Circuit description

AN2983

8/32

Doc ID 15679 Rev 1

Equation 5

Equation 6

2.2

L6562A controller

The L6562A is used in a "fixed off time" and "peak current mode" topology. Figure 6

represents the controller with its main functional blocks, the FOT_Delay circuitry and the

power section.

Figure 6.

Controller diagram

At power-on, the "starter" sets the flip-flop, whose output (Q) goes high activating the gate

driver (GD).

The power MOSFET transistor is turned on and the load current (I_Led) flows through the

LED diodes, inductor, power MOSFET transistor and sense resistor.

This voltage is applied to the CS input of the controller where it is compared to the reference

voltage Vth = 1.08 V (nom.)

When Vs becomes higher than Vth, the comparator's output goes high, activating the reset

input of the FF.

The FF Q output is set to low and the gate driver output voltage goes to gnd.

The power MOSFET is turned off, Vs goes to zero and the I_Led current decreases, flowing

through the LEDs, inductor and Flywheel diode.

rip

_

I

2

1

pk

_

Led

_

I

avg

_

Led

_

I

−

=

toff

L

VLed

2

1

pk

_

Led

_

I

avg

_

Led

_

I

∗

⎥⎦

⎤

⎢⎣

⎡

−

=