FAN100 View Datasheet(PDF) - Fairchild Semiconductor

Part Name

Description

Manufacturer

FAN100

Primary-Side-Control PWM Controller

Fairchild Semiconductor 

Functional Description

The proprietary topology of FAN100 enables simplified

circuit design for battery charger applications. Without

secondary feedback circuitry, the CV and CC control are

achieved accurately. As shown in Figure 23, with the

frequency-hopping PWM operation, EMI problems can

be solved by using minimized filter components.

FAN100 also provides many protection functions. The

VDD pin is equipped with over-voltage protection and

with under-voltage lockout. Pulse-by-pulse current

limiting and CC control ensure over-current protection at

heavy loads. The GATE output is clamped at 15V to

protect the external MOSFET from over-voltage

damage. Internal over-temperature-protection function

shuts down the controller with latch when over-heated.

further power savings and meeting international power

conservation requirements.

Figure 24. Green Mode Frequency vs. VCOMV

Figure 23. Frequency Hopping

Startup Current

The startup current is 10µA. Low startup current allows

a startup resistor with a high resistance and a low-

wattage to supply the startup power for the controller. A

1.5MΩ, 0.25W, startup resistor and a 10µF/25V VDD

hold-up capacitor are sufficient for an AC-to-DC power

adapter with a wide input range (100VAC to 240VAC)

Constant Voltage (CV) and Constant

Current (CC) Operation

An innovative technique allows the FAN100 to

accurately achieve CV/CC characteristic output without

secondary side voltage or current-feedback circuitry. A

feedback signal for CV/CC operation from the reflected

voltage across the primary auxiliary winding is

proportional to secondary winding, so it provides the

controller the feedback signal from the secondary side

and achieves constant voltage output property. In

constant-current-output operation, this voltage signal is

detected and examined by the precise constant current

regulation controller, which then determines the on-time

of the MOSFET to control input power and provide

constant current output property. With feedback voltage

VCS across current-sense resistor, the controller can

obtain input power of power supply. Therefore, the

region of constant current output operation can be

adjusted by the current-sense resistor.

Operating Current

The operating current has been reduced to 3.5mA. The

low operating current results in higher efficiency and

reduces the VDD hold-up capacitance requirement. Once

FAN100 enters “deep” green mode, the operating

current is reduced to 1.2mA, which assists the power

supply meeting power conservation requirements.

Green Mode Operation

Figure 24 shows the characteristics of the PWM

frequency vs. the output voltage of the error amplifier

(VCOMV). The FAN100 uses the positive, proportional,

output load parameter (VCOMV) as an indication of the

output load for modulating the PWM frequency. In heavy

load conditions, the PWM frequency is fixed at 42KHz.

Once VCOMV is lower than VN, the PWM frequency starts

to linearly decrease from 42KHz to 550Hz, providing

Temperature Compensation

Built-in temperature compensation provides better

constant voltage regulation at different ambient

temperatures. This internal compensation current is a

positive temperature coefficient (PTC) current that can

compensate the forward-voltage drop of the secondary

diode of varying with temperature. This variation causes

output voltage rising at high temperature.

© 2008 Fairchild Semiconductor Corporation

FAN100 Rev. 1.0.0

10

www.fairchildsemi.com

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