SLYS023A December 2020 – May 2022 INA229
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 (7E90h).
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.
Values stored in the alert limit registers are set to the default values after VS power cycle events and need to be reprogrammed each time power is applied.