Communication only possible with 80% of LTC4332s

Question

I'm using the LTC4332s as shown in the "typical application" graphic in the datasheet, except Vcc is 5V in my case. 
 For testing purposes I use simple 20cm long wires to connect the local and remote side. Unfortunately, around 20% of the PCBAs with the remote master configured extender, a connection cannot be established. To clarify, the local side always stays the same and I replace the remote side hardware, which only works 80%. All output pins stay high (3.3V on the SPI pins and 2.3V on Y and Z), except the LINK pin which has ~1.8V. The local side continuously sends messages through A and B. Could somebody help me with this issue? Thanks.

ericb · Accepted Answer

Hello, 
 I'm assuming that the output pins you are referring to are on the remote side LTC4332. 
 The nLINK pin's voltage of 1.8V is expected when the link isn't present/operating. The voltage isn't the supply voltage because there is a capacitive voltage divider present formed by the pulldown NMOS and diode's parasitic capacitance present when the devices are off. 
 The remote side MOSI and SCK pins should be pulled down low once the part completes its start up sequence. The fact that they are measuring high suggests that the remote side part is not completing its internal power up sequence. 
 The fact you have about 80% of boards working suggests that your realization of the circuit works, so likely no simple/clear design errors. Bad parts could be an explanation; however a 20% failure rate is very high, especially considering that 100% of all shipped parts tested good. I would suggest looking closely at your boards for assembly or manufacturing defects. 
 
 Eric)

SLA Status	Assignee	Support Status
SLA Closed. Met after 7 hours	ericb AndreaRusso	Assigned

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Communication only possible with 80% of LTC4332s

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