AMC1306E05_17 Datasheet, PDF (26/40 Pages) Texas Instruments – Small, High-Precision, Reinforced Isolated Delta-Sigma Modulators with High CMTI

AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25
SBAS734 – MARCH 2017
www.ti.com
9.2.1.2 Detailed Design Procedure
The high-side power supply (AVDD) for the AMC1306 device is derived from the power supply of the upper gate
driver. Further details are provided in the Power Supply Recommendations section.
The floating ground reference (AGND) is derived from one of the ends of the shunt resistor that is connected to
the negative input of the AMC1306 (AINN). If a four-pin shunt is used, the inputs of the device are connected to
the inner leads and AGND is connected to one of the outer shunt leads.
Use Ohm's Law to calculate the voltage drop across the shunt resistor (V_SHUNT) for the desired measured
current: V_SHUNT = I × R_SHUNT.
Consider the following two restrictions to choose the proper value of the shunt resistor R_SHUNT:
• The voltage drop caused by the nominal current range must not exceed the recommended differential input
voltage range: V_SHUNT ≤ ±250 mV
• The voltage drop caused by the maximum allowed overcurrent must not exceed the input voltage that causes
a clipping output: V_SHUNT ≤ V_Clipping
The typically recommended RC filter in front of a ΔΣ modulator to improve signal-to-noise performance of the
signal path is not required for the AMC1306. By design, the input bandwidth of the analog front-end of the device
is limited as specified in the Electrical Characteristics table.
For modulator output bitstream filtering, a device from TI's TMS320F2807x family of low-cost microcontrollers
(MCUs) or TMS320F2837x family of dual-core MCUs is recommended. These families support up to eight
channels of dedicated hardwired filter structures that significantly simplify system level design by offering two
filtering paths per channel: one providing high accuracy results for the control loop and one fast response path
for overcurrent detection.
9.2.1.3 Application Curve
In motor control applications, a very fast response time for overcurrent detection is required. The time for fully
settling the filter in case of a step-signal at the input of the modulator depends on the filter order; that is, a sinc³
filter requires three data updates for full settling (with f_DATA = f_CLK / OSR). Therefore, for overcurrent protection,
filter types other than sinc³ can be a better choice; an alternative is the sinc² filter. Figure 53 compares the
settling times of different filter orders.
The delay time of the sinc filter with a continuous signal is half of the settling time.
16
14
12
10
8
6
4
sinc¹
2
sinc²
sinc³
0
0 2 4 6 8 10 12 14 16 18 20
Settling Time (µs)
D041
Figure 53. Measured Effective Number of Bits versus Settling Time
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