Q: TPS61045 Output Voltage Variation by 568858

Team,

Customer is testing is TPS61045 EVM and they currently have a 2k ohm load on the output set to 17.5V.  When they vary the input voltage from 2V to 5V they see the output increase or decrease by a few hundred mV.  Is this expected?  I'm trying to get some scope plots but wanted to get some feedback going.

 
A: Re: TPS61045 Output Voltage Variation [Avago] by 10449

Yes, fairly large line and load regulation are expected.  Because of the TPS61045 hysteretic control topology that turns the power FET on when the FB voltage drops below a specific voltage level and then turns it off when the inductor current goes above a certain level, the line and load regulation are not very small.  You can improve the line and load regulation by using a smaller inductor value or a larger output capacitor value.  This minimizes the voltage ripple on the output and on the FB pin which improves line and load regulation.  If necessary, you can also add some capacitance from FB to ground to form a capacitive divider that reduces the voltage ripple on the FB pin.  This also improves line and load regulation.  Be sure that the voltage ripple on the FB pin remains above 50mV.  If you reduce the voltage ripple on the FB pin to less than 50mV, the ICs operation will have more jitter and frequency variation.  This is normal and expected operation and will not damage the IC.