0
\$\begingroup\$

I'm using the MCP2021A for my project. In this component, there is a voltage regulator but I have no use for it. They usually power microcontroller like the PIC18F2455 but I'm using a Raspberry Pi which consumes too much current.

If I don't use this regulator, I have no output on my LIN BUS.

Can someone explain to me how it works so I can find a solution ?

Schematic:

enter image description here

I just connected pin 3 of IC (MCP2021A) to an unused Arduino so I can have VREG_OK which I don't have if it's floating.

\$\endgroup\$
6
  • \$\begingroup\$ The MCP2021A is the only chip I had an unlimited supply of, this is why I choose it. \$\endgroup\$
    – Graggon
    Dec 8, 2020 at 11:28
  • \$\begingroup\$ There's nothing to do with the internal regulator output, and you don't have to use it. If I don't use this Regulator I have no output on my LIN BUS. What do you mean? Did you mean "left floating" by "not using"? The problem should be somewhere else. \$\endgroup\$ Dec 8, 2020 at 11:35
  • \$\begingroup\$ Yes, If I left it floating it's not working. I'm doing everything so it enters operation mod but if i disconnect Vreg from the Arduino that I power (just so it works, i don't need an arduino), it stops working. I think it's VREG_OK that goes to 0 \$\endgroup\$
    – Graggon
    Dec 8, 2020 at 11:48
  • \$\begingroup\$ Disconnect from Arduino? In the question, you said that you are using an RPi. Anyway, you'd better post a schematic/connection diagram. It'd help us a lot. \$\endgroup\$ Dec 8, 2020 at 11:59
  • \$\begingroup\$ I just added a schematic, it should be more comprehensive. The arduino is just here so Vreg is not floating \$\endgroup\$
    – Graggon
    Dec 8, 2020 at 12:08

1 Answer 1

0
\$\begingroup\$

I think it's VREG_OK that goes to 0

The problem is about the Vreg pin, but not about drawing a current from that pin. VREG_OK does not indicate if the Vreg pin is floating. Vreg is the output voltage of an on-chip regulator and the chip uses this voltage for the internals (look at the block diagram at p.2). It's not a must that you should draw current from that voltage.

However, this pin requires a bypass capacitor for stability (First sentence at p.9):

enter image description here Img Src: Datasheet, p.19.

So, if you connect a low-ESR capacitor with a capacitance of at least 10uF then everything will be fine.

but if i disconnect Vreg from the Arduino that I power (just so it works, i don't need an arduino), it stops working. ... The arduino is just here so Vreg is not floating

Arduino's input line bypass capacitors are fixing the instability here :)

\$\endgroup\$
2
  • \$\begingroup\$ So everything makes sense now! Thank you for taking the time to explain it to me. Çok teşekkür ederim :) \$\endgroup\$
    – Graggon
    Dec 8, 2020 at 12:42
  • \$\begingroup\$ @Graggon rica ederim :) \$\endgroup\$ Dec 8, 2020 at 12:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.