MSP430FR2532: Protection by TVS and Decoupling cap

Hi Dennis,

Customer has issue with +9kV that the capacitive does not sence and does not re-turn on at thier ESD test.

EMC/ESD page you gave me says "folloed by low-capacitance TVS diode clamps if needed" as attached.

Can we connect TVS to capacitive touch pin if SNR design has no issue?

Best regards,

Kento

Hi Kento,

I am so sorry for the error in my response.  Yes, the TVS diode is recommended, but make sure the customer chooses one with the least amount of parasitic capacitance.  TI has a selection of devices that are only a few pF.

thank you.

I chose 0.42pF TVS and 470Ω resistor.

Design guide recommends a resistor value range of 470Ω to 1kΩ,

but what are the concerns when connecting a resistor value outside this range?

Values smaller than 470 ohm may not provide sufficient current limiting during an ESD discharge and values larger than 1k will start to impact the Captivate signal, as this R plus the sensor capacitance C form an RC network.  The affect causes the Captivate square wave signal to become rounded off, causing inaccurate measurements.