AM335x RTC feature disabled pin config

shriram

Other Parts Discussed in Thread: AM3359

Hallo,

We are developing our custom board based on AM3359 and starter kit schematics. Due to the errata + current consumption restrictions of the internal RTC in AM335x, we would like to disable it and use the RTC in the power management IC.

After reading the forums and the schematic checklist wiki, I am a little confused about the proper pin configuration for this particular mode. Especially regarding PWRONRSTn and External LDO for VDDS_RTC.

I have listed the configuration as per my understanding and would be very thankful if someone could confirm the following pin configuration for the RTC disabled mode.

Pin	RTC feature disabled Configuration
VDDS_RTC	external LDO
CAP_VDD_RTC	VDD_CORE
RTC_KALDO_ENn	VDDS_RTC
RTC_PWRONRSTn	VSS
PMIC_POWER_EN	No Connect
EXT_WAKEUP	VSS
XTAL Pins	No Connect

Thanks a lot in advance.

Ram

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Shriram,

One comment only: VDDS_RTC can be connected to any 1.8V processor power supply, it doesn't have to be a specific LDO.

0 GeoD over 12 years ago

Intellectual 325 points

Hello ,

If not using the RTC functionality at all AND still want to use the internal RTC LDO for the CAP_VDD_RTC pin (i prefer not to use an external 1.1V LDO) where I should connect the RTC_KALDO_ENn PIN? will this need to be to ground then so the internal LDO is enabled?

what about the other pins in this case?

Thanks.

0 Biser Gatchev-XID over 12 years ago in reply to GeoD

TI__Guru**** 393215 points

The possible combinations are described here: http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#RTC

0 GeoD over 12 years ago in reply to Biser Gatchev-XID

Intellectual 325 points

Hello,

If I look this table only then:

It shows also that 'RTC_KALDO_ENn' connects to ' VDDS_RTC '(high). But if the 'RTC_KALDO_ENn' is high does this not mean the internal LDO is disabled?

If I want the internal LDO to be enabled when not using the RTC should I not connect this pin to VSS then and not to the VDDS_RTC? I am sorry but it is not clear to me from this table all the possible combinations.

Thanks.

0 Biser Gatchev-XID over 12 years ago in reply to GeoD

TI__Guru**** 393215 points

From the AM335X Datasheet, Rev.F, page 102: "The CAP_VDD_RTC terminal operates as an input to the RTC core voltage domain when the internal RTC LDO is disabled by connecting the RTC_KALDO_ENn terminal to VDDS_RTC. If the internal RTC LDO is disabled, CAP_VDD_RTC should be sourced from an external 1.1-V power supply."

If you want the internal RTC LDO to be enabled, then you must connect RTC_KALDO_ENn to ground (through a 10kOhm pulldown resistor), you have to connect 1uF capacitor to CAP_VDD_RTC and you must supply VDDS_RTC from 1.8V power supply.

0 Daisuke Maeda over 10 years ago in reply to Biser Gatchev-XID

Guru 20205 points

Hi Biser,

I understand that the internal RTC LDO can be used regardless of the use situation of RTC. Why do the possible combinations in wiki not describe that? What advantage does it have to be supplied from an external power supply without using internal RTC LDO?

Best regards,

Daisuke

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AM335x RTC feature disabled pin config