FUNCTIONAL BLOCK DIAGRAM
BUF
VDD
CLKIN
AD7740
VIN
FOUT
2.5V
REFERENCE
VOLTAGE-TO-
FREQUENCY
MODULATOR
CLKOUT
GND
CLOCK
GENERATION
REFIN/OUT
X1
a
AD7740*
FEATURES
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 V
REF
True –150 mV Capability Without Charge Pump
V
REF
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
APPLICATIONS
Isolation of High Common-Mode Voltages
Low-Cost Analog-to-Digital Conversion
Battery Monitoring
Automotive Sensing
GENERAL DESCRIPTION
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 V
REF
, the out-
put frequency goes from 10% to 90% of f
CLKIN.
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
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.
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.
5. The specified voltage reference range on REFIN is from
2.5 V to the supply voltage, VDD.
3 V/5 V Low Power, Synchronous
Voltage-to-Frequency Converter
*Protected under U.S. Patent # 6,147,528.
Rev. C Document Feedback
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