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PDF AD7740 Data sheet ( Hoja de datos )
| Número de pieza | AD7740 | |
| Descripción | 3 V/5 V Low Power/ Synchronous Voltage-to-Frequency Converter | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
Synchronous Operation
Full-Scale Frequency Set by External System Clock
8-Lead SOT-23 and 8-Lead microSOIC 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
APPLICATIONS
Isolation of High Common-Mode Voltages
Low-Cost Analog-to-Digital Conversion
Battery Monitoring
Automotive Sensing
3 V/5 V Low Power, Synchronous
Voltage-to-Frequency Converter
AD7740*
FUNCTIONAL BLOCK DIAGRAM
REFIN/OUT
VDD
AD7740
2.5V
REFERENCE
VIN X1
VOLTAGE-TO-
FREQUENCY
MODULATOR
FOUT
BUF
CLOCK
GENERATION
GND
CLKOUT CLKIN
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 microSOIC
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 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.
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 microSOIC 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.
*Patents pending.
REV. 0
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
1 page  
AD7740
TERMINOLOGY
INTEGRAL NONLINEARITY
For the VFC, Integral Nonlinearity (INL) is a measure of the maxi-
mum deviation from a straight line passing through the actual
endpoints of the VFC transfer function. The error is expressed in
% of the actual frequency span:
Frequency Span = FOUT(max) – FOUT(min)
OFFSET ERROR
Ideally, the output frequency for 0 V input voltage is 10% of
fCLKIN in unbuffered mode. The deviation from this value referred
to the input is the offset error at BUF = 0. In buffered mode the
minimum output frequency (corresponding to 0.10 V minimum
input voltage) is 13.2% of fCLKIN at VREF = 2.5 V. The deviation
from this value referred to the input is the offset error at BUF = 1.
Offset error is expressed in mV.
GAIN ERROR
This is a measure of the span error of the VFC. The gain is the
scale factor that relates the input VIN to the output FOUT.
The gain error is the deviation in slope of the actual VFC transfer
characteristic from the ideal expressed as a percentage of the full-
scale span. See Figure 2.
POWER SUPPLY REJECTION RATIO (PSRR)
This indicates how the apparent input voltage of the VFC is
affected by changes in the supply voltage. The input voltage is
kept constant at 2 V, VREF is 2.5 V and the VDD supply is varied
Ϯ10% at 3.3 V and ±5% at 5 V. The ratio of the apparent change
in input voltage to the change in VDD is measured in dBs.
OUTPUT
FREQUENCY
FOUT
0.9 fCLKIN
GAIN ERROR
0.1
fCLKIN
0 OFFSET
ERROR
REFIN
Figure 2. Offset and Gain
IDEAL
WITH OFFSET
ERROR ONLY
WITH OFFSET
ERROR AND
GAIN ERROR
INPUT
VOLTAGE
VIN
OFFSET ERROR DRIFT
This is a measure of the change in Offset Error with changes in
temperature. It is expressed in µV/°C.
GAIN ERROR DRIFT
This is a measure of the change in Gain Error with changes in
temperature. It is expressed in (ppm of span)/°C.
REV. 0
–5–
5 Page 
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead microSOIC
(RM-8)
0.122 (3.10)
0.114 (2.90)
8
0.122 (3.10)
0.114 (2.90)
1
5
0.199 (5.05)
0.187 (4.75)
4
PIN 1
0.0256 (0.65) BSC
0.120 (3.05)
0.120 (3.05)
0.112 (2.84)
0.112 (2.84)
0.006 (0.15)
0.002 (0.05)
0.043 (1.09)
0.037 (0.94)
33؇
0.018 (0.46)
SEATING 0.008 (0.20)
PLANE
0.011 (0.28) 27؇
0.003 (0.08)
0.028 (0.71)
0.016 (0.41)
8-Lead SOT-23
(RT-8)
0.122 (3.10)
0.110 (2.80)
8765
0.071 (1.80)
0.059 (1.50)
1234
PIN 1
0.026 (0.65) BSC
0.077 (1.95)
BSC
0.051 (1.30)
0.035 (0.90)
0.006 (0.15)
0.000 (0.00)
0.057 (1.45)
0.035 (0.90)
10؇
0.015 (0.38) SEATING 0.009 (0.23) 0؇
0.009 (0.22) PLANE 0.003 (0.08)
0.022 (0.55)
0.014 (0.35)
AD7740
REV. 0
–11–
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet AD7740.PDF ] | |
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