TPS40170: TPS40170 start up issue

Siva Rama Krishna Yerkareddy

Part Number: TPS40170

Hi I am using TPS40170 regulator to convert 16V to 32 V range input to 3.3V output,4A circuit. with the initial design some boards are functional at all input ranges ,but some boards are not functional at 16V at room temperature and -40C.

I'm using 10nf soft start capacitor and when I changed Css to 47nf all boards are functional at all cases . With 10nf soft start capacitor I have seen a weird behavior with this supply, at 16V module will not turn on , but it is functional at 8V and 24V at all temperature ranges.

over 5 years ago

0 Timothy Hegarty over 5 years ago

TI__Mastermind 49732 points

Hi Siva,

Can you share the schematic and layout?

Regards,
Tim

0 Siva Rama Krishna Yerkareddy over 5 years ago in reply to Timothy Hegarty

Prodigy 70 points

Hi Tim,

I have attached schematic and layout files for your referencedb336991.pcb_1.pdf .Thanks

Siva

0 Timothy Hegarty over 5 years ago in reply to Siva Rama Krishna Yerkareddy

TI__Mastermind 49732 points

Hi Siva,

The faster ramp time of the output voltage implies that the output capacitors require more current to charge to the output voltage setpoint. As a result, it appears that the current limit is engaging during the fast ramp interval.

In terms of the layout, one recommendation is to reduce the area of the SW node copper pour as this results in e-field coupling and increased high-frequency EMI.

Regards,
Tim

0 Timothy Hegarty over 5 years ago in reply to Timothy Hegarty

TI__Mastermind 49732 points

Siva,

Noting the 10k resistor on LDRV to ground - changing that to open circuit or 20k selects a higher threshold for high-side SCP detection. This might help it start if hiccup is occurring during start-up. The VIN pin filter might also cause SCP detect issues.

If the problem isn’t SCP or OCP, it could be board layout / noise.

Also, the 1nF on the low-side gate increases the total gate drive loss - it is only required if Cdv/dt shoot-through is an issue.

Regards,
Tim

0 Siva Rama Krishna Yerkareddy over 5 years ago in reply to Timothy Hegarty

Prodigy 70 points

Thanks Tim,

I modified the board with 20K resistor on LDRV to ground, working at 16V @ room temperature , but it is not functional at -40C.

When ever module is not turning ON, We observed 7 pulses on SW pin and it shuts off, means it's problem with OCP or SCP.

Thanks

Siva

0 Timothy Hegarty over 5 years ago in reply to Siva Rama Krishna Yerkareddy

TI__Mastermind 49732 points

Siva,

Try increasing the soft-start cap. Also, the RC filter to the VIN pin may have an affect here.

Regards,
Tim

0 Timothy Hegarty over 5 years ago in reply to Timothy Hegarty

TI__Mastermind 49732 points

Hi Siva,

If there's no further activity, you can click on Resolved to close this thread.

Regards,
Tim

0 Siva Rama Krishna Yerkareddy over 5 years ago in reply to Timothy Hegarty

Prodigy 70 points

Hi Tim,

I apologize for my delayed response . I have changed the soft start capacitor to 47nF from 10nf on more than 100 modules and tested at all the cases. Still three modules are failing at room temperature and at cold temperature at 16V , unable to turn on this module.

Thanks

Siva

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TPS40170: TPS40170 start up issue