TPS54140:It outputs -15V with 15V input, but it does not start up according to the design value of soft start.

hi,

thanks.

sch is below.

ss pin waveform is below.

thank you.

hi， Keitaro，

I have found a very same application note as your designed, HERE, figure 13,14 is the right Vout waveform . It's strange your waveform looks in an opposite

position, could you upload layout or more information, I will double check. is Vout stable in -15v , what's loading current at Vout .

Elena

thanks .

My design is below .

rayout is below .

I want to launch -15V as soon as possible. If Tss is as designed, it will be resolved. Thank you.

it looks like in a long time device not start, please change C216  to 0.1u ,and retest if it works. also share me the top lay of PCB trace, thank you.

and at least a 50V 0.1u cap, better 100V 0.1u.

hi.

I changed C216 to 0.1u,but unchanged waveforms.

And open ENpin .

PCB rayout is below.

please tell me this solution.

thanks.

is the inductor current right ? sw switching when start ? all the sch and layout looks good.

C216 cap move close to diode, 0.1uf, 50V,

check Vin, EN (do not float), IL(inductor current), CSS ,Vo, waveform. disconnect loading, 

if not work , try to remove C217 , then check waveform again.

thanks.

The improvement has already been implemented and the waveform has not changed.

However, after removing R552, R553, and C227, some PBs started up normally.

The waveform is below.

However, there were some PBs that started up slowly under the same conditions.

The waveform is below.

Is it related to the difference in the rise of P15?

If you have a past case that output 15V to -15V, please send it.

thanks.