TPS650864: Kindly Review the Schematic of TPS650864 for 0.72V core voltage generation of WEBENCH

TI, I am Waiting for a response

Kindly have a look

Hi Shyam

    To help with the schematic review, can you please update the schematic for TPS544B25 with the voltage rating of capacitors? 

Regards,

Gerold

Gerold Dhanabalan - Online Design Tools said:

Hi Shyam

    To help with the schematic review, can you please update the schematic for TPS544B25 with the voltage rating of capacitors? 

Regards,

Gerold

The Generated Schematic from WEBENCH is as it is followed, the attachment of WEBENCH design contains voltage ratings MPN everything

Waiting for response

Thanks

Hi Shyam

  Here is some feedback.

1. Looks like you are not using PMBUS to set the outpt voltage. This means that you will have to use the feedback divider network to appropriately set Vout without which you will not have output voltage set to 0.72V. 

2. add an extra 100nf of cap on bp6 (with appropriate voltage rating) for high frequency noise filtering.

3. The 47uF capacitor at the output should be X5R or X7R or better. It should not be X6S.

4. the boot resistor value of 100mohm value could be larger. You can leave it as a place holder for now.

5. Some of the resistor recommended by WEBENCH are 0201. If that is too small for your flow, please use 0402 instead of 0201.

This is a PMBUS device and you dont seem to be using the functionality. Any specific reason you have chosen this device?

Regards,

Gerold

1. True I am not using any PMBUS, i rely on feedback divider CKT for generating 0.72V, isnt the CKT attached following it ?, if not kindly help in choosing the necessary feedback divider

2. Noted and SCH modified accordingly

3. Noted will take care

4. How much larger ? 1 Ohm ? or 10Ohm kindly suggest, so that i can carry a backup

5. Noted, i shall stick to 0402 Only

6. I have no special reason to choose this device, it is as per suggestion in section 6.3 of 

Thanks

Will be waiting for your reply, i have to launch my design this week

Hi Shyam,

    Its a little tricky to get this device to boot to 0.72V without using PMBUS. Can you please send me your detailed requirements? We will recommend the right product.

Vinmin, Vinmax, Vout, Ioutmax

Vout accuracy requirements, Load transient requirements

Any specific feature needed (e.g. SYNC pin etc.)

1. The references of TI mostly suggest in using B/C variant of TPS544x25, and the literature no where mentions that PM bus is must  example1 , example2

Kindly explain this first.

2. i need a exact replacement of device TPS544x25 as it adheres to characteristics required

3. Yet if 1,2 are not explainable here are the parameters

Vinmin=10v, Vinmax=14v these would come from a 28V to 12V converter DCDC,

Vout =0.72v,Accuracy is a key parameter which is +/- 0.02v in other words Max ripple 2%

Ioutmax = 20A, Iout nominal 12A, i could not find the transient conditions from xilinx literature but one of the TI reference is speaking on it (Info on Transient Load )

4. Importantly i want to tie the LDO3P3 of PMIC to Enable of 0.72v dcdc so that it boots first , so a Enable pin is must , for sequencing i need  PGOOD pin from 0.72v dcdc

Kindly re look in to my choice of using TPS544x25, as its suggested by many TI documentations and development boards

Hi Shyam,

  If you download the schematics file, you can find the PMBUS connector to program the device using a separate USB-2-GPIO hardware.

http://www.ti.com/tool/PMP12004-HE?keyMatch=PMP12004&tisearch=Search-EN-everything&usecase=part-number

The issue is because of Vout of 0.72V because the minimum reference on the device is 0.8V without using PMBUS. With PMBUS I can achieve  low as 0.5V.

Our recommendation for a device without PMBUS would be the TPS543B20 that can help you meet your requirements.

Please let us know if you have more questions.

Regards,

Gerold

Hi Shyam,

     The TPS56221 does not have remote sense. For these high currents and given the accuracy requirements, it might be good to have remote sense.

Here is another design using the TPS548B22.  I tried to optimize the WEBENCH design to meet your transient requirements. This capability will be released for this device on the tool in a couple of weeks. In the meantime I tried to optimize it using an internal version of the tool.

You can scroll to the operating values section of the pdf and see that the Vout ripple, Vout over/undershoot are well within the specs.

You can add a couple of place holders in the schematic for some caps such as 2x47uF, 2x1uF caps as well to minimize any noise peaks due to resonance.

Regards,

Gerold

WBDesign10752.pdf

Here is the Full Schematic of my updated design using TPS548B22 and PMIC, kindly review for Power Good and Wakeup of tps548b22

One thing i feel is, it kills plenty of space, is there a way i can reduce ? over all area shown by tool is around 800mm2

Waiting for response for updated design upload,

Kindly respond

Thanks very much for your detailed review

I have done all modifications suggested, please find the attachment and give final comments

my only doubt is, the datasheet says a 1uF cap between AGND and VDD is enough, the reference board has caps with reference to DRND

please resolve the confusion

Hope i can go to fabrication with the above Final Schematic

i used 220E for R1,R2 and C291 to 22uF, VOSNS to ouput, RSN to GND as suggested

Kindly confirm

Hi Shyam,

    The snubber capacitor is C286 and should be connected to PGND and NOT the RSP pin.

You dont need R425 and R424.

22uF for C291 looks pretty high - did you calculate using the formula that was given?

regards,

Gerold

I shall change the snubber accordinly,

From the formula given above,  making R1,R2 as same that is 220E will result a Capacitance of 22uF at 2-5Mhz frequency

now you are saying R1,R2 from above formula are not required

Kindly explain