ETC AD628ARN

High Common-Mode Voltage
Programmable Gain Difference Amplifier
AD628
APPLICATIONS
High Voltage Current Shunt Sensing
Programmable Logic Controllers
Analog Input Front End Signal Conditioning:
+5 V, +10 V, ±5 V, ±10 V and 4 to 20 mA
Isolation
Sensor Signal Conditioning
Power Supply Monitoring
Electro-Hydraulic Control
Motor Control
FUNCTIONAL BLOCK DIAGRAM
REXT2
+VS
100k
REXT1
RG
10k
–IN
G = +0.1
–IN
AD628
–IN
OUT
A2
10k
+IN
A1
+IN
100k
+IN
10k
–VS
VREF
CFILT
130
120
110
100
CMRR – dB
FEATURES
High Common-Mode Input Voltage Range
±120 V at VS = ±15 V
Gain Range +0.01 to +100
Operating Temperature Range
–40ºC to +85ºC
Supply Voltage Range
Dual Supply: ±2.25 V to ±18 V
Single Supply: +4.5 V to +36 V
Excellent AC and DC Performance
Offset Temperature Stability RTI
10 V/ºC Max
Offset
±1.5 V mV Max
CMRR RTI
75 dB Min, DC to 500 Hz, G = 1
VS = ⴞ15V
90
80
70
VS = ⴞ2.5V
60
GENERAL DESCRIPTION
The AD628 is a precision difference amplifier that combines
excellent dc performance with high common-mode rejection over
a wide range of frequencies. When used to scale high voltages, it
allows simple conversion of standard control voltages or currents
for use with single-supply A/D converters. A wideband feedback
loop minimizes distortion effects due to capacitor charging of
sigma-delta A/D converters.
A reference pin (VREF) provides a dc offset for converting bipolar to single-sided signals. The AD628 converts +5 V, +10 V,
±5 V, and ±10 V and 4 to 20 mA input signals to a single-ended
output within the input range of single-supply A/D converters.
The AD628 has an input common-mode and differential mode
operating range of ±120 V. The high common-mode input
impedance makes the device well suited for high voltage measurements across a shunt resistor. The buffer amplifier inverting input
is available for making a remote Kelvin connection.
50
40
30
10
100
1k
FREQUENCY – Hz
10k
100k
Figure 1. CMRR vs. Frequency of the AD628
A precision 10 k⍀ resistor connected to an external pin is provided for either a low-pass filter or to attenuate large differential
input signals. A single capacitor implements a low-pass filter.
The AD628 operates from single- and dual-supplies and is
available in an 8-lead SOIC package. Contact the factory for
availability in MSOP package. It operates over the standard
industrial temperature range of –40ºC to +85ºC.
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
that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks
and registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2002 Analog Devices, Inc. All rights reserved.
AD628–SPECIFICATIONS (T = 25ⴗC, V = ⴞ15 V, R = 2 k⍀, R
A
Parameter
DIFF-AMP + OUTPUT AMP
Gain Equation
Gain Range
Gain Drift
Offset Voltage
Versus Temperature
CMRR
Drift (RTI)
PSRR (RTI)
Input Voltage Range
Common Mode
Differential
Dynamic Response
Small Signal BW –3 dB
Full Power Bandwidth
Settling Time
Slew Rate
Noise (RTI)
Spectral Density
S
L
= 10 k⍀, REXT2 = ⴥ, unless otherwise noted.)
