Rev. 1.00

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Rev. 1.00

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HT7L4091

Universal Step-Down PWM Control

For High Brightness LED Lighting Control

Start-up Current and Auxiliary Power Source

the rectified AC source whose voltage is much higher than the voltage used by the device. For

efficiency improvements, a small start-up current from the rectified AC source is used to start up

winding.

using the follow equation:

in

UVLO(H)

start up

inst

start up

CV

II

t

−

−

×

=

+

The current from auxiliary power source should be:

aux

INSP

start up

II

I

−

=

−

The start-up current allows a start-up resistor with a high resistance and a low-power rating. The

min,AC

UVLO(H)

INST

start-up

2V

V

R

I

⋅−

=

Linear Dimming

The Linear Dimming pin is used to control the LED current. The VDD pin voltage can be connected

adjust the current level to reduce the illumination intensity of the LEDs. To adjust the external LD

pin voltage from 0mV to 250mV can adjust the LED current during operation. To use the internal

250mV as the reference voltage, the LD pin can be connected to VDD.

PWM Dimming

An external enable input named PDM is provided and can be utilized for PWM dimming of the LED

string. When the external PWM signal is zero, the gate driving circuitry is turned off while the gate

driving circuits are turned on when the PWM signal is high.

LED Open and Short Circuit Protection

There will be no abnormal behavior if the LEDs are open circuit. While some LEDs are shorted, the

output voltage will be adjusted automatically for the condition.