AMC1100_15 Datasheet, PDF (13/33 Pages) Texas Instruments – AMC1100 Fully-Differential Isolation Amplifier

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AMC1100
SBAS562A – APRIL 2012 – REVISED DECEMBER 2014
7.3 Feature Description
The differential analog input of the AMC1100 is a switched-capacitor circuit based on a second-order modulator
stage that digitizes the input signal into a 1-bit output stream. The device compares the differential input signal
(V_IN = VINP – VINN) against the internal reference of 2.5 V using internal capacitors that are continuously
charged and discharged with a typical frequency of 10 MHz. With the S1 switches closed, C_IND charges to the
voltage difference across VINP and VINN. For the discharge phase, both S1 switches open first and then both
S2 switches close. C_IND discharges to approximately GND1 + 0.8 V during this phase. Figure 31 shows the
simplified equivalent input circuitry.
VDD1
GND1
GND1
CINP = 3 pF
S1
S1
CINN = 3 pF
GND1
GND1
400 :
400 :
S2
CIND = 3.6 pF
S2
GND1 + 0.8 V
Equivalent
Curcuit
GND1 + 0.8 V
Figure 31. Equivalent Input Circuit
1
R _IN
f _CLK * C _IND
(fCLK = 10 MHz)
3 pF
RIN = 28 k:
3 pF
GND1
The analog input range is tailored to directly accommodate a voltage drop across a shunt resistor used for
current sensing. However, there are two restrictions on the analog input signals, VINP and VINN. If the input
voltage exceeds the range GND1 – 0.5 V to VDD1 + 0.5 V, the input current must be limited to 10 mA to protect
the implemented input protection diodes from damage. In addition, the device linearity and noise performance
are ensured only when the differential analog input voltage remains within ±250 mV.
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