c5535 LDO not powering up - powering CVDDRTC

gkuzmiszyn

Already it is known, that internal LDOs will not start, if there is no power at CVDDRTC pins during powerup.

We do not use internal RTC (RTC_XO=GND, RTC_XI=cvddrtc). Where I can found information what is maximum current draw from CVDDRTC pins in such application (required to enable internal LDO)?

in application note there is additional LDO to power CVDDRTC pins, but...

I am interested if simple resistive voltage divider will be adequate solution to power CVDDRTC pins and if all 3 LDO runs at power up then.

For example:

Kind Regards,

over 12 years ago

0 Mark M over 12 years ago

TI__Mastermind 30120 points

Hello,

A resistor divider is a viable solution - CVDDRTC sources less than ~20uA of current even when RTC is used.

You can refer to the power estimation tool:
Estimating Power Consumption on the TMS320C5504/05/14/15/32/33/34/35 DSPs

DSP_LDO and ANA_LDO will turn on at power up, but USB_LDO is software controlled - it turns on when the bootloader attempts a USB boot or when your program

When RTC is disabled, you cannot access RTC registers. This includes the RTC Power Management Register which provides control to the on-chip LDOs and WAKEUP and RTC_CLKOUT pins.

Hope this helps,
Mark

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c5535 LDO not powering up - powering CVDDRTC