Precision amplifier for bridge circuits
AM457
PRINCIPLE FUNCTION
Adjustable amplification of differential voltage signals (±5 to
±100mV
FS)
to an adjustable, ratiometric output voltage of between
0.2 and Vcc-0.2Volt with a diagnostic unit
V
CC
= 5V
±
5%
Differential input
voltages
( 5... 100mV FS)
Diagnostic unit
AM457
e.g. V
OUT
= 0.2...V
CC
-0.2V
(adjustable)
e.g. 0.5...4.5V
ratiometric
I
out
= 2mA
TYPICAL APPLICATIONS
•
Precision amplifiers for bridge circuits with
low sensitivity:
for ceramic measurement cells
for DMS sensing elements
for GMR sensing elements
•
Sensor amplification with functional control
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
1/10
Rev. 2.2
Precision amplifier for bridge circuits
TABLE OF CONTENTS
Features
Block diagram
General description
Electrical specifications
Circuit
Description of functions
Example application
Block diagram and pinout
Delivery options
Further reading
AM457
3
3
3
4
5
6
7
9
10
10
TABLE OF FIGURES AND TABLES
Table 1: Specifications
Table 2: Circuit
Table 3: Pin configuration
Figure 1: Block diagram
Figure 2: Schematic circuit diagram for resistance bridges with low sensitivity
Figure 3: Block diagram of AM457
Figure 4: AM457 Pin out
Figure 5 : SOP 8 Package dimensions
4
5
9
3
7
9
9
10
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
2/10
Rev. 2.2
Precision amplifier for bridge circuits
AM457
•
High input sensitivity
•
Wide differential input voltage range
(±5...±100mV FS)
•
Low offset
•
Low offset drift
•
Low input noise
•
High CMRR: > 120dB
•
Wide operating temperature range:
-40... +125°C
•
Adjustable output voltage
•
Rail-to-rail output stage:
V
OUT
= 0.2V ...
V
cc
– 0.2V
•
Sink/source output
•
Single ratiometric supply:
V
CC
= 5V
•
Integrated current source:
≤
2mA
•
Integrated diagnostic unit
•
Separate function groups
•
Integrated EMV protective circuitry
•
Short-circuit-proofing
•
Small-scale design
FEATURES
GENERAL DESCRIPTION
AM457 is a high-precision integrated amplifier which
has been developed to condition signals from small
differential input voltages within a range of a few
millivolts (±5 to
±100mV
FS). The chief component
of the IC is a highly accurate, low-noise amplifier
circuit (AMP). An additional integrated operational
amplifier (OP) can be used to supply a sensing
element with current or record temperature for sensor
bridges powered by voltage, for example. The entire
system (sensing element plus amplifier) is monitored
by the integrated diagnostic unit which logs any
sensing element errors or defects, system
undervoltage, AMP overloads and excessive
temperature. The various function groups are not
mutually dependent on one another; the AMP can be
operated independently of the OP, for example. The
functionality of both component groups (AMP and
OP) is autonomous with regard to the diagnostic unit.
AM457 is a combination of high-impedance precision
amplifier, additional OP and extensive diagnostic unit,
enabling a self-monitoring sensor system to be
assembled using very few components.
BLOCK DIAGRAM
AM457
OUTOP
7
8 VCC
OP
1k
9k
V
CC
IN+
_
INOP
6
AMP
Temp
Diagnostic
unit
5 DIAG
1 OUT
4
GND
Figure 1:
Block diagram
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
3/10
Rev. 2.2
Precision amplifier for bridge circuits
ELECTRICAL SPECIFICATIONS
T
amb
= 25°C,
V
CC
= 5V (unless otherwise stated)
Parameter
Voltage Range
Quiescent Current
Temperature Specifications
Operating
Storage
Junction
Thermal Resistance
Amplifier AMP
Offset Voltage
V
OS
vs. Temperature
V
OS
vs. Temperature
Input Bias Current
I
B
vs. Temperature
Differential Input Voltage
Input Offset Current
I
OS
vs. Temperature
Input Resistance
Input Capacitance
Common Mode Input Range
Common Mode Rejection Ratio
Open Loop Gain
Adjustable Gain
Output Voltage Range
Output Current
Output Load Capacitance
Output Load Resistance
Power Supply Rejection Ratio
Gain Bandwidth Product
V
OS
dV
OS
/dT
dV
OS
/dT
I
B
dI
B
/dT
V
IN
I
OS
dI
OS
/dT
R
IN
C
IN
CMIR
CMRR
G
0
G
V
OUT
I
OUT
C
L
R
L
PSRR
GBW
G
= 10;
C
1
= 1nF;
R
L
= 20kΩ
Including filters for EMC
protection
Non Linearity
Slew Rate
Input Voltage Noise
SR
e
n
G
≤
100
C
1
= 1nF;
R
L
= 20kΩ
T
amb
, ;Rs
=
1kΩ;
V
CC
=
5V
Rs
= Source Impedance
0.3
0.8
30
10
-4
Sink and source
Sink and source
1
120
120
10
0.2
250
1
20
90
110
30
5
135
140
T
amb
= -45…105°C
T
amb
= 105…125°C
V
CM
= 2.5V
T
amb
= -45…125°C
V
IN
=V
IN+
–
V
IN-
V
CM
= 2.5V
T
amb
= -45…125°C
V
CM
/
I
B,typ
(V
CM
= 2.5V)
±5
±0.5
±2.5
100
90
30
–130
±0.1
±0.5
±0.3
±1.2
±120
200
–600
±100
±5
±30
T
amb
T
st
T
J
Θ
ja
Θ
ja
DIL8 plastic package
SO8 narrow plastic package
111
181
-45
-55
125
150
150
Symbol
V
CC
I
CC
T
amb
= -40...+85°C
Conditions
Min.
