Part Number: SN74CBT3251
Vcc will be 5V however the Select and OE pins will be driven by MCU at 3.3V. On the SN74CBT3251, are the Select & OE pins isolated from Vcc? Or do we need to ensure that the MCU has 5V tolerant pins?
The SN74CBT3251 can have Vcc = 5V and the SEL and OE pins will work at 3.3 V since the Vih min voltage is 2 V. Since the logic control pins are not at Vcc or ground you may some additional Icc current.
More information on the extra current consumption can be seen in this application note Implications of slow or floating CMOS inputs.
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In reply to Adam Torma:
In reply to Cassidy Aarstad:
1) The digital control logic is an input buffer so it will not drive any current out of the control logic pin and damage the MCU.
2) Correct, the additional Icc is due to the input buffer on the control logic.
3) The extra current consumption will be ~1mA according to the app note for the SN74CBTXXXX family. There will not be any issues with Vcc effecting the signal path since it is basically connected to the gate of the FET switch and has almost no leakage for the SN74CBTXXXX family.
Let me know if you have additional questions.
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