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Part Number: SN74CBTLV3383
See the schematic excerpt below for reference.
Data corruption is occurring on the A1-B2 path when A1 is connected to B2 and A2 is connected to B1.
Two experiments tested thus far:
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In reply to Cassidy Aarstad:
This device has a bandwidth of 200MHz so you shouldn't be seeing too much attenuation with your 40MHz signals so I agree it might not be a vih/vil issue on the signal path to the flash memory.
The vih and vil on the OE pins for this device with Vcc = 3.3 V are 2 V and 0.8 V respectively.
In the experiments tested thus far:
1. Stopping the data transmission makes the problem go away? Are you thinking that there is a cross talk issue? Do you have scope plots of the data on A1 and B1 and A2 and B2 in the failing and non failing case? You can also try removing the IC from the board and short the signal path to see if the issue goes away. This will help determine if the cross talk is through the IC or through the board.
2. You have a very strong pull down resistor and you change it to a stronger one pulling it to ground through 0ohms that will always enable the switch. It seems odd to me that changing this pull down resistor by 220 ohms solves the issue. How repeatable is this? Do you have a scope shot seeing what voltage is on this node in both cases?
A) How many boards is this failing signature seen?
B) Does replacing the IC solve the issue? Does the removed device cause a good board to fail?
In reply to Adam Torma:
We determined that the /BE pin was not having an effect on failure rate.
However, we know that crosstalk in the IC is in someway causing the failure (if we blue-wire the connections we don't get failures). Capturing the precise moment when failure occurs has been difficult, the times we have caught failure it appears that the flash is actually clocking out incorrect data (however tests showed this is likely because an error occurred during a write operation). After further tests we saw that some boards experienced read failures while others experienced write failures. Write failures appear to occur far more frequently than read failures.
The flash IC (which is connected to the B side of the switch) has a very strong drive strength/fast rising edge and when multiple lines rising edges are synced they cause a significant amount of crosstalk. Tying pins 3 & 4 of the switch to GND via 0ohms has eliminated all errors in all cases thus far. We suspect that tying those pins to GND helps attenuate some of the crosstalk in their system. We are also recommending that the series resistors on the communication lines be increased to help slow down the flash's rising edge.
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