AM3352: RTC implementation

Manjunath B

Part Number: AM3352

Hi,

We are using AM3352BZCZA100 processor with TPS65217CRSLT PMIC.We want to implement RTC using battery backup from CR2032 coin cell.The output of the battery is connected directly to the VDDS_RTC(D7) pin of AM3352 processor.

1) Can this only battery power(1.8V) to VDDS_RTC pin is enough to run processor in RTC only mode and enable internal RTC ?

2) Is there any delay during swtching off processor from normal operation mode to RTC only mode ie, Main power switched off and only battery backup of 1.8V is provided to VDDS_RTC(D7) pin of AM3352 processor ?

3) In case any delay is there, that delay time also required to be taken into account for calculating current time using RTC ?

Thanks & regards

Manjunath.B

over 7 years ago

0 Biser Gatchev-XID over 7 years ago

TI__Guru**** 393215 points

Hi,

Manjunath B said:
The output of the battery is connected directly to the VDDS_RTC(D7) pin of AM3352 processor.

This is absolutely forbidden and a violation of device specifications. VDDS_RTC must be a regulated 1.8V power supply.

0 Manjunath B over 7 years ago in reply to Biser Gatchev-XID

Intellectual 360 points

Hi,

Thanks for the reply.

OK then in absence of main power, 32.768KHz clock input is only enough for RTC implementation ?

Thanks & Regards,

Manjunath.B

0 Biser Gatchev-XID over 7 years ago in reply to Manjunath B

TI__Guru**** 393215 points

This is called RTC-only mode. It is described in detail in sections 8.1.4.3.5 and 20.3.3.8 of the AM335x TRM Rev. P. The VDDS_RTC supply must be present for the RTC timer to function.

0 Manjunath B over 7 years ago in reply to Biser Gatchev-XID

Intellectual 360 points

Hi sir,

Thanks for the reply.

As per the above suggestions, We changed connections.

Battery backup now has been connected BAT1,BAT2 and BAT_SENSE pins of TPS65217C PMIC.

i) In datasheet of TPS65217C PMIC it has been mentioned to use rechargeable battery.Is it necessary to use rechargeable battery only or CR2032 Lithium 3V Coin cell is enough ?

ii) During RTC only mode, Internal 32.768KHz crystal will be enabled.So need of providing external 32.768KHz clock input.But during ACTIVE mode is it necessary to provide external 32.768KHz clock ?

Thanks & Regards,

Manjunath.B

0 Biser Gatchev-XID over 7 years ago in reply to Manjunath B

TI__Guru**** 393215 points

1. TPS65217C has a battery charger. Connecting a coin cell to these pins may cause the battery to explode.
2. If you want the RTC to work continuously you must have a 32.768kHz crystal connected on OSC1 pins.

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AM3352: RTC implementation