MPR121 Touch Pad Schematic Review

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MPR121 Touch Pad Schematic Review

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Contributor III

Dear All,

One of my customer wants develop a touchpad for their end product. Below is the customer requirement.

1. 4 Touch Pad

2. 4 LED Indication

3. I2C interface for host processor

I'm promoting MPR121 and have made a rough schematic for total BOM conclusion. Please review my schematic and suggest if any changes needs to be done.

Thanks in advance

Regards

Mithun

FAE

WTMEC

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NXP TechSupport
NXP TechSupport

Mithun,

Looks fine, just a few comments:

1. As VDD is higher than 2.75V, the VDD and VREG pins should not be connected together. Use a separate 0.1μF decoupling ceramic capacitor on VREG to VSS as shown in figure 2 of the datasheet.

2. In the final schematic, do not forget to connect the ADDR pin accordingly.

3. If the customer is going to use the IRQ output, use a level translator also on this line. I do not have much experience with discrete MOSFETs, I usually use an integrated solution such as the PCA9306DCUR from TI.


Regards,

Tomas

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NXP TechSupport
NXP TechSupport

Mithun,

Looks fine, just a few comments:

1. As VDD is higher than 2.75V, the VDD and VREG pins should not be connected together. Use a separate 0.1μF decoupling ceramic capacitor on VREG to VSS as shown in figure 2 of the datasheet.

2. In the final schematic, do not forget to connect the ADDR pin accordingly.

3. If the customer is going to use the IRQ output, use a level translator also on this line. I do not have much experience with discrete MOSFETs, I usually use an integrated solution such as the PCA9306DCUR from TI.


Regards,

Tomas

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Contributor III

Hi Tomas,

Thanks for your above suggestions, I will make necessary changes.

As I want to give both options to customer ASIC based & MCU based please help me reviewing the MCU based schematic which I have attached.

Thanks again for your help.

Regards

Mithun

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NXP TechSupport
NXP TechSupport

Hi Mithun,

Two comments:

1. Both PTA2 (SDA) and PTA3 (SCL) pins are used for I2C communication, so you cannot use them to drive LED3 and LED4. Use PTB4 and PTB5 pins to drive these LEDs.

2. In the final schematic, do not forget to connect a crystal or ceramic resonator to the XTAL and EXTAL pins as shown in Figure 2-7 of the MC9S08PT16 Reference Manual, unless you make use of the internal reference within the MC9S08PT16.


Regards,

Tomas

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Contributor III

Dear Tomas,

I will make use of Internal clock.

Regards

Mithun

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