Conditions
Min
G = 0.1[REXT4/(REXT4 + 10 k⍀)] (1+ REXT1/REXT2)
Figure 4
0.01*
Typ
Max
4
100
5
+1.5
8
–1.5
500 Hz
75
75
VS = ±10 V to ±18 V
77
1
94
4
±120
±120
G = 0.1
600
5
–0.1
nV/ Hz
µV p-p
0.1
+0.01
3
220
55
75
1
75
Output Resistance
Error
4
10
–0.1
V
V
300
15
–1.5
Overtemperature
500 Hz
V/V
V/V
ppm/ºC
mV
µV/ºC
dB
dB
(µV/V)/ºC
dB
0.3
40
1 kHz
0.1 Hz to 10 Hz
Unit
kHz
kHz
µs
V/µs
G = 0.1, to 0.01%, 100 V Step
DIFF-AMP
Gain
Error
Versus Temperature
Nonlinearity
Versus Temperature
Offset Voltage (RTI)
Versus Temperature
Input Impedance
Differential
Common Mode
CMRR (RTI)
OUTPUT AMPLIFIER
Gain Equation
Nonlinearity
Offset Voltage
Versus Temperature
Output Voltage Swing
EXT1
+0.1
5
5
10
+1.5
8
V/V
%
ppm/ºC
ppm
ppm
mV
µV/ºC
k⍀
k⍀
dB
(µV/V)/ºC
dB
k⍀
+0.1
%
G = (1 + REXT1/REXT2)
0.5
–0.15
+0.15
0.6
–13.8
+13.6
–14.2
+14.1
1.5
3
0.2
0.5
130
130
V/V
ppm
mV
µV/ºC
V
V
nA
nA
dB
dB
POWER SUPPLY
Operating Range
Quiescent Current
±2.25
±18
1.6
V
mA
TEMPERATURE RANGE
–40
+85
ºC
G = 1, VOUT = ±10 V
RL = 2 k⍀
RL = 10 k⍀
Bias Current
Offset Current
CMRR
Open-Loop Gain
VCM = ±13 V
VOUT = ±13 V
Specifications subject to change without notice.
–2–
REV. 0
AD628
SPECIFICATIONS (T = 25ⴗC, V = 5 V, R = 2 k⍀, R
A
Parameter
DIFF-AMP + OUTPUT AMP
Gain Equation
Gain Range
Offset Voltage
Versus Temperature
CMRR
Drift (RTI)
PSRR (RTI)
Input Voltage Range
Common Mode*
Differential
Dynamic Response
Small Signal BW –3 dB
Full Power Bandwidth
Settling Time
Slew Rate
Noise (RTI)
Spectral Density
S
L
EXT1
Conditions
Min
G = 0.1[REXT4/(REXT4 + 10 k⍀)] (1+ REXT1/REXT2)
Figure 4
VOCM = 2.25 V
0.01*
–3.0
500 Hz
75
75
VS = 4.5 V to 10 V
VREF = 2.5 V
77
Typ
Max
6
100
+3.0
15
1
94
–12
G = 0.1
G = 0.1, to 0.01%, 30 V Step
1 kHz
0.1 Hz to 10 Hz
DIFF-AMP
Gain
Error
Nonlinearity
Versus Temperature
Offset Voltage (RTI)
Versus Temperature
Input Impedance
Differential
Common Mode
CMRR (RTI)
–0.1
4
+17
440
30
15
0.3
kHz
kHz
µs
V/µs
350
15
nV/ Hz
µV p-p
0.1
+0.01
+0.1
3
10
2.5
10
75
1
4
75
10
–0.1
V/V
V/V
mV
µV/ºC
dB
dB
(µV/V)/ºC
dB
V
V
220
55
Output Resistance
Error
Unit
±15
3
Overtemperature
500 Hz
OUTPUT AMPLIFIER
Gain Equation
Nonlinearity
Offset Voltage
Versus Temperature
Voltage Swing
= 10 k⍀, REXT2 = ⴥ, unless otherwise noted.)
