continuously converting the shunt voltage, bus voltage, and temperature. If the default power up conditions do

8.2.2.3 Program the Shunt Calibration Register

properly report any result based on current. The first step in properly setting this register is to calculate the LSB

value for the current by using Equation 3. Applying this equation with the maximum expected current of 10 A

results in an LSB size of 19.0735 μA. Applying Equation 2 to the Current_LSB and selected value for the shunt

resistor results in a shunt calibration register setting of 4050d (FD2h). Failure to set the value of the shunt

calibration register will result in a zero value for any result based on current.

8.2.2.4 Set Desired Fault Thresholds

Fault thresholds are set by programming the desired trip threshold into the corresponding fault register. The list

of supported fault registers is shown in Table 7-1. Since the fault limit registers are 16 bits in length, the effective

LSB size for these registers is 16 times greater than the corresponding 20 bit LSB used in calculating returned

values for bus voltage and current.

An over current threshold is set by programming the shunt over voltage limit register (SOVL). The voltage that

needs to be programmed into this register is calculated by multiplying the over current threshold by the shunt

resistor. In this example the over current threshold is 10 A and the value of the current sense resistor is 16.2 mΩ,

which give a shunt voltage limit of 162 mV. Once the shunt voltage limit is known, the value for the shunt over

voltage limit register is calculated by dividing the shunt voltage limit by the shunt voltage LSB size.

In this example, the calculated value of the shunt over voltage limit register is 162 mV / (312.5 nV × 16) =

32400d (7 E90h).

An over voltage fault threshold on the bus voltage is set by programming the bus over voltage limit register

(BOVL). In this example the desired over voltage threshold is 52 V. The value that needs to be programmed into

this register is calculated by dividing the target threshold voltage by the bus voltage fault limit LSB value of 3.125

mV. For this example, the target value for the BOVL register is 52 V / (195.3125 μV × 16) = 16640d (4100h).

When setting the power over-limit value, the LSB size used to calculate the value needed in the limit registers

will be 256 times greater than the power LSB. This is because the power register is a 24 bits in length while the

power fault limit register is 16 bits.

reprogrammed each time power is applied.

8.2.2.5 Calculate Returned Values

Parametric values are calculated by multiplying the returned value by the LSB value. Table 8-4 below shows the

returned values for this application example assuming the design requirements shown in Table 8-3.

Table 8-4. Calculating Returned Values

PARAMETER

Returned Value

LSB Value

Calculated Value

Shunt voltage (V)

311040d

312.5 nV/LSB

0.0972 V

Current (A)

314572d

6 A

Bus voltage (V)

245760d

195.3125 µV/LSB

48 V

Power (W)

4718604d

Current LSB x 3.2 = 61.035156 µW/LSB

288 W

Energy (J)

1061683200d

Power LSB x 16 = 976.5625 µJ/LSB

1036800 J

Charge (C)

1132462080d

Current LSB = 19.073486 µC/LSB

21600 C

Temperature (°C)

3200d

7.8125 m°C/LSB

25°C

Shunt Voltage, Current, Bus Voltage (positive only), Charge, and Temperature return values in two's complement

format. In two's complement format a negative value in binary is represented by having a 1 in the most

significant bit of the returned value. These values can be converted to decimal by first inverting all the bits and

adding 1 to obtain the unsigned binary value. This value should then be converted to decimal with the negative

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