Datasheet > CAT4238

CAT4238

更新时间： 2022-04-23 23:00:11

品牌	Logo	应用领域
CATALYST		转换器升压转换器
页数	文件大小	规格书
14页	280K
描述
High Efficiency 10 LED Boost Converter

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CAT4238 数据手册

CAT4238

DIMMING CONTROL

Filtered PWM Signal

There are several methods available to control the

LED brightness.

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 CAT4238 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.

¯¯¯¯¯

PWM signal on the SHDN Pin

LED brightness dimming can be done by applying a

¯¯¯¯¯

PWM signal to the SHDN input. The LED current is

repetitively turned on and off, so that the average

current is proportional to the duty cycle. A 100% duty

¯¯¯¯¯

cycle, with SHDN always high, corresponds to the

LEDs at nominal current. Figure 1 shows a 1kHz

VIN

¯¯¯¯¯

signal with a 50% duty cycle applied to the SHDN pin.

CAT4238

The recommended PWM frequency range is from

100Hz to 2kHz.

SHDN

GND

V_FB= 300mV

LED

3.73kΩ

3.1kΩ

1kΩ

25V

PWN

Signal

Current

VIN

R_A

R_B

R₂

15Ω

0.22µF

Figure 2. Circuit for Filtered PWM Signal

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.

FILTERED PWM DIMMING [0V to 2.5V]

Figure 1. Switching Waveform

¯¯¯¯¯

with 1kHz PWM on SHDN

10 20 30 40 50 60 70 80 90 100

PWM DUTY CYCLE [%]

Doc. No. 5019 Rev. A

Characteristics subject to change without notice

1...7 8 91011 12 13 14

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