+0.1
V/V
%
ppm
ppm
mV
µV/ºC
k⍀
k⍀
dB
(µV/V)/ºC
dB
k⍀
%
G = (1 + REXT1/REXT2)
0.5
0.15
0.6
1
4
0.9
4.1
1.5
3
0.2
0.5
130
130
V/V
ppm
mV
µV/ºC
V
V
nA
nA
dB
dB
POWER SUPPLY
Operating Range
Quiescent Current
±2.25
+36
1.6
V
mA
TEMPERATURE RANGE
–40
+85
ºC
Bias Current
Offset Current
CMRR
Open-Loop Gain
G = 1, VOUT = 1 V to 4 V
RL = 2 k⍀
RL = 10 k⍀
VCM = 1 V to 4 V
VOUT = 1 V to 4 V
*Greater values of voltage are possible with greater or lesser values of VREF.
Specifications subject to change without notice.
REV. 0
–3–
AD628
ABSOLUTE MAXIMUM RATINGS*
1.5
TJ = 150ⴗC
POWER DISSIPATION – W
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±18 V
Internal Power Dissipation . . . . . . . . . . . . . . . . . . . See Figure 2
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . ±120 V
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . ±120 V
Output Short Circuit Duration . . . . . . . . . . . . . . . . . . Indefinite
Storage Temperature . . . . . . . . . . . . . . . . . . . . –65ºC to +125ºC
Operating Temperature Range . . . . . . . . . . . . . –40ºC to +85ºC
Lead Temperature Range (10 sec Soldering) . . . . . . . . . . .300ºC
*Stresses greater than those listed under Absolute Maximum Ratings may cause
permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the
operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
8-LEAD SOIC PACKAGE
1.0
0.5
0
–50 –40 –30 –20 –10
0
10
20
30
40
50
60
70
80 90
AMBIENT TEMPERATURE – ⴗC
Figure 2. Maximum Power Dissipation vs. Temperature
ORDERING GUIDE
Model
Temperature Range
AD628ARN
–40ºC to +85ºC
AD628ARM
–40ºC to +85ºC
(Contact Factory)
AD628AR-E VAL
Package Description
Package Option
8-Lead SOIC
8-Lead MSOP
RN-8
RM-8
Evaluation Board
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate
on the human body and test equipment and can discharge without detection. Although the AD628 features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
PIN FUNCTION DESCRIPTIONS
PIN CONFIGURATION
+IN 1
8
–IN
7 +VS
AD628
–VS 2
TOP VIEW
VREF 3 (Not to Scale) 6 RG
CFILT 4
5
OUT
Pin No.
1
2
3
4
5
6
7
8
–4–
Mnemonic
+IN
–VS
V REF
CFILT
OUT
RG
+VS
–IN
Function
Noninverting Input
Negative Supply Voltage
Reference Voltage Input
Filter Capacitor Connection
Amplifier Output
Output Amplifier Inverting Input
Positive Supply Voltage
Inverting Input
REV. 0
Typical Performance Characteristics–AD628
40
140
8440UNITS
UNITS
8440
G = +0.1
35
120
100
25
PSRR – dB
% OF UNITS
30
20
15
80
–15V
+2.5V
10
40
5
20
0
–1.6
+15V
60
–1.2
–0.8
–0.4
0.4
0
0
0.8
1.2
1.6
2.0
0.1
1
10
INPUT OFFSET VOLTAGE – mV
100
1k
10k
100k
1M
FREQUENCY – Hz
TPC 4. PSRR vs. Frequency, Single and Dual Supplies
TPC 1. Typical Distribution of Input Offset Voltage,
VS = ±15 V, SOIC Package
1000
