OE_bar input for SN74LVC8T245

Mark Liang

Other Parts Discussed in Thread: SN74LVC8T245

Hello,

There is an user example for SN74LVC8T245 on Sheet 16 of the EVM: ARM MPU AM437X Industrial EVM (Document Number: am437x_industrial_evm_3k0008.dsn; Rev: 1.3A; August 8, 2014) from TI.

In the example, the OE_bar is connected to V3_3D through a 10K resistor: R542, it also is connected to DGND through a 0 ohm resister: R541.

We would like to know the reason for OE_bar connecting to V3_3D through a 10k resistor, since it is connected to DGND.

Best regards,

Mark

over 8 years ago

0 aozer over 8 years ago

TI__Mastermind 30025 points

Hello Mark,

This is most likely for debugging purposes. It would not make sense to have VCCA connected to ground. Instead, only one resistor should be installed at any given time to either tie OE to VCCA or to GND.

0 Mark Liang over 8 years ago in reply to aozer

Intellectual 740 points

Hello Aozer,

Thank you for the reply. When OE_bar is only connected to GND, would that cause any problem during power up of IC?

Best regards,
Mark

0 aozer over 8 years ago in reply to Mark Liang

TI__Mastermind 30025 points

Hello,

It can lead to glitches during start up. Best practice would be to connect the OE pin to VCCA and a control pin to ensure high impedance during start up. When VCCA has reached steady state the OE can the be pulled low by the control pin to allow for translation.

0 Mark Liang over 8 years ago in reply to aozer

Intellectual 740 points

Thanks.

Best regards,
Mark

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OE_bar input for SN74LVC8T245