Touchpad vs. Single Keys, Power consumption?

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Hawk
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Hello, 

I have noticed that 9 single capacitive keys require about half as much power compared to a touchpad with 3x rows, 3x columns and set to self capacitance. Is that correct?

Thanks

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Hari
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Hi @Hawk 

 

Yes, this is normal. When the resolution is decreased by a single bit, the scan time reduces by half. So the difference between 16 bits and 10 bits is 64 times and a higher current consumption is expected for the touchpad. You can go to the CapSense configurator -> advanced tab -> Scan order and see the scan time in each configuration. 

 

Best regards, 
Hari

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Hari
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Hi @Hawk 

 

For a 3x3 CSD touchpad, the number of sensing elements would only be 6. Compared to the 9 button sensors, for each scan loop, the number of sensors are fewer in touchpad and therefore, the scan time is also lowered (assuming other hardware parameters such as resolution and Fsw are same). 

Touchpads do have more processing to be done to determine the centroid position and gestures (if enabled) but these would not cause a serious increase in processing time. 

 

Can you let me know how you are measuring the power consumption? Are you going to any low power state after each scan?

 

Best regards, 
Hari

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Hawk
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@Hari

Thanks, we use for both version the software example CE210291.
Hardware  (CY8C4025..) / Outline size is the same. Resolution of touchpad and sense frequency we have set to maximum, because otherwise it does not work reliable.
At sleep mode, the current consumption is similar, but not in active / fastscan-mode.
We measure the current consumption between the VDD line.

9 Single Keys, around 5mW (1mA at 5V, fast-scan mode)
3x3 Touchpad, ~15mW (3mA at 5V, fast-scan mode)

Best regards

Edit:
For single keys we use the full-auto tune setup, here the setup is usually 9..10bit per key and 6000kHz sense frequency. If we set to manual tuning and 16 bit resolution per key, the power consumption is similar to the touchpad, is that normal?

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Hari
Moderator
Moderator
Moderator
750 replies posted 500 replies posted 250 solutions authored

Hi @Hawk 

 

Yes, this is normal. When the resolution is decreased by a single bit, the scan time reduces by half. So the difference between 16 bits and 10 bits is 64 times and a higher current consumption is expected for the touchpad. You can go to the CapSense configurator -> advanced tab -> Scan order and see the scan time in each configuration. 

 

Best regards, 
Hari

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