25
–
VOLTAGE NOISE DENSITY – nV/ Hz
8440 UNITS
% OF UNITS
20
15
10
5
0
–74
100
–78
–82
–86
–90
–94
–98
–102 –106
1
–110
10
100
1k
10k
100k
FREQUENCY – Hz
CMRR – dB
TPC 5. Voltage Noise Spectral Density, RTI, VS = ±15 V
TPC 2. Typical Distribution of Common-Mode Rejection, SOIC Package
1000
130
–
VOLTAGE NOISE DENSITY – nV/ Hz
120
110
CMRR – dB
100
VS = ⴞ15V
90
80
70
VS = ⴞ2.5V
60
50
40
30
10
100
100
1k
10k
1
100k
100
1k
10k
100k
FREQUENCY – Hz
FREQUENCY – Hz
TPC 6. Voltage Noise Spectral Density, RTI, VS = ±2.5 V
TPC 3. CMRR vs. Frequency
REV. 0
10
–5–
AD628
40
9638UNITS
UNITS
8440
35
1s
100
30
25
% OF DEVICES
NOISE – 5␮V/DIV
90
20
15
10
10
0
5
0
0
5
10
0
1
3
2
4
5
6
60
9
10
150
UPPER CMV LIMIT
50
G = +100
COMMON-MODE VOLTAGE – V
100
30
GAIN – dB
8
TPC 10. Typical Distribution of +1 Gain Error
TPC 7. 0.1 Hz to 10 Hz Voltage Noise, RTI
40
7
GAIN ERROR – ppm
TIME – Sec
G = +10
20
10
G = +1
0
–10
G = +0.1
–20
–40ⴗC
50
0
+25ⴗC
+25ⴗC
–40ⴗC
+85ⴗC
–50
–100
LOWER CMV LIMIT
–30
–40
100
1k
10k
100k
1M
–150
10M
5
0
10
15
20
VS – ⴞV
FREQUENCY – Hz
TPC 8. Small Signal Frequency Response,
VOUT = 200 mV p-p, G = +0.1, +1, +10, and +100
TPC 11. Common-Mode Operating Range
vs. Power Supply Voltage for Three Temperatures
60
500 ␮V
50
100
OUTPUT ERROR – ␮V
40
G = +100
GAIN – dB
30
G = +10
20
10
G = +1
0
–10
G = +0.1
–20
VS = ⴞ15V
RL = 1kΩ
90
RL = 2kΩ
10
RL = 10kΩ
0
4.0V
–30
–40
10
100
1k
10k
100k
1M
OUTPUT VOLTAGE – V
FREQUENCY – Hz
TPC 12. Normalized Gain Error vs. VOUT, VS = ±15 V
TPC 9. Large Signal Frequency Response,
VOUT = 20 V p-p, G = +0.1, +1, +10 and +100
–6–
REV. 0
AD628
VS = 2.5V
100 V
500mV
RL = 1k
100
100
OUTPUT ERROR – V
90
90
RL = 2k
RL = 10k
10
10
0
0
500mV
50mV
4 ␮s
OUTPUT VOLTAGE – V
TPC 16. Small Signal Pulse Response, RL = 2 k⍀,
CL = 0 pF, Top: Input, Bottom: Output
TPC 13. Normalized Gain Error vs. VOUT, VS = ±2.5 V
4.0
500mV
100
BIAS CURRENT – nA
3.0
90
2.0
10
1.0
0
50mV
0
–40
–20
0
20
40
60
80
4 ␮s
100
TEMPERATURE – ⴗC
TPC 17. Small Signal Pulse Response, RL = 2 k⍀,
CL = 1000 pF, Top: Input, Bottom: Output
TPC 14. Bias Current vs. Temperature, Buffer
15
–40oC
–25oC
OUTPUT VOLTAGE SWING – V
10
100
+85oC
90
10.0 V
+25oC
5
0
10.0 V
–40oC
–5
10
–25oC
0
+25oC
+85oC
–10
40 ␮s
–15
0
5
10
15
20
25
OUTPUT CURRENT – mA
TPC 18. Large Signal Pulse Response, RL = 2 k⍀,
CL = 1000 pF, Top: Input, Bottom: Output
TPC 15. Output Voltage Operating Range
vs. Output Current
REV. 0
–7–
AD628
100
100
90
90
5V
5V
10mV
10mV
10
10
0
0
100s
100s
TPC 20. Settling Time to 0.01%, 0 V to –10 V Step
TPC 19. Settling Time to 0.01%, 0 V to 10 V Step
–8–
REV. 0
AD628
Test Circuits
HP3589A
HP3561A
SPECTRUM ANALYZER
SPECTRUM ANALYZER
+VS
AD628
10k
–IN
+IN
OUT
–IN
–IN
G = +0.1
+IN
RG
AD628
10k
100k
