–4–

PIN FUNCTION DESCRIPTIONS

8-LEAD microSOIC PIN NUMBERS

*

Pin

No.

Mnemonic

Function

1

CLKOUT

The crystal/resonator is tied between this pin and CLKIN. In the case of an external clock driving CLKIN, an

inverted clock signal appears on this pin and can be used to drive other circuitry provided it is buffered first.

2

CLKIN

The master clock for the device may be in the form of a crystal/resonator tied between this pin and CLKOUT.

An external CMOS-compatible clock may also be applied to this input as the clock for the device. If CLKIN

is inactive low for 1 ms (typ), the AD7740 automatically enters power-down.

3

GND

Ground reference for all the circuitry on-chip.

4

REFIN/OUT

Voltage Reference Input. This is the reference input to the core of the VFC and defines the span of the VFC.

If this pin is left unconnected, the internal 2.5 V reference is the default reference. Alternatively, a precision

external reference may be used to overdrive the internal reference. The internal reference has high output

impedance in order to allow it to be overdriven.

5

VIN

±150 mV overrange. If buffered, it draws virtually no current

from whatever source is driving it.

6

VDD

Power Supply Input. These parts can be operated at 3.3 V

± 10% or 5 V ± 5%. The supply should be

adequately decoupled with a 10

µF and a 0.1 µF capacitor to GND.

7

FOUT

8

BUF

Buffered Mode Select Pin. When BUF is tied low, the VIN input is unbuffered and the range on the VIN

pin is –0.15 V to VDD + 0.15 V. When it is tied high, VIN is buffered and the range on the VIN pin

is restricted to 0.1 V to VDD – 0.2 V.

*Note that the SOT-23 and microSOIC packages have different pinouts.

ORDERING GUIDE

Package

Branding

Model

Temperature Range

Package Description

Option

Information

AD7740KRM

0

°C to 85°C

microSOIC Package

RM-8

VOK

AD7740YRT

–40

°C to +105°C

SOT-23 Package

RT-8

VOY

AD7740YRM

–40

°C to +105°C

microSOIC Package

RM-8

VOY

PIN CONFIGURATIONS

8-Lead microSOIC

microSOIC

TOP VIEW

(Not to Scale)

8

7

6

5

1

2

3

4

CLKOUT

CLKIN

GND

REFIN/OUT

BUF

FOUT

VDD

VIN

AD7740

8-Lead SOT-23

SOT-23

TOP VIEW

(Not to Scale)

8

7

6

5

1

2

3

4

BUF

FOUT

VDD

VIN

CLKOUT

CLKIN

GND

REFIN/OUT

AD7740

REV. A

AD7740