AP2007

Synchronous PWM Controller

Anachip Corp

www.anachip.com.tw

Rev. 1.0 Apr 1, 2005

4/7

Typical Application Circuit

8

7

6

5

1

2

3

4

D1

Option

VCC

SS/SHDN

FB

DRVP

GND

PHASE

DRVN

Q1

Q2

L1

10uH

C8

470u/16V

C9

Vout=3.2V*

+

-

Vin

+

-

C1

R2

1K

R3

3K*

* Vout = 0.8 x (1+R3/R2)

AP2007

C4

330n

C3

330n

R1

12Ω

V

REF

10n

470u/16V

470u/16V

AF9435

C5

AF9410

C2

0.1u

C6

47n

C7

0.1u

1Ω Option

1Ω Option

R2 1K ~ 10K

≅

(4835)

(4412)

Virtual Frequency Control

Virtual

Frequency

Control



combines

the

advantages of constant frequency and constant

off-time control in a single mode of operation. This

allows fix frequency, precision switching voltage

regulator control with fast transient response and

the smallest solution size. Switch duty cycle can be

adjusted from 0% to 100% on a pulse by pulse basis

when responding to transient conditions. Both 0%

and 100% duty cycle operation can be maintained

for extended periods of time in response to load or

line transients. Figure 1 depicts a simplified

operation

of

the

Virtual

Frequency

Control

technique: The VFC oscillator generates a pulse of

a known duration (VFC_Pulse). The regulator loop

responds by returning a complementary feedback

pulse (FB_Pulse). The FB_Pulse duration is a result

of external conditions such as inductor size, the

voltage across the inductor and the duration of the

VFC_Pulse. A VFC control loop is then formed

whereby the duration of the VFC_Pulse is modified

as a result of the FB_Pulse duration. The VFC loop

arrives at a state of equilibrium, where the operating

frequency remains inherently constant.

GATE

CONTROL

LOGIC

VIRTUAL FREQ

OSCILLATOR

+

-

FB Pulse

VFC Pulse

Vref

ERROR

COMP

V

IN

Lout

Cout

Vout

Rfb1

Rfb2

Figure 1: Virtual Frequency Control Loop-

Synchronous single supply application.