About PCA8885 LOW POWER MODE

[hoyle_xu]

Hi,

I have a mass remote product, this remote include with LCD and touch screen【PCA8885 IC】

My design ideas are as follows

1. The touch function of the remote can enter the low power mode【Sleep mode】 when no user operate it.
2. The remote can exit the sleep mode immediately as soon as possible when user touch it

I read the SPEC of PCA8885 to know the sleep mode

Question is:

1. Whether my idea can be achieved? If not ,why?
2. I have some doubts about the contents from SPEC as follows

The charges in the CPC capacitors however cannot be guaranteed, as there is no limitation on the duration of the sleep mode. Therefore the analog part has to perform a normal start-up phase, including the fast start procedure for the CPC capacitor charging

Question: 

1. Whether the normal start-up phase, including the fast start procedure for the CPC capacitor charging can be guaranteed or not?
2. what about the IDD(sleep) If the normal start-up phase, including the fast start procedure for the CPC capacitor charging can be guaranteed。

The other question is ：

what the difference between idle state and sleep mode?

Thanks

[reyes]

Hi,

No, it is not possible to wake the PCA8885 when touching because during sleep mode, the charges in the CPC capacitors cannot be guaranteed. Therefore the analog part has to perform a normal start-up phase, including the fast start procedure for the CPC capacitor charging. This means that if the analog blocks are power-down, no guarantee that the CPC capacitors are charged, therefore, it is not possible to sense a touch in this mode.

Sleep and idle modes are very much different, idle state is the steady state after completed power-on, without any mode change and without any activity on the sensor plates, and the voltages on the reservoir capacitors CCPC are settled. Translating this to your specific case, idle state will be achieved after the remote is power-on, when the remote is left untouched, in this case, the IDD supply current would be typically about 10uA.

If this consumption is acceptable for your application, you can use the PCF8885.

Have a great day,
Jose

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[hoyle_xu]

Thanks, Jose

I still have question as follows:

1. How I can enter idle mode?
2. Whether I can wake up IC through user touch or not?
3. If it can be  waken up through user touch, What about the response time exit from idle mode
4. Whether IC can send command through I2C when exit idle mode in the same time? or need another operate?
5. What the detail difference between normal mode and idle mode?

Thanks

[reyes]

Hi,

Answering to your questions:

1. How I can enter idle mode?

[A1] Idle mode refers to the steady state after completed power-on and when there are no activities going on the sensor plates or digital configuration. It can be seen as the same mode as the normal power mode, so no configuration is needed to enter to the Idle mode.

2. Whether I can wake up IC through user touch or not?

[A2] No, there are only two ways to wake up the IC once it enters in sleep mode: by the wake-up command (if the device was put to sleep using the sleep command), or by setting the SLEEP pin to LOW (if the device was put to sleep using the SLEEP pin to HIGH).

For the case of Idle mode, there are no need to wake up the device since Idle is part of the normal mode.

3. If it can be  waken up through user touch, What about the response time exit from idle mode

[A3] PCF8885 cannot be wake up through user touch.

4. Whether IC can send command through I2C when exit idle mode in the same time? or need another operate?

[A4] Idle is part of the normal mode, so, you can send command through I2C when you are in this Idle mode, but yes, a transition from “Idle” to “normal” mode will be caused by activities on the device while I2C communication.

5. What the detail difference between normal mode and idle mode?

[A5] These are the same, the only difference is that when there are activities like I2C communication or CPC capacitor charging, etc (a.k.a. Normal mode), more current is consumed that during Idle mode, how much extra current consumption is consumed? It is not characterized because it would depend on the type of activity and customer design.

Have a great day,
Jose

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[hoyle_xu]

Hi, Jose

Thanks for your answer

So I think you mean that PCA8885 will enter into  IDLE mode automatically? If it is.

Question:

1. How long will it take enter into IDLE mode after without any mode change and without any activity on the sensor plates?
2. Do you mean IC still can response to user actions when  IC is  in idle state? In fact, I mean the IC can send command to main MCU through I2C when  IC is  in idle state once user touch screen.

