Input Voltage limit on VNH5050 Diag/ENA pin

[onlinestoreemail]

Posted on August 14, 2014 at 03:20

Hi

I'm designing a very compact quad VNH5050 12V Motor Driver board.

I can optimize my design if I can pull-up the DIAG/ENA pins to 12V rather than the 5V Logic level.

There is nothing else connected to these pins.  All I want is the bare minimum components.

None of the specs seem to provide a max upper voltage limit for these open drain inputs.

If I can use 12V, what is a suitable resistor value?

Thanks.

phil.

#vnh5050-motor-driver-diag-ena

[Brugus]

Posted on August 18, 2014 at 11:26

Hi Phil,

do you confirm these ENx/DIAGx pins are not connected to GPIOs and there are only pull-up resistors?

Best regards,

Marco

[onlinestoreemail]

Posted on August 21, 2014 at 04:26

Yes..

I think I made that pretty clear when I said::  

>>>>   There is nothing else connected to these pins.

Sigh!

[Brugus]

Posted on August 21, 2014 at 09:34

DIAGA/ENA and DIAGB/ENB are connected the digital block (see figure 1 in the datasheet). The pull-up resistor must be connected to Vdd level (+5V).

Best regards,

Marco

[onlinestoreemail]

Posted on August 25, 2014 at 16:26

Hi

Based on your answer, I don't understand why you asked me if the pins were connected to anything else external... since you say I can't pull them up to VCC anyway...

However, let me explore further...

In figure 1, there is a Logic block in the diagram, but no mention of Vdd or 5V. 

In fact, if I painstakingly search the document there is no mention of Vdd anywhere, or that the chip uses 5V logic. (Yes, it's implied by the circuit examples and test conditions, but not stated anywhere).  Search for yourself.

Also, on the block diagram, there is a signal clamp function, which seems to be applicable here.  In table 9, the ENa and ENb lines show an input clamp between 5.5 and 7.5 V at 1 mA. I assume this is to protect and condition the inputs.

So if I use a 100K pullup to 12V on these inputs, then I'm limiting the input current to 0.06mA so wouldn't the input clamps do their job and reduce the input level to an appropriate voltage?  If not, why are the input clamps there?

If I've misinterpreted the sheet, then perhaps some clarification would help out.

Specify the desired/max limits on these pins (Current and voltage)

Phil.

[Brugus]

Posted on August 29, 2014 at 16:35

Hi,

you can design a voltage divider to have +5V and connect the Diag/EN pin.

A voltage level higher than +5V connected to Diag/EN is not suggested.

The input clamp is used to protect the input pins.

Best regards,

Marco