Functional Description
Question 1
How the Cref pin used in the BS80xB devices?
Answer
The Cref pin in the BS80xB devices can be used in the following way to adjust the sensitivity of all the switches. (For actual implementation please see the BS80xB application note)
a. Connect a 0pF~10pF capacitor between the Cref pin and ground.
b. Connect a PADCref to the Cref pin.
Question 2
What’s the difference between the BS80xC and BS80xB series MCUs?
Answer
The following table indicates the differences with 1-key touch switch devices.
Part No. |
Operating Mode |
Response Time |
Power Consumption |
BS801B |
Wake-up from standby mode |
400mS |
1.5μA |
Normal Mode |
100mS |
3.0μA |
BS801C |
Normal Mode |
100mS |
3.0μA |
From the above table, the main differences lie in the Key Response Time and Power Consumption.
Question 3
With the exception of the operating mode, key response time and power consumption, are there any other differences between the BS80xC and BS80xB?
Answer
There are no other differences as the design of the BS80xC series device is based on the BS80xB series.
Question 4
What is the difference in the SCD functional specification between the BS80xC and BS80xB series MCUs?
Answer
As the two series have different operating modes, the SCD commands also differ. However, both the SCD transmission protocol and specifications are the same. (For detailed SCD commands refer to the BS80xC/BS80xB datasheet)
Question 5
Are the BS80xC series package types compatible with the BS80xB series?
Answer
They are fully compatible.
Question 6
Is there any other FAQ information for the BS80xC series MCUs?
Answer
As the BS80xC is based on the BS80xB, for any other related questions refer to the BS80xB FAQs.
Question 7
What are the real differences between the BS80xC and BS80xB in terms of their different operating modes?
Answer
※ BS801C v.s. BS801B |
Part No. |
Operating Mode |
Key Response Time |
Power Consumption |
BS801B |
Wake-up from standby mode |
400mS |
1.5μA |
Normal Mode |
100mS |
3.0μA |
BS801C |
Normal Mode |
100mS |
3.0μA |
※ BS802C v.s. BS802B |
Part No. |
Operating Mode |
Key Response Time |
Power Consumption |
BS802B |
Wake-up from standby mode |
400mS |
2.0μA |
Normal Mode |
100mS |
5.0μA |
BS802C |
Normal Mode |
100mS |
5.0μA |
※ BS804C v.s. BS804B |
Part No. |
Operating Mode |
Key Response Time |
Power Consumption |
BS804B |
Single Key Wake-up Mode from standby mode |
400mS |
1.5μA |
Any Key Wake-up from standby mode |
400mS |
3.0μA |
Normal Mode |
100mS |
8.0μA |
BS804C |
Single Key Mode (Note 1) |
100mS |
3.0μA |
Normal Mode |
8.0μA |
※ BS806C v.s. BS806B |
Part No. |
Operating Mode |
Key Response Time |
Power Consumption |
BS806B |
Single Key Wake-up from standby mode |
400mS |
1.5μA |
Any Key Wake-up Mode from standby mode |
400mS |
4.0μA |
Normal Mode |
100mS |
14μA |
BS806C |
Single Key Mode (Note 1) |
100mS |
3.0μA |
Normal Mode |
14μA |
※ BS808C v.s. BS808B |
Part No. |
Operating Mode |
Key Response Time |
Power Consumption |
BS808B |
Single Key Wake-up Mode from standby mode |
400mS |
1.5μA |
Any Key Wake-up Mode from standby mode |
400mS |
5.0μA |
Normal Mode |
100mS |
18μA |
BS808C |
Single Key Mode (Note 1) |
100mS |
3.0μA |
Normal Mode |
18μA |
Note 1: In the single key wake-up mode, KEY0 must be pressed before the system enters
the normal mode at which point all the keys will be effective.
Application Description
Question 1
How is an external MCU used with the BS80xB devices?
Answer
There are two methods:
a. Use I/O pins on the MCU to connect to the Kout pins.
b. Connect the MCU to the SCD serial interface pin on the devices.
Points to Note
Question 1
What are the limitations on the sense PAD shape and size?
Answer
There are no special restrictions on the sense PAD shape. Regarding the PAD size, using a circular share as an example, it is recommended that it has a diameter of 5~10mm, with a minimum size of 4mm. Larger PAD areas will result in higher sensitivities.
