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WD3138 Schematic ( PDF Datasheet ) - WillSEMI

Teilenummer WD3138
Beschreibung White LED Driver
Hersteller WillSEMI
Logo WillSEMI Logo 




Gesamt 23 Seiten
WD3138 Datasheet, Funktion
WD3138
White LED Driver with Digital and PWM
Brightness Control in Tiny Package
WD3138
Http//:www.sh-willsemi.com
With a 40-V rated integrated power switch MOSFET,
the WD3138 is a boost converter that drives up to 10
White LEDs in series. The WD3138 operates at
600kHz fixed switching frequency to reduce output
ripple, improve conversion efficiency, and allows for
the use of small external components.
The default Full-Scale White LED current is set by an
external sensor resistor with regulated 200mV
feedback voltage, as shown in typical application.
During operation, the LED current can be controlled
using the 1-wire digital interface through EN pin.
Alternately, a Pulse Width Modulation (PWM) signal
can also be applied on the EN pin, through which the
PWM Duty-Cycle determines the feedback reference
voltage and then the White LED current. In either
1-Wire digital or PWM mode, the WD3138 does not
burst the LED current; therefore, it does not generate
audible noises on the ceramic output capacitor. For
maximum protection, the device features integrated
open LED protection that disables the WD3138 to
prevent the output voltage from exceeding the
absolute maximum ratings during open LED
conditions.
The WD3138 is available in a PCB space saving DFN
2mm x 2mm-6L Package with bottom thermal pad.
Standard product is Pb-free and Halogen-free.
FB 1
COMP 2
GND 3
6 VIN
5 EN
4 LX
DFN 2mm x 2mm-6L
Pin configuration (Top view)
B38D
Y
W
Marking
= Device Code
= Year Code
= Week Code
Order information
Device
Package
Shipping
WD3138D-6/TR DFN-2x2-6L 3000/Reel&Tape
Features
2.7V~5.5V Input voltage range
38V Open LED Protection
200mV Reference Voltage
600kHz Switching frequency
Up to 91% Efficiency
Flexible Digital and PWM Brightness Control
PWM Dimming Duty ranges from 1% to 100%
Built-in Soft-Start and Over-Current limit
Applications
Smart Phones
Tablets
Portable games
Will Semiconductor Ltd.
1 Jun, 2015 - Rev. 1.0






WD3138 Datasheet, Funktion
Low Time Low Bit
High Time High Bit
Low Time High Bit
Acknowledge Output Voltage
Low
Acknowledge Valid Time
Duration of Acknowledge
Condition
Thermal Shutdown
Thermal Shutdown
Temperature
TSD Hysteresis
Shutdown Delay
tL_LB
tH_HB
tL_HB
VACKNL
tvalACKN
tACKN
TSD
TSD-HYS
tSHDN
Logic 0
Logic 1
Logic 1
Open Drain,
RPULL_UP=15k
Note 2
Note 2
2xtH_LB
2xtL_HB
2
WD3138
360 μs
360 μs
180 μs
0.4 V
2 μs
512 μs
160 °C
30 °C
ms
Note 1: To enter in 1-wire digital dimming mode, the EN pin has to be low for more than t1W_DET during t1W-WIN
Note 2: Acknowledge condition active 0, this condition will only be applied in case the RFA bit is set. Open
drain output, line needs to be pulled high by the host with resistor load
Will Semiconductor Ltd.
6 Jun, 2015 - Rev. 1.0

6 Page









WD3138 pdf, datenblatt
WD3138
dimming mode is PWM dimming. To enter the 1 wire
mode, the following digital pattern on the EN pin
must be recognized by the IC every time the IC
starts from the shutdown mode.
1. Pull EN pin high to enable the WD3138, and to
start the 1 wire detection window.
2. After the 1 wire detection delayt1W_DELAY, 100us
expires, drive EN low for more than the 1 wire
detection timet1W_DET, 260us.
3. The EN pin has to be low for more than 1 wire
detection time before the 1 wire detection
window (t1W_WIN, 1ms) expires. 1 wire detection
window starts from the first EN pin low to high
transition.
PWM Brightness Dimming
When the EN pin is constantly high, the FB voltage
is regulated to 200mV typically. However, the EN
pin allows a PWM signal to reduce this regulation
voltage; therefore, it achieves LED brightness
dimming. The relationship between the duty cycle
and FB voltage is given by Equation 2.
VFB = Duty 200mV
(2)
Where
Duty = Duty Cycle of the PWM signal
200mV = Internal Reference Voltage
The IC immediately enters the 1 wire mode once the
above three conditions are met. The 1 wire
communication can start before the detection
window expires. Once the dimming mode is
programmed, it cannot be changed without another
start up. This means the IC needs to be shut down
by pulling the EN low for 2.5ms and restart. See the
Dimming Mode Detection and Soft Start (Figure 1)
for a graphical explanation.
As shown in Figure 2, the IC chops up the internal
200mV reference voltage at the duty cycle of the
PWM signal. The pulse signal is then filtered by an
internal low pass filter. The output of the filter is
connected to the error amplifier as the reference
voltage for the FB pin regulation. Therefore,
although a PWM signal is used for brightness
dimming, only the WLED DC current is modulated,
which is often referred as analog dimming.
Insert battery
EN
PWM
mode
high
low
Startup
delay
FB
PWM signal
FB ramp
200mV × duty cycle
shutdown delay
t
Insert battery
EN
one wire
Mode
FB
high
Enter one wire
timing window
Programming
code
Programming
code
low
t1w_DELAY
t1w_DET
Startup delay
Shutdown delay
FB
Ramp
if
not
Programmed value
programmed 200mV
default
50mV
IC shutdown
Enter one wire
mode
FB Ramp
Startup delay
50mV
Figure 1. Dimming Mode Detection and Soft Start PWM Brightness Dimming
Will Semiconductor Ltd.
12 Jun, 2015 - Rev. 1.0

12 Page





SeitenGesamt 23 Seiten
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