Rev. C 03/22

9

PFS5173-5178/5274

www.power.com

The Power Good function is not valid under the following conditions:

A. VCC or VDR are not in a valid range of operation. VCC below

UVLO- or VDR below VDR

UV- the power good function is not valid

with the POWER GOOD pin in a high-impedance state.

B. Power Good will go to high-impedance state when a soft shutdown

is initiated by an over-temperature fault to provide early indication

to secondary circuits of an OT (over-temperature) fault.

C. PGT is outside the valid programming range of between 225 V and

360 V. PGT voltages above this range, including PGT floating, will

prevent PG from transitioning to active pull-down. PGT voltages

below this range result in PG de-assertion at the output under-

voltage (V

FB(UV)) threshold.

D. Once the start-up sequence check has passed and the converter

goes into start-up, if PGT is opened, then the PG signal will remain

latched in the high-impedance state until the controller is reset.

Output Voltage

Rising

Output Voltage

Falling

tPGD

tPGD

tPG

PG = High Impedance

PG = High Impedance

PG = On-State

Set internally

by VPG+

95% VO (365 V)

100% VO (385 V)

87.5% VO (337 V)

Set externally

by RPGT

..

.

R

IA

V

k

0875 385

10

337

337

PG

PG

×

µ

Ω

=

=

=

PI-7229a-030922

Boost-Follower For PFS527xF

The HiperPFS-5 IC’s feature a Boost Follower (BF) circuit which

controls the output voltage as a function of input voltage. This

feature improves efficiency at low-line by reducing the target output

voltage. When the input peak voltage indicates low-line, the PG/BF

pin is in a high impedance state (internal switch is in off-state). When

the input peak voltage is sensed to be in high-line, the PG/BF pin is

turned on (low impedance) state (internal switch is switched to

ground). The low-line and high-line hysteresis is set at 140 VAC and

170 VAC.

As shown in Figure 11, at high-line input, the output voltage is equal

to:

VV

R//R

RR //R

OFB

BF

DWN

UPPBFDWN

#

=

+

dn

and at low-line input, the output voltage is equal to:

VV

R

RR

OFB

DWN

UPPDWN

#

=

+

cm

Figure 10. Power Good Function Description.

Figure 11. Boost Follower Low-Line and High-Line operation vs. Input Voltage.

PI-7255a-031022

~170 VAC

V

IN

~140 VAC

Low-

Line

High-

Line

+

PI-9302d-031122

AC

IN

X Capacitor

RBF

RUPP

RDWN

DC

OUT

REF

FB

PS PGT

VS

V

XD1

XD2

S

D

VCC

PG

G

C

CONTROL

HiperPFS-5

VDR

Figure 12. System Schematic with a Line Dependent V

OUT (Boost Follower).