TPS65218: Issue with DCDC4 startup

Aleksey Derstuganov

Prodigy 40 points

Part Number: TPS65218

Good day,

We faced with the floating problem that sometimes DCDC4 can't start after power up. Our startup sequence:

1) DCDC6 - Ok,

2) DCDC5 - Ok,

3) LDO1 - Ok,

4) DCDC3 - Ok,

5) DCDC4 - Fail. Restart after 500ms. Go to the step 1)

After that we decided to place 200pF ceramic capacitor between GND and L4A (pin 13). Now it work wonderfull.

Can you explain what the problem is? Can we use this solution (200pF capacitor) at mass production? Can you provide any other solution?

P.S.

Link to the schematic files: www.dropbox.com/.../schematic.7z

over 6 years ago

0 Gordon Varney over 6 years ago

TI__Expert 8840 points

Aleksey,
I have not seen this before. I am passing your question to our specialist to see if he has any ideas.

Thank you for using E2E.

0 Aleksey Derstuganov over 6 years ago in reply to Gordon Varney

Prodigy 40 points

Dear Gordon, than you, we will wait with impatience.
Some additions, at another forum branch we found alike problem (which was not solved):
e2e.ti.com/.../2187210
and TI Employee Paul Kundmueller offers the following:
"...could try placing either the schottky diode or capacitor from GND to L4A?..."
But this capacitor (or diode) not situated on the TI Schematic sample. Because of this we are not sure that this solution perfect.

0 Aleksey Derstuganov over 6 years ago in reply to Aleksey Derstuganov

Prodigy 40 points

Gordon, can you provide internal schematic of the DCDC4? We will try to solve this problem ourselves. There is no time to expect more.

0 Nick Jakse49 over 6 years ago

TI__Expert 4155 points

Aleksey,

Sorry for the late reply.

This is an issue caused by a large inrush current on DCDC4. Our recommended work around is to either place a shottky diode or a 100pf-300pF capacitor from ground to the L4A pin. A better ground connection to the DCDC4 output cap with multiple vias connecting to the powerpad, and putting the output cap close to the PMIC on the same side of the board can also help.

Currently this is the best work around we have. We should have a new silicon revision sometime next year that fixes this issue as well so depending on when this is going into production it could be a temporary fix, or if needed a more permanent one.

Thank you,
Nick

0 Aleksey Derstuganov over 6 years ago in reply to Nick Jakse49

Prodigy 40 points

Nick,
thanks a lot

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TPS65218: Issue with DCDC4 startup