HV9903 (334632 байта)

HV9903 (334632 байта)
HV9903
Initial Release
White LED Driver
Features
❑
Power efficiency of up to 85%
❑
Drives up to 6 White LEDs
❑
2.6V to 4.6V Supply
power stage can operate at 1.8V (see page 8)
❑
Built-in Soft Start
❑
DC and PWM Dimming Control
❑
Built-in Open LED protection
❑
Open LED indicator (via RSET)
❑
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 MLP (3mm x 3mm) package
(similar to 6-pin SOT-23)
Applications
❑
Color LCD Backlighting
❑
Cell phones, smart phones
❑
PDAs, pocket PCs
❑
Organizers
❑
Digital Cameras
❑
MP3 Players
Description
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 (VDD)
is 2.6 to 4.6V. Operation of the driver at lower
voltages is possible as long as a 2.6–4.6V lowcurrent 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 RSET 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 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.
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
Package Option
Device
Demo Kit
MLP (3mm x 3mm)
HV9903
HV9903K6*
HV9903DB1
*Product supplied on 3000 piece carrier tape reels
Absolute Maximum Ratings
VDD
6V
VSW , SW Voltage
+35V
VSHDN
-0.5V to 6V
IRset
10mA
VRset
VDD + 0.5V
Storage Temperature
-65ºC to +150ºC
Operating Temperature
-40ºC to +85ºC
Recommended Operating Conditions
Symbol
VDD
Parameter
Min
Supply voltage
2.6
ISW(pk)
Peak switch current
TAMB
Operating temperature
ILED
LED current
Specifications
Symbol
OVP
Typ
Max
Unit
4.6
V
600
mA
-40
85
ºC
5
40
mA
Conditions
(unless otherwise specified: TA = 25ºC, VDD = 2.6V)
Parameter
Min
Typ.
Max
Unit
Over voltage protection
28
33
35
V
Conditions
IDD
VDD supply current
1.6
mA
VRset =0.2V
IDDQ
Total leakage current when
disabled
(ISW(off) + IDD(off) + ILED(off))
500
nA
VSHDN =0V, RSET = 1.5KΩ
RSW
Switch on resistance
0.6
1.0
Ω
VDD = 2.7V
Switch current limit
900
mA
VRset
Rset pin voltage
100
mV
RSET = 1.5KΩ
VLED
LED pin voltage
mV
RSET = 1.5KΩ, VDD < VOUT
ILED
LED pin current
ISW(lim)
TC
ILED Tempco
180
5
RSET = 4.53KΩ
12.5
15
17.5
17
20
23
25
30
36
RSET = 750Ω
33
38
45
RSET = 562Ω
0.02
2
RSET = 1.5KΩ
mA
mA/ºC
RSET = 1.13KΩ
ILED = 15mA
HV9903
HV9903
Symbol
Parameter
ISHDN
Min
Typ.
SHDN input current
Max
Unit
Conditions
-100
nA
VSHDN = 0V
100
fSW
Inductor switching frequency
DMAX
0.8
1.2
90
95
Maximum duty cycle
VIL
IC Shutdown voltage (SHDN pin),
Off
VIH
IC Start-up voltage (SHDN pin),
On
1.2
VOpen
Open LED indicator at RSET lead
2.0
ISW(off)
Switch Off leakage current
Pin Configuration
VDD
SW
GND
LED
SHDN
RSET
Pin
VDD = 2.6 to 4.6V
%
V
VDD0.4V
VDD
V
VOUT > 33V, RSET = 562Ω, VDD =
2.7V
100
nA
VSW = 5V
Name Description
1
SW
2
GND
Ground. The underside pads are internally connected to pin 2.
3
LED
Cathodes of the LEDs are connected to this pin.
4
RSET
For programming the LED current and dimming function.
Internal switch connection.
Also functions as a Fault output to indicate an open LED condition. RSET
is pulled to VDD 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 VRset
again falls below 100mV.
Pin 1
Bottom View
MHz
0.9
Top View
GND
1.6
VSHDN = 2V
5
SHDN
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.
6
VDD
Input voltage supply pin. It is common practice to use a bypass
capacitor as close as possible to the device on this pin.
3
HV9903
HV9903
Functional Block Diagram
L
D
VDD
CDD
COUT
VDD
SW
HV9903
PWM
OVP
LED
1. 2MHz
R
S
enable
Q
Soft
Start
ILED
SHDN
err
amp
VDD
100mV
22. 5V
RSET
VDD
current
mirror
1:3
7 5R
RSET
Fault
R
GND
RSET
Note: This drawing is a generalized representation of the HV9903. Actual internal circuitry may differ.
