APW7066 datasheet(23/35 Pages) ANPEC

23 / 35 page

Rev. A.8 - Aug., 2009

APW7066

www.anpec.com.tw

Figure 6. FS/SYNC Resistance vs. Frequency

Figure 7. Connecting the LGATE signal from other regu-

lator to FS/SYNC pin

Shunt Regulator (Cont.)

Function Description (Cont.)

VCC (5.8V)

VCC12

OPTIONAL R

FOR SHUNT

REGULATOR

Figure 5.

Oscillator

The APW7066 provides the oscillator switching frequency

adjustment. Connect a resistor from FS/SYNC pin to the

ground, the nominally 300kHz oscillator switching fre-

quency is increased according to the value of the resistor.

The adjustment range of the switching frequency is

300kHz to 800kHz.

Conversely, connecting a resistor from FS/SYNC pin to

the VCC12 reduces the switching frequency.The adjust-

ment range of the switching frequency is 70kHz to 300kHz.

100

200

300

400

500

600

700

800

900

1000

100 200 300 400 500 600 700 800

Switching Frequency

FS to GND

FS to

VCC12

SYNC

Figure 8 shows the switching timing of the synchroni-

zation function. The rising edge of external signal

and the falling edge of UGATE of APW7066 are fixed; there

is a delay time between the rising edge of external sig-

nal and the falling edge of UGATE, the delay time is

about 500ns. Figure 9 shows the timing chart of the

synchronization function. An external signal is connected

to the FS/SYNC pin and the switching frequency of

APW7066 will track the frequency of external signal after

an additional 300

µs delay time to avoid false triggering. If

another converter’s signal is lost, the APW7066 will re-

turn to internal oscillator. This allows the two switch-

ing converters operating at the same frequency to avoid the

interference from the independent frequencies between

them. The acceptable frequency is a range of 150kHz to

800kHz.

APW7066

FS/

SYNC

Other

Regulator

UGATE

LGATE

VIN

VOUT

External Clock (10V/div)

LGATE1 (10V/div)

UGATE1 (10V/div)

LGATE2 (10V/div)

Time (0.5

µ/div)

Figure 8. The switching timing of synchronization func-

tion

The switching frequency also can be synchronized to an

external frequency. If there are two switching convert-

ers on the same board, taking the LGATE signal from

another switching converter, go through a 10k

Ω resistor,

and connecting to the FS/SYNC pin (see Figure 7).

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