LM1085: Do you have any graph of ESR range for LM1085 like Figure 16 in AN-1148 application report?

 Hi Stephan,

 Thank you very much for your reply.

 The customer checked LM1085IS-3.3 output waveform on their own PCB with several POSCAP as the below.

             Cout(uF)    ESR(mohm)    Fzero(kHz)

                               (@500kHz)     (Fzero=1/(2pi*Cout*ESR))

CAP1:  47              41                    82.6

CAP2:  33              53.3                 90.5

CAP3:  22              44.1                 164

CAP4:  10              48                    331.6

CAP5:   5.6            66.5                 427.4

 As the result, CAP1 case was most stable output voltage and CAP5 was most unstable.

( Output waveform stable CAP1 > CAP2 > CAP3 > CAP4 > CAP5 unstable)

 In case of CAP5, the output voltage was oscilated with 100kHz and 70mVp-p at light load.

 In case of CAP1, the output voltage was stabled at the light load.

 The customer though CAP5 case is most stable because the E2E post you wrote said Fzero should be set to 500kHz for LM1085.

 But the customer experiment result showed CAP1 is the best for output voltage stability and CAP5 is the worst.

 My questions are...

1. Is 500kHz for LM1085 Fzero correct? May lower frequency than 500kHz be actual Fzero?

2. If 500kHz is not correct, what is the actual Fzero. Which frequency is recommended for LM1085 Fzero?

 Could you please give me your reply?

 Thank you again and best regards,

 Kazuya. 

Hi Kazuya,

Thank you for the detailed information and post.
I need some additional information before I can fully reply to the customers concerns.

Was the test at room temperature?
Can the customer provide the specific manufacturing part numbers of each capacitor, as well as their output voltage?

If so, we can do a review of the capacitance including bias effects, which will change the actual capacitor value.

Can the customer provide an oscilloscope plot showing the condition where the linear regulator was unstable (Cap 5 with 100kHz frequency oscillation)?
What load is considered light load to the customer?

Thanks,

- Stephen

 Hi Stephen,

 Thank you very much for the pronmpt reply.

 >Was the test at room temperature?
>Can the customer provide the specific manufacturing part numbers of each capacitor, as well as their output voltage?

 Yes. The test was at room temperature and each capacitor part number is the follow.

CAP1: Panasonic 10TPB47M

CAP2: Panasonic 10TPB33M

CAP3: Panasonic 8TPC22M

CAP4: Panasonic 8TPC22M

CAP5: Panasonic 25TQC5R6M

>Can the customer provide an oscilloscope plot showing the condition where the linear regulator was unstable (Cap 5 with 100kHz frequency oscillation)?
>What load is considered light load to the customer?

 The customer don't want to disclosed the waveform they took to E2E.

 If it is no problem, could you please tell me your e-mail address?

 Thank you again and best regards,

 Kazuya.

Hi Kazuya,

I have sent you an E2E friendship request.
If you accept the request you can send me the data directly.

Thanks,

- Stephen

 Hi Stephen,

 Thank you for your the friendship request.

 I accepted it and sent you a private message.

 Could you please review the message?

 Thank you again and best regards,

 Kazuya.

Hi Kazuya,

I reviewed the capacitors.  They are all tantalum polymer capacitors so no bias effect will be seen.

I have your waveforms and the results by the customer are interesting.
I need to investigate this on our end to try and replicate the results.
I will reply back within 2 business days with an update.
If we have components in our lab, I should have some test data collected.
If not, it will take up to 5 business days for shipping to send the components to our lab, then another 1-2 business days to collect the data.

Thanks,

- Stephen

 Hi Stephen,

 Thank you very much for your reply and your cooperation.

 I see.

 I'm looking forward to receive your experiment result.

 Thank you again and best regards,

 Kazuya.

Hi Kazuya,

I have provided some feedback through a private message.
Please review and reply when you can.

Thanks,

- Stephen

 Hi Stephen,

 Thank you for your reply.

 I replied you through a private message.

 Could you please check it?

 Thank you again and best regards,

 Kazuya.