40
5
Min
2.6
Typ
Max
4.6
600
85
40
Unit
V
mA
ºC
mA
Conditions
Specifications
Symbol
OVP
I
DD
I
DDQ
Parameter
(unless otherwise specified: T
A
= 25ºC, V
DD
= 2.6V)
Min
28
Typ.
33
Max
35
1.6
500
Unit
V
mA
nA
V
Rset
=0.2V
V
SHDN
=0V, R
SET
= 1.5KΩ
Conditions
Over voltage protection
V
DD
supply current
Total leakage current when
disabled
(I
SW(off)
+ I
DD(off)
+ I
LED(off)
)
Switch on resistance
Switch current limit
Rset pin voltage
LED pin voltage
LED pin current
R
SW
I
SW(lim)
V
Rset
V
LED
I
LED
0.6
900
100
1.0
Ω
mA
mV
V
DD
= 2.7V
R
SET
= 1.5KΩ
R
SET
= 1.5KΩ, V
DD
< V
OUT
R
SET
= 4.53KΩ
180
5
12.5
17
25
33
15
20
30
38
0.02
2
mV
17.5
23
36
45
mA/ºC
mA
R
SET
= 1.5KΩ
R
SET
= 1.13KΩ
R
SET
= 750Ω
R
SET
= 562Ω
I
LED
= 15mA
TC
I
LED
Tempco
HV9903
HV9903
Symbol
I
SHDN
Parameter
SHDN input current
Min
Typ.
Max
-100
100
f
SW
D
MAX
V
IL
V
IH
V
Open
I
SW(off)
Inductor switching frequency
Maximum duty cycle
IC Shutdown voltage (SHDN pin),
Off
IC Start-up voltage (SHDN pin),
On
Open LED indicator at R
SET
lead
Switch Off leakage current
1.2
2.0
V
DD
-
0.4V
V
DD
100
V
nA
V
OUT
> 33V, R
SET
= 562Ω, V
DD
=
2.7V
V
SW
= 5V
0.8
90
1.2
95
0.9
V
1.6
MHz
%
Unit
nA
Conditions
V
SHDN
= 0V
V
SHDN
= 2V
V
DD
= 2.6 to 4.6V
Pin Configuration
Pin
1
2
3
4
Name Description
SW
GND
LED
R
SET
Internal switch connection.
Ground. The underside pads are internally connected to pin 2.
Cathodes of the LEDs are connected to this pin.
For programming the LED current and dimming function.
Also functions as a Fault output to indicate an open LED condition. R
SET
is pulled to V
DD
when an open LED condition is detected. The driver is
then latched off. To reset, the SHDN input must be asserted low.
An externally applied voltage greater than 100mV causes the LED
switch and PWM boost converter to shut off. The IC does not go into
low power standby and the soft-start circuit is not reactivated when V
Rset
again falls below 100mV.
SW
GND
LED
V
DD
SHDN
R
SET
Top View
GND
Pin 1
5
SHDN
V
DD
Shut down input. A logic low disables the IC and places it in low power
standby. A logic high enables the IC via a soft-start sequence.
Input voltage supply pin. It is common practice to use a bypass
capacitor as close as possible to the device on this pin.
Bottom View
6
3
HV9903
HV9903
Functional Block Diagram
L
V
DD
C
DD
V
DD
SW
D
C
OUT
HV9903
OVP
R
S
Q
PWM
1. 2MHz
enable
LED
Soft
Start
err
amp
SHDN
I
LED
22. 5
V
R
SET
V
DD
100mV
current
mirror
V
DD
1:3
7 5R
R
GND
Fault
R
SET
R
SET
Note: This drawing is a generalized representation of the HV9903. Actual internal circuitry may differ.
Operation
The HV9903 operates as a boost converter that
regulates output current rather than output voltage.
To maintain constant output current, LED current is
monitored via the LED pin and the boost converter’s
PWM duty cycle is adjusted accordingly to maintain
the desired current level. LED current is controlled
100% via the PWM boost converter – the MOSFET
connected to the LED pin is fully turned on during
normal operation and is not regulated to maintain
constant LED current. This minimizes voltage drop at
the LED pin, maximizing overall efficiency.
