INA210 datasheet(22/39 Pages) TI1

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2mW

SHUNT

10A

Load

+12V

VCM

GND

IN+

IN-

PowerRegister

I C

Interface

CurrentRegister

VoltageRegister

SDA

SCK

0.1 F

10 F

+3.3Vto+5V

V (SupplyVoltage)

INA220

SBOS459D – JUNE 2009 – REVISED SEPTEMBER 2010

www.ti.com

CONFIGURE/MEASURE/CALCULATE

shunt voltage. By knowing the value of the shunt

EXAMPLE

resistor, the device can then calculate the amount of

current that created the measured shunt voltage drop.

In this example, the 10A load creates a differential

The first step when calculating the calibration value is

voltage of 20mV across a 2m

Ω shunt resistor. The

setting the current LSB. The Calibration Register

voltage present at the VIN– pin is equal to the

value is based on a calculation that has its precision

common-mode voltage minus the differential drop

capability limited by the size of the register and the

across the resistor. The bus voltage for the INA220 is

Current Register LSB. The device can measure

measured at the external VBUS input pin, which in this

bidirectional current; thus, the MSB of the Current

example is connected to the VIN– pin to measure the

voltage level delivered to the load. For this example,

bits to be used for the Current Register value. It is

the voltage at the VIN– pin is 11.98V. For this

common when using the current value calculations to

particular

range

(40mV

full-scale),

this

small

use a resolution between 12 bits and 15 bits.

difference is not a significant deviation from the 12V

Calculating the current LSB for each of these

common-mode voltage. However, at larger full-scale

resolutions provides minimum and maximum values.

ranges, this deviation can be much larger.

These values are calculated assuming the maximum

current that will be expected to flow through the

Note that the Bus Voltage Register bits are not

current shunt resistor, as shown in Equation 2 and

right-aligned. In order to compute the value of the

Equation 3. To simplify the mathematics, it is

Bus Voltage Register contents using the LSB of 4mV,

common to choose a round number located between

the register must be shifted right by three bits. This

these two points. For this example, the maximum

shift puts the BD0 bit in the LSB position so that the

current LSB is 3.66mA/bit and the minimum current

contents can be multiplied by the 4mV LSB value to

LSB would be 457.78µA/bit assuming a maximum

compute the bus voltage measured by the device.

expected current of 15A. For this example, a value of

The shifted value of the bus voltage register contents

1mA/bit was chosen for the current LSB. Setting the

is now equal to BB3h, a decimal equivalent of 2995.

current LSB to this value allows for sufficient

This value of 2995 multiplied by the 4mV LSB results

precision while serving to simplify the math as well.

in a value of 11.98V.

Using Equation 4 results in a Calibration Register

The Calibration Register (05h) is set in order to

value of 20480, or 5000h.

provide the device information about the current

shunt resistor that was used to create the measured

Figure 22. Example Circuit Configuration

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