SN65HVS885PWP clarification

Harini Ramanujam

Hi,

One of our customers has some clarifications regarding SN65HVS885PWP.

With the i/ps DB0 and DB1, they have several in parallel, using pull down resistors. If they don't ground them, then what size resistors should be used?

Also, from the truth table, if they used the reserved case as the normal or startup, then what would that affect?

Thanks!

over 15 years ago

0 Thomas Kugelstadt over 15 years ago

TI__Mastermind 28265 points

1) The DB0 and DB1 pins have internal pull-up resistors of 200 k ohms. For external pull-down resistors use 10k or 20k ohms.

2) The reserved condition (both DB0 and DB1 to ground) also bypasses the internal debounce filter, (so tdb = 0ms).

Regards,

Thomas

0 Thomas Kugelstadt over 15 years ago

TI__Mastermind 28265 points

Just to clarify one thing,

the internal pull-ups for DB0 and DB1 are 200k ohms. If your customer, for example, uses 4 HVS885 and connects 4 DB0 inputs and 4 DB1 inputs all to one pull-down resistor, than you must make the following calculation.

All 8 inputs have their pull-up resistors parallel. So the total pull-up resistor value is reduced to 200k / 8 = 25k ohms. then make your external pull-down resistor 1/10th of this value, so 2.5k ohms.

Pleas let me know whether this is clear.

Regards,

Thomas

0 Harini Ramanujam over 15 years ago in reply to Thomas Kugelstadt

TI__Prodigy 635 points

Yes, this is clear. They are going with 1K Ohm pull-downs (have 7 devices). Thanks for your help

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SN65HVS885PWP clarification