CAT4201_15 Datasheet, PDF (10/12 Pages) ON Semiconductor – High Efficiency Step Down LED Driver

CAT4201
300
250
200
150
100
50
0
100
80
60
40
20
0
DUTY CYCLE [%]
Figure 25. LED Current vs. Duty Cycle
VBAT
12 V C1
4.7 mF
R1
10 kW
VBAT
CAT4201
RSET
CTRL _SW
GND
PWM
control
5V
0V
R4
1 kW
R5
47 kW
D
C2
10 mF
L
22 mH
R2
1 kW
Q1
NPN
Figure 26. Circuit for PWM on CTRL
PWM on RSET Pin
Another dimming method is to place in parallel to R1
another resistor with a FET in series, as shown on Figure 27.
R1 sets the minimum LED current corresponding to 0% duty
cycle. The combined resistor of R1 and Rmax sets the
maximum LED current corresponding to 100% duty cycle.
VBAT
13 V C1
4.7 mF
Rmax
VBAT
CAT4201
RSET
R1
CTRL SW
GND
PWM
control
OFF _ON
D
C2
10 mF
L
22 mH
R2
1 kW
Q1
NPN
Figure 27. Circuit for PWM on RSET
A resistor value for R1 of less than 90 kW is recommended
to provide better accuracy.
Operation from High Supply Voltage Above 14 V
For operation from a supply voltage above 14 V, it is
recommended to have a slew rate of 1 ms or more for every
5 V increase in VBAT supply. When using a high supply
voltage of 24 V, a 1 W or 2 W resistor in series with the supply,
as shown on Figure 28, is recommended to limit the slew rate
of the supply voltage. A 4.7 mF minimum ceramic capacitor
is placed between the VBAT pin and ground. The
combination of the series resistor R3 and input capacitor C1
acts as a low pass filter limiting the excessive in−rush
currents and overvoltage transients which would otherwise
occur during “hot−plug” conditions, thereby protecting the
CAT4201 driver.
VBAT ^R3
24 V _{1 W} C1
4.7 mF
R1
10 kW
VBAT
CAT4201
RSET
CTRL _SW
GND
D1 _C2
4.7 mF
L
33 mH
300 mA
R1
1 kW
Figure 28. 24 V Application with 5 LEDs
Operation from High Supply Voltage of 36 V
When powering from a high supply voltage of 36 V, a 2 W
resistor in series with the supply is recommended, as shown
on Figure 29, to limit the slew rate of the supply voltage.
Inductor value should be 33 mH or higher.
VBAT ^R3
36 V _{2 W} C1
4.7 mF
R1
10 kW
VBAT
CAT4201
RSET
CTRL _SW
GND
D1 _C2
2.2 mF
L
47 mH
300 mA
R2
1 kW
Figure 29. 36 V Application with 6 LEDs
Parallel Configuration for Driving LEDs Beyond
350 mA
Several CAT4201 devices can be connected in parallel for
driving LEDs with current in excess of 350 mA. The
CAT4201 driver circuits are connected to the same LED
cathode. Figure 30 shows the application schematic for
driving 1 A into one LED with three CAT4201 connected in
parallel. Each CAT4201 is driving the LED with a current set
by its RSET resistor. The resulting LED current is equal to
the sum of each driver current.
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