THVD1500: THVD1500

Wim M

Part Number: THVD1500

Hi,

Within the datasheet of the THVD1500 the Absolute Maximum Ratings are mentioned. For Vcc this is 7V.

https://www.ti.com/lit/ds/symlink/thvd1500.pdf?ts=1598511064612&ref_url=https%253A%252F%252Fwww.ti.com%252Finterface%252Frs-485-rs-422%252Fproducts.html%253Fpqs%253Dpaqs%2526familyid%253D545

For the logic pin (D, DE, RE) maximum rating is 5.7V specified. I expected a maximum voltage e.g. of Vcc +0.3V (also at many other devices).

Is the 5.7V correct or is Vcc +0.3V allowed ?

Regards,

Wim

over 3 years ago

0 Hao L over 3 years ago

TI__Mastermind 25705 points

Wim,

It's a good observation. Unfortunately 5.7V is only allowed at logic pins in THVD1500. The abs max value depends on the internal circuitry and the structure.

Regards,

Hao

0 Wim M over 3 years ago in reply to Hao L

Prodigy 75 points

Hao,

Thank's for your response.

The THVD1500 is supplied from an unregulated isolated DC/DC converter. The logic input pins have pull-up resistors ( 1kohm) to Vcc and the transistor of an optocoupler for switching low.

If Vcc rises temporary to 6.5V, does the THVD1500 continue to operate because the input current is limited by the pull-up resistor ?

Regards,

Wim

0 Hao L over 3 years ago in reply to Wim M

TI__Mastermind 25705 points

Wim,

THVD1500 should still work with Vcc=6.5V however the operation above the abs max is not guaranteed. The reliability concern is a statistical result, which means with longer duration and higher voltage, it's more likely the device will get damaged. Is the D pin pulled up to Vcc? How long does the Vcc stay at 6.5V?

Regards,

Hao

0 Clemens Ladisch over 3 years ago in reply to Wim M

Guru 243980 points

The logic inputs pins do not have a protection diode to V_CC, so no current flows. (See [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?.) A series resistor does not limit current, and cannot prevent damage.

0 Wim M over 3 years ago in reply to Hao L

Prodigy 75 points

Hao,

D pin is indeed pulled to Vcc. Normaly Vcc is 5.5V. The 6.5V accurs only in the 10-100msec range.

I also received an answer from Clemens Ladisch about devices without the positive clamping diode.

To prevent higher input voltages on the inputs, I can add a few zener diodes.

Regards,

Wim

0 Wim M over 3 years ago in reply to Clemens Ladisch

Prodigy 75 points

Clemens,

Thank's for the explanation. I can add some zener diodes to prevent a higher input voltage as mentioned in the datasheet.

Regards,

Wim

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THVD1500: THVD1500