Question 2
What thickness of touch key outer covering can be used? What is the sense distance?
Answer
The touch key outer covering/sense distance and the sense PAD size, as well as if there is space between the PAD and the outer covering are all related. For this reason the actual PAD size, and if the actual PAD is firmly bonded to the outer covering and the actual material used for the outer covering must be used for device setup.
Question 3
Why is a PADCref required? Are their limits on its use?
Answer
A PADCref can be used in place of Cs to reduce the number of external components. When using a PADCref note that it cannot be touched, therefore it must be enough space for it to be concealed.
Question 4
Why can PADCref not be touched?
Answer
The PADCref is used to change the overall sensitivity of the touch switches. If it is touched or experiences interference, then all the switch sensitivities will increase which could cause erroneous operation.
Question 5
Can curved touch switch outer coverings be used?
Answer
The sense pad and the external touch key outer covering must be closely bound. If there is space between them, then the touch switch sensitivity will be substantially reduced. For this reason only flat outer coverings should be used. However, if because the product in question requires to use a curved surface design, then the sense pad must still be closely bound to this curved surface.
Question 6
What can be done if there is no way to fully bond the sense pad the outer covering?
Answer
If due to height restrictions the sense Pad cannot be fully in contact with the outer covering, then a spring (or other conducting material) to implement an extension to the Pad.
Question 7
Are there any limitations on PAD to PAD spacing ?
Answer
The smallest distance between adjacent pads should be 2mm.
Question 8
What are the methods of adjusting the touch key sensitivity?
Answer
Factors which affect touch switch sensitivity are the value of Cs, the PAD size, the thickness of the touch key outer covering and the touch key external covering material. The value of Cs should be as close to the capacitance of the sense pad as possible. Larger sense pad areas will result in higher touch key sensitivities, at the same time the Cs value should also be increased, however the related touch switch reaction time will be reduced.
Question 9
Are there limitations regarding the size of the sense Pad?
Answer
The pad size of course will be limited by the product, however the smallest diameter should not be less than 4mm.
Question 10
During volume production, how can testing be implemented? How can faults be detected?
Answer
The Holtek touch product production test tools can be consulted for an explanation.
Question 11
Why sometimes is the key reaction speed slow?
Answer
When the BS80xB enters the low power mode, the first touch reaction time is slower (about 0.4 sec). The time after which the BS80xB will enter the low power mode is shown in the table:
Question 12
In multi-key applications, is it possible to adjust the sensitivity of individual keys?
Answer
The size of each sense PAD can be changed to adjust its sensitivity?
Question 13
Are there limits on the material used for the outer covering?
Answer
For materials which are in direct contact with the sense PAD, metallic or carbon containing conducting materials must not be used. The following table (most popular physical dielectric constant table) can be consulted. It is recommended that a material with a dielectric constant, K, of value between 1.5 and 4 is used. Examples would be glass, acrylic, plastic etc.
Dielectric Constant Table:
Question 14
If the sensitivity is too high, what can be done to reduce the sensitivity?
Answer
a. Reduce the PAD area
b. Reduce the Cs capacitor value
c. Increase the thickness of the external covering
d. Change the covering material
e. An Rs resistor (0Ω~75KΩ) can be placed in series with the line connecting the
sense Pad and the BS80xB KIN pin.
f. On the surrounding are of the sense Pad and the connecting layout line a ground net
can be added.
Others
Question 1
Are their any patent issues with the BS80xB devices?
Answer
There are no patent infringement issues as the BS80xB devices have their own patents.
Question 2
Is it possible to modify the specification according to the users needs?
Answer
Because the BS80xB is an ASIC structure there is no way to change its specification.
Question 3
How can the Demo Board be used with real product external coverings for layout and how is the sensitivity setup?
Answer
Prepare a piece of actual product external covering material of similar thickness, and bond this to the BS80xB Demo Board Sense Pad to test the sensitivity. If the sensitivity is too low, then short the solder points on the back of the Sense Pad to increase the Pad area, thus increasing the sensitivity. In this way the most suitable sensitivity value can be found. This corresponding Pad size should be recorded and when implementing the PCB layout, this size should be used for the layout sense pad.
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