About the power supply of RTC in iMX283 chip

[x10]

Hi, all

The board I'm developing is an one based on iMX283. The main power supply is +5V without Li-ion battery. But the RTC is required. Is it possible to connect a button-battery(normally 3V only) to support RTC inside of iMX28? What I can do is:

    (1) pin BATT -> 3V battery which is NOT chargeable;

    (2) pin DCDC_BATT -> NC

    (3) call PowerStopCharger( ) in xldr.c

    (4) BattDrv.all is NOT installed

I'm not sure if 3V is enough to support RTC working. Please let me know if anybody has some experiece about this issue. Thanks advance!

BR

Cheng Shi 

Emtronix

[Ramtry]

Hi Cheng Shi,

I followed this discussion about RTC. I am trying to connect RTC (ISL1208) to my board. ISL1208 is I2C interface. But for my application, there is an audio codec IC (STGL5000) used and it sharing the I2C0 channel. And I2C1 is used for Touch Screen. How did you connect your ISL1208 IC to your board. Have you used Audio Codec IC in your application? Please share your idea.

Thank you,

RAM

[x10]

Hi, RAM

I just use GPIO simulate an I2C interface to access ISL1208. During initialization, the time message stored in ISL1208 is synchrounized to iMX28's rtc, so the driver doesn't cost CPU payload.

BR

ChengShi

[Ramtry]

Thank you ChengShi,

Now am trying to use I2c0 to interface RTC(ISL1208).. There are driver already present in LTIB. So, just trying to configure for I2C0 Channel.

Thank you,

RAM

[imravi]

HI Ram,

Were you able to interface isl1208 to your board. I am also trying to use i2c0 to connect to isl1208 but the check in the driver for the device fails each time. (i2c_validate_client)

[Radist]

Thanks for helping! I Found the problem - pin LRADC0 also was connected to the battery, and it took ~46mA (strange as for me!!!). but now i have I=10.6uA and RTC looks like working :)

Another question, does somebody know how to configure iMX28 for going to shutdown mode after disconnectig main power?

I guess there is some brownout that can shutdown MCU after 5V disconnecting? Now when i am making shutdown - MCU tries to get power from small battery. I want to prevent it.

[Radist]

Hi Cheng Shi,

thank you,

strange situation.. i have the same code, device going to power down, but Current still 46mA...

And nothing except battery and LADC is connected to battery net.
 
Cheng Shi said:

Hi Sergii

My code is almost the same:

after BF_WR(POWER_RESET,UNLOCK,BV_POWER_RESET_UNLOCK__KEY);

then 

HW_POWER_RESET_WR((BV_POWER_RESET_UNLOCK__KEY BP_POWER_RESET_UNLOCK) | BM_POWER_RESET_PWD);

Note, unlock key code is required when writing POWER_RESET register.

regards

Cheng Shi

[x10]

Hi Sergii

My code is almost the same:

after BF_WR(POWER_RESET,UNLOCK,BV_POWER_RESET_UNLOCK__KEY);

then 

HW_POWER_RESET_WR((BV_POWER_RESET_UNLOCK__KEY << BP_POWER_RESET_UNLOCK) | BM_POWER_RESET_PWD);

Note, unlock key code is required when writing POWER_RESET register.

regards

Cheng Shi

Sergii Makovetskyi said:

Hi Cheng Shi,

thanks a lot for your answer,

i made next things:

HW_RTC_PERSISTENT0_CLR(BM_RTC_PERSISTENT0_AUTO_RESTART);

while(((HW_POWER_STS_RD() & BM_POWER_STS_PSWITCH) >> BP_POWER_STS_PSWITCH) == ((BM_POWER_STS_PSWITCH >> BP_POWER_STS_PSWITCH) & 0x1));

BF_WR(POWER_RESET,UNLOCK,BV_POWER_RESET_UNLOCK__KEY);

// Chip power off

//enable the master shutdown switch, write ENABLE_MASK to the register

HW_POWER_RESET_WR( ENABLE_MASK );

//To power down the device, write PWD_MASK to the register

HW_POWER_RESET_WR( PWD_MASK );

Than device was shuted down, but battery supply current was 46mA.

Is it possible, can you share your code with me please? where you are making XTAL power down.

--

Best regards,

Sergii Makovetskyi
 
Cheng Shi said:

You have to turn off XTAL, only 32768Hz working which keeps RTC, and result in 20uA. XTAL unit will comsume about 200uA if it working.

