How to configure unused LF pins in FXTH87?

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How to configure unused LF pins in FXTH87?

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sunrme
Contributor III

I designed TPMS sensor on FXTH87. And I don't want to use LF receiver, so I have to configure LF pins to avoid a floating input. What I have to do? leave pin not connected or connect to Vss, or something else?

Really appreciate your help.

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franklatona-r49
NXP Employee
NXP Employee

From a hardware point of view, let the LFA (pin 17) and LFB (pin 16) float.  As described in Section 2.3.7 of the datasheet, each LF[A:B] pin will always have an impedance of approximately 500K Ohm to Vss due to the LF receiver input circuitry.  The LF[A:B] pins are used by the LF receiver when the LFEN control bit is set, and are not functional when the LFEN control bit is clear.  The LFEN bit is in the LFCTL1 register.

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franklatona-r49
NXP Employee
NXP Employee

From a hardware point of view, let the LFA (pin 17) and LFB (pin 16) float.  As described in Section 2.3.7 of the datasheet, each LF[A:B] pin will always have an impedance of approximately 500K Ohm to Vss due to the LF receiver input circuitry.  The LF[A:B] pins are used by the LF receiver when the LFEN control bit is set, and are not functional when the LFEN control bit is clear.  The LFEN bit is in the LFCTL1 register.

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sunrme
Contributor III

Hi Frank,

Thank you for your reply, I will let the LFA (pin 17) and LFB (pin 16) float.

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