cat4237 Catalyst Semiconductor, cat4237 Datasheet - Page 10
cat4237
Manufacturer Part Number
cat4237
Description
High Voltage Cmos Boost White Led Driver
Manufacturer
Catalyst Semiconductor
Datasheet
1.CAT4237.pdf
(14 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
cat4237TD-GT3
Manufacturer:
ON Semiconductor
Quantity:
105
Part Number:
cat4237TD-GT3
Manufacturer:
ON/安森美
Quantity:
20 000
Part Number:
cat4237TD-T3
Manufacturer:
ON/安森美
Quantity:
20 000
Part Number:
cat4237TD-TG3
Manufacturer:
CATALYST
Quantity:
20 000
CAT4237
DIMMING CONTROL
There are several methods available to control the
LED brightness.
PWM signal on the SHDN
LED brightness dimming can be done by applying a
PWM signal to the SHDN
repetitively turned on and off, so that the average
current is proportional to the duty cycle. A 100% duty
cycle, with SHDN
LEDs at nominal current. Figure 1 shows a 1kHz
signal with a 50% duty cycle applied to the SHDN
The recommended PWM frequency range is from
100Hz to 2kHz.
Doc. No. MD-5013, Rev. B
Figure 1. Switching Waveform
¯¯¯¯¯ always high, corresponds to the
with 1kHz PWM on SHDN
¯¯¯¯¯ Pin
¯¯¯¯¯ input. The LED current is
¯¯¯¯¯
¯¯¯¯¯ pin.
10
Signal
PWN
Filtered PWM Signal
A filtered PWM signal used as a variable DC voltage
can control the LED current. Figure 2 shows the PWM
control circuitry connected to the CAT4237 FB pin.
The PWM signal has a voltage swing of 0V to 2.5V.
The LED current can be dimmed within a range from
0mA to 20mA. The PWM signal frequency can vary
from very low frequency up to 100kHz.
A PWM signal at 0V DC, or a 0% duty cycle, results
in a max LED current of about 22mA. A PWM signal
with a 93% duty cycle or more, results in an LED
current of 0mA.
2.5V
0V
Figure 2. Circuit for Filtered PWM Signal
25
20
15
10
5
0
0
VIN
10
FILTERED PWM DIMMING [0V to 2.5V]
20
3.73kΩ
R
0.22µF
PWM DUTY CYCLE [%]
A
30
C1
40
Characteristics subject to change without notice
3.1kΩ
SHDN
VIN
GND
R
50
B
CAT4237
60
FB
© Catalyst Semiconductor, Inc.
i
V
SW
FB
70
= 300mV
1kΩ
80
R
2
90 100
R 1
15Ω
LED
Current