TPS65131: TPS65131

Hi Jie,

What is the ripple frequency?

BR

Patrick

Hi Patrick，

Frequency response is one of our test items, with an electronic load connected at 15V or -15V, providing alternating loads of 25% (200mA), 75% (200mA) at 100Hz. For example, 50mA->150mA->50mA->150mA, so repeatedly test the output voltage ripple is very large and the waveform is not normal. Test the output voltage full load 200mA ripple normal in about 30mVpp, dynamic response should be in 60 ~ 100mVpp or so, but -15V up to 200 ~ 300mVpp, the circuit component parameters in accordance with the specifications and there is a margin. Adjust the feedforward capacitance of the feedback loop has not been significantly improved.

Another question I want to ask you, the output of the -15V feedback circuit is unstable when there is only a feedforward capacitor, and then the output is normal when a 51k resistor is connected in series with the capacitor, why is this?

Looking forward to your reply.

JIE

Hi JIE,

The feedforward capacitor will provide an additional zero and pole to the loop, and the zero frequency is much smaller than the pole so usually we only consider the impact of the zero, it will help to improve the bandwidth of the loop and phase margin. But to avoid coupling noise to the control loop, we also suggest to in series a resistor with this cap.

BR

Patrick

Hi Patrick，

Thanks for answering the second question. 

Thanks for answering the second question. How do we reduce the output voltage ripple of dynamic loads, how do we set the qualifying range, and does it make sense to set the output ripple at 2x the full load voltage?

Hi JIE,

If you mean the voltage spike when load is changing from 50mA->150mA->50mA->150mA, this is related to transient response, you can also adjust feedforward capacitor and resistor to adjust the zero to improve the bandwidth. 

BR

Patrick