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TPS65910 32kHz source fallback

Sam Parkinson
Prodigy 85 points
Other Parts Discussed in Thread: TPS65910, AM3354

Hi All,

We are currently working on a design integrating the TPS65910 with an AM3354 processor. This will be coupled with DDR3 RAM.

The TPS65910 must be configured to use BOOT1 = 0 / BOOT0 = 1. Otherwise the initial start-up voltage of VDD2_REG will cause fire :)

What this means is that the CK32K_CTRL Bit in the DEV_CTRL register will be configured to use an external crystal (or 32k square wave).

Section 6.4 of the users manual

"Switching from the 32-kHz crystal oscillator or external square-wave clock to the RC oscillator is not supported."

Questions:

1. If an external crystal is not available will the TPS65910 revert to using its internal oscillator?

2. If it does revert to the internal oscillator does it change the state of the CK32K_CTRL bit?

3. I'm assuming that the quoted paragraph above refers to switching while maintaining product operation? Can the register be changed and the product power cycled to change source? What is the behaviour when the register is changed? Does the TPS6910 crash?

Cheers, Sam

  • 0
    TI__Genius 10885 points
    Hi Sam,

    1) Yes. The TPS65910 initially starts with the internal oscillator, so if the external source is not present it can still operate.
    2) I would not suspect so, but I don't have proof. This could be an interesting test.
    3) Yes, this refers to while operating. No, the register will reset to it's default after power cycling. The device has the potential to fail, but depending on when the bit is switched and how the device is being used there may be no noticeable effect other than a measurable change on the clock output.

    Which TPS65910 device are you using? How will the initial VDD2 voltage damage your system?
  • 0 in reply to Richard Solarski
    Prodigy 85 points
    Thanks Richard,

    1) Perfect, thanks
    2) I can try it once we get some hardware up and running
    3) I assumed that since this register was an eeprom setting it would persist across power cycling:
    "CK32K_CTRL Internal 32-kHz clock source control bit (EEPROM bit)"
    Possibly another option I can look into and report back.

    As for the TPS65910 I had incorrectly relied on the default datasheet (SWCS046U) which while mentioning the A3 part only shows two possible boot modes, what I will be using in practice is the A3 part which wont have the issues mentioned above.