Configuration register (0h). The conversion times can be set independently for the shunt voltage and bus voltage

measurements to allow added flexibility when configuring the monitoring of the power-supply bus.

The internal ADC is based on a delta-sigma (ΔΣ) front-end with a 500-kHz (±10% max) sampling rate.

This architecture has good inherent noise rejection; however, transients that occur at or very close to the

sampling rate harmonics can cause problems. These signals are at 1 MHz and higher and can be managed by

incorporating filtering at the device input. The high frequency enables the use of low-value series resistors on the

filter with negligible effects on measurement accuracy. In general, filtering the device input is only necessary if

there are transients at exact harmonics of the 500 kHz (±10% max) sampling rate (greater than 1 MHz). Filter

using the lowest possible series resistance (typically 100 Ω or less) and a ceramic capacitor. Recommended

values for this capacitor are between 0.1 µF and 1 µF. Figure 8-1 illustrates the device with a filter added at the

input.

<100

<100

IN+

IN-

VS

GND

100 nF

Load

Load

Supply

0.1µF to 1µF

Figure 8-1. Input Filtering

Overload conditions are another consideration for the device inputs. The device inputs are specified to tolerate

26 V across the inputs. A large differential scenario can be a short to ground on the load side of the shunt.

This type of event can result in full power-supply voltage across the shunt (as long the power supply or energy

storage capacitors can support this voltage). Removing a short to ground can result in inductive kickbacks

that can exceed the 26-V differential and 28-V common-mode rating of the device. Inductive kickback voltages

are best controlled by Zener-type, transient-absorbing devices (commonly called transzorbs) combined with

sufficient energy storage capacitance. The Current Shunt Monitor with Transient Robustness Reference Design

describes a high-side, current-shunt monitor used to measure the voltage developed across a current-sensing

resistor and how to better protect the current-sense device from transient overvoltage conditions.

In applications that do not have large energy storage electrolytics on one or both sides of the shunt, an input

overstress condition can result from an excessive dV/dt of the voltage applied to the input. A hard physical

short is the most likely cause of this event, particularly in applications with no large electrolytics present. This

problem occurs because an excessive dV/dt can activate the ESD protection in the device in systems where

large currents are available. Testing demonstrates that the addition of 10-Ω resistors in series with each input of

the device sufficiently protects the inputs against this dV/dt failure up to the 28-V rating of the device. Selecting

these resistors in the range noted has minimal effect on accuracy.

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SBOS844 – MAY 2021

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