ncl30160 ON Semiconductor, ncl30160 Datasheet - Page 7

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

switching operation of the FET will begin. However, until
the V
provide the expected gate drive voltage to the FET. This
could result in the R
expected or there not being enough gate drive capability to
operate at the maximum rated switching frequency. For
optimal performance, it is recommended to operate the part
at a V
Setting The Output Current
middle of the peak and valley of the output current, set by the
CS comparator thresholds. The nominal average output
current will be the current value equivalent to 200 mV at the
CS pin. The proper R
output current can be calculated by:
PWM Dimming
therefore the brightness of the LED, can be set to a lower
value through the DIM/EN pin. When the DIM/EN pin is
brought low, the internal FET will turn off and switching
will remain off until the DIM/EN pin is brought back into its
high state.
When V
The average output current is determined as being the
For a given R
IN
IN
voltage reaches 8 V, the VCC regulator may not
voltage of 8 V or greater.
IN
Figure 6. Short-Circuit Protection
rises above the UVLO threshold voltage,
SENSE
R
DS(on)
SENSE
value, the average output current, and
SENSE
+
of the FET being higher than
value for a desired average
200 mV
I
LED
http://onsemi.com
7
output current can be adjusted to the duty ratio of the pulsed
signal. It is recommended to keep the frequency of the
DIM/EN signal above 100 Hz to avoid any visible flickering
of the LED.
Inductor Selection
frequency the driver operates at. The value of the inductor
sets the slope at which the output current rises and falls
during the switching operation. The slope of the current, in
turn, determines how long it takes the current to go from the
valley point of the current ripple to the peak when the FET
is on and the current and rising, and how long it takes the
current to go from the peak point of the current to the valley
when the FET is off and the current is falling. These times
can be approximated from the following equations:
t
+
By applying a pulsed signal to DIM/EN, the average
The inductor that is used directly affects the switching
ON
VIN * V
LED
Figure 8. Dimming Performance
Figure 7. Dimming Waveforms
* I
OUT
FET
L
R
DS
DI
(on) ) DCR
L
) R
SENSE