Operation
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 RSET 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 VDD.
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.
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.
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 RSET resistor is used as a reference for
LED current control. LED current is regulated at 225
times RSET current.
I LED =
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
22.5V
R SET
Current through the RSET pin is monitored. If it falls
below 1.5µA, both the PWM boost converter switch
4
HV9903
HV9903
inductor rating. Choosing an inductor with lower
resistance results in more efficient operation.
fairly low frequency so that the 1ms soft-start interval
does not introduce much error. The RSET input is
better for PWM dimming, as it does not include softstart. (See below for PWM dimming techniques.)
Inductor Value for 2.7V Operation
Soft Start
100 H
Select the next lower standard value,
taking inductor tolerance into account.
Inductor Value
SHDN
IIN
50mA/div
ILED
5mA
10 H
10mA
15mA
ILED
20mA
25mA
30mA
35mA
40mA
1 H
10mA/div
5V
10V
15V
20V
25V
VLED-STRING + (ILED · 5? ) + VD
VLED-STRING + (ILED -5Ω) +VD
Inductor Rating for 2.7V Operation
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.
40mA
1A
35mA
30mA
25mA
Exceeds max recommended SW current
20mA
15mA
Peak Inductor Current
Should the voltage at the SW pin exceed 33V, the
driver latches off and the RSET pin is pulled to VDD,
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.
10mA
5mA
100mA
ILED
Apply correction factor and select an
inductor with an equal or higher rating.
Inductor Selection
10mA
5V
10V
15V
20V
25V
VLED-STRING + (ILED · 5? ) + VD
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 lithiumion 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 VLED-STRING. VD is the diode’s
forward voltage drop. Always select the next lower
standard value inductor and be conservative on
VLED-STRING + (ILED -5Ω) +VD
When selecting the next lower standard value
inductor, the current rating must be adjusted
according to the following equation.
ICORRECTED
IGRAPH
LGRAPH
LSELECTED
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
and 20mA is 3.7µH and rating is 320mA. The next
5
HV9903
HV9903
lower standard value is 3.3µH (10% tolerance) and
the corrected rating is then:
ICORRECTED
320 mA
3.7µH
3.3µH
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, however, greater efficiency can be
achieved by increasing inductance. The bottom graph
shows continuous mode operation, which must be
avoided.
359 mA
Inductor data sheets may rate the inductor in terms of
DC current, RMS current, or saturation current. The
DC or saturation 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 indicated in the diagram
below. Normally, the voltage at the SW pin should be
a fairly linear ramp, as the linear rise in inductor
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.
SW Waveform with Various Inductor Values
Inductance too low
VIN
Gnd
idle
time
Inductance ideal
SW Waveform Showing Inductor Saturation
VIN
Gnd
Inductance too high
VIN
Gnd
(continuous mode)
Normal
VIN
Gnd
Saturated
Capacitor Selection
Gnd
Proper selection of CDD and COUT is essential to the
efficient operation of the LED driver. Both CDD and
COUT should be around 1µF with good high frequency
characteristics (low ESR and ESL).
Ceramic
capacitors are a practical choice for their high
volumetric efficiency and good high frequency
characteristics, but pay attention to the capacitor’s
voltage coefficient. Some small, high value ceramic
capacitors can lose 75% of their capacitance at their
rated voltage! X5R, Y5V, and Z5U formulations are
more susceptible to this effect, as well as possessing
higher temperature coefficients. X7R formulations are
a better choice.
Note: ringing or noise may be present.
Also, confirm that the driver is operating in
discontinuous mode by observing the voltage at the
SW pin while at minimum 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 1015% idle time should be allowed to assure
discontinuous mode operation.
Idle time is the
interval when there is no inductor current flowing, as
The voltage rating of CDD should be greater than the
maximum supply voltage. To be compatible with the
HV9903’s open LED protection, COUT’s voltage rating
should be 35V or more.
6
HV9903
HV9903
Diode Selection
DC Dimming Frequency Response
Since the HV9903 operates at a 1.2MHz switching
frequency, the output rectifier must be fast – 20ns or
less. The faster the diode, the more efficiently the
driver operates. Also, choose a diode with low
capacitance to improve performance. A Schottkey
need not be used, although its lower forward voltage
drop improves efficiency. Peak current rating is the
same as for the inductor. Average current is simply
the LED current. To be compatible with the HV9903’s
open LED protection, the diode’s reverse voltage
rating should be 35V or more. Otherwise, the diode’s
voltage rating should be greater than the LED string’s
voltage drop plus 1 volt.
