PFS7526H datasheet(14/36 Pages) POWERINT

14 / 36 page

Rev. A 06/15

PFS7523-7529/7533-7539

www.power.com

Output Capacitor

For a 385 V nominal PFC, use of an electrolytic capacitor with 450 V

or higher continuous rating is recommended. The capacitance

required is dependent on the acceptable level of output ripple and

any hold up time requirements. The equations below provide an easy

way to determine the required capacitance in order to meet the

hold-up time requirement and also to meet the output ripple require-

ments. The higher of the two values would be required to be used:

calculated using the equation:

PFC output capacitance in F.

PFC output power in watts.

HOLD-UP

Hold-up time specification for the power supply

in seconds.

OUT

Lowest nominal output voltage of the PFC in volts.

OUT(MIN)

Lowest permissible output voltage of the PFC at

the end of hold-up time in volts.

Capacitance required for meeting the low frequency ripple specifica-

tion is calculated using the equation:

Input frequency in Hz.

ΔV

Peak-peak output voltage ripple in volts.

PFC

PFC operating efficiency.

O(MAX)

Maximum output current in amps.

Capacitance calculated using the above method should be appropri-

ately increased to account for ageing and tolerances.

Power Supply for the IC

A 12 V regulated supply should be used for the HiperPFS-3. If the

VCC exceeds 15 V, the HiperPFS-3 may be damaged. In most

applications a simple series pass linear regulator made using an NPN

transistor and Zener diode is adequate since the HiperPFS-3 only

requires approximately I

CC(ON) maximum for its operation.

It is recommended that a 1 µF or larger, low ESR ceramic capacitor

be used to decouple the VCC supply. This capacitor should be placed

directly at the IC pin on the circuit board.

Line-Sense Network

The line-sense network connected to the VOLTAGE MONITOR pin

provides input voltage information to the HiperPFS-3. A value of 16 MΩ

is chosen in this example design to minimize power consumption in

these resistors. Only 1% tolerance resistors are recommended.

A decoupling capacitor of 470 pF is required to be connected in

parallel with the bottom resistor from the VOLTAGE MONITOR pin to

the GROUND pin of the HiperPFS-3. This capacitor should be placed

directly at the IC pin on the circuit board.

Feedback Network

A resistor divider network that provides 3.85 V at the FEEDBACK pin at

the rated output voltage should be used for optimal performance. It

should be scaled in direct proportion to the VOLTAGE MONITOR pin

resistor divider network in order to ensure proper regulation and

power delivery. The HiperPFS-3 controller has been optimized for

operation with an output voltage of 385 VDC. Applications requiring

voltages that deviate from this nominal parameter, thereby requiring

a FEEDBACK pin divider ratio other than the recommended 100:1,

need to be evaluated for trade-offs of the key target parameters of

the specific design. E.g.: the VOLTAGE MONITOR pin divider ratio can

be modified to be equivalent to that of the feedback divider in order

to optimize power factor. However, this will have an impact on power

limit, as well as brown-in/brown-out thresholds, etc. Modification of

within ±10 V of nominal should not result in dramatically compro-

mised performance, but should be thoroughly verified. Changes in

excess of this are not recommended. Itemized trade-offs of this type

are outside the scope of this data sheet.

The recommended circuit and the associated component values are

shown in Figure 14.

Resistors, R1 to R4 comprise of the main output voltage divider

network. The sum of resistors R1, R2 and R3 is the upper divider

resistor and the lower feedback resistor is R4. Capacitor C1 is to filter

any switching noise from coupling into the FEEDBACK pin. Resistor R5,

capacitor C2 and C3 is the loop compensation network required to

tailor the loop response to ensure low cross-over frequency and

sufficient phase margin. The recommended values for the compo-

nents used are as follows:

R1 = 3.74 MΩ

R2 = 6.2 MΩ

R3 = 6.2 MΩ

R5 = 30.1 kΩ

C1 = 470 pF

C2 = 1 µF

C3 = 100 nF

When the above component values are used, the value of resistor R4

can be calculated using the equation below:

^ h

Output voltage.

FB(REF)

FEEDBACK pin voltage, 3.85 V.

PI-7258-061615

PGT

VCC

B+

CREF

REF

CONTROL

HiperPFS-3

Figure 14. Recommended Feedback Circuit.

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