• 13107.2 x 10e6 is an internal fixed value used to ensure scaling is maintained properly

CURRENT_LSB =

Maximum Expected Current

2

19

(3)

Note that the current is calculated following a shunt voltage measurement based on the value set in the

SHUNT_CAL register. If the value loaded into the SHUNT_CAL register is zero, the current value reported

through the CURRENT register is also zero.

After programming the SHUNT_CAL register with the calculated value, the measured current in Amperes can be

read from the CURRENT register. The final value is scaled by CURRENT_LSB and calculated in Equation 4:

Current [A] = CURRENT_LSB x CURRENT

(4)

where

• CURRENT is the value read from the CURRENT register

The power value can be read from the POWER register as a 24-bit value and converted to Watts by using

Equation 5:

Power [W] = 3.2 x CURRENT_LSB x POWER

(5)

where

• POWER is the value read from the POWER register.

• CURRENT_LSB is the lsb size of the current calculation as defined by Equation 3.

The energy value can be read from the ENERGY register as a 40-bit unsigned value in Joules units. The energy

value in Joules is converted by using Equation 6:

Energy [J] = 16 x 3.2 x CURRENT_LSB x ENERGY

(6)

The charge value can be read from the CHARGE register as a 40-bit, two's complement value in Coulombs. The

charge value in Coulomb is converted by using Equation 7:

Charge [C] = CURRENT_LSB x CHARGE

(7)

where

• CHARGE is the value read from the CHARGE register.

• CURRENT_LSB is the lsb size of the current calculation as described in Equation 3.

Upon overflow, the ENERGY and CHARGE registers will roll over and start from zero. The register values can

also be reset at any time by setting the RSTACC bit in the CONFIG register.

For a design example using these equations refer to Section 8.2.2.

8.1.3 ADC Output Data Rate and Noise Performance

The INA229 noise performance and effective resolution depend on the ADC conversion time. The device also

supports digital averaging which can further help decrease digital noise. The flexibility of the device to select

INA229

SLYS023 – DECEMBER 2020

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