4.5
Typ.
5
1.5
Max.
5.5
2.5
AM457
Unit
V
mA
°C
°C
°C
°C/W
°C/W
mV
µV/°C
µV
nA
pA/°C
mV
nA
pA/°C
MΩ
pF
VCC
– 1.3
V
dB
dB
VCC
– 0.2
V
µA
nF
kΩ
dB
kHz
V/µs
nV/√Hz
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
4/10
Rev. 2.2
Precision amplifier for bridge circuits
Error Monitoring (Diagnosis)
Output Voltage on Error (high)
Output Voltage without Error (low)
Output Current on Error
Output Current without Error
V
DIAG
V
DIAG
I
ERR
I
NOERR
V
DIAG
= 2.5V
V
DIAG
= 2.5V
1.5
-6
105
250
3.8
With regard to the sensing element
VCC
– 1.8
0.4
VCC
– 0.2
GND+
0.2
3.5
-3.5
6
-1.5
143
800
4.3
AM457
V
V
µA
µA
°C
µA
V
V
V
Threshold for Temperature Error Monitor-
T
ERR
ing
Threshold for Output Current (AMP) Error
Monitoring
Threshold for Supply Voltage Error
Monitoring
Threshold for High Input Voltage (AMP)
Error Monitoring
Threshold for Low Input Voltage (AMP)
Error Monitoring
Operational Amplifier (OP)
Offset Voltage
V
OS
vs. Temperature
V
OS
vs. Temperature
Input Bias Current
I
B
vs. Temperature
Input Resistance
Input Capacitance
Common Mode Input Range
Open Loop Gain
Output Voltage Range
Output Source Current
Output Load Capacitance
Gain Bandwidth Product
Slew Rate
V
OS
dV
OS
/dT
dV
OS
/dT
I
B
dI
B
/dT
R
IN
C
IN
CMIR
G
0
G
0.2mA
V
OUT
I
OUT
C
1
GBW
SR
G
GAIN
= 10;
C
1
= 1nF;
R
L
= 1.25kΩ
G
GAIN
= 100;
C
1
= 1nF;
R
L
= 25kΩ
PNP Open Collector Output
I
0ut
=0.1mA
I
0ut
=2mA
T
amb
= -45…125°C
V
CM
/
I
B,typ
(V
CM
= 0.5V)
T
amb
= -45…105°C
T
amb
= 105…125°C
I
IA,ERR
V
CC,ERR
V
IN,high,ERR
V
IN,low,ERR
VCC
– 0.8
0.9
±4
±10
80
100
6.25
30
0
90
75
0
1
0.9
0.2
1.4
0.7
0.5
110
90
±8
±40
±320
300
400
mV
µV/°C
µV
nA
pA/°C
MΩ
pF
1
V
dB
dB
VCC
– 0.2
2
5
V
mA
nF
MHz
V/µs
Table 1:
Specifications
Currents flowing into the IC are negative. Positive input of the o
perational amplifier (fixed internally): 0.1⋅V
CC
V
CM
Input Common Mode Voltage
CIRCUIT
Parameter
AMP Output Capacitor
Compensation Capacitor
DIAG
Output Capacitor (optional)
OP Output Capacitor (optional)
Stabilization Capacitor (optional)
EMV Protection Capacitor (optional)
Load Resistor
Symbol
C
1
C
2
C
3
C
4
C
5
C
6
R
L
20
1
100
470
Conditions
Min.
1
100
3.3
5
Typ.
Max.
5
Unit
nF
pF
nF
nF
nF
pF
kΩ
Table 2:
Circuit Components
Recommendation: Ceramic capacitor
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Phone:
Fax:
Email:
+49 (0)6131/91 073 – 0
+49 (0)6131/91 073 – 30
info@analogmicro.de
May 2005
5/10
Rev. 2.2
单片机
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