[reyes]

Hi,

Correct, PCA8885 will enter into  IDLE mode automatically when there is no analog (like charging the CPC capacitor) or digital (like I2C configuration) activities going on.

A1. There is no characterization on how long does it takes to enter into the IDLE mode after without any mode change and without any activity on the sensor plates, since it depends on each design, but it is typically right after the CPC capacitor is fully charged and stable.

A2. Yes, PCA8885 can still response to user actions when  IC is  in idle state. The IC can send command to main MCU through I2C when  IC is  in idle state once user touch screen.

Just take in mind that once user touch the electrode, will discharge the CPC capacitor, which counts as an analog activity to automatically change the state from Idle to Normal mode.

Have a great day,
Jose

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[hoyle_xu]

Hi, Jose

Sorry to disturb you again

Because my ODM supplier have some different opinion with me

They think the IDLE mode will entered in only when the following cases

[2] Idle state is the steady state after completed power-on, without any mode change and without any activity on the sensor plates, and the voltages on the reservoir capacitors CCPC are settled

ODM Supplier thinks that this sentence mean

• Idle state only entered in one time after power-on.
• PCA8885 will not entered in Idle mode again after any configure for example Frequency allocation

So How I understand mode change here?

Thanks

[reyes]

Hi,

No, Idle state is not only entered in one time after power-on, the PCF8885 also enter automatically in Idle mode when there is no analog (like charging the CPC capacitor) or digital (like I2C configuration) activities going on once that CPC capacitor is fully charged and stable.

Have a great day,
Jose

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[hoyle_xu]

Hi, Jose

I let my supplier test the current according the bellow method

1. Test current when only weld main MCU on PCBA
2. Add PCA8885 and relevant Peripheral circuits such cap on PCBA
3. Test current when no any operation to PCA8885, the current is about 20uA, It seems that the value is idle current
4. Then test current after Initialize the PCA8885 as followed:

•  Software reset, PCA8885 registers restore default values;
•  Configure the output mode of INT ;
• Setting PCA 8885 to work with maximum clock value (Fosc = 140 KHZ Fclk = Fosc Fs = 17.5 KHZ);
• Clear PCA8885 interruption mark;

And no any other operation, The current become to about 147uA

I don't know why....

Thanks your help and support

[reyes]

Hi,

To help to reduce the current consumption, the internal voltage regulator should be shut down by setting bit VROF logic 1.

Also try to set bit MSKMODE to logic 1 in register CONFIG, this way only the enabled channels are sampled. Reducing the number of sampled channels also reduces the power consumption.

Have a great day,
Jose

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[hoyle_xu]

Hi , Jose

Thank your reply

To help to reduce the current consumption, the internal voltage regulator should be shut down by setting bit VROF logic 1.

——I think I can’t set bit VROF logic 1 because I need keep PCA8885 can work for detect touch

Also try to set bit MSKMODE to logic 1 in register CONFIG, this way only the enabled channels are sampled. Reducing the number of sampled channels also reduces the power consumption.

——I think you mean this mode can keep PCA8885 working for detect touch?

——Or you this way can disable channels are sampled?, If it is, also I think I can’t set bit VROF logic 1 because I need keep PCA8885 can work for detect touch

Have any other way to reduce current consumption when no operate but can keep PCA8885 always can detect touch?

Thanks so mcuh

Best Regards

Hoyle Xu/徐后勇 EMC Dept

KOHLER

Shanghai KOHLER Electronics, Ltd.

No.1955 FengXiang Road, BaoShan District , Shanghai

上海市宝山区丰翔路1955号 邮编 : 200444

Tel : 021-26096397

[reyes]

Hi Hoyle Xu,

The channel masking register MASK (MSK[7:0]) allows individual sensor channels to be enabled or disabled. When bit MSKMODE in register CONFIG is set logic 1, only channels which are enabled are sampled.

Regards,

Jose

NXP Semiconductor

[hoyle_xu]

Thanks so much