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NCL30160DR2G

P1-P3P4-P6P7-P9P10-P10
NCL30160
http://onsemi.com
7
Figure 6. Short-Circuit Protection
When V
IN
rises above the UVLO threshold voltage,
switching operation of the FET will begin. However, until
the V
IN
voltage reaches 8 V, the VCC regulator may not
provide the expected gate drive voltage to the FET. This
could result in the R
DS(on)
of the FET being higher than
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
IN
voltage of 8 V or greater.
Setting The Output Current
The average output current is determined as being the
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
SENSE
value for a desired average
output current can be calculated by:
R
SENSE
+
200 mV
I
LED
PWM Dimming
For a given R
SENSE
value, the average output current, and
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.
Figure 7. Dimming Waveforms
By applying a pulsed signal to DIM/EN, the average
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.
Figure 8. Dimming Performance
Inductor Selection
The inductor that is used directly affects the switching
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:
+
L DI
VIN * V
LED
* I
OUT
ǒ
FET
R
DS
(on) ) DCR
L
) R
SENSE
Ǔ
t
ON
NCL30160
http://onsemi.com
8
t
OFF
+
L DI
V
LED
) V
diode
) I
OUT
DCR
L
Where DCR
L
is the dc resistance of the inductor, V
LED
is
the forward voltages of the LEDs, FET
RDS(ON)
is the
on-resistance of the power MOSFET, and V
diode
is the
forward voltage of the catch diode.
The switching frequency can then be approximated from
the following:
f
SW
+
1
t
ON
) t
OFF
Higher values of inductance lead to slower rates of rise
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
The catch diode needs to be selected such that average
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:
I
avg_diode
+ I
OUT
t
OFF
t
ON
) t
OFF
It is also important to select a diode that is capable of
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
The off-time setting resistor (R
OT
) programs the
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
OT
value can be calculated
using the following equation:
R
OT
+ t
OFF
10
11
W
Where t
OFF
is the expected off time during normal
switching operation, calculated in the Inductor Selection
section above.
Input Capacitor
A decoupling capacitor from VIN to ground should be
used to provide the current needed when the power
MOSFET turns on. A 4.7 mF ceramic capacitor is
recommended.
NCL30160
http://onsemi.com
9
Figure 9. Efficiency, 350 mA, V
f_LED
= 3.5 V Figure 10. Efficiency, 700 mA, V
f_LED
= 3.5 V
Figure 11. Efficiency, 1 A, V
f_LED
= 3.5 V Figure 12. IQIN vs. VIN
Figure 13. LED Current vs. Dimming Duty
Ratio
100
95
90
85
80
75
70
65
60
0 5 10 15 20 25 30 35 40
VIN (V)
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
0 5 10 15 20 25 30 35 40
VIN (V)
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
0 5 10 15 20 25 30 35 40
VIN (V)
EFFICIENCY (%)
1.70
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
5 10 15202530 3540
VIN (V)
IQIN (mA)
DIMMING DUTY RATIO (%)
LED CURRENT (mA)
020406080100
700
600
500
400
300
200
100
100 Hz
10 kHz
−40 −20 0 20 40 60 80 100 120
240
220
200
180
160
140
120
100100
SWITCHING FREQUENCY (kHz)
Figure 14. Switching Frequency vs.
Temperature (12 V V
IN
, 3 LEDs, 0.7 A, 0.47 mH)
TEMPERATURE (°C)
P1-P3P4-P6P7-P9P10-P10

NCL30160DR2G

Mfr. #:
Buy NCL30160DR2G
Manufacturer:
ON Semiconductor
Description:
LED Lighting Drivers 40V LED Buck Regltr
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