3 V/5 V Low Power, Synchronous Voltage-to-Frequency Converter

The AD7740 is a low-cost, ultrasmall synchronous Voltage-to-Frequency Converter (VFC). It works from a single 3.0 V to 3.6 V or 4.75 V to 5.25 V supply consuming 0.9 mA. The AD7740 is available in an 8-lead SOT-23 and also in an 8-lead MSOP package. Small package, low cost and ease of use were major design goals for this product. The part contains an on-chip 2.5 V bandgap reference but the user may overdrive this using an external reference. This external reference range includes VDD.

The full-scale output frequency is synchronous with the clock signal on the CLKIN pin. This clock can be generated with the addition of an external crystal (or resonator) or supplied from a CMOS-compatible clock source. The part has a maximum input frequency of 1 MHz.

For an analog input signal that goes from 0 V to VREF, the output frequency goes from 10% to 90% of fCLKIN. In buffered mode, the part provides a very high input impedance and accepts a range of 0.1 V to VDD – 0.2 V on the VIN pin. There is also an unbuffered mode of operation that allows VIN to go from –0.15 V to VDD + 0.15 V. The modes are interchangeable using the BUF pin.

The AD7740 (Y Grade) is guaranteed over the automotive temperature range of –40°C to +105°C. The AD7740 (K Grade) is guaranteed from 0°C to 85°C.

Product Highlights

* The AD7740 is a single channel, single-ended VFC. It is

available in 8-lead SOT-23 and 8-lead MSOP packages, and is

intended for low-cost applications. The AD7740 offers

considerable space saving over alternative solutions.

* The AD7740 operates from a single 3.0 V to 3.6 V or 4.75 V

to 5.25 V supply and consumes typically 0.9 mA when the

input is unbuffered. It also contains an automatic power-down

function.

* The AD7740 does not require external resistors and capacitors

to set the output frequency. The maximum output

frequency is set by a crystal or a clock. No trimming or calibration

is required.

* The analog input can be taken to 150 mV below GND for

true bipolar operation.

* The specified voltage reference range on REFIN is from

2.5 V to the supply voltage, VDD.

Applications

* Isolation of high common-mode voltages

* Low-cost analog-to-digital conversion

* Battery monitoring

* Automotive sensing

* Synchronous operation

* Full-scale frequency set by external system clock

* 8-lead SOT-23 and 8-lead MSOP packages

* 3 V or 5 V operation

* Low power: 3 mW (Typ)

* Nominal input range: 0 to VREF

* True –150 mV capability without charge pump

* VREF range: 2.5 V to VDD

* Internal 2.5 V reference

* 1 MHz max input frequency

* Selectable high impedance buffered input

* Minimal external components required