+10
ILED Response (dB)
0
-10
-20
-30
-40
-50
100
1k
10k
100k
Frequency (Hz)
Dimming
Dimming may be accomplished in one of two ways:
DC dimming or PWM dimming. DC dimming linearly
regulates the current through the LEDs in a
continuous fashion, while PWM dimming rapidly turns
the LEDs on and off while maintaining a constant ‘on’
current. In PWM dimming, the ratio of on to off time
determines perceived brightness.
The on/off
frequency must be high enough to prevent visible
flickering – typically above 70Hz.
The claimed
advantage of PWM dimming is less color shift as the
LED is dimmed, although the effect is virtually
imperceptible.
PWM dimming may be implemented via the SHDN
input or via RSET. Since SHDN reactivates soft-start, a
delay is introduced (~1ms) to LED turn-on. For this
reason, it is better to use the RSET pin for PWM
dimming, as it does not include the soft-start delay.
PWM dimming frequency should be in the range of
70-100Hz to minimize the effect of turn-on delays
while avoiding flicker.
PWM Dimming via SHDN
DC dimming is accomplished by applying a bias to the
RSET resistor.
L
D
VDD
DC Dimming
HV9903
COUT
L
D
VDD
HV9903
COUT
1 SW
2 GND
3
LED
SHDN
5
ILED ( avg)
Shutdown
RSET 4
RBIAS
VDIM
RSET
ILED
225
100mV
RSET
2 GND
3 LED
CDD
VDD 6
1 SW
VDIM 100mV
RBIAS
7
D 22.5V
R SET
CDD
VDD 6
SHDN
5
PWM
RSET 4
RSET
HV9903
HV9903
PWM Dimming via RSET
DC dimming may be implemented in discrete steps
using logic signals, as shown below.
L
D
Multi-level Logic Dimming
VDD
HV9903
COUT
CDD
VDD 6
1 SW
2 GND
SHDN
3 LED
5
VDD
Shutdown
RSET 4
HV9903
PWM
RSET
ILED ( avg)
(1
D)
L
D
COUT
22.5V
R SET
1 SW
CDD
VDD 6
2 GND
SHDN
3 LED
RSET
5
Shutdown
4
RSET
The logic signal must have a low output impedance
relative to RSET and be capable of going to within a
few millivolts of ground. The following modification
provides higher immunity to the logic low voltage level
(VLO).
It also minimizes the effect of voltage
differences between the HV9903’s ground and the
PWM signal source’s ground.
Dual-cell Alkaline Operation
The HV9903 LED driver may be used in 2-cell alkaline
battery applications (1.8V min) by powering the power
stage directly from the batteries, while powering the
HV9903 from an available 3.3V supply. Supplying the
power stage directly from the batteries reduces the
load on the 3.3V supply, which in turn increases
overall efficiency and keeps components small. The
same dimming techniques used in the single-supply
application may be used in this dual-supply
application.
PWM Dimming via RSET
L
D
VDD
HV9903
COUT
CDD
VDD 6
1 SW
2 GND
SHDN
3 LED
5
Shutdown
RSET 4
PWM
RSET
R PWM
R SET
2-cell Alkaline Circuit
RPWM
L
D
1.8–3.0V
VHI
1
100mV
CIN
HV9903
ILED ( avg)
225 (1 D)
100 mV 100 mV VLO
R SET
R PWM
COUT
1 SW
2 GND
3 LED
VDD 6
SHDN
5
RSET 4
2.6–4.6V
Shutdown
Fault
RSET
8
VDD
CDD
HV9903
HV9903
Board Layout
Component selection is similar to the Li-ion battery
application with the exception of the inductor and CDD
capacitor. Since high current is no longer being
drawn from VDD, CDD may be lowered to around 10nF.
CIN should be 1µF. In selecting the inductor, use the
following graphs.
Since high frequencies are involved, PCB layout is
critical. To minimize parasitic inductance and radiated
EMI, the loop area of the high frequency paths must
be kept to a minimum. Second, try to keep the two
loop areas as concentric as possible. Lastly, make
traces as short and wide as possible. To avoid LED
current errors, keep the RSET ground connection
separate from high current ground paths and connect
directly to pin 2.
Inductor Value for 1.8V Operation
Inductor Value
100 H
The following schematic depicts the high frequency
paths and their enclosed areas.
Select the next lower standard value,
taking inductor tolerance into account.
L
D
VDD
10 H
ILED
ILED
20mA
25mA
30mA
35mA
40mA
5mA
CDD
10mA
15mA
1 H
5V
10V
15V
20V
25V
Keep these
areas small
VLED-STRING + (ILED · 5? ) + VD
VLED-STRING + (ILED -5Ω) +VD
HV9903
1 SW
COUT
SW closed
SW open
VDD 6
2
GND SHDN 5
3
RSET 4
LED
The following PCB layout is recommended.
