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High-Voltage Difference Amplifier
A Burr-Brown Application
The INA146 is an integrated precision difference amplifier in
an SO-8 style package. It can operate with a common mode
input voltage in excess of the supply voltage to the IC. With a
single sided +5 V supply this IC can handle common mode
input voltages up to +40 V or ±100 V with a symmetrical ±15
V supply. The IC is ideally suited for use in applications such
as high precision current shunt measuring in high voltage test
equipment, as a sensor amplifier, as a monitoring device for
powered vehicles or as a voltage controlled current source.
The internal circuit for this device makes use of on-chip pre-
cision resistors, laser trimmed to ensure accurate gain (achiev-
ing a gain error of only 0.025 %) and high (80 dB) common
mode rejection. Excellent temperature coefficient of these on
chip elements also ensures that the device maintains accuracy
over a temperature range of –40-+85 °C.
The INA146 has two internal amplifiers, the first difference
amplifier has a gain of 0.1 V/V and the second buffer amplifier
allows the gain of the device to be selected by fitting two
external resistors R
G1
and R
G2
. Setting this gain to 1 will allow
voltages up to 100 V to be measured. The output voltage of the
device is given by:
tor between pin 6 and pin 5. R
G1
and R
G2
are not fitted in this
instance. The output current from pin 8 is given by:
I
OUT
= (V
IN
+
– V
IN
-
) / 10 kΩ
15V
R
G1
R
G2
R
B
100n
+U
S
7
5
U
IN
–
U
IN
–
R1
R2
INA146
2
U
O
U
O
100k
10k
6
R5
A2
A1
U
IN
+
10k
U
IN
+
R3
R4
100
Ω
3
100k
10k
4
1
8
–U
S
U
O1
U
O1
15V
V
O
=(V
IN
+
– V
IN
-
)⋅0.1⋅(1+R
G2
/ R
G1
)
R
T
Offset Adj. Range
± 15 mV
100k
100n
Commonly used values of gain are shown in the table.
To use the INA146 as a voltage controlled current source
connect pin 1 to the output (pin 6) and connect a 10 kΩ resis-
100k
15V
15V
004053 - 11
22
Elektor Electronics
12/2000
SMALL CIRCUITS
COLLECTION
resistor shown at the input (pin 3) and the network
connected to pin 1 is optional and only required if you need to
make a correction of the offset voltage. Using the values
shown, the offset adjustment range is ±15 mV at the output.
The offset correction network should only be used when it is
necessary. To maintain good common-mode rejection, the
source impedance connected to pin 1 should be less than 10
Ω
Gain total
Gain de A2
R
G1
(
Ω
)
R
G2
(
Ω
)
R
B
(
Ω
)
(V/V)
(V/V)
0.1
1
-
10 k
-
0.2
2
20 k
20 k
-
0.5
5
12.4 k
49.9 k
-
Ω
and the resistor added to the positive input should be 10 times
this value or 100
1 10
11.0 k
100 k
-
2 20
10.5 k
200 k
-
.
The input impedance of the INA146 is determined by the
input resistor network and is approximately 100 k
Ω
5 50
10.2 k
499 k
-
10
100
10.2 k
1 M
-
. The
source impedance at the two input terminals must be nearly
equal to maintain good common-mode rejection. A 12-
Ω
20
200
499
100 k
9.53 k
50
500
100
49.9 k
10 k
mis-
match between these two impedances will result in a 8 dB
degradation in the common-mode rejection ratio. Source
impedances greater than 800 Ω are not recommended even if
they are perfectly matched.
More information on the INA146 may be found on
Ω
100
1000
100
100 k
10 k
http://www.burr-brown.com
(004053-1)
The 100
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