LED current is set by the value of the resistor
connected to the R
SET
pin. The voltage at the R
SET
pin
is maintained at 100mV and the resulting current
through the R
SET
resistor is used as a reference for
LED current control. LED current is regulated at 225
times R
SET
current.
I
LED
22.5V
=
R
SET
and LED switch are turned off. Soft-start is not reset
and the IC does not go into low power standby. Such
a condition can occur two ways: 1) if R
SET
is greater
than about 66kΩ, or 2) an external voltage greater
than 100mV is applied to the R
SET
pin. Internal
blocking prevents reverse current flow into the R
SET
pin if the externally applied voltage exceeds 100mV.
However, applied voltage must not exceed V
DD
.
The control loop is designed for discontinuous mode
operation. That is, inductor current is allowed to
return to zero between PWM conversion cycles. To
assure discontinuous mode operation, the inductor
value must be below a certain value for given
conditions of supply voltage and LED string voltage
drop. The Inductor Selection section provides further
information.
The PWM boost converter is a current mode controller
operating at an internally fixed 1.2MHz.
A soft-start circuit minimizes inrush current when
power is initially applied or the device is enabled via
the SHDN input. Inrush current is typically limited to
130% of steady-state current. Although the soft-start
period is short (~1ms), it means that if using SHDN for
PWM dimming, the PWM dimming signal should be
4
Current through the R
SET
pin is monitored. If it falls
below 1.5µA, both the PWM boost converter switch
HV9903
HV9903
fairly low frequency so that the 1ms soft-start interval
does not introduce much error. The R
SET
input is
better for PWM dimming, as it does not include soft-
start. (See below for PWM dimming techniques.)
inductor rating. Choosing an inductor with lower
resistance results in more efficient operation.
Inductor Value for 2.7V Operation
Soft Start
100 H
SHDN
Inductor Value
Select the next lower standard value,
taking inductor tolerance into account.
I
LED
10 H
5mA
I
IN
50mA/div
10mA
15mA
20mA
25mA
30mA
35mA
40mA
I
LED
10mA/div
1 H
5V
10V
15V
20V
25V
V
LED-STRING
+ (I
LED
· 5? ) + V
D
V
LED-STRING
+ (I
LED
-5Ω) +V
D
Open LED Protection
Open LED protection is integrated into the HV9903.
Without open LED protection, output voltage would
climb to destructive levels as the driver attempts to
correct for the open LED condition.
Should the voltage at the SW pin exceed 33V, the
driver latches off and the R
SET
pin is pulled to V
DD
,
indicating a fault condition. To reset the latch, assert
SHDN low for at least 200ns. When SHDN is again
brought high, the driver will be re-enabled, including
soft-start. If the open LED condition persists, the
HV9903 will again latch off.
Peak Inductor Current
Inductor Rating for 2.7V Operation
1A
Exceeds max recommended SW current
40mA
35mA
30mA
25mA
20mA
15mA
10mA
5mA
100mA
I
LED
Apply correction factor and select an
inductor with an equal or higher rating.
Inductor Selection
The HV9903 is designed for discontinuous mode
operation. Control loop stability may be compromised
if the converter is allowed to operate in continuous
mode. To assure discontinuous mode operation, the
inductor must not exceed a certain value depending
on supply voltage, output current, and output voltage.
The following graphs show the maximum permissible
inductor value and inductor current rating for a lithium-
ion battery application (2.7V minimum battery
voltage). When calculating LED string voltage drop,
use maximum LED voltage. If using paralleled LED
strings with current balancing resistors, include the
resistor voltage drop in V
LED-STRING
. V
D
is the diode’s
forward voltage drop. Always select the next lower
standard value inductor and be conservative on
10mA
5V
10V
15V
20V
25V
V
LED-STRING
+ (I
LED
· 5? ) + V
D
V
LED-STRING
+ (I
LED
-5Ω) +V
D
When selecting the next lower standard value
inductor, the current rating must be adjusted
according to the following equation.
I
CORRECTED
I
GRAPH
L
GRAPH
L
SELECTED
As an example, 4 LEDs with 4V max drop are to be
driven at 20mA. LED string drop is 16V plus 0.6V for
the diode plus 0.1V for LED pin voltage, for a total of
16.7 volts. From the graphs, inductor value at 16.7V
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