Regards

Cheng Shi
 

[Radist]

Hi Cheng Shi,

thanks a lot for your answer,

i made next things:

HW_RTC_PERSISTENT0_CLR(BM_RTC_PERSISTENT0_AUTO_RESTART);

while(((HW_POWER_STS_RD() & BM_POWER_STS_PSWITCH) >> BP_POWER_STS_PSWITCH) == ((BM_POWER_STS_PSWITCH >> BP_POWER_STS_PSWITCH) & 0x1));

BF_WR(POWER_RESET,UNLOCK,BV_POWER_RESET_UNLOCK__KEY);

// Chip power off

//enable the master shutdown switch, write ENABLE_MASK to the register

HW_POWER_RESET_WR( ENABLE_MASK );

//To power down the device, write PWD_MASK to the register

HW_POWER_RESET_WR( PWD_MASK );

Than device was shuted down, but battery supply current was 46mA.

Is it possible, can you share your code with me please? where you are making XTAL power down.

--

Best regards,

Sergii Makovetskyi
 
Cheng Shi said:

You have to turn off XTAL, only 32768Hz working which keeps RTC, and result in 20uA. XTAL unit will comsume about 200uA if it working.

Regards

Cheng Shi
 

[x10]

You have to turn off XTAL, only 32768Hz working which keeps RTC, and result in 20uA. XTAL unit will comsume about 200uA if it working.

Regards

Cheng Shi

Sergii Makovetskyi said:

Hi Cheng Shi!

Can you tell me please, how did you got 20uA current with using battery? i can't force imx28 to power down mode.

I think in that mode cussrent will be about 20uA.

Thanks and waiting for your reply :)

--

Regards, Sergii
 
Cheng Shi said:

Hi, Juanma

It is OK to connect  a battery thourgh a double-diode to BATT pin to keep RTC within the chip. But the current is about 20 uA which is still a little high to a coin battery  with capacity of 50mAH. So I add a RTC chip (ISL1208) to my board, the chip costs only 6uA.

Regards

Cheng Shi

Juanma Alvarez said:

Hello Cheng Shi,

I have the same questios as yours.

How did you solve this?

Regards,

Juanma

[Radist]

Hi Cheng Shi!

Can you tell me please, how did you got 20uA current with using battery? i can't force imx28 to power down mode.

I think in that mode cussrent will be about 20uA.

Thanks and waiting for your reply :)

--

Regards, Sergii
 
Cheng Shi said:

Hi, Juanma

It is OK to connect  a battery thourgh a double-diode to BATT pin to keep RTC within the chip. But the current is about 20 uA which is still a little high to a coin battery  with capacity of 50mAH. So I add a RTC chip (ISL1208) to my board, the chip costs only 6uA.

Regards

Cheng Shi

Juanma Alvarez said:

Hello Cheng Shi,

I have the same questios as yours.

How did you solve this?

Regards,

Juanma

[x10]

Thanks, Juanma! Thanks for the reference.

[BillRandle]

Thanks for the reference schematic from Freescale!

[JuanmaAlvarez]

Thank you!!!

Try PCF8523 (NXP) for low current rtc (150nA typ)

I have received response for Freescale. They give me an schematic for 'only 5V without Ion-Li battery with iMX23'.

It has the same PMU than iMX28.

Find the attached file.

Regards,

Juanma

[x10]

Hi, Juanma

It is OK to connect  a battery thourgh a double-diode to BATT pin to keep RTC within the chip. But the current is about 20 uA which is still a little high to a coin battery  with capacity of 50mAH. So I add a RTC chip (ISL1208) to my board, the chip costs only 6uA.

Regards

Cheng Shi

Juanma Alvarez said:

Hello Cheng Shi,

I have the same questios as yours.

How did you solve this?

Regards,

Juanma

[JuanmaAlvarez]

Hello Cheng Shi,

I have the same questios as yours.

How did you solve this?

Regards,

Juanma

[x10]

Yes, it's my application needs RTC, :-)  By the way, I redesign my board and try to test the RTC on chip with powered of coin battery. The most thing I worry about is if it is safe or not. 

Richard He said:

What do you mean by "RTC is required"?   Do you mean your application needs RTC or the system need RTC?    I asked Freescale guys about the question and the answer I got is that RTC is optional but not necessory.  Can you clarify?

[admin]

What do you mean by "RTC is required"?   Do you mean your application needs RTC or the system need RTC?    I asked Freescale guys about the question and the answer I got is that RTC is optional but not necessory.  Can you clarify?

[darron]

The IMX residential gateway reference design appears to use a coin cell for the RTC.

There's virtually no documentation on that use case, so I just put an external RTC on my imx283 board.

I'd like to know if there's a way to do this safely.  For now, I've decided the risk of the chip going into a high-current mode with the coin cell is too great.