AMC1210 Datasheet, PDF (40/47 Pages) Burr-Brown (TI) – Quad Digital Filter for 2nd-Order Delta-Sigma Modulator

AMC1210
SBAS372A – APRIL 2006 – REVISED OCTOBER 2006
www.ti.com
APPLICATION INFORMATION (continued)
Current Measurement
The AMC1210 can also serve as a stand-alone digital filter for modulator signals coming from current-shunt
measurements. Performing the digital filtering in the AMC1210 frees resources in the microcontroller or DSP
from having to perform the constant processing required to ensure nonstop monitoring of the motor currents. For
example, a common application may require both real-time monitoring of motor over-current situations as well as
constant high-resolution data to monitor motor speed. A single filter module in the AMC1210 can perform both
high-resolution data filtering as well as provide a fast response, programmable over-current interrupt flag.
Current Shunt Measurement
Current shunt measurements require a small differential signal range (< 1V) and high voltage isolation. This
configuration can be incorporated with the AMC1210 with a delta-sigma modulator on the shunt side and a
digital isolation device providing common-mode voltage isolation; see Figure 25.
Floating
HV+ ^{Power Supply}
5.0V
0.1mF
R_SENSE
Gate
Drive
R₁
Circuit
R₂
27W
Power
Supply
D₁
5.1V
C₁
0.1mF
C₂
0.1mF
Gate
Drive
Circuit
ADS1203
M0
V_DD
V_IN+
V_IN-
M1
MCLK
MDAT
GND
BVDD CVDD DVDD
ISO721
V_CC1
V_CC2
IN
GND2
V_CC1
OUT
GND1 GND2
AMC1210
INx
CLK
32 MHz
AGND
GND
HV-
Figure 25. Application Diagram—Isolated Current Measurement
The AMC1210 offers two different ways of current measurement from a modulator. For stable currents, using the
modulator along with the Sinc³ filter offers up to 18.9 effective bits of resolution at an OSR = 256 at a modulator
rate of 10MHz.
For unstable currents, the integrator can be used in place of (or in combination with) the digital filter to give an
average filter value. When used with the time measurement unit, the integrator provides additional filtering
(averaging). This averaging is achieved by using the timer in Mode 2 and the integrator in Sample-and-Hold
Mode. On a rising edge of the selected Sample-and-Hold signal, both the integrator and the timer store their
current values, reset and begin again. These values, once read from their respective registers, are used to
calculate the average value by simply dividing the integrator value by the timer value. Figure 26 illustrates this
functionality.
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