Hi,
I have a mass remote product, this remote include with LCD and touch screen【PCA8885 IC】
My design ideas are as follows
I read the SPEC of PCA8885 to know the sleep mode
Question is:
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:
The other question is :
what the difference between idle state and sleep mode?
Thanks
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
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Thanks, Jose
I still have question as follows:
Thanks
Hi,
Answering to your questions:
[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.
[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.
[A3] PCF8885 cannot be wake up through user touch.
[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.
[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
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Hi, Jose
Thanks for your answer
So I think you mean that PCA8885 will enter into IDLE mode automatically? If it is.
Question:
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
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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
So How I understand mode change here?
Thanks
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
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Hi, Jose
I let my supplier test the current according the bellow method
And no any other operation, The current become to about 147uA
I don't know why....
Thanks your help and support
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
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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
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
Thanks so much