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TPS6521855: Definitive use with AM64x?

Marcus Bainbridge
Prodigy 110 points
Part Number: TPS6521855
Other Parts Discussed in Thread: LP8733, TPS65218

Will there be a revised datasheet for the TPS6521855?  To say the current one (August 2021) is a bit of a mess is an understatement.

Firstly, the voltage outputs are confusing.  Is DCDC4 really 2.5V now?  Everywhere else in the datasheet, and in all the diagrams, it's still listed as 3.3V.

What is the default output of LDO1?  Is it 3.3V as stated on the front page, or 1.8V as hinted in the Electrical Characteristics and stated in the diagram in 7.2.

What is the default resistor required for DC34SEL?  If the device has been programmed for 1.8V and 2.5V, none of these are options in table 7.2.

What is the point of table 8-1?  This is a device-specific requirement for a different PMIC.   Please only use examples for the target part, namely the AM64x.

From the Appnote for the LP873364/TPS65218xx, where does the PGOOD from this device connect to?  (If it's no needed, don't include it?)

On the other linked Appnote (Powering the AM64x with the LP8733xx) PGOOD looks like it's connected to the EN signal of the same device!

Thanks for any clarifications!

  • +1
    TI__Mastermind 20076 points

    Hi Marcus,

    Thanks for reaching out. I'm sorry to hear the information in our datasheet has caused some confusion. We are here to help. Please find my feedback below and let me know if you need additional information:

    • DCDC4 output voltage is 2.5V. This applies specifically to TPS6521855. This information can be found in the front page of the datasheet as well as in the DCDC4 output voltage register (address 0x19 / bits 5:0). In some places of the datasheet it will appear as 3.3V because it was the setting used for some of the test conditions in the electrical characteristic tables, in the typical characteristic plots and in the application example. 

    Note under datasheet table Table 8-1. Design Parameters...

    Note under datasheet Figure 7-8. Typical Power-Up Sequence...

    • DCDC4 SEL: If you want to use the default pre-programmed output voltages on TPS6521855 (DCDC3= 1.8V and DCDC4=2.5V), then you can put a 0Ohm resistor to GND. This can also be found in the AM64x SK EVM schematic and I totally agree it should be more clear in our spec, specifically for the TPS6521855 version. 

    • LDO1 output voltage is 3.3V on TPS6521855. The output voltage register for LDO1 is in address 0x1B, bits: 5:0.

    Thanks,

    Brenda

  • 0 in reply to Brenda Diaz
    Prodigy 110 points

    Thanks for the clarification, Brenda!

    On a similar theme, the Technical Reference manual for the LP873364, Table 2-3 says that LDO0's default output voltage is 1.8V, yet the EVM lists it as 0.85V.  Which is correct?

  • 0 in reply to Marcus Bainbridge
    TI__Genius 11020 points

    Hello Marcus,

    Technical reference manual has the latest information for that particular OTP variant. EVMs are more generic for any orderable part number/OTP spin for this product family and you can use GUI to change the settings. 

    Which EVM exactly are you referring to?

    Thanks.

    Regards,

    Tomi Koskela

  • 0 in reply to Tomi Koskela
    Prodigy 110 points

    Sorry, my mistake.   I got confused by all of the different Appnotes and EVM schematics, all using similar but not quite identical parts.  I was looking at the block diagram of the AM64x_SKEVM, but that's using the -45 part that's been re-programmed to 0;85V.