3 V/5 V Low Power, Synchronous
Voltage-to-Frequency Converter
a
AD7740*
FEATURES
FUNCTIONAL BLOCK DIAGRAM
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
REFIN/OUT
VDD
AD7740
2.5V
REFERENCE
True –150 mV Capability Without Charge Pump
V
REF Range: 2.5 V to VDD
VOLTAGE-TO-
FREQUENCY
MODULATOR
X1
VIN
Internal 2.5 V Reference
1 MHz Max Input Frequency
FOUT
Selectable High Impedance Buffered Input
Minimal External Components Required
CLOCK
GENERATION
APPLICATIONS
Isolation of High Common-Mode Voltages
Low-Cost Analog-to-Digital Conversion
Battery Monitoring
BUF
CLKOUT
CLKIN
GND
Automotive Sensing
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
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.
1. 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.
2. 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 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.
3. The AD7740 does not require external resistors and capaci-
tors to set the output frequency. The maximum output
frequency is set by a crystal or a clock. No trimming or cali-
bration is required.
4. The analog input can be taken to 150 mV below GND for
true bipolar operation.
For an analog input signal that goes from 0 V to VREF, the out-
put 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.
5. The specified voltage reference range on REFIN is from
2.5 V to the supply voltage, VDD.
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.
*Protected under U.S. Patent # 6,147,528.
Rev. C
Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 ©2001–2016 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com