Hello,
Input voltage may be changed from 2.8V to 3.8V. Output voltage is 3.3V. Load current is 1mA max.
Figure 5 of datasheet, VDO is almost 0V in condition. I think no issue if Vout is almost VIn condition is ok between 2.8V to 3.3V.
Please let me confirm if it is no issue or not. If no issue, how much is the max VDO approximately at 1mA load current?
Best regards.
Toshihiro Watanabe
Hi Toshihiro,
When operating in dropout, the control loop of the LDO biases the pass FET in the triode region so that it allows as much current to the output as possible. As such, the FET behaves like a resistor with a value Rds,on. From Ohm's law, the dropout voltage is:
Vdo = Iout * Rds,on
Rds,on is independent of the output current, so the equation can be rearranged for Rds,on to calculate Vdo for any output current:
Rds,on = Vdo@150 mA/150 mA = Vdo@1 mA/1 mA
Using the maximum values in the datasheet for Vout = 3.3 V:
Vdo(max)@1 mA = Vdo(max)@150 mA/150 mA * 1 mA = 540 mV/150 mA * 1 mA = 3.6 mV
You are correct in thinking that Vout is almost Vin when Vin is between 2.8 V and 3.3 V. With only 1 mA load current, the maximum difference will be Vdo = 3.6 mV.
Thanks,
Gerard
