SO16N datasheet(24/51 Pages) STMICROELECTRONICS

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Application information

L6566BH

24/51

Doc ID 16610 Rev 2

prevent any malfunction during transients from minimum to maximum load the normal

(higher) UVLO threshold is re-established when the voltage at the COMP pin exceeds

VCOMPL and Vcc has exceeded the normal UVLO threshold (see Figure 13). The normal

UVLO threshold ensures that at full load the MOSFET is driven with a proper gate-to-source

voltage.

5.5

PWM control block

The device is specific to secondary feedback. Typically, there is a TL431 on the secondary

side and an optocoupler that transfers output voltage information to the PWM control on the

primary side, crossing the isolation barrier. The PWM control input (pin 9, COMP) is driven

directly by the phototransistor’s collector (the emitter is grounded to GND) to modulate the

duty cycle (

Figure 14, left-hand side circuit).

In applications where a tight output regulation is not required, it is possible to use a primary-

sensing feedback technique. In this approach the voltage generated by the self-supply

winding is sensed and regulated. This solution, shown in

Figure 14, right-hand side circuit,

is cheaper because no optocoupler or secondary reference is needed, but output voltage

regulation, especially as a result of load changes, is quite poor.

Figure 14.

Possible feedback configurations that can be used with the L6566BH

Figure 13.

Adaptive UVLO block

AM11489v1

VCOMPL

VCOMPO

VCOMP

(pin 9)

Vcc

(pin 5)

VccOFF1

VccOFF2

(*) VccOFF2< VccOFF1is selected when Q is high

UVLO

Vcc OFF1

Vc c

L6566BH

COMP

Vcc OFF2

(*)

VCOMPL

VCOMPO

AM11490v1

Vout

TL431

L6566BH

COMP

L6566BH

Vcc

Naux

COMP

Secondary feedback

Primary feedback

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