W-6137 Datasheet, PDF (9/16 Pages) Copal Electronics – CMOS Boost Converter

W-6137
Device Operation
The W-6137 is a fixed frequency (1 MHz), low noise,
inductive boost converter providing constant current to the
load. A high voltage internal CMOS power switch is used to
energize the external inductor. When the power switch is
then turned off, the stored energy inductor is released into
the load via the external Schottky diode.
The on/off duty cycle of the power switch is internally
adjusted and controlled to maintain a constant regulated
voltage of 0.3 V across the external feedback resistor
connected to the feedback pin (FB). The value of external
resistor will accurately set the LED bias current accordingly
(0.3 V/R1).
During the initial power-up stage, the duty cycle of the
internal power switch is limited to prevent excessive in-rush
currents and thereby provide a “soft-start” mode of
operation.
While in normal operation, the device will comfortably
deliver up to 30 mA of bias current into a string of up to 5
white LEDs.
In the event of a “Open-Led” fault condition, where the
feedback control loop becomes open, the output voltage will
continue to increase. Once this voltage exceeds 24 V, an
internal protection circuit will become active and place the
device into a very low power safe operating mode. In
addition, an internal clamping circuit will limit the peak
output voltage to 29 V. If this fault condition is repaired, the
device will automatically resume normal operation.
Thermal overload protection circuitry has been included
to prevent the device from operating at unsafe junction
temperatures above 150$C. In the event of a thermal
overload condition the device will automatically shutdown
and wait till the junction temperatures cools to 130$C before
normal operation is resumed.
V_IN
C1
V_IN
SHDN
1 MHz
Oscillator
V_REF ^{300 mV} –
A₁
+
Enable
R_C
+
A₂
–
C_C
Thermal
Shutdown
& UVLO
Current
Sense
SW
Over Voltage
Protection
PWM &
Logic
Driver
N₁
R_S
Figure 23. Block Diagram
V_OUT
C2
I_LED
GND
FB
R1
15
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