+IN
10k
100
+VS
–
AD829
+
FET
PROBE
–IN 100k
10k
+IN 100k
–IN
G = +0.1
+IN
G = +100
100k
–IN
10k
+IN
10k
CFILT
VREF
10k
RG
VREF
–VS
–VS
Test Circuit 3. Noise Tests
–
AD707
+
Test Circuit 1. CMRR vs. Frequency
SCOPE
+VS
1 VAC
AD628
–IN
10k
+15V
G = +100
10k
+IN
20
100k
+IN
–IN
–IN
G = +0.1
+IN
OUT
+
AD829
–
G = +100
100k
10k
VREF
CFILT
RG
–VS
Test Circuit 2. PSRR vs. Frequency
REV. 0
CFILT
–9–
OUT
AD628
APPLICATIONS
100k
Gain Adjustment
10k
–IN
G = +0.1
–IN
–IN
OUT
A2
10k
+IN
A1
The AD628 system gain is provided by an architecture consisting
of two amplifiers. The gain of the input stage is fixed at 0.1; the
output buffer is user-adjustable as follows:
+IN
G = 1+
100k
+IN
REXT1
REXT 2
10k
The system gain is then:
Ê
ˆ
R
G = 0.1 ¥ Á1 + EXT1 ˜
REXT 2 ¯
Ë
VREF
Figure 3. Simplified Schematic
THEORY OF OPERATION
The AD628 is a high common-mode voltage difference amplifier,
combined with a user-configurable output amplifier (see
Figures 3 and 4). Differential mode voltages in excess of 150 V are
accurately scaled by a precision 11:1 voltage divider at the input.
A reference voltage input is available to the user at Pin 3. The
output common-mode voltage of the difference amplifier will be
whatever voltage is applied to the reference pin. If the uncommitted amplifier is configured for gain, connecting Pin 3 to one end
of the external gain resistor establishes the output common-mode
voltage at Pin 5.
At 2 nA maximum, the input bias current of the buffer amplifier
is very low and any offset voltage induced at the buffer amplifier
by its bias current may be neglected (2 nA ⫻ 10 k⍀ = 20µV.)
However to absolutely minimize bias current effects, REXT1 and
REXT2 may be selected so that their parallel combination is
10 k⍀. If practical resistor values force the parallel combination
of REXT1 and REXT2 below 10 k⍀, a series resistor (REXT3) may be
added to make up for the difference. Table I lists several values of
gain and corresponding resistor values.
Table I. Nearest Standard 1% Resistor Values
Various Gains (See Figure 3)
Total
A2
REXT2
REXT3
REXT1
Gain
Gain
(⍀)
(⍀)
(⍀)
(V/V)
(V/V)
0.01
1k
0
0.1
•
0.02
2k
0
0.2
•
0.05
4.99
k
0
0.5
•
0.1
1
10
0
•
0.2
2
20 k
20 k
0
0.25
2.5
25.9 k 18.7 k
0
0.5
5
49.9 k 12.4 k
0
1
10
100 k 11 k
0
2
20
200 k 10.5 k
0
5
50
499 k 10.2 k
0
10
100
1M
10.2 k
0
The output of the difference amplifier is internally connected to a
10 k⍀ resistor trimmed to better than ±0.1% absolute accuracy.
The resistor is connected to the noninverting input of the output
amplifier and is accessible to the user at Pin 4. A capacitor may
be connected to implement a low-pass filter, a resistor to further
reduce the output voltage or a clamp circuit to limit the
output swing.
