How to solve the power supply ripple

lx331lx

How to solve the power supply ripple [Copy link]

 

I designed a project, which is similar to the previous project. There are LDO33 and LDO120 inside, but the ripple of 3.3 and 1.2 measured by myself is very large. The filter circuits are the same and the positions are similar. Why is this?

lx331lx

The ripple I measured before was about 20, but my own measurement showed it was 60-70

gmchen

Have you considered the routing and grounding of the printed circuit board?

Have you considered the grounding position of the probe during testing?

qwqwqw2088

How did you measure the ripple of the previous project?

Ripple is related to the measurement method

This time the ripple is very large. How large is it? What is the order of magnitude?

It is recommended to exclude the test first, and then focus on detecting the difference between the circuit and the previous one.

Gen_X

Look at the frequency and size distribution of the ripples, and take equal measures, adding inductors for high frequencies, capacitors for low frequencies, or both.

btty038

The layout is the same as the first time. There is also grounding and power ground. Find the source of input and output

annysky2012

How did you measure the ripple of the previous project? The ripple is related to the measurement method. This time the ripple is very large. How large is it? What is the order of magnitude? It is recommended to exclude the test first, and then focus on testing the circuit to see if it is different from the previous one.

Agree

Gen_X

If it is a 3.3 and 1.2 power supply, it must be that the bottom line layout is unreasonable. There is no other problem. Increase the total area of the bottom line.

chunyang

If the load changes dramatically, filtering needs to be strengthened. Also, pay attention to the PCB design and the impedance of the power supply loop should be as small as possible.

freebsder

Add filtering and add filtering, big and small capacitors and inductors, all added.

lx331lx

chunyang posted on 2021-5-11 14:11 If the load changes dramatically, the filtering needs to be strengthened. In addition, pay attention to the PCB design. The impedance of the power supply circuit should be as small as possible.

I looked carefully and found that I connected the diode directly to the chip pin after voltage reduction, and then connected the capacitor filter to the pin. Will this affect the ripple of SYS and thus affect LDO33 and LDO120?

chunyang

lx331lx posted on 2021-5-13 16:08 I looked carefully and found that I connected the diode directly to the chip pin after reducing the voltage, and then connected the capacitor filter to the pin. Will this affect SYS...

Your description is unclear, please post a picture.

lx331lx

chunyang posted on 2021-5-13 16:48 Your description is not clear, why not post a picture?

lx331lx

chunyang posted on 2021-5-13 16:48 Your description is not clear, why not post a picture?

The POWER_SYS on the left is stepped down by a diode

chunyang

lx331lx posted on 2021-5-13 16:57

Schematic diagram, all connections of related nodes must be complete.