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How to configure unused LF pins?

sunrome

Jul 21, 2015
2
Joined
Jul 21, 2015
Messages
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I designed TPMS sensor on freescale 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?

from datasheet:
Each LF[A:B] pin will always have an impedance of approximately 500 kOhm to VSS due to the LFR input circuitry. The LFA/LFB
pins are used by the LFR when the LFEN control bit is set and are not functional when the LFEN control bit is clear.

Really appreciate your help.
 

davenn

Moderator
Sep 5, 2009
14,260
Joined
Sep 5, 2009
Messages
14,260
just terminate them with a 1k resistor to ground :)
the value isn't critical
 

sunrome

Jul 21, 2015
2
Joined
Jul 21, 2015
Messages
2
Thank you for you reply, but if value isn't critical, can I connect directly to the ground? Is a value of impedance affects the choice of resistor? I just want to understand why it is necessary to do so.
 
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