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TMS320F28386D: digital inputs specifications

Part Number: TMS320F28386D

Case Number:       CS0679559

 

Short Description:  Overdriving the DSP with +5V SN65LBC170DB transceivers

 

Customer
Response

Number: CS0679559
Contact: Marcin Brylak
First name: Marcin
Last name: Brylak
Short description: Overdriving the DSP with +5V SN65LBC170DB transceivers
Phone: 4366488632262
Email: marcin.brylak@avl.com
Company: AVL
Company phone:
Language: English
State: Open
Provide case details or comments:

The specs of DSP are not exactly clear; it may be interpreted that the input clamping (protection) circuits on the digital inputs, for the positive input voltage, are actually activated at 4.6 V.

At that voltage each input is able to take 20 mA momentary (and total for all inputs), and 2 mA continuous. Together with the series resistors that you have -- this may explain why it works without blowing up.

 

On the other hand, a more traditional understanding is that the protection diodes will kick in at VDDIO+0.3V , especially considering the note (2) in the spec below.

 

Second issue:

If I use SN65LBC170DB with +5V supply can I go with 22 Ohm in series on RX and 15 Ohm in series on DSP side without any issue?

Can be the lifetime reduced?

 

 

 

  • the projection diodes conduct at VDD+0.3V.

    I would recommend using a level shifter where possible. If you cannot use one then please make sure that you never exceed VDDIO on the input pins, the protection diodes are not intended to be used constantly, rather for intermittent issues.

    Regards,
    Cody