Supertex inc.
White LED Driver IC
Features
►
Power efficiency of up to 85%
►
Drives up to six white LEDs
►
2.6 - 4.6V supply power stage can operate at 1.8V
(see page 7)
►
Built-in soft start
►
DC and PWM dimming control
►
Built-in open LED protection
►
Open LED indicator (via R
SET
)
►
1.2MHz fixed switching frequency
►
500nA max leakage current when disabled
►
No leakage current path through LEDs when
disabled
►
Resistor-programmable LED current
►
Small 6-Lead DFN (3.00mm x 3.00mm) package
HV9903
General Description
Applications
►
►
►
►
►
►
bs
V
IN
=
1.8 - 12.5V
Color LCD backlighting
Cell phones, smart phones
PDAs, pocket PCs
Organizers
Digital cameras
MP3 players
Typical Application Circuit
O
ol
V
DD
=
2.6 - 4.6V
Shutdown
VDD
SHDN
RSET
SW
GND
LED
R
SET
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
et
e
●
●
●
The Supertex HV9903 is a fixed frequency DC-DC 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 - 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 is at
fixed frequency of 1.2MHz that allows use of small value
inductors. The LED current can be adjusted from 5.0 - 40mA
by an external resistor connected between the RSET and the
GND pins. The amount of current through the LED can also
be adjusted via DC voltage or a pulse width modulated (PWM)
signal to the RSET 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 RSET 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.
HV9903
HV9903
Ordering Information
Device
HV9903
3.00x3.00mm body
1.00mm height (max)
0.95mm pitch (punched type)
6-Lead DFN
HV9903K6-G
-G indicates package is RoHS compliant (‘Green’)
Absolute Maximum Ratings
Parameter
V
DD
V
SW
, SW voltage
V
SHDN
I
RSET
V
RSET
Storage temperature range
Operating temperature range
Value
6.0V
+30V
Pin Configuration
SW
GND
LED
1
et
10mA
(top view)
-0.5V to +6.0V
V
DD
+0.5V
-65°C to +150°C
-40°C to +85°C
Product Marking
ol
Min
2.6
-
Typ
-
-
-
-
Max
4.6
600
85
40
-40
5.0
Min
24.5
-
-
-
-
-
-
Typ
-
-
-
0.6
900
100
-
Max
29.0
1.6
500
1.0
-
-
200
Stresses beyond those listed under “Absolute Maximum Ratings” may
cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond
those indicated in the operational sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.
H903
YWLL
Package may or may not include the following marks: Si or
Sym
V
DD
T
A
bs
Parameter
Supply voltage
Peak switch current
LED current
Operating temperature
Parameter
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
Recommended Operating Conditions
Units
V
mA
O
I
SW(PK)
I
LED
O
Electrical Characteristics
Sym
I
DD
OVP
(The specifications are at T
A
= 25°C and V
DD
= 2.6V, unless otherwise noted.)
Units
V
mA
nA
Ω
mA
mV
mV
I
DDQ
R
SW
I
SW(LIM)
V
RSET
V
LED
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
2
e
VDD
SHDN
RSET
6-Lead DFN (K6)
GND
Y = Last Digit of Year Sealed
W = Code for Week Sealed
L = Lot Number
= “Green” Packaging
6-Lead DFN (K6)
Conditions
---
---
---
---
C
mA
Conditions
---
---
V
SHDN
= 0V, R
SET
= 1.5kΩ
V
DD
= 2.7V, I
SW
= 100mA
---
R
SET
= 1.5kΩ
R
SET
= 1.5kΩ, V
DD
< V
OUT
HV9903
Electrical Characteristics
(cont.)
Sym
Parameter
(The specifications are at T
A
= 25°C and V
DD
= 2.6V, unless otherwise noted.)
Min
-
12.5
Typ
5.0
15
20
30
38
0.02
-
-
Max
-
17.5
23
36
45
-
-100
100
1.8
-
-
0.9
Units
Conditions
R
SET
= 4.53kΩ
R
SET
= 1.5kΩ
25
33
TC
I
SHDN
f
SW
D
MAX
V
IL
V
IH
V
OPEN
I
SW(OFF)
I
LED
Tempco
SHDN input current
Inductor switching frequency
Maximum duty cycle
IC shutdown voltage (SHDN pin), off
IC start-up voltage (SHDN pin), on
Open LED indicator at RSET pin
Switch off leakage current
-
-
-
1.0
85
-
1.2
2.0
-
mA/
O
C
nA
ol
V
DD
-0.4V
-
V
DD
100
C
DD
L
SW
PWM
Functional Block Diagram
V
DD
bs
VDD
OVP
1.2MHz
R
Q
S
enable
O
SHDN
V
DD
Note:
This drawing is a generalized representation of the HV9903. Actual internal circuitry may differ.