The uncommitted amplifier is a high open-loop gain, low offset,
low drift op amp, with its noninverting input connected to the
internal 10 k⍀ resistor. Both inputs are accessible to the user.
Careful layout design has resulted in exceptional common-mode
rejection at higher frequencies. The inputs are connected to Pin 1
and Pin 8, which are adjacent to the power Pin 2 and Pin 7. Since
the power pins are at ac ground, input impedance balance and therefore common mode rejection are preserved at higher frequencies.
REXT2
100k
RG
10k
–IN
G = +0.1
–IN
AD628
–IN
OUT
+IN
+IN
100k
+IN
10k
VREF
CFILT
•
•
•
•
•
•
•
•
Industrial signal conditioning and control applications typically
require connections between remote sensors or amplifiers and
centrally located control modules. Signal conditioners provide
output voltages up to ±10 V full scale; however, A/D converter or
microprocessors operating on single 3.3 V to 5 V logic supplies are
becoming the norm. Thus, the controller voltages require further
reduction in amplitude and reference.
A2
10k
A1
–VS
REXT4
(⍀)
1.1 k
249 k
10 k
Voltage Level Conversion
REXT1
REXT3
+VS
for
REXT4
Figure 4. Circuit Connections
Furthermore, voltage potentials between locations are seldom
compatible, and power line peaks and surges can generate
destructive energy between utility grids. The AD628 is an ideal
solution to both problems. It attenuates otherwise destructive
signal voltage peaks and surges by a factor of 10 and shifts the
differential input signal to the desired output voltage.
Conversion from voltage-driven or current-loop systems is easily accommodated using the circuit in Figure 5. Here, a circuit
for converting inputs of various polarities and amplitudes, to the
input of a single-supply A/D converter, is illustrated.
–10–
REV. 0
AD628
Table II shows resistor and reference values for commonly used
single-supply converter voltages.
Note that the common-mode output voltage can be adjusted by
connecting Pin 3 and the lower end of the 10 k⍀ resistor to the
desired voltage. The output common-mode voltage will be the
same as the reference voltage.
Table II. Nearest 1% Resistor Values for Voltage
Level Conversion Applications
The design of such an application may be done in a few
simple steps:
1. Determine the required gain. For example, if the input voltage
must be transformed from ±10 V to 0 V to +5 V, the gain is
5/20 or 0.25.
2. Determine if the circuit common-mode voltage must be
changed. An AD7715-5 A/D converter is illustrated for this
example. When operating from a 5 V supply, the commonmode voltage of the AD7715 is 1/2 the supply or 2.5 V. If the
AD628 reference pin and the lower terminal of the 10 k⍀
resistor are connected to a 2.5 V voltage source, the output
common-mode voltage will be 2.5 V.
Input
Voltage
(V)
ADC
Supply
Voltage
(V)
Desired
Output
Voltage
(V)
VREF
(V)
REXT1
(k⍀)
±10
±5
+10
+5
±10
±5
+10
+5
5
5
5
5
3
3
3
3
2.5
2.5
2.5
2.5
1.25
1.25
1.25
1.25
2.5
2.5
2.5
2.5
1.25
1.25
1.25
1.25
15
40
40
90
AD7715-5
SERIAL CLOCK
CLOCK
NC
+VS
+5V
AD628
–IN
100k⍀
10k⍀
10k⍀
–IN
VIN
A2
ⴜ10
MCLK OUT
DVDD
+5V
DIN
CS
DOUT
RESET
DRDY
AVDD
AGND
AIN(+) REF IN(–)
–IN
AIN(–) REF IN(+)
A1
REXT1
+IN
+IN
MCLK IN
DGND
OUT
+IN
(SEE
TABLE II)
SCLK
(SEE
TABLE II)
100k⍀
+2.5V
10k⍀
VREF
–VS
AD680
RG
CFILT
10k⍀
(SEE
TABLE II)
Figure 5. Level Shifter
REV. 0
–11–
+5V
AD628
Current Loop Receiver
the loop, and the resultant common-mode voltage will often
exceed commonly used supply voltages. Note that with large
value shunt values a resistance of equal value must be inserted
in series with the inverting input to compensate for an error at
the noninverting input.
