PFS7323L datasheet(15/30 Pages) POWERINT

15 / 30 page

Rev. D 06/15

PFS7323-7329

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introduces a low frequency zero required to tailor the loop

response to ensure low cross-over frequency and sufficient

phase margin. Resistor R6 isolates the fast portion (resistor

voltage divider network comprising of resistors R1 to R4) and

the slow feedback loop compensator circuit (resistor R7 and

capacitor C3). Diode D1 is included to cover a single point fault

condition wherein capacitor C3 is shorted. In the event C3 is

short-circuited, the FEEDBACK pin is forced below the FB

OFF

threshold through diode D1 and subsequently turns the

HiperPFS-2 off. Only a standard recovery diode should be

used for D1. Use of ultrafast or fast recovery diode is not

recommended including small signal diodes (e.g. 1N4148),

which are typically also fast recovery.

The recommended values for the components used are as

follows:

R4 = 60.4 k

R3 = 1.6 M

R2 = 787 k

C1 = 47nF, 200 V X7R/NPO

R6 = 487 k

R7 = 7.5 k

C3 = 2.2

Cc = 22 nF

D1 = BAV116 W or 1N4007 (A general purpose standard

recovery diode should only be used).

When the above component values are used, the value of

resistor R1 can be calculated using the following equation:

Figure 16. Heat Sink Assembly – using Thermally Conductive Adhesive.

10010

The value of resistor R7 will have to be adjusted in some designs

and as a guideline the value from the following calculation can

be used:

Maximum continuous output power in watts

Nominal PFC output voltage in volts

PFC output capacitance in farads

Improvement in low frequency phase margin can be achieved

by increasing the value of the capacitor C3 however increase in

value of capacitor C3 will result in some increase in overshoot at

the output of the PFC during transient loading and should be

verified.

Heat Sinking and Thermal Design

Figure 16, 17, 18 shows examples of the recommended

assembly for the HiperPFS-2. In these assemblies as shown,

no insulation pad is required and HiperPFS-2 can be directly

connected to heat sink by clip or adhesive thermal material.

The HiperPFS-2 back metal is electrically connected to the heat

sink and the heat sink is required to be connected to the

HiperPFS-2 source terminal in order to reduce EMI.

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