AMC1100 Datasheet, PDF (12/22 Pages) Texas Instruments – Fully-Differential Isolation Amplifier for Energy Metering

AMC1100
SBAS562 – APRIL 2012
APPLICATION INFORMATION
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CURRENT MEASUREMENT
A typical operation of the AMC1100 is a current-measurement application, as shown in Figure 32. Measurement
of the current through the phase of a power line is done via the shunt resistor R_SHUNT (in this case, a two-terminal
shunt). For better performance, the differential signal is filtered using RC filters (components R₂, R₃, and C₂).
Optionally, C₃ and C₄ can be used to reduce charge dumping from the inputs. In this case, care should be taken
when choosing the quality of these capacitors; mismatch in values of these capacitors leads to a common-mode
error at the modulator input.
Phase
Isolation
Barrier
R₁
R_SHUNT
R₂
12 W
R₃
12 W
C₁₍₁₎
0.1 mF
C₂₍₁₎
330 pF
C₃
10 pF
(optional)
C₄
10 pF
(optional)
Device
1 _{VDD1 VDD2} 14
2
13
VINP VOUTP
3 _{VINN VOUTN} 11
4 _{GND1 GND2} 9
C₅₍₁₎
0.1 mF R
R
TMC320
C/F28xxx
C
ADC
(1) Place these capacitors as close as possible to the AMC1100.
Figure 32. Typical Application Diagram for the AMC1100
The high-side power supply for the AMC1100 (VDD1) is derived from the system supply. For lowest cost, a
Zener diode can be used to limit the voltage to 5 V ± 10%. A 0.1-µF decoupling capacitor is recommended for
filtering this power-supply path. This capacitor (C₁ in Figure 32) should be placed as close as possible to the
VDD1 pin for best performance. If better filtering is required, an additional 1-µF to 10-µF capacitor can be used.
For higher power efficiency, a step-down converter can be used (such as the TPS62120) to generate the
AMC1100 supply voltage.
The floating ground reference (GND1) is derived from the end of the shunt resistor, which is connected to the
negative input of the AMC1100 (VINN). If a four-terminal shunt is used, the inputs of the AMC1100 are
connected to the inner leads while GND1 is connected to one of the outer shunt leads. The differential input of
the AMC1100 ensures accurate operation even in noisy environments.
The differential output of the AMC1100 can either directly drive an analog-to-digital converter (ADC) input or can
be further filtered before being processed by the ADC.
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