AD652BQ2 datasheet(13/28 Pages) AD

13 / 28 page

AD652

Rev. C | Page 13 of 28

The one-shot capacitor controls the pulse width of the

frequency output. The pulse is initiated by the rising edge of the

clock signal. The delay time between the rising edge of the clock

and the falling edge of the frequency output is typically 200 ns.

The width of the pulse is 5 ns/pF, and the minimum width is

about 200 ns with Pin 9 floating. If the one-shot period is

accidentally chosen longer than the clock period, the width of

the pulse defaults to equal the clock period. The one-shot can be

disabled by connecting Pin 9 to +VS (Figure 17); the output

pulse width is then equal to the clock period. The one-shot is

activated (Figure 18) by connecting a capacitor from Pin 9 to

+VS, −VS, or Digital Ground (+VS is preferred).

ONE

SHOT

AND

"D"

FLOP

QCK

1mA

20k

Ω

AD652

SYNCHRONOUS

VOLTAGE-TO-

FREQUENCY

CONVERTER

REFERENCE

+VS

Figure 17. One-Shot Disabled

ONE

SHOT

AND

"D"

FLOP

QCK

1mA

20k

Ω

AD652

SYNCHRONOUS

VOLTAGE-TO-

FREQUENCY

CONVERTER

REFERENCE

COS

ANY AC GND

(+VS,–VS, OR DIGITAL GND)

Figure 18. One-Shot Enabled

DIGITAL GROUND

Digital Ground can be at any potential between −VS and

(+VS – 4 V). This can be very useful in systems with derived

grounds rather than stiff supplies. For example, in a small

isolated power circuit, often only a single supply is generated

and the ground is set by a divider tap. Such a ground cannot

handle the large currents associated with digital signals. With

the AD652 SVFC, it is possible to connect the Digital Ground to

–VS for a solid logic reference, as shown in Figure 19.

+VS

–

VIN

ONE

SHOT

AND

"D"

FLOP

QCK

1mA

20k

Ω

AD652

SYNCHRONOUS

VOLTAGE-TO-

FREQUENCY

CONVERTER

REFERENCE

CLOCK

FREQ

OUT

CINT

COS

–VS

Figure 19. Digital GND at −VS

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