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HT7L4091

Universal Step-Down PWM Control

For High Brightness LED Lighting Control

Current Sense

The current sense input is connected to the non-inverting inputs of two comparators. The inverting

terminal of one comparator is tied to an internal 250mV reference whereas the other comparator

inverting terminal is connected to the LD pin. The outputs of both these comparators are fed into an

OR gate and the output of the OR gate is fed into the reset pin of a flip-flop. If a flip-flop reset event

is triggered by the OR gate output a signal occurs where the external MOSFET gate driving circuitry

will be turned off. Therefore, the comparator which has the lower voltage at the inverting terminal

determines when the gate driving output is turned off.

Leading-Edge Blanking

Each time the power MOSFET is switched on, a turn-on transient spike will occur on the CS pin.

during the MOSFET switch turn-on to prevent false triggering of the current sense comparator.

During this blanking period, the current-limit comparator is disabled and the gate driving circuitry

will not be switched off.

In certain rare situations, the internal blanking time might not be long enough to filter out the turn-

on spike. In such situations, it will be necessary to add an external RC filter between the external

Frequency Jitter Function

The device also includes a frequency jitter function. The frequency has a variation range of +4%

to -4% within four milliseconds. The frequency jitter function helps reduce power supply line EMI

emissions with minimum line filters.

Input Supply Current

The input supply current is determined by the input operating current and the current drawn by the

external MOSFET gate driver. This means that the input supply current depends upon the switching

frequency and the external MOSFET gate charge.