Q: TPS61251 Current Limit by 1594102

The TPS61251 EVM was modified to set a maximum input current of 160mA and a 3F supercap was added.  During startup, the input current has two different values and changes from one value to another value as the supercap charges.  Any ideas on what causes this to occur?


A: Re: TPS61251 Current Limit by 10449

When the TPS61250 input voltage is greater than the output voltage, the IC delivers a constant current to the load.  The TPS61250 sets this current to be less than the maximum programmed current (set by Rilim)  When Vout rises to Vin, the IC starts switching and the average input current rises to the value defined by Rilim.  The datasheet provides more details on the startup current functionality.  The waveform matches what is expected.  The startup waveforms in the datasheets are identical.