Settling Time (µs)

0

2

4

6

8

10

12

14

16

18

20

0

2

4

6

8

10

12

14

16

D041

sinc1

sinc2

sinc3

30

AMC1306E05, AMC1306E25, AMC1306M05, AMC1306M25

SBAS734C – MARCH 2017 – REVISED JANAURY 2020

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Product Folder Links: AMC1306E05 AMC1306E25 AMC1306M05 AMC1306M25

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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 (VSHUNT) for the desired measured

current: VSHUNT = I × RSHUNT.

Consider the following two restrictions to choose the proper value of the shunt resistor RSHUNT:

•

The voltage drop caused by the nominal current range must not exceed the recommended differential input

voltage range: VSHUNT ≤ ±250 mV

•

The voltage drop caused by the maximum allowed overcurrent must not exceed the input voltage that causes

a clipping output: |VSHUNT| ≤ |VClipping|

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 fDATA = fCLK / OSR). Therefore, for overcurrent protection,

filter types other than sinc3 can be a better choice; an alternative is the sinc2 filter. Figure 58 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.

Figure 58. Measured Effective Number of Bits versus Settling Time