8.3 What to Do and What Not to Do

Do not leave the analog inputs INP and INN of the AMC3301-Q1 unconnected (floating) when the device is

powered up. If the device input is left floating, the input bias current may drive the inputs to a positive value that

exceeds the operating common-mode input voltage and the output of the device is undetermined.

Connect the high-side ground (HGND) to INN, either directly or through a resistive path. A DC current path

between INN and HGND is required to define the input common-mode voltage. Take care not to exceed the input

common-mode range as specified in the Electrical Characteristics table in Section 6. For best accuracy, set the

ground connection to a separate trace that connects directly to the shunt resistor rather than shorting HGND to

INN directly at the input to the device. See Section 10 for more details.

9 Power Supply Recommendations

The AMC3301-Q1 is powered from the low-side power supply (VDD) with a nominal value of 3.3 V (or 5 V) ±

10%. TI recommends a low-ESR decoupling capacitor of 1 nF (C8 in Figure 9-1) placed as close as possible to

the VDD pin, followed by a 1-µF capacitor (C9) to filter this power-supply path.

The primary-side of the DC/DC converter is decoupled with a low-ESR 100-nF capacitor (C4) positioned close to

the device between the DCDC_IN and DCDC_GND pins. Use a 1-µF capacitor (C2) to decouple the secondary

side in addition to a low-ESR, 1-nF capacitor (C3) placed as close as possible to the device and connected to

the DCDC_OUT and DCDC_HGND pins.

For the secondary-side LDO, use low-ESR capacitors of 1-nF (C6), placed as close as possible to the

AMC3301-Q1, followed by a 100-nF decoupling capacitor (C5).

The ground reference for the secondary-side (HGND) is derived from the terminal of the shunt resistor which is

connected to the negative input (INN) of the device. For best DC accuracy, use a separate trace to make this

connection instead of shorting HGND to INN directly at the device input. The high-side DC/DC ground terminal

(DCDC_HGND) is shorted to HGND directly at the device pins.

DCDC_OUT

Resonator

And

Driver

DCDC_HGND

HLDO_IN

HLDO_OUT

HGND

INP

INN

LDO

Rectifier

LDO

Diagnostics

DCDC_IN

DCDC_GND

LDO_OUT

VDD

OUTP

OUTN

GND

AMC3301-Q1

DIAG

NC

C2

1 µF

C6

1 nF

C5

100 nF

C3

1nF

C1

100 nF

R2

10 Ÿ

R4

10 Ÿ

C10

8.2 nF

C9

1 µF

C8

1 nF

C4

100 nF

R1

47 NŸ

3.3 V / 5 V supply

to ADC / analog filter

to ADC / analog filter

to MCU (optional)

GND

I

Figure 9-1. Decoupling the AMC3301-Q1

AMC3301-Q1

SBASA73 – JULY 2020

www.ti.com

26

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