SN65HVD1793: Pull-up/down resistors for DE and RE

Jun Ishida

Part Number: SN65HVD1793

Hi team,

When fix DE(pin#4) to High with pull-up and RE(pin#3) to Low with pull-down, could you please tell us what the recommended pull-up resistor for DE and pull-down resistor for RE are, respectively? (Vcc=5V)

Regards,

Jun

over 6 years ago

0 Miguel Robertson over 6 years ago

TI__Guru 62920 points

Hello Ishida-san,

Common values are 1 kOhm or 4.7 kOhm. In general, though, you can compute the maximum allowed external resistance based on the maximum input current to each pin (which is +/- 100 uA for DE and /RE) and the required input voltage levels. For example, you could compute a maximum pull-down value based on the maximum VIH level as follow: (0.8 V) / (100 uA) = 8 kOhm. For a pull-up, you could use the minimum VCC and the minimum VIH specs: (4.5 V - 2 V) / (100 uA) = 25 kOhm. Please let me know if this is not clear.

Regards,
Max

0 Jun Ishida over 6 years ago in reply to Miguel Robertson

TI__Expert 5640 points

Hi Max-san,

Thank you for your comments. BTW, is it possible to directly connect the DE to Vcc(5V) and the RE to GND without any resistors?

Regards,
Jun

0 Miguel Robertson over 6 years ago in reply to Jun Ishida

TI__Guru 62920 points

Ishida-san,

Yes, it is OK to tie these pins directly to either VCC or ground. Of course, in this case the configuration would remain fixed and it would not be possible to also control these pins via MCU GPIO controls.

Regards,
Max

0 Jun Ishida over 6 years ago in reply to Miguel Robertson

TI__Expert 5640 points

Hi Max-san,

Thank you for your answer. I well understand it.

Regards,
Jun

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SN65HVD1793: Pull-up/down resistors for DE and RE