TPS65400: TPS65400 recommended power up sequence

Jing-Ming Zhang

Part Number: TPS65400
Other Parts Discussed in Thread: TMS320F28P550SJ

Tool/software:

Hi Ti team

The following are questions that have not been answered before. Can you reply again?

We hope that during system startup or charging, no power is supplied to chips other than the TMS320F28P550SJ. When needed, the MCU should control the PMIC to supply power. To achieve this, we need an "always power" source for the MCU to maintain minimal operation even when the PMIC's SW is off. The TPS65400's VDDD might meet this need, but the datasheet doesn't clearly state if VDDD is suitable. If not, what other solutions would you recommend?

Currently, the idea is to use the SW output, possibly with a MOS to block power to other chips first. However, there are some issues. Could you help answer the following questions?

Is the VDDD of the TPS65400 suitable as the always power for the TMS320F28P550SJ? If not feasible, what other solutions would you suggest?
As shown in the schematic, to confirm the SW compensation configuration settings, if Rload is about 30 ohms, Fsw = 500 kHz, Vout = 12 V, is it feasible to choose Rs = 200 kohm, Cc = 7.5 nF, Croll = 1.5 pF?
When using WEBENCH@POWER DESIGN to configure the TPS65400 EVM, we want to set Vout1 to 12 V, but it shows "Design update failed - calculated duty cycle exceeds limits." How can this be resolved?

Best regards,

Johnny

4 months ago

0 Himanshu Nigudkar 4 months ago

TI__Intellectual 1850 points

Hi Johnny,

I couldn't find any schematic attached. Also I think you are referring to some old e2e thread. Please help us with the link to understand the background.

Regards,

Himanshu

0 Jing-Ming Zhang 4 months ago in reply to Himanshu Nigudkar

Prodigy 80 points

Hi Himanshu,

Here is the link to the previous E2E question for your reference,thsnks,

0 Himanshu Nigudkar 4 months ago in reply to Jing-Ming Zhang

TI__Intellectual 1850 points

Hi Johnny,

1. The typical output voltage of VDDD is 3.2V, it should be good use to power up the MCU, however you might need to check the current that MCU would draw and if VDDD can support that.

2. You can refer to table 8.3 in the datasheet to verify the values.

3. I dont see this part on webench. Not sure what error you are getting.

Regards,

Himanshu

0 Jing-Ming Zhang 4 months ago in reply to Himanshu Nigudkar

Prodigy 80 points

Hi Himanshu,

Himanshu Nigudkar said:
I dont see this part on webench. Not sure what error you are getting.

Below are some previous questions for your reference,

Currently, on the customer's schematic, PP3V3_S4 is supposed to be used as power supply for MCU, but there is an error with the net label, it should be PP3V3_S2 instead.

They intended to use VDDD as power supply for MCU, but this is not recommended since the maximum output current of VDDD is only 30mA. Therefore, one feasible approach is to implement a switching sequence similar to what is described in Figure 9-13 of the datasheet.

Here's how it works: EN_SW2 is pulled high via a pull-up resistor to VDDD, and after VDDD reaches stable, PP3V3_S2 can be used as power supply for MCU. Meanwhile, EN_SW1, 3, and 4 are pulled low via pull-down resistors to GND and controlled by the MCU.

Thanks so much for your reply,

Best regards,

Johnny

0 Himanshu Nigudkar 4 months ago in reply to Jing-Ming Zhang

TI__Intellectual 1850 points

Hi Johnny,

Yes the daisy chaining should work. However you would need to ensure that CE is pulled high to activate VDDD.

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TPS65400: TPS65400 recommended power up sequence