AMP01
combination of these unique features in an instrumentation
amplifier allows low-level transducer signals to be conditioned
and directly transmitted through long cables in voltage or cur-
rent form. Increased output current brings increased internal
dissipation, especially with 50 Ω loads. For this reason, the
power-supply connections are split into two pairs; pins 10 and
13 connect to the output stage only and pins 11 and 12 provide
power to the input and following stages. Dual supply pins allow
dropper resistors to be connected in series with the output stage
so excess power is dissipated outside the package. Additional
decoupling is necessary between pins 10 and 13 to ground to
maintain stability when dropper resistors are used. Figure 34
shows a complete circuit for driving 50 Ω loads.
If heavy output currents are expected and the load is situated
some distance from the amplifier, voltage drops due to track or
wire resistance will cause errors. Voltage drops are particularly
troublesome when driving 50 Ω loads. Under these conditions,
the sense and reference terminals can be used to “remote sense”
the load as shown in Figure 33. This method of connection puts
the I×R drops inside the feedback loop and virtually eliminates
the error. An unbalance in the lead resistances from the sense
and reference pins does not degrade CMR, but will change the
output offset voltage. For example, a large unbalance of 3 Ω will
change the output offset by only 1 mV.
DRIVING 50 ⍀ LOADS
Output currents of 50 mA are guaranteed into loads of up to
50 Ω and 26 mA into 500 Ω. In addition, the output is stable
and free from oscillation even with a high load capacitance. The
V+
R
IN4148 DIODES ARE OPTIONAL. DIODES LIMIT THE OUTPUT
VOLTAGE EXCURSION IF SENSE AND/OR REFERENCE LINES
BECOME DISCONNECTED FROM THE LOAD.
S
*
14
18
1
15
+IN
SENSE
12
11
13
10
*
*
7
9
R
G
AMP01
REMOTE
LOAD
8
TWISTED
PAIRS
2
3
REFERENCE
–IN
OUTPUT
GROUND
V–
Figure 33. Remote Load Sensing
POWER BANDWIDTH, G = 100, 130kHz
POWER BANDWIDTH, G = 10, 200kHz
T.H.D.~0.04% @ 1kHz, 2Vrms
+15V
R1
130⍀
1W
0.047F
R
5k⍀
S
C1
0.047F
14
18
15
+IN
12
SENSE
13
10
1
7
V
OUT
9
R
G
؎3V MAX
AMP01
8
50⍀
LOAD
2
REFERENCE
11
C2
0.047F
3
–IN
R2
130⍀
1W
0.047F
–15V
S
VOLTAGE GAIN, G =
(
)
R
G
RESISTERS R1 AND R2 REDUCE IC DISSIPATION
Figure 34. Driving 50 Ω Loads
REV. D
–14–
ADI [ ADI ]
