Tool/software:
Hello:
The schematic diagram of LDO is as follows: TPS7A4701RGWR
The PCB part is as follows:
The following is the debugging process:
Board level testing shows output ripple:
There is a ripple of 10~12mV (around 60KHz, and FFT low-frequency noise is very obvious); The source of the bottom noise during machine testing should be the LDO output ripple;
LDO has output ripple regardless of whether it is loaded or unloaded (unloaded means removing two series connected diodes, LDO's output capacitor is still present); Increase ESR of output capacitor (replace ceramic capacitor with tantalum capacitor or aluminum capacitor, with or without load):
Remove the output ceramic capacitor (with or without load):
Under no-load conditions, connect a resistor to ground at the LDO output terminal to maintain the LDO load current at around 100mA
As mentioned above, even with a load current of 100mA, there is still ripple in the LDO output,
Remove all other components from a motherboard, leaving only the LDO circuit, which still has a 7mV ripple:
