LDS8724
40 WLED Driver with Boost Converter
FEATURES
High efficiency boost converter with the input
voltage range from 2.7 to 5.5 V
No external Schottky Required (Internal
synchronous rectifier*)
250 mV current sense voltage
Drives up to 5 LEDs per string with up to 42
LED in 6 strings at 25 mA
1 MHz Switching Frequency
Efficiency greater than 83%
PWM LED Dimming Control Mode
Over-voltage, under-voltage, over-current,
and over-temperature protection
Low Shutdown Current (<1µA)
Available in 2 x 3 x 0.8 mm 8-pin TDFN
package
resistance. Under-voltage protection disables the part
when V
IN
voltage reaches 2.0 V
The LDS8724 has thermal shutdown set at 150 C.
Above this value , the boost converter stops
switching. The part resumes normal operations when
0
temperature drops below 130 C.
The over-current protection provides cycle-by-cycle
current limit.
The internal output over-voltage protection prevents
damage in the case of a faulty LED disconnect.
The PWM control ensures brightness adjustment with
a frequency from 100 Hz up to 30 KHz.
The EN/PWM logic input functions as a chip enable
and LED current PWM contol pin.
The device is available in 8-pin TDFN 2 x 3 mm
package with a max height of 0.8 mm.
Table 1 Matrix configuration for LDS8724
Number of
strings
1-6
7, 8
9
10
11
12
Number of
LED per string
5
5
5
4
4
3
String
Current
max, mA,
30
25
25
25
25
30
V
IN
MIN
,
0
APPLICATION
Color Display Backlight
Portable Navigation and GPS Receivers
Smart phones
Digital Photo Frames
Portable DVD Players, Notebooks
DESCRIPTION
The LDS8724 is a fixed frequency current mode
boost converter with internal synchronous rectifier
and cycle-by-cycle switch current limit specifically
designed to drive matrix of LEDs in respect with the
Table 1. Operation at 1 MHz allows use of small
value low profile inductor (10 – 33 µH) and 1 µF 50 V
ceramic capacitor.
The use of integrated synchronous rectifier makes
the efficiency dependent on only inductor DC
V
2.7
2.7
3.0
2.7
3.0
3.0
TYPICAL APPLICATION CIRCUIT
*) Patent pending
© 2010 IXYS Corp.
Characteristics subject to change without notice
1
Doc. No. 8724DS, Rev. N1.0
LDS8724
ABSOLUTE MAXIMUM RATINGS
Parameter
V
IN
voltage
V
OUT
, SW, LEDS, V
HVB
voltage
EN/SET voltage
Storage Temperature Range
Junction Temperature Range
8-pin TDFN package Thermal Resistance
Soldering Temperature
Rating
6
40
V
IN
+ 0.7V
-65 to +160
-40 to +125
65
300
Unit
V
V
V
°C
°C
°C/W
°C
RECOMMENDED OPERATING CONDITIONS
Parameter
V
IN
Ambient Temperature Range
Rating
2.7 to 5.5
-40 to +85
Unit
V
°C
Typical application circuit with external components is shown on page 1.
ELECTRICAL OPERATING CHARACTERISTICS
(Over recommended operating conditions unless specified otherwise) V
IN
= 3.6V,T
AMB
= 25°C, C
IN
= 1 µF, C
OUT
= 1 µF, L = 22 µH
Name
Quiescent Current
Shutdown Current
LED Current Accuracy
Oscillator Frequency
Maximum Duty Cycle
NMOSFET Switch On Resistance
PMOSFET Switch On Resistance
Switch Leakage Current
Switch Current Limit
Dropout/Current sense voltage
PWM Frequency
EN/PWM Input Resistance (pull down)
Pin
High
Logic Level
Low
Thermal Shutdown
Thermal Hysteresis
Over-Voltage Protection
Soft Start Time
Delay Time to Shutdown
Conditions
V
IN
= 3.6 V, V
OUT
open
V
IN
= 3.6 V, I
LED
=
25 mA @ V
OUT
=36 V
V
IN
= 5.5V, EN = 0V
At factory preset value
Min
Typ
1
3
Max
Units
mA
1
±3
1.0
92
0.3
1.5
0.1
1.9
250
0.1
250
1.4
0.4
150
20
16
1.5
10
30
At factory preset value
µA
%
MHz
%
Ω
Ω
µA
A
mV
kHz
kΩ
V
°C
V
ms
ms
EN = 0
© 2010 IXYS Corp.
