Other Parts Discussed in Thread: TPS65131
Hi, Brigitte
For this question :We saw similar waveforms at other customers and the problem was layout. Please check with the customer if there might be noise coupling into the FBN node. Even if at the moment the problem seems to be solved by changing the capacitor, if the layout of FBN is in a noisy area, it could come back later in mass production.
below as schematic:
and also we saw client layout FBN was not loop output cap, it`s look like coupling noise issue.
and Could you explain this phenomenon? why we fine tune R and C value can fixed issue.
as below was client change R and C test result.
C116(pF) |
R108(K ohm) |
R113+R114(K ohm) |
C116*(R113+R114) |
AVDDN |
FBN |
2 |
15.4 |
82.6 |
165.2 |
no Ripple,voltage level is correct(-6.5V) |
stable |
2 |
47.5 |
255 |
510 |
no Ripple,voltage level is correct(-6.5V) |
stable |
22 |
15.4 |
82.6 |
1817.2 |
have Ripple(-6.0~-8.0) |
sometime unstable |
8 |
15.4 |
255 |
2040 |
have Ripple(-6.0~-8.0) |
sometime unstable |
22 |
47.5 |
255 |
5610 |
no Ripple,voltage level is wrong(-9V) |
unstable |
A. C116*(R113+R114)if increase R and C Value (almost 5610*10-9)FBN was unstable,AVDDN was wrong voltage.
B.C116*(R113+R114) If decrease R and C Value (almost 510*10-9)FBN was stable,AVDDN voltage was correct.
C.C116*(R113+R114) almost 2040*10-9時FBN sometime unsaable,AVDDN have Ripple
if any, Please advise me.
Thanks,
Best regards,
Lawrence.