LM5116: LM5116 PMIC failure

Mutum Meenakshi

Part Number: LM5116
Other Parts Discussed in Thread: LM76003, CSD19538Q3A

We have used LM5116 PMIC to output 14.4V/3A from max input of 60V in our product design.

PMIC is repeatedly failing with failure mode of output 0V. When debugged Pins HB, HO,SW Impedance always found to be low [some cases shorted to GND potential].

What could be the possible reason?

SCH attached for reference

over 4 years ago

0 Timothy Hegarty over 4 years ago

TI__Guru 73152 points

Hi Mutum,

What's the voltage feeding the VCCX pin? If it's only 5V, then that is likely not enough gate drive for the FETs. I can't read the FET part number, but check the Miller plateau voltage from the flat part of the Qg vs. Vgs curve in the FET datasheet. Typically it's 4-5V for 100V FETs, meaning > 7.5V gate drive is required. Please test with VCCX tied to GND (use the internal VCC regulator).

Also, take a look at app note snva803 for power stage layout recommendations. The ceramic input caps must be very close to the FETs.

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

We are using internal Vccx i.e Vccx pin is tied to GND potential [cap position with 0R in SCH] in our design.

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

Mutum,

Can you check the FET is compatible with the gate drive amplitude from the LM5116. Or send the FET part number.

Regards,

Tim

0 Timothy Hegarty over 4 years ago in reply to Timothy Hegarty

TI__Guru 73152 points

Also, please complete the LM5116 quickstart calculator so we can review component selection. What's the ESR of the output electrolytic? What's the loop crossover frequency? Have you got waveforms to show the behavior?

Note that the LM76003 60V/3.5A converter (with integrated FETs) provides a smaller/easier solution here.

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

Please find the below details,

MOSFET MPN -SUD80460E-GE3

Output caps [in parallel]- 1 56uF electrolytic with ESR 30mohm & 4 10uF ceramic X7R caps

The failure is becoming a bottleneck in design and the product is in market and changing the solution is not feasible at this stage.

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

Hi Mutum,

The FET is a DPAK with large area and somewhat high parasitic inductance. 150V rating for a 60V input is unnecessary. Check that the ceramic input capacitor is located very close to both FETs (to keep the switching loop area tight and the loop inductance as low as possible).

Please forward the completed quickstart calculator so we can verify compensation. Also, please send the layout and switching waveforms for review.

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

Please find the attachment - quickstart calculator for LM5116LM5116_quickstart_shared.xlsx

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

Mutum,

Just looking at the quickstart, the SS cap at 10nF is a bit low (very fast soft-start time, so it may engage current limit while charging the output cap).

Here are some items to check:

SW voltage waveform stable during steady state full-load with no evidence of excessive ringing, shoot-through, etc.
Load transient response
Inductor sat current rating

We need more detail on how the failure is occurring (waveforms, etc.). Also, I recommend changing the FETs to 100V devices, e.g. CSD19538Q3A high side and CSD19537Q3A for the low-side FET. Take a look at app note snva803 for layout guidance.

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

Hi Tim,

We have checked the points listed earlier during design and found to be ok. Max load is 0.5A for the PMIC however its design for higher load. Isat of the inductor used is 9A.

We have tried to simulate failure on bench-setup but failure has not occurred.

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

If you need further assistance, send on the layout for review. App note snva803 has details on placement of power stage component (FETs and input caps).

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

please find the layout attached in 3D view

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

Hi Mutum,

Please ensure that the VCC and BOOT caps are placed close to their respective pins. Also, the gate drive traces should be 20-25 mils wide with HO and SW routed as a dfif pair. Send on the power stage for review.

Regards,

Tim

0 Mutum Meenakshi over 4 years ago in reply to Timothy Hegarty

Prodigy 120 points

Hi,

Please share your email Id, will send Gerber over mail.

0 Timothy Hegarty over 4 years ago in reply to Mutum Meenakshi

TI__Guru 73152 points

tim dot hegarty at ti dot com

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LM5116: LM5116 PMIC failure