SN74LVC8T245 Power sequence

Patrick Chen(TPE System & Application)

Other Parts Discussed in Thread: SN74LVC8T245

Hi Sir,

My Customer are using SN74LVC8T245 an found that if the 3.3V (VCCB) apply first, then apply 1.8V(VCCA), we will see a 100us High on B side when 1.8V apply. Even we set the OE# as low when apply 1.8V or set the direction.

If we apply 1.8V first, then it will be ok.

Here is my question that need your help.

1. Is this a known issue?

2. Do we have any document said that teh VCCA should apply before VCCB?

Thanks,

Patrick

over 8 years ago

0 ShreyasRao over 8 years ago

TI__Guru 58530 points

Hi Patrick ,

I will move this into voltage translation forum for better support .

0 Jennifer Joseph over 8 years ago

TI__Intellectual 2530 points

Hi Patrick

1) Power up sequence of Vcca/Vccb is irrelevant with pull-up resistors on I/O ports. If pull down resistors are present glitches occur on the output port.

2) When Vcca comes up first, the DIR and nOE pin reach their defined state first. If DIR is tied to GND, part direction is from B to A. B becomes the input port and A is the output port. Glitch is present on A port.

Please refer to section 8 of this application note. Workround is using pull up resistors at input ports.

http://www.ti.com/lit/an/slva746/slva746.pdf

Thanks

Logic

Logic forum

SN74LVC8T245 Power sequence