FAN100(2010_01) View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

Manufacturer

FAN100
(Rev.:2010_01)

Design and Application of Primary-Side Regulation (PSR) PWM Controller

Fairchild Semiconductor 

AN-6067

increasing again. When VDD reaches 16V, all the internal

circuits, including the temperature sensing circuit, start

operating normally. If the junction temperature is still higher

than 145°C, the PWM controller shuts down immediately.

This continues until the temperature drops below 120°C.

GATE Output

The PSR controller BiCMOS output stage is a fast totem

pole gate driver. Cross conduction design elimination was

used to minimize heat dissipation, increase efficiency, and

enhance reliability. The output driver is clamped by an

internal 15V Zener diode for the protection of power

MOSFET against over-voltage gate signals.

Brownout Protection

The PSR controller has a built-in brownout protection

circuit to shut down the PWM output. As the input voltage

decreases, the flowing current from VS pin is less than IVS-

UVP, the PWM output shuts down immediately and enters an

auto restart mode. The VDD voltage gradually drops to the

UVLO voltage.

R VS

Vs

PSR

Controller

I VS-UVP

Auxiliary

Winding

MOS turns on

Figure 22. Brownout Protection

Cable Compensation

The FAN102/FSEZ1216 PWM controller has a cable

compensation function used to compensate the output

voltage drop due to output cable loss. Use an external

resistor connected from COMR pin to GND adjusts the

amount of cable compensation.

In CV regulation control, the on-time of MOSFET only

regulates on-board voltage, not including output cable.

Different cable wire gauge or length results in different

output voltage. As previous mentioned in the CC regulation

control section that can calculate the output current. This

calculated signal can provide the controller the output load

condition and determine the amount of cable compensation,

then rescue output voltage drop. To calculate compensation

percentage, use the equation below:

RCOMR

=

Percentage

100.8 ×10 −6

(5)

APPLICATION NOTE

For example, a power board for a charger application is

5V/1A. Short the COMR pin to GND first and measure the

output voltage from light load to maximum load. If the

output voltage with cable is 4.7V at 1A, the percentage to

5V is 6%. Calculate the RCOMR as:

RCOMR

=

6

100.8 ×10

−6

≅ 59.5KΩ

(6)

Choose the approximate value of RCOMR and let the output

voltage compensate gradually. Figure 23 is RCOMR compared

to percentage curve for reference.

12

10

8

6

4

2

0

10 20 30 39 51 60 68 81 91 100

RCOMR (K ohm)

Figure 23. RCOMR vs. Percentage

Lab Note

Before reworking or soldering / desoldering on the power

supply, discharge the primary capacitors by way of the

external bleeding resistor. If not, the PWM IC may be

destroyed by external high-voltage discharge during the

soldering / desoldering.

© 2008 Fairchild Semiconductor Corporation

Rev. 1.0.1 • 1/26/10

9

www.fairchildsemi.com

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