ncl30160 ON Semiconductor, ncl30160 Datasheet - Page 8

• Manufacturer Part Number: ncl30160
• Description: Constant Current Buck Regulator For Driving High Power Leds
• Manufacturer: ON Semiconductor

the forward voltages of the LEDs, FET
on-resistance of the power MOSFET, and V
forward voltage of the catch diode.
the following:
and fall of the output current. This allows for smaller
discrepancies between the expected and actual output
current ripple due to propagation delays between sensing at
the CS pin and the turning on and off of the power MOSFET.
However, the inductor value should be chosen such that the
peak output current value does not exceed the rated
saturation current of the inductor.
Catch Diode Selection
current through the diode does not exceed the rated average
forward current of the diode. The average current through
the diode can be calculated as:
Where DCR
The switching frequency can then be approximated from
Higher values of inductance lead to slower rates of rise
The catch diode needs to be selected such that average
t
OFF
L
I
avg_diode
+
is the dc resistance of the inductor, V
V
LED
f
SW
) V
+ I
+
OUT
t
diode
ON
L
) t
1
) I
t
DI
OFF
ON
OUT
t
OFF
) t
OFF
DCR
RDS(ON)
L
diode
http://onsemi.com
LED
is the
is the
is
8
withstanding the peak reverse voltage it will see in the
application. It is recommended to select a diode with a rated
reverse voltage greater than VIN. It is also recommended to
use a low-capacitance Schottky diode for better efficiency
performance.
Selecting The Off-Time Setting Resistor
NCL30160 with the initial time duration that the MOSFET
is turned off when the switching operation begins. During
subsequent switching cycles, the voltage at the CS pin is
sensed every time the MOSFET is turned on, and the
off-time will be adjusted depending on how much of a
discrepancy exists between the sensed value and the CS
lower limit threshold value. The R
using the following equation:
switching operation, calculated in the Inductor Selection
section above.
Input Capacitor
used to provide the current needed when the power
MOSFET turns on. A 4.7 mF ceramic capacitor is
recommended.
It is also important to select a diode that is capable of
The off-time setting resistor (R
Where t
A decoupling capacitor from VIN to ground should be
OFF
is the expected off time during normal
R
OT
+ t
OFF
OT
10
11
value can be calculated
W
OT
) programs the