Debugging question for switching power

Have to debug another person's design.
On this board a switching power chip always was burned. After checking datasheet, I think I have to try using inductor with higher forward current and using diode with less reverse current.

But some one has suggested the capacitor connected at the voltage output port maybe effect the working efficient such as sinking too much current.

According to my experience, capacitors do not have big impact on switching power the circuit; only thing they can affect is the noise filtering efficiency.

How do you think?

Any ideas are appreciated.

Without knowing more details on this power supply IC it is difficult to provide you with any sensible advice ..

Regards,
IanP

it is TPS65100 triple LCD power supply chip. the problem happens at Vo1.

I just want to know general ideas.

Thank you.

Most of the design issues are almost perfectly described in the ICs data sheet ..
( https://focus.ti.com/lit/ds/symlink/tps65100.pdf )

What I would like to emphasize is the selection of an inductor ( current rating, dc resitance and self-resonant frequency ..) and type of Schottky diode used in this circuit ..
Values of input and output capacitors are usually not critical (see selection of in/out caps in the data sheet) ..

Regards,
IanP

since that person's PCB layout of TPS65100 didn't isolate high frequecy and senstive feedback circuit, maybe this is one of the reason why that chip was burned.

since dielectric has relation with frequecy, Do you think dielectric of PCB can produce this problem?

Thank you.

I just found out this design is complicated.

The whole system needs four voltage output 22V, 3.3V,-7V and 5V and one big current 2.0A.
The detail working flow is as following:
1.Power up.
2.MAX6338 is triggered by 3.3V input voltage.
3.Out1 of Max6338 enables LT1371CR for getting 15V and 2.0A.
4.The voltage produced by LT1371CR triggers MAX6338 again.
5.Out2 of Max6338 enables TPS65100 for getting 22V and -7V.
The 15V output pin of TPS65100 and 15V output pin of LT1371CR are not connected., but those two chips are grounded together.
The max current of TPS65100 is 400mA and max current of LT1371CR is 2.0A.
The selected inductor upper current limit of TPS65100 is 1.16A and the selected inductor upper current limit of LT1371CR is 2.0A.
At the beginning I think the big current from LT1371 burn TPS65100, but they do not have physic connection except ground.

This design works well for a while then TPS65100 is burned. How to solve this headache?

Appreciate any suggestions.

I would disconnect load and try to run this smps with a small (almost no load) load build of 2 resistors: one for 400mA and one for 2A .. something like <10% of the nominal load .. 390Ω and 75Ω respectively ..
Maybe you have heat dissipation problem on this PCB? ..

Regards,
IanP

Is it possible to amplify the output current of switching power chip TPS65100 from 400mA to 2.6A?

Should I used OPAM ?

The input to this OPAM is 13V to 15V.

Do you have any suggestions for me to realize this idea?

Thank you.

To convert 13-15V input (under condition that there is enough current behid it) to 15V@2.5A output you should use a switching step-up converter such as LT1171, LM2577 or similar ..
If I understand correctly what are you trying to do, you can use the 15V output from the TPS chip to control the other converter ( run or shutdown - see attached picture) ..

An opamp will not convert lower input "power" (voltage * current) to higher output voltage ..

Regards,
IanP

Thank you.

Please Keep in touch.

Added after 45 minutes:

One more question.

If I use TPS65100 to control other start-up coverter, the big current will not burn TPS65100?

Thank you.

If you use a transistor as is shown in the example (see the previous post), the control current to the base of a transistor can be <1mA, wich is almost no-load situation for the TPS65100 ..

Regards,
IanP

I am going to try.

According to my measurement, The Vo1 (we don’t use this port even its’ out put is 15V) and Vo4 (3.3V) of are working right since the output voltages at those two ports are right.
Voltage outputs at Vo2 (22V) and V03 (-7V) are wrong, Do you think it is possible Vo3 sinks two much current from LT1317 (15V 26A)? TPS and LT1317 are grounded together.

Maybe the impedances of those two chips are not compatible.

It is possible?

Thank you.