THVD1500: THVD1500

jayashree

Intellectual 680 points

Part Number: THVD1500
Other Parts Discussed in Thread: SN74LVC1G34, THVD1450, THVD1410

Hi Team,

I am using THVD1500 RS485 transceiver (5V) and interfacing it to a 3.3V level processor.

I am attaching the VOH,VOL,VIH, VIL levels comparision. I found that there is some mismatch in VIH level.

Can I use this 5V level IC with my 3.3V processor?

I am also attaching the pdf of the schematics for your reference.

With regards,

Jayashree.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 243180 points

The schematic did not attach.

Please note that V_OL/V_OH are specified for a high load current, but that CMOS inputs (as used with the THVD and your microcontroller) have a very high impedance, with an input current of at most a few µA. So the actual output voltage will be at the rails. (See [FAQ] What is the output voltage (VOH or VOL) when the output current is X or the supply voltage is Y?)

0 jayashree over 3 years ago in reply to Clemens Ladisch

Intellectual 680 points

Hi,

In above I had attached schematics as a screenshot. In this I am attaching the snapshot of schematics in a document.

Please go through it and let me know your inputs.

With regards,

Jayashree.THVD1500 RS485 sch.docx

0 Clemens Ladisch over 3 years ago in reply to jayashree

Guru 243180 points

If the processor does not have overvoltage-tolerant inputs, the you cannot connect a 5 V output to it directly.

To shift the signal from 5 V to 3.3 V, you can use any buffer with an overvoltage-tolerant input, such as the SN74LVC1G34.

0 jayashree over 3 years ago in reply to Clemens Ladisch

Intellectual 680 points

Hi Clemes,

Thanks for the reply.

May I use THVD1450 in place of THVD1500 to resolve this issue?

Because THVD1450 can be supply with both 3.3V and 5V rail.

With regards,

Jayashree.

0 Clemens Ladisch over 3 years ago in reply to jayashree

Guru 243180 points

Yes, running the transceiver at 3.3 V is the simplest way to solve this problem.

Please not that fast signal edges can introduce EMI problems; you should replace the THVD1500 with a similarly slow device, i.e., the THVD1410.

0 jayashree over 3 years ago in reply to Clemens Ladisch

Intellectual 680 points

Hi,

In the datasheet of THVD1410 it is mentioned that VCC supply can be from 3.3V to 5V and the bus voltage (A, B) is given as -18V to 18V.

Is the bus voltage dependent or independent of VCC supply.

For example if I supply VCC with either 3.3V or 5V the bus voltage level will remain the same right. Please correct me if I am wrong.

With regards,

Jayashree.

0 Clemens Ladisch over 3 years ago in reply to jayashree

Guru 243180 points

The bus voltage is independent from the supply voltage. (The driver must be able to generate a differential voltage of ± 1.5 V.)

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THVD1500: THVD1500