40mA
35mA
30mA
25mA
20mA
Exceeds max recommended SW current
15mA
Peak Inductor Current
10mA
VDD
5mA
L
D
ILED
CDD
100mA
HV9903
COUT
Apply correction factor and select an
inductor with an equal or higher rating.
10mA
5V
10V
15V
20V
25V
VLED-STRING + (ILED · 5? ) + VD
VLED-STRING + (ILED -5Ω) +VD
Don’t forget to apply the correction factor and confirm
that the inductor is not saturating and the driver is
operating in discontinuous mode, as outlined earlier.
9
GND
Fault
RSET
Keep ground
connection seperate
and direct to pin 2
Inductor Rating for 1.8V Operation
1A
Shutdown
RSET
SHDN
HV9903
HV9903
Split Supply Operation
It is also good practice to run the LED’s supply and
return traces as close together as possible, reducing
The HV9903 LED driver may be used in Split Supply
application by powering the power stage directly from
the batteries, while powering the HV9903 (VDD) from
an available regulated supply within 2.6V to 4.6V.
The power stage voltage (VIN) can be higher than
4.6V so long as the inductor is being operated in
discontinues mode.
the loop area of the LED path. Running the return
trace on a separate layer directly underneath the
supply trace would be the ideal layout.
Supplying the power stage directly from the batteries
reduces the load on the regulated supply, which in
turn increases overall efficiency and keeps
components small. The same dimming techniques
used in the single-supply application may be used in
this dual-supply application.
L
D
VIN
CIN
HV9903
COUT
1 SW
2 GND
3 LED
VDD 6
SHDN
5
RSET 4
2.6–4.6V
Shutdown
Fault
RSET
The 3 pads along the centerline on the underside of
the HV9903 are internally connected to pin 2 and
need not be connected externally to ground.
The HV9903’s MLP package fits in most pad layouts
designed for a 6-pin SOT-23.
10
VDD
CDD
HV9903
HV9903
Typical Performance
COUT=Murata GRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500
L
D
VIN
CIN
HV9903
COUT
1
SW
VDD 6
2.6–4.6V
2
GND SHDN 5
Shutdown
3
LED
RSET 4
VDD
CDD
Fault
RSET
VDD = VIN
CIN
L
RSET
COUT
LEDs
IIN
VOUT
3.3V
10.0µF
4.7µH, Murata
LQH32CN4R7M11
1.5KΩ
1.0µF,
50V
4
78.5mA
13.1V
6
111.2mA
19.4V
ILED
15.5mA
Other Examples
COUT=Murata CRM32RR71H105KA01L, LEDs = Nichia NSPW500BS, D = Zetex ZHCS400 or ZHCS500
VDD = VIN
CIN
L
RSET
COUT
LEDs
IIN
VOUT
3.3V
10.0µF
4.7µH, Murata
LQH32CN4R7M11
1.0KΩ
1.0µF,
50V
4
111.3mA
13.6V
6
166.9mA
19.9V
IIN
VOUT
ILED
13.0V
16.5mA
19.4V
16.5mA
VDD
VIN
CIN
L
RSET
COUT
LEDs
1.8V
22.8mA
154.8
6.0V
3.0V
ILED
10.0µF
9.0V
6.0V
4.7µH, Murata
LQH32CN4R7M1
1
4
1.5KΩ
1.0µF,
50V
40.2mA
26.1mA
6
9.0V
63.4mA
41.3mA
VDD = VIN
CIN
L
RSET
COUT
LEDs
IIN
VOUT
ILED
3.3V
10.0µF
10µH, Murata
LQH2MC100K02
1.5KΩ
1.0µF,
50V
4
77.9mA
12.92V
16.8mA
10/7/03
11
1235 Bordeaux Drive • Sunnyvale • CA • 94089
Telephone: (408) 222-8888 • Fax: (408) 222-4895
Package Outlines
6-Lead MLP Package Outline (k6) (3mm x 3mm)
0.118
3.0
0.005
0.125
.
0.118
3.0
TOP VIEW
0.005
0.125
10° + 2°
0.039 ± 0.002
0.7 ± 0.05
SIDE VIEW
SEATING
PLANE
0.008 ± 0.002
0.2 ± 0.05
Exposed
Pad
0.037
0.95
0.015 ± 0.002
0.38 ± 0.05
HEAT SLUG
Measurement =
Inches
millimeters
BOTTOM VIEW
0.048
1.22
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