Characteristics subject to change without notice
2
Doc. No. 8724DS, Rev. N1.0
LDS8724
TYPICAL CHARACTERISTICS
Vin = 3.6V, I
OUT
= 75mA ( 3 strings with 4 LEDs at 25 mA per string, C
IN
= 1
μ
C
OUT
= 1μ L = 22 µH, T
AMB
= 25°C unless otherwise specified
F,
F,
Power Efficiency vs. Input Voltage
LED Current per string vs. Input Voltage
LED Current vs. PWM Duty Cycle
LED Current Error vs. PWM Frequency
Soft Start Waveforms
Operating Waveforms
Ch 1 (yellow) – EN pin, Ch 2 (green) – SW node voltage
Ch 3 (red) – Inductor current, Ch 4 (blue) - V
OUT
Ch 1 (yellow) - SW node voltage,
Ch 3 (red) – Inductor current
© 2010 IXYS Corp.
Characteristics subject to change without notice
3
Doc. No. 8724DS, Rev. N1.0
LDS8724
TYPICAL CHARACTERISTICS
Vin = 3.6V, I
OUT
= 30mA (4 LEDs per string), C
IN
= 1
μ
C
OUT
= 1μ L = 22 µH, T
AMB
= 25°C unless otherwise specified
F,
F,
Waveforms at PWM LED Current Regulation
Waveforms at PWM LED Current Regulation
Ch 1 (yellow) – PWM signal at 1 kHz 5% duty cycle
C2 (green) – SW node voltage, Ch 3(red) – LED Current.
Ch4 (blue) - V
OUT
Ch 1 (yellow) – PWM signal at 1 kHz 98% duty cycle
C2 (green) – SW node voltage, Ch 3(red) – LED Current.
Ch4 (blue) - V
OUT
Waveforms at PWM LED Current Regulation
Waveforms at PWM LED Current Regulation
Ch 1 (yellow) – PWM signal at 30 kHz 25% duty cycle
C2 (green) – SW node voltage, Ch 3(red) – LED Current.
Ch4 (blue) - V
OUT
Ch 1 (yellow) – PWM signal at 30 kHz 98% duty cycle
C2 (green) – SW node voltage, Ch 3(red) – LED Current.
Ch4 (blue) - V
OUT
© 2010 IXYS Corp.
Characteristics subject to change without notice
4
Doc. No. 8724DS, Rev. N1.0
LDS8724
PIN DESCRIPTION
Pin #
1
2
3
4
5
6
7
8
PAD
Function
Input Voltage, connect to battery or power supply
Analog Ground
Power Ground
Switch input; Connect inductor terminal to this pin
Output voltage; Connect the LED string anode
V
OUT
terminal to this pin.
High Voltage Bypass; Connect a 470 pF capacitor
HVB
between this point and V
OUT
Current Sense input. Connect LED string cathode
LEDS
terminal to this pin
EN/PWM Device Enable (active high) and Dimming Control
PAD
Connect to GND on the PCB
Name
V
IN
GND
PGND
SW
Top view: TDFN 8-lead 2 X 3 mm
PIN FUNCTION
V
IN
is the supply pin for the driver. A small 1
μ
F
ceramic bypass capacitor is required between the V
IN
pin and ground near the device. The operating input
voltage range is from 2.7 V to 5.5 V. If the input
supply voltage falls below the under-voltage
threshold, switch is disabled, and the device enters
shutdown mode.
HVB
is the internal high voltage reference point.
Connect a 4700 pF capacitor between this point and
V
OUT
.
EN/PWM
is the enable and PWM control logic input.
Guaranteed levels of logic high and logic low are set
at 1.4 V and 0.4 V respectively. When EN/PWM is
initially taken high, the device becomes enabled and
LED current sets to maximum programmed value..
To place the device into shutdown mode, the
EN/PWM pin must be held low for more than 10 ms.
V
OUT
is the driver output. Connect it to the LED
anode. A ceramic bypass capacitor of 1 µF requires
between the V
OUT
pin and ground near the device.
GND
is the ground reference for the analog circuits.
The pin must be connected to the ground plane on
the PCB. Avoid high currents flowing trough traces
connecting this pin with EN/PWM signal source.
PGND
is the current return for high current circuits.
The pin must be connected to the ground plane on
the PCB. Connect GND and PGND as close to the
driver as possible.
LEDS
is the Current Sense pin that provides internal
regulated current sink for LED string. Connect LED
string cathode to this pin. This pin enter high-
impedance zero current state whenever the device is
in shutdown mode.
PAD
is the exposed pad underneath the package.
For best thermal performance, the pad should be
soldered to the PCB and connected to the ground
plane
© 2010 IXYS Corp.
Characteristics subject to change without notice
5
Doc. No. 8724DS, Rev. N1.0
stm32/stm8
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