AM3352 RTC configuration question clarify

JIANDE WU1

Prodigy 180 points

Other Parts Discussed in Thread: AM3352, TPS65910A

There are three conditions to set AM3352 RTC features.

1. RTC-only mode

2. Using RTC feature but without RTC-only mode support

3. RTC features disable

Does it mean AM3352 internal RTC LDO is actived for souring on chip 32.768KHz and can use it for RTC-only

power saving mode and all RTC functions at condition 1?

At condition 3, internal RTC LDO logic is disabled totally and on chip 32.768KHz lose its function.

RTC function is totally disabled.

At condition 2, internal RTC LDO logic is disabled partially and on chip 32.768KHz lose its function,also.

If we want to use RTC function,we should add an external 32.768KHz for supporting this features.

right?

over 11 years ago

0 Biser Gatchev-XID over 11 years ago

TI__Guru**** 393215 points

JIANDE WU1 said:
At condition 2, internal RTC LDO logic is disabled partially and on chip 32.768KHz lose its function,also. If we want to use RTC function,we should add an external 32.768KHz for supporting this features. right?

No, this means that RTC will be functional as long as 1.8V is provided on VDDS_RTC. See this wiki for details: http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#RTC

0 Biser Gatchev-XID over 11 years ago in reply to Biser Gatchev-XID

TI__Guru**** 393215 points

On your first question, the AM335X RTC starts on the internal RC oscillator by default. However be aware that this is quite inaccurate. RTC clock can also be provided by external 32.768kHz external crystal, external 32.768kHz oscillator (1.8V level), or the Peripheral PLL (which can generate the 32.768kHz clock from the main system clock).

0 JIANDE WU1 over 11 years ago in reply to Biser Gatchev-XID

Prodigy 180 points

Are mentioned condition 1 & condition 3 correct ?

About condition 2, internal RTC LDO is disable also?

As long as 1.8V is porivded on VDDS_RTC,on chip 32.728KHz is functional in condition 2,also ?

We can connect external 32.768 KHz and disable onchip 32.768KHz for better current consumption and accuracy in condition2 ?

0 Biser Gatchev-XID over 11 years ago in reply to JIANDE WU1

TI__Guru**** 393215 points

Are mentioned condition 1 & condition 3 correct ? Yes

About condition 2, internal RTC LDO is disable also? No

As long as 1.8V is porivded on VDDS_RTC,on chip 32.728KHz is functional in condition 2,also ? Yes

We can connect external 32.768 KHz and disable onchip 32.768KHz for better current consumption and accuracy in condition2 ? Yes

0 JIANDE WU1 over 11 years ago in reply to Biser Gatchev-XID

Prodigy 180 points

On condition 2, if we also want to use PMIC_POWER_EN as PMIC power enable signaling, how can we set to correspondent RTC portion?

0 Biser Gatchev-XID over 11 years ago in reply to JIANDE WU1

TI__Guru**** 393215 points

PMIC_POWER_EN is on the VDDS_RTC power domain, so that when 1.8V is provided to this rail the PMIC_POWER_EN signal will go high.

0 JIANDE WU1 over 11 years ago in reply to Biser Gatchev-XID

Prodigy 180 points

PMIC_POWER_EN usage is independent from AM3352's internal RTC LDO disable?

From http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist

The pin doesn't have functions.

But from Rev G datasheet Figure 6-5, there exists PMIC_POWER_EN from AM3352.

It really makes me confused.

0 Biser Gatchev-XID over 11 years ago in reply to JIANDE WU1

TI__Guru**** 393215 points

Yes, you are right, it's a bit confusing. If you are using the TPS65910A PMIC you have two other options:

1. Connect PMIC pin PWRHOLD to one of the 3.3V PMIC LDO's. This option will work if you have a power-on pushbutton connected to PMIC pin PWRON. The PMIC will not start directly when input voltage is applied.

2. Connect PMIC pin PWRHOLD to the input power supply (possibly through a resistive divider to guarantee you don't exceed max. voltage on pin) . This option will turn on PMIC when input voltage is applied.

In both cases PMIC_POWER_EN can be left unconnected.

0 JIANDE WU1 over 11 years ago in reply to Biser Gatchev-XID

Prodigy 180 points

Unfortunately, we plan on using TPS65217C.

Could you help us confirm this point?

We will connect PWR_EN pin of PMIC to input power supply as a backup sloution.

Thank you!!!

0 Biser Gatchev-XID over 11 years ago in reply to JIANDE WU1

TI__Guru**** 393215 points

In this case simply connect as shown here: http://www.ti.com/lit/ug/slvu551h/slvu551h.pdf

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AM3352 RTC configuration question clarify