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dc-dc converter with dsPIC and CAN bus

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bhargav6

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hello all ,

I am currently stuck at a point where I wish to regulate the pos and neg output from both the SMPS IC which are dc-dc converters one with pos and other with neg voltage. There is a digital potentiometer at to change the output voltages of this IC.


I wish to control them using dsPIC, (do i need a comparator circuit with clamping diodes which will give me then either of the pos or neg ouputs from the ICs.

I am not sure, if i can connect them directly via DIGI POT to the dsPIC30f4011..

Any assistance is appreciated..


Thanks
 

Hi,

please explain:
* you want to adjust postitive output voltage only
* you want to adjust positive and negative voltage symmetrically
* you want to adjust positive and negative voltage independently

What resolution and accuracy? Give values with units.

****
As I recommended in other threads: use SMPS ICs with local, analog feedback and use a DAC to "manipulate" the feedback.... and thus the output voltage.

Klaus
 

Hi,

please explain:
* you want to adjust postitive output voltage only
* you want to adjust positive and negative voltage symmetrically
* you want to adjust positive and negative voltage independently

What resolution and accuracy? Give values with units.

****
As I recommended in other threads: use SMPS ICs with local, analog feedback and use a DAC to "manipulate" the feedback.... and thus the output voltage.

Klaus

I want to adjust both pos and neg voltage independently....

As the output of pos will be some volts (pin KL30)

And similarly the neg will be some volts (pin KL31)

Both to the ECUs..

Can I some how use voltage offset ?

for eg If I wish to have 0V at the output from the neg DC-DC converter output as this IC has the capacity to give output as low as -0.4V , and the first IC as low as +0.8V ....

Can I use both this voltage and have 0V at the pin KL31 (ie at neg output)

Do you think it will be feasible?

Thanks
 

Hi,

you speak as if you already have some SMPS IC in mind. --> show us the manufacturer, exact device name and datasheet.
Then we have the same information to talk about.

Klaus
 

Hi,

Read: https://www.edaboard.com/showthread.php?t=370852&p=1587887&viewfull=1#post1587887
With the LM25117 you may use this method.
For the negative supply I recommend to additionally use an inverting OPAMP.

Sadly you didn´t answer my question about resolution and accuracy.

What do you mean?

For the LM25117 the 0.8V limitation is because of it´s 0.8V feedback voltage....as soon as you apply the "feedback manupulation circuit" you may go down to 0V.

Let´s go into details for the negative supply after the positive works.

Klaus


Did you mean efficiency to achieve and required output voltage and current when you say about resolution and accuracy ?

And 0.8V is the minimum output voltage the IC is able to deliver ...I will check the thread you have given..

Ya lets evaluate in detail once the pos is in place.

Bhargav
 

Hi,

### sorry for the wrong order of posts ###

Read: https://www.edaboard.com/showthread.php?t=370852&p=1587887&viewfull=1#post1587887
With the LM25117 you may use this method.
For the negative supply I recommend to additionally use an inverting OPAMP.

Sadly you didn´t answer my question about resolution and accuracy.
Can I some how use voltage offset ?
What do you mean?

For the LM25117 the 0.8V limitation is because of it´s 0.8V feedback voltage....as soon as you apply the "feedback manupulation circuit" you may go down to 0V.

Let´s go into details for the negative supply after the positive works.

Klaus

- - - Updated - - -

Hi,

resoution and accuracy have nothing to do with efficiency.

There are many good articles in the internet.
Like wikipedia: https://en.wikipedia.org/wiki/Accuracy_and_precision

in short: resolution is the step size or the granularity.
Alternatively: You may say how many steps you like or what bit-width your DAC has.

Klaus
 

Oh I get you now.

The DIGI POT, I have is 8 bit The MCP42010 is a dual-channel, 8-bit digital potentiometer features 10kΩ end-to-end resistance value with an SPI serial interface

with 256 steps ..

And dsPIC30F4011 PIC microcontroller .

To be precise .
I have ordered and also received parts of the design
for eg both the ICs, CAN Transceiver, and dsPIC

I will check the thread for pos output, for the neg out, (I am still skeptical
 

Hi,

I´d prefer a DAC against the pots.
The pots have limited step count = big steps aand because of the varying output resistance the stepsize varies.
40V with 256 steps gives a stepsize of about 0.156 Volts.

Klaus
 

Hi,

so let me tell you the current situation. The firm LT has provided me the evaluation board of LT3863 with (4.5V to 16V input voltage range and fixed output voltage -1.5V,5A .


I initially planned to design a PCB and mount the SMD components on it. However, things dint work out well and I shifted to testing the complete circuit on a general purpose perfboard, before going to the actual design.

But both my ICs (LM25117 and LTC3863) are of housing type MSOP12 and HTSSOP 20 resp.

IC adpaters wont help me achieve as thermal shutdown factor comes in place and the pin remain exposed to the pad

So, I thought of using this evaluation board with my perfboard design .?

Do you think it will work if, I

Use the evaluation board of LTC3863 with, a perfboard with (LM25117 IC and its components)

As I am out of time I cannot order a PCB, as it will be costly and take time ...


Thanks
 

Hi,

A perfoboard is not suitable for high speed switching power applications. Maybe you get it work, but don´t surprise if it fails with time, with temperature with modified IO situations.
In either case it won´t comply with EMI/EMC regulations.

You need to fulfill the PCB layout (and all other) requirements given in the datasheet (for every IC). This usually can´t be made wihtout proper PCB layout.

If you don´t have a proper PCB layout, then the evaluation board is the only safe way to get reliable and stable results. Connections from/to the evaluation board are less critical. (because it´s more DC style)

Klaus
 

Hi,

A perfoboard is not suitable for high speed switching power applications. Maybe you get it work, but don´t surprise if it fails with time, with temperature with modified IO situations.
In either case it won´t comply with EMI/EMC regulations.

You need to fulfill the PCB layout (and all other) requirements given in the datasheet (for every IC). This usually can´t be made wihtout proper PCB layout.

If you don´t have a proper PCB layout, then the evaluation board is the only safe way to get reliable and stable results. Connections from/to the evaluation board are less critical. (because it´s more DC style)

Klaus



Hi,


I want to clear doubt regarding the MCP42010 digital potentiometer connections with the LM25117-Q1 DC-DC converter. LM25117.PNG

Adding an extra resistor and then to the pin SI or other pin with any external passive components.

The dsPIC30F has SPI interface, for that matter it will be then directly connected to Digi-pot ?


Regards,

Bhargav
 

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