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TPS65910 Max Load During Sleep

Brad Griffis
Guru*** 125430 points
Other Parts Discussed in Thread: TPS65910A

For AM335x with TPS65910A, the app note SWCU093C "TPS65910Ax User's Guide For AM335x Processors" makes the following statement:

  • in SLEEP state the LDO voltage is maintained but transient and load capability are reduced

Can this be quantified?  In particular, I want to make sure that the startup current consumption of the AM335x does not temporarily exceed this current before we can set the GPIO pin back high to get back to normal operation.

  • 0
    TI__Genius 10885 points

    Hi Brad,

    Rated output currents for the LDOs in sleep mode are listed in the datasheet as "Low-Power Mode".

    http://www.ti.com/product/TPS65910/datasheet/specifications#SWCS046356

    If a particular current is too low for your application, you can force an LDO to stay in Full-Power mode during sleep through the SLEEP_KEEP_LDO_ON_REG register.

  • 0 in reply to Richard Solarski
    TI__Guru*** 125430 points
    I see that for all the LDOs. On quick glance, it looks like they all have a 1mA rating in low power mode. What about the SMPS's?
  • 0 in reply to Brad Griffis
    TI__Genius 10885 points
    The SMPS do not set a current limit like the LDOs do in low power mode, instead they can operate in pulse-skipping mode, which will adapt to the current demands from the load but will not necessarily provide a constant PWM switching output.
  • 0 in reply to Richard Solarski
    TI__Guru*** 125430 points
    I had some further discussion on the phone with Rick (thanks!) and he provided some additional interesting points that I wanted to share:

    Quick summary:
    • By default, the SLEEP signal does nothing. You need to set DEVCTRL_REG[1] DEV_SLP to 1 in order to “activate” the signal.
    • By default, the SLEEP signal is active low. However, it is configurable through DEVCTRL2_REG[3] SLEEPSIG_POL.
    • So if you have activated the SLEEP signal, the transition between PFM and PWM mode is controlled by the SLEEP signal.
    • The approximate contribution of each rail to the overall power savings can be found by looking at the “ground current” for each rail. This is the quiescent current for the rail for each mode of operation.

    So it looks like we save approximately 7.5mA on each of SMPS1 and SMPS2 by going from PWM mode to PFM mode. It looks like you save 1-2 mA on each LDO when going to low power mode.