8.2.1 Design Requirements

Table 8-1 lists the parameters for this typical application.

Table 8-1. Design Requirements

PARAMETER

VALUE

High-side supply voltage

3.3 V or 5 V

Low-side supply voltage

3.3 V or 5 V

Voltage drop across RSHUNT for a linear response

±250 mV (maximum)

Signal delay (50% VIN to 90% OUTP, OUTN)

3 µs (maximum)

8.2.2 Detailed Design Procedure

In Figure 8-1, the high-side power supply (VDD1) for the AMC1301 is derived from the floating power supply of

the upper gate driver.

The floating ground reference (GND1) is derived from the end of the shunt resistor that is connected to the

negative input of the AMC1301 (INN). If a four-pin shunt is used, the inputs of the AMC1301 are connected to

the inner leads and GND1 is connected to the outer lead on the INN-side of the shunt. To minimize offset and

improve accuracy, route the ground connection as a separate trace that connects directly to the shunt resistor

rather than shorting GND1 to INN directly at the input to the device. See the Layout section for more details.

8.2.2.1 Shunt Resistor Sizing

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 when selecting the value of the shunt resistor, RSHUNT:

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

voltage range for a linear response: |VSHUNT| ≤ |VFSR|

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

a clipping output: |VSHUNT| ≤ |VClipping|

8.2.2.2 Input Filter Design

Place a differential RC filter (R1, R2, C5) in front of the isolated amplifier to improve signal-to-noise performance

of the signal path. Design the input filter such that:

• The cutoff frequency of the filter is at least one order of magnitude lower than the sampling frequency of the

ΔΣ modulator (20 MHz)

• The input bias current does not generate significant voltage drop across the DC impedances (R1, R2) of the

input filter

• The impedances measured from the analog inputs are equal (R1 equals R2)

Capacitors C6 and C7 are optional and improve common-mode rejection at high frequencies (>1 MHz). For best

performance, C6 must match the value of C7 and both capacitors must be 10 to 20 times lower in value than C5.

For most applications, the structure shown in Figure 8-2 achieves excellent performance.

VDD1

GND1

INP

INN

AMC1301

VDD2

OUTP

OUTN

GND2

R2

10

R1 10

C5

10 nF

C6

1 nF

C7

1 nF

Figure 8-2. Differential Input Filter

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AMC1301

SBAS667G – APRIL 2016 – REVISED APRIL 2023

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