INA180 datasheet(21/32 Pages) TI1

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SENSE

Total Offset Error (V)

Total Offset Error (%) =

100%

INA180

Power Supply, VS

2.7 V to 5.5 V

Load

Supply

RSENSE

GND

Load

IN±

IN+

OUT

CBYPASS

0.1 µF

VOUT

INA180, INA2180

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SBOS741A – APRIL 2017 – REVISED AUGUST 2017

Product Folder Links: INA180 INA2180

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9.2 Typical Application

Figure 41. Low-Side Sensing

9.2.1 Design Requirements

The design requirements for the circuit shown in Figure 41, are listed in Table 3

Table 3. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Power-supply voltage, VS

5 V

Low-side current sensing

VCM = 0 V

Mode of operation

Unidirectional

RSENSE power loss

< 900 mW

Maximum sense current, IMAX

40 A

Accuracy

Less than 1.5% at maximum current, TJ = 25°C

Small-signal bandwidth

> 80 kHz

9.2.2 Detailed Design Procedure

The maximum value of the current sense resistor is calculated based on the maximum power loss requirement.

By applying Equation 1, the maximum value of the current-sense resistor is calculated to be 0.563 mΩ. This is

the maximum value for sense resistor RSENSE; therefore, select RSENSE to be 0.5 mΩ because it is the closest

standard resistor value that meets the power-loss requirement.

The next step is to select the appropriate gain and reduce RSENSE, if needed, to keep the output signal swing

within the VS range. Using Equation 2, and given that IMAX = 40 A and RSENSE = 0.5 mΩ, the maximum current-

sense gain calculated to avoid the positive swing-to-rail limitations on the output is 248.5. To maximize the output

signal range, the INA180A4 (gain = 200) device is selected for this application.

To calculate the accuracy at peak current, the two factors that must be determined are the gain error and the

offset error. The gain error of the INAx180 is specified to be a maximum of 1%. The error due to the offset is

constant, and is specified to be 125 µV (maximum) for the conditions where VCM = 0 V and VS = 5 V. Using

Equation 6, the percentage error contribution of the offset voltage is calculated to be 0.75%, with total offset error

= 150 µV, RSENSE = 0.5 mΩ, and ISENSE = 40 A.

(6)

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