AMC1204_15 Datasheet, PDF (25/37 Pages) Texas Instruments – AMC1204 20-MHz, Second-Order, Isolated Delta-Sigma Modulator

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AMC1204, AMC1204B
SBAS512E – APRIL 2011 – REVISED SEPTEMBER 2015
Typical Application (continued)
8.2.3.1 Design Requirements
In such applications, a resistor divider (R₁ and R₂) is used to match the relatively small input voltage range of the
AMC device. R₂ and the input resistance R_IN of the AMC1204 also create a resistor divider resulting in additional
gain error. With the assumption that R₁ and R_IN have a considerably higher value than R₂, use Equation 4 to
estimate the resulting total gain error.
G_ERRTOT
=
G_ERR
+
R₂
R_IN
where
• G_ERR = the gain error of AMC device.
(4)
9 Power Supply Recommendations
In a typical frequency inverter application, the high-side power supply (AVDD) for the AMC1204 and AMC1204B
is derived from the power supply of the upper gate driver. For lowest cost, a Zener diode can be used to limit the
voltage to 5 V ±10%. TI recommends a decoupling capacitor of 0.1 µF for filtering this power-supply path. This
capacitor (C₁ in Figure 53) should be placed as close as possible to the AVDD pin for best performance. If better
filtering is required, an additional 1-µF to 10-µF capacitor can be used. The floating ground reference AGND is
derived from the end of the shunt resistor, which is connected to the negative input (VINN) of the AMC1204 and
AMC1204B. If a four-terminal shunt is used, the inputs of AMC1204 and AMC1204B are connected to the inner
leads, while AGND is connected to one of the outer leads of the shunt. Both digital signals, CLKIN and DATA,
can be directly connected to a digital filter.
Floating
HV+ ^{Power Supply}
Isolation
Barrier
To Load
R_SHUNT
Gated
Drive
Circuit
Power
Supply
R₁
D₁
R₂
5.1V 12W
R₃
12W
C₂
330pF
C₃
10pF
(optional)
C₄
10pF
(optional)
C₁₍₁₎
0.1mF
AMC1204
AMC1204B
AVDD DVDD
VINP DATA
VINN CLKIN
AGND DGND
Gated
Drive
Circuit
HV-
(1) Place C₁ close to the AMC1204 and AMC1204B.
Figure 53. Zener-Diode-Based High-Side Power Supply
For better performance, the differential input 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: any mismatch in the capacitor values can cause a common-mode
error at the input of the modulator.
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