Analog data transmitted on 4–20 mA current loop may be
detected with the receiver shown in Figure 6. The AD628 is
an ideal choice for such a function, since the current loop
must be driven with a compliance voltage sufficient to stabilize
+15V
+VS
AD628
250
100k
10k
10k
+IN
A2
OUT
–IN
A1
–IN
–IN
10
+IN
250
0V TO 5V
TO A/D
CONVERTER
100k
REXT1
100k
+IN
10k
4–20mA
SOURCE
–VS
VREF
–15V
CFILT
REXT2
11k
2.5V
REF
Figure 6. Level Shifter for 4–20 mA Current Loop
Monitoring Battery Voltages
The resistor divider action is well suited for the measurement of
many power supply applications, such as those found in battery
chargers or similar equipment.
Figure 7 illustrates how the AD628 may be used to monitor a
battery charger. Voltages approximately eight times the power
supply voltage may be applied to the input with no damage.
5V
+VS
nVBAT(V)
–IN
100k
10k
+IN
A1
–IN
10
+IN
CHARGING
CIRCUIT
+1.5V
BATTERY
OTHER
BATTERIES IN
CHARGING
CIRCUIT
100k
0V TO 5V
TO A/D
CONVERTER
10k
A2
–IN
OUT
REXT1
10k
AD628
+IN
10k
–VS
VREF
Figure 7. A Battery Voltage Monitor
–12–
REV. 0
AD628
Filter Capacitor Values
Kelvin Connection
A capacitor may be connected to Pin 4 to implement a low-pass
filter. The capacitor value will be:
In certain applications it may desirable to connect the inverting
input of an amplifier to a remote reference point. This eliminates
errors resulting in circuit losses in interconnecting wiring. The
AD628 is particularly suited for this type of connection (see
Figure 8).
C = 15.9 f t (mF )
where ft is the desired 3 dB filter frequency.
5V
Table III shows several frequencies and their closest standard
capacitor values.
+VS
–IN
100k
10k
250
A1
–IN
10
+IN
Table III. Capacitor Values for Various
Filter Frequencies
Frequency
(Hz)
10
50
60
100
400
1k
5k
10 k
Capacitor
Value (␮F)
1.5
0.33
0.27
0.15
0.039
0.015
0.0033
0.0015
100k
10k
+IN
A2
–IN
AD628
+IN
10k
–VS
VREF
VS /2
Figure 8. Kelvin Connection
REV. 0
–13–
OUT
CIRCUIT
LOSS
LOAD
AD628
OUTLINE DIMENSIONS
8-Lead MSOP Package [MSOP]
(RM-8)
Dimensions shown in millimeters
3.00
BSC
8
5
4.90
BSC
3.00
BSC
1
4
PIN 1
0.65 BSC
1.10 MAX
0.15
0.00
0.38
0.22
COPLANARITY
0.10
0.80
0.40
8
0
0.23
0.08
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-187AA
8-Lead Standard Small Outline Package [SOIC]
Narrow Body
(RN-8)
Dimensions shown in millimeters and (inches)
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
8
5
1
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
SEATING
0.10
PLANE
6.20 (0.2440)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.33 (0.0130)
0.50 (0.0196)
45
0.25 (0.0099)
8
0.25 (0.0098) 0 1.27 (0.0500)
0.41 (0.0160)
0.19 (0.0075)
COMPLIANT TO JEDEC STANDARDS MS-012AA
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
–14–
REV. 0
–15–
–16–
PRINTED IN U.S.A.
C02992–0–11/02(0)