LM21215+LM10011 for TMS320C6678 SmartReflex power supply

Philly

Other Parts Discussed in Thread: LM10011, LM21215A, LM21215

Hi,

I used the LM21215A as the Buck with LM10011　as the programmable VID control device to be the power source of C6678 CVDD(SmartReflex) on my board . Our schematic shows bellow:

Here comes the problem : when the three beads (FB1~FB3) aren’t connected , the output is 1.03v。Then ,I connected them, I mean the C6678 becomes the real load , the output voltage drop to 0.92V, which can reluctantly make the C6678 finish the system reset, then we can link the board using XDS560 emulator, but when I try to load the test program to c6678 ,the CVDD dropped to 0.7V fiercely, which makes C6678 can’t work any more, because the CVDD power doesn’t meet the requirement 0.9V to 1.1V. I don’t know how it comes. Is there any problem with our schematic or the scheme LM21215+LM10011 isn’t able to carry the load C6678?

Best Regards,

Philly

over 11 years ago

0 Timothy Hegarty over 11 years ago

TI__Guru 73502 points

Hi Philly,

It's somewhat difficult to read the schematic - can you send to me as a pdf? Perhaps the ferrite beads are affecting the loop stability. Can you take a scope plot of the SW node voltage?

The LM21215 quickstart calculator is available in the product folder to assist in choosing compenastion components (the LM10011 does not affect this). Also, note that there is an e2e blog on this topic - please search for my name in PowerHouse blogs and it should appear.

Regards,

Tim

0 Philly over 11 years ago in reply to Timothy Hegarty

Intellectual 310 points

Hi Tim,

Thank you. Firstly, it's not the beads' problem,since I used three power resistors instead. Still , the situation didn't change at all. and I found the neither the power resistor nor the inductance L1 generate some heat, that means there wasn't a large output current passed through them, so ,there were not any voltage drop over the three power resistors and the inductance. Then, you should know ,the SW node voltage is 1.03V before the FB1 to FB3 connected, then it was 0.92v when connected.

one more a detail: the C6678_CVDD is connected to C6678 pin pad straightly, that says there are not any other power consumption components in the link。

Finally, could you please send me the blog web link you told me before , Because I try ,but I couldn't find it. Thanks.

Best Regards,

Philly.7624.CVDD_Schematic.pdf

0 Timothy Hegarty over 11 years ago in reply to Philly

TI__Guru 73502 points

http://e2e.ti.com/blogs_/b/powerhouse/archive/2013/10/03/how-to-optimize-your-dsp-power-budget.aspx

0 Timothy Hegarty over 11 years ago in reply to Timothy Hegarty

TI__Guru 73502 points

Please ensure that the EN pin of the LM10011 is tied high. Also, is the LM21215 regulator functioning correctly when the LM10011 is not installed?

0 Philly over 11 years ago in reply to Timothy Hegarty

Intellectual 310 points

From the LM10011datasheet, We read that the EN pin is pulled high by internal source .

Like you said , LM21215 may not work correctly .Because when I removed the LM10011 chip from my board, the situation didn't change. If the LM21215 didn't function correctly,what caused this problem ? The chip is broken? or there are some other reasons.

Thanks.

0 Timothy Hegarty over 11 years ago in reply to Philly

TI__Guru 73502 points

Hi Philly - did you use the LM21215 quickstart tool to verify the stability of your design? If so, please forward. Also, can you send a scope shot of the SW node waveform? Finally, I would like to review your PCB layout. Note that if a SYNC signal isn't applied, the default switching frequency should be 500kHz.

Regards,

Tim

0 Philly over 11 years ago in reply to Timothy Hegarty

Intellectual 310 points

Hi Tim,

It has been a long time .I just want to tell you that my board works correctly recently .It's nothing about the PCB layout as well as the stability issue. Because , when I changed another LM21215 to my board, the problem didn't exist any more.

0 Timothy Hegarty over 11 years ago in reply to Philly

TI__Guru 73502 points

Glad to know it's working now. I hope you liked the blog post and associated article discussing the LM21215 and LM10011.

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LM21215+LM10011 for TMS320C6678 SmartReflex power supply