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TL720M05-Q1: TL720M05-Q1

Rogers Chen
Intellectual 825 points
Part Number: TL720M05-Q1
Other Parts Discussed in Thread: LM5161,

Hi,

We are developing a new automotive product within a temperature sampling circuit, we use LM5161 to step down the auto battery voltage(12V) to 8V, and the secondary power circuit we use a TL720M05-Q1 to regulate 8V to 5V as the power supply for the amplifier IC. But we found the output voltage ripple is very bad. The Vpp value of the ripple is about 100mV, and it can't meet the requirement. The schematic of the power supply circuits and the input voltage ripple photo are shown below. I have measured the ripple of the input voltage, and it is also about 100mV. My question is, why can't the LDO suppress the ripple? The high ESR Cin and Cout capacitors are recommended in the datasheet, I don’t understand the principle very well. Could this be the cause of the large output ripple? Thanks!

  • 0
    TI__Mastermind 38195 points

    Hi Rogers,

    If you are measuring the same noise at the input as the output, this is evidence that the noise is coming from the output side of the LDO instead of the input side. Otherwise the noise would be attenuated by the PSRR. 

    Is the amplifier that the LDO is supplying a chopper? I am seeing a very period, basically exactly 100Hz noise signal. Is there something in your system that is operating at 100Hz? 

    I don't think the ESR would cause noise like this, but the datasheet does not set a requirement for large ESR as you mentioned. The application section actually says to use low-ESR capacitors. 

    Regards,

    Nick