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
3
et
V
SHDN
= 0V
V
SHDN
= 2.0V
---
---
---
1.4
90
-
-
MHz
%
V
V
V
nA
V
SW
= 5.0V
D
C
OUT
●
●
●
HV9903
LED
Soft
Start
err
amp
100mV
current
mirror
V
DD
1:3
75R
Fault
RSET
R
SET
e
R
SET
= 750Ω
R
SET
= 562Ω
I
LED
= 15mA
V
DD
= 2.6 to 4.6V
V
OUT
> 29.0V, R
SET
= 1.13kΩ,
V
DD
= 2.7V
V
OUT
I
LED
LED pin current
17
mA
R
SET
= 1.13kΩ
I
LED
=
22.5V
R
SET
R
GND
HV9903
Operation
LED current is set by the value of the resistor connected to
the RSET pin. The voltage at the RSET 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
bs
Supertex inc.
Current through the RSET pin is monitored. If it falls be-
low 1.5µA, both the PWM boost converter switch 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 RSET
pin. Internal blocking prevents reverse current flow into the
RSET pin if the externally applied voltage exceeds 100mV.
However, applied voltage must not exceed V
DD
.
The control loop is designed for discontinuous mode oper-
ation. 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 oper-
ating 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 (~1.0ms), it
means that if using SHDN for PWM dimming, the PWM dim-
ming signal should be fairly low frequency so that the 1.0ms
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.)
O
ol
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
4
et
e
I
LED
10mA/div
The HV9903 operates as a boost converter that regulates
output current rather than output voltage. To maintain con-
stant 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 cur-
rent 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.
Soft Start
SHDN
I
IN
50mA/div
Open LED Protection
Open LED protection is integrated into the HV9903. Without
open LED protection, output voltage would climb to destruc-
tive levels as the driver attempts to correct for the open LED
condition.
Should the voltage at the SW pin exceed 24.5V, the driver
latches off and the RSET 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 con-
dition persists, the HV9903 will again latch off.
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 dis-
continuous mode operation, the inductor must not exceed
a certain value depending on supply voltage, output current,
and output voltage. The following graphs show the maxi-
mum 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 conser-
vative on inductor rating. Choosing an inductor with lower
resistance results in more efficient operation.
Inductor Selection
HV9903
Inductor Value for 2.7V Operation
100µH
Select the next lower standard value
taking inductor tolerance into account.
Inductor Value
I
LED
indicated in the diagram below. Normally, the voltage at the
SW pin should be a fairly linear ramp, as the linear rise in in-
ductor current through the SW resistance produces a linear
voltage ramp. When the inductor saturates, the rapid rise in
current produces a likewise rapid rise in SW voltage. Test
using an HV9903 with a low switching frequency.
10µH
5.0mA
10mA
15mA
20mA
25mA
30mA
35mA
40mA
1.0µH
V
LED-STRING
+ V
LED
+ V
D
Inductor Rating for 2.7V Operation
1.0A
Exceeds max recommended SW current
40mA
35mA
30mA
25mA
20mA
15mA
10mA
Peak Inductor Current
100mA
Apply correction factor and select an
inductor with an equal or higher rating.
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
)
bs
10V
15V
20V
24V
10mA
5.0V
V
LED-STRING
+ V
LED
+ V
D
As an example, 4 LEDs with 4.0V 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 16.7V. From the
graphs, inductor value at 16.7V and 20mA is 3.7μH and rat-
ing is 320mA. The next lower standard value is 3.3μH (10%
tolerance) and the corrected rating is then:
I
CORRECTED
= (320mA) (3.7μH / 3.3μH) = 359mA
Inductor data sheets may rate the inductor in terms of DC
current, RMS current, or saturation current. The DC or satu-
ration ratings should be used. Confirm that the inductor is
not saturating by observing the SW pin. When an inductor
saturates, current begins to climb rapidly. This condition is
evidenced by a breakpoint in the SW voltage waveform as
O
Supertex inc.
ol
5.0mA
I
LED
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
5
et
Normal
5.0V
10V
15V
20V
24V
V
IN
GND
GND
Note:
ringing or a noise may be present
Also, confirm that the driver is operating in discontinuous
mode by observing the voltage at the SW pin while at mini-
mum supply and maximum LED current. For worst-case test
purposes, select components within their tolerance range as
follows:
Inductor: high value
LED: high voltage drop
HV9903: high switching frequency
Some ringing in the SW waveform will be evident, but is not
a concern as the energy is very low. About 10-15% idle time
should be allowed to assure discontinuous mode operation.
Idle time is the interval when there is no inductor current
flowing, as indicated when the SW voltage is at the supply
voltage level (with some ringing).
The following graphs show the SW waveform with various
inductor values and can assist in selecting an inductor. The
top graph shows an inductor value that is acceptable, how-
ever, greater efficiency can be achieved by increasing induc-
tance. The bottom graph shows continuous mode operation,
which must be avoided.
e
Saturated
SW Waveform Showing Inductor Saturation
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