TPS65400 overshoot problem

Mitja Gustin

Other Parts Discussed in Thread: TPS65400

Hi,

We observed a strange behavior of the TPS65400 DC/DC (full code: TPS65400RGZT) on some outputs.

At the power-up of the device, the output present a high and long (about 1ms) overshoot ( of 12V) instead of the set 5V:

Here it is the zoom of the overshoot:

Do you have any idea how to fix the problem?

Regards.

over 9 years ago

0 Eric Guo1 over 9 years ago

TI__Intellectual 2590 points

I can't see this issue before, could you please give me an waveforms which including SW, VIN, VOUT? Vout connect to 44uF big cap, should not increase and decrease the voltage so quickly.

thanks!

0 Mitja Gustin over 9 years ago in reply to Eric Guo1

Prodigy 60 points

I agree the output Capacitor should not increase and decrease the voltage quickly, so it seems that the DC/DC is driving the overshoot.

Here there are some additional data.

This is the overshoot problem on another board:

The Vin is stable on 12V.

The behavior of the SW (red) and Vout (green) is the following:

Zooming on the overshoot we have the following situation:

Do you have any suggestion?

0 Eric Guo1 over 9 years ago in reply to Mitja Gustin

TI__Intellectual 2590 points

Would you please hlep provide the SCH to me? have you change any internal set up using PMbus?
thanks!

0 Mitja Gustin over 9 years ago in reply to Eric Guo1

Prodigy 60 points

Here it is:

0 Mitja Gustin over 9 years ago in reply to Mitja Gustin

Prodigy 60 points

This is the FDB network:

0 Eric Guo1 over 9 years ago in reply to Mitja Gustin

TI__Intellectual 2590 points

how many channel have the overshoot problem? Don't find any obviously problem in the schematics. COMP pin connects to VDDA directly without resistor if you use crrent sharing mode. One more questins, why customer need so long SS time?
thanks!

0 Mitja Gustin over 9 years ago in reply to Eric Guo1

Prodigy 60 points

We find that connecting the COMP pin to VDDa without resistors helps, but in your datasheet it is indicated that a 4-kΩ resistor is needed:

The TPS65400 offers the ability to output rails of higher currents by connecting SW1 and SW2 in parallel, or by connecting SW3 and SW4 in parallel. To configure this option, the COMP2 or COMP4 terminal must be tied to VDDA through a 4-kΩ resistor.

One more thing: we are able to use some channels only in CCM mode. If we try to put the channel in the mixed CCM/DCM mode, the output is higher than expected (for example on the 5V output the output goes to 5.3V).
Do you have any additional suggestion?

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TPS65400 overshoot problem