SNOSDC0A October 2020 – December 2020 LM7310
The Power Good assertion threshold can be set using the resistors R4 & R5 connected to the PGTH pin whose values can be calculated as:
Because R4 and R5 leak the current from the output rail VOUT, these resistors must be selected to minimize the leakage current. The current drawn by R4 and R5 from the power supply is IR45 = VOUT / (R4 + R5). However, leakage currents due to external active components connected to the resistor string can add error to these calculations. So, the resistor string current, IR123 must be chosen to be 20 times greater than the PGTH leakage current expected.
From the device electrical specifications, PGTH leakage current is 1 μA (max), VPGTH(R) = 1.2 V and from design requirements, VPG = 11.4 V. To solve the equation, first choose the value of R4 = 47 kΩ and calculate R5 = 5.52 kΩ. Choose nearest 1% standard resistor value as R5 = 5.6 kΩ.