SN74AXC1T45: SN74AXC1T45 can shift 2.5V signal to 1.8V, but not shift 1.8V signal to 2.5V

user5351823

Part Number: SN74AXC1T45

As the below PIC

D0_2V5 on U2-PIN3 can be shifted to U2-PIN4 as D0_1V8
but
D1_1V8 on U3-PIN4 can not be shited to U3-PIN3 as D1_2V5

Debug @:
1, inpedance of U2-PIN3/PIN4 and U3-PIN3/PIN4 is about 42K ohm
2, diode characteristic of U2/U3-PIN1/3/4/6 is about 0.45V

so, any suggestion to debug ? thanks

Wang

over 7 years ago

0 Emrys Maier over 7 years ago

TI__Guru* 97046 points

Hello,
Can you post a scope shot of the operation in each direction?

Also, can you show the output load of the device that is having trouble?

0 user5351823 over 7 years ago in reply to Emrys Maier

Prodigy 20 points

Hello Sir

I attach one pdf file, please refer

tksSN74AXC1T45 Problem Explain.pdf

0 Emrys Maier over 7 years ago in reply to user5351823

TI__Guru* 97046 points

Thanks for taking the scope shots, but they really don't help me any since the time scale is huge and the input/output signals are not on the same display -- I can't tell what is happening in your circuit from these.

Do you have a full schematic that you can share, or at least one that shows all connections to U3-PIN3?
It would also be helpful to see a layout of your circuit (or a picture if a digital layout is not available).

I would suspect one of two possible issues:
(1) ESD damage to the device could cause it to have no output
(2) something else is holding the line either high or low and preventing the device from normal operation

Logic

Logic forum

SN74AXC1T45: SN74AXC1T45 can shift 2.5V signal to 1.8V, but not shift 1.8V signal to 2.5V