7 Detailed Description

7.1 Overview

The INA781 device is a digital current sense amplifier with an integrated current sensing element. The device

measures current, bus voltage and internal temperature while calculating power, energy and charge necessary

for accurate decision making in precisely controlled systems. Programmable registers allow flexible configuration

for measurement precision as well as continuous or triggered operation. Detailed register information is found in

Register Maps.

7.2 Functional Block Diagram

GND

20 – bit

ADC

V

I

Common-mode Voltage

(-0.1 V to 85 V)

TI Device

IS+

IS-

±0.5% Oscillator

VBUS

IN+

IN-

SH+

SH-

Power

Current

Bus Voltage

Temperature

Energy

Charge

Alert_Diag

Shunt TC

Compensation

Registers

V

I

I

2C / SMBus

Interface

A0

A1

ALERT

SDA

SCL

0.1 µF

VS

Supply Voltage

(2.7 V to 5.5 V)

7.3 Feature Description

7.3.1 Integrated Shunt Resistor

The INA781 is a precise, low-drift, digital power monitor that provides accurate measurements over the entire

specified ambient temperature range of –40°C to +125°C. The integrated current-sensing resistor is internally

compensated to provide measurement stability over temperature, while simplifying printed circuit board (PCB)

layout and size constraints.

Access to the on-chip current-sensing resistor is provided by the IS+ and IS- pins. This resistor features internal

sense connections that are brought out on the SH+ and SH- pins. Access to the digital power monitor is

provided by the IN+ and IN- pins. When the shunt sense connections are connected to the digital power monitor

inputs, the sensed voltage is calibrated and temperature compensated to achieve a high level of accuracy.

The construction of this resistor does not allow it to be used as a stand-alone component for accurate current

measurement. The INA781 is system-calibrated to ensure that the current-sensing resistor and digital power

monitor are both precisely matched to one another.

The nominal pin-to-pin resistance from IS+ to IS- is approximately 535 μΩ, while the internal resistance seen by

the SH+ and SH- pins is nominally 400 μΩ. The power dissipation requirements of the system and package are

based on the total package resistance between the IS+ and IS– pins.

7.3.2 Safe Operating Area

The heat generated by the device power dissipation limits the maximum current that can be safely handled by

the package. The current consumed to power the device is low, therefore the primary source of heating is due

to the current flow through the internal shunt resistor. The maximum safe-operating current level shown in Figure

7-1 is set to ensure that the heat generated in the package is limited so that the internal junction temperature of

the silicon does not exceed 165°C. This data was collected on the INA781 evaluation module (SENS119E0).

INA781

SBOSAC0 – JULY 2023

www.ti.com

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