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PDF WD3138 Datasheet ( Hoja de datos )

Número de pieza WD3138
Descripción White LED Driver
Fabricantes WillSEMI 
Logotipo WillSEMI Logotipo
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WD3138 datasheet

1 Page

WD3138 pdf
WD3138
Electronics Characteristics (Ta=25oC, VIN=3.6V, VEN=VIN, CIN=COUT=1μF, unless otherwise noted)
Parameter
Symbol
Supply Current
Operation Voltage Range
VIN
Under Voltage Lockout
VUVLO
UVLO Hysteresis
VUVLO-HYS
Quiescent Current
IQ
Supply Current
IS
Shutdown Current
ISD
Enable and Reference Control
EN Threshold Voltage
EN Pull-down Resistance
EN Shutdown Pulse Width
1-wire Digital Brightness
Detection Time
VENL
VENH
REN
tOFF
t1W_DET
1-wire Digital Brightness
Detection Delay
t1W_DELAY
1-wire Digital Brightness
Detection Window Time
t1W_WIN
Voltage and Current Control
Feedback Reference
VREF
Feedback Input Bias Current
Operation Frequency
Maximum Duty Cycle
PWM Dimming Clock Rate
PWM Dimming Duty Cycle
Power Switch
On Resistance
N-channel Leakage Current
OC and OLP
Current Limit
Open LED Protection
Threshold
1-wire Digital Timing
Start Time of Program Stream
End Time of Program Stream
Start Time of Data-Byte
Stream
High Time Low Bit
IFB
fOSC
DMAX
RON
ILN_NFET
ILIM
ILIM_START
VOLP
tSTART
tEOS
tSOD
tH_LB
Test Conditions
VIN Rising
No Switching
Switching
VEN < 0.4V
EN High to Low
EN Pin Low,
Note 1
100% Full Scale
1% Dimming
Recommended
Recommended
VIN=3.6V
VLX=40V, TA=25ºC
Start-up
LED Open,
Measured on LX
Logic 0
Min
2.7
1.8
1.5
2.5
260
100
1
196
500
92
5
1
0.68
36
2
2
2
2
Typ Max Unit
-- 5.5 V
2.2 2.5 V
0.1 V
0.4 1 mA
1 2 mA
1 μA
0.4 V
V
800 k
ms
μs
μs
ms
200 204 mV
2 mV
2 μA
600 700 kHz
95 %
100 KHz
100 %
0.6
1 μA
0.8
0.4
38 40
A
A
V
μs
360 μs
360 μs
180 μs
Will Semiconductor Ltd.
5 Jun, 2015 - Rev. 1.0

5 Page

WD3138 arduino
WD3138
Operation Information
Operation
The WD3138 is a high efficiency, high output
voltage boost converter in a small package size.
The device is ideal for driving white LED in series.
The serial LED connection provides even
illumination by sourcing the same output current
through all LEDs, eliminating the need for expensive
factory calibration. The device integrates 40V/0.8A
switch FET and operates in pulse width modulation
(PWM) with 600kHz fixed switching frequency. For
operation see the block diagram. The duty cycle of
the converter is set by the error amplifier output and
the current signal applied to the PWM control
comparator. The control architecture is based on
traditional current-mode control; therefore, slope
compensation is added to the current signal to allow
stable operation for duty cycles larger than 50%.
The feedback loop regulates the FB pin to a low
reference voltage (200mV typical), reducing the
power dissipation in the current sense resistor.
Soft Start-up
Soft-start circuitry is integrated into the IC to avoid a
high inrush current during start-up. After the device
is enabled, the voltage at FB pin ramps up to the
reference voltage in 32 steps with each step taking
213us. This ensures that the output voltage rises
slowly to reduce the input current. Additionally, for
the first 5msec after the COMP voltage ramps, the
current limit of the switch is set to half of the normal
current limit spec. During this period, the input
current is kept below 400mA (typical). See the
start-up waveform of a typical example.
Open LED Protection
Open LED protection circuitry prevents IC damage
as the result of white LED disconnection. The
WD3138 monitors the voltage at the LX pin and FB
pin during each switching cycle. The circuitry turns
off the switch FET and shuts down the IC when both
of the following conditions persist for 8 switching
clock cycles: (1) the LX voltage exceeds the VOVP
threshold and (2) the FB voltage is less than half of
regulation voltage. Then, the WD3138 turns off the
power switch FET and shuts down IC until EN or
power supply is recycled to enable IC.
Shutdown
The WD3138 enters shutdown mode when the EN
voltage is logic low for more than 2.5ms. During
shutdown, the input supply current for the device is
less than 1μA (max). Although the internal FET
does not switch in shutdown, there is still a DC
current path between the input and the LEDs
through the inductor and Schottky diode. The
minimum forward voltage of the LED array must
exceed the maximum input voltage to ensure that
the LEDs remain off in shutdown. However, in the
typical application with two or more LEDs, the
forward voltage is large enough to reverse bias the
Schottky and keep leakage current low.
Current Program
The FB voltage is regulated by a low 0.2V reference
voltage. The LED current is programmed externally
using a current-sense resistor in series with the LED
string. The value of the RSET is calculated using
Equation 1:
ILED
=
VFB
RSET
=
200mV
RSET
(1)
Where
ILED = output current of LEDs
VFB = regulated voltage of FB
RSET = current sense resistor
The output current tolerance depends on the FB
accuracy and the current sensor resistor accuracy.
LED Brightness Dimming Mode Selection
The EN pin is used for the control input for both
dimming modes: PWM dimming and 1 wire dimming.
The dimming mode for the WD3138 is selected
each time the device is enabled. The default
Will Semiconductor Ltd.
11 Jun, 2015 - Rev. 1.0

11 Page





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