PT2001 why inhibit Vboost?

[Fast]

Why is the Vboost generator inhibited by an injector boost phase? Code comments just describe action, no reason.

[Fast]

Thank you David. Yes AN4849 is a useful document, sure there is a high current draw from Vboost, but why not top it up while it is being drained?

[Fast]

Hi David, did you get support from the designer?

[Fast]

Elsewhere it is stated (3 questions about MC33PT2000 ) that if the Vboost is generated by different means then the local Vboost is a Do Not Populate. Is the inhibition of Asynchronous operation only needed for a local DC to DC? 

To avoid regulation disturbances, the boost voltage regulation is stopped by the mean of the internal flag 0 when an injection phase starts. From AN4849 But why is it disturbed, when in switching? Is it only the negative overcurrent detection disturbed?

David any news from designer?

[diazmarin09]

Hello Fast,

I am pleased to contact you again. Your patience is greatly appreciated.

Please review the response from our specialist below:

Why is the Vboost generator inhibited by an injector boost phase?

This is really depending on how Vboost cap is connected, if connected directly GND no issue since it will not disturb boost shunt. If connected to shunt we disable Vboost because the current will flow from shunt to cap to injector so shunt measurement will be incorerect

Elsewhere it is stated (3 questions about MC33PT2000 ) that if the Vboost is generated by different means then the local Vboost is a Do Not Populate. Is the inhibition of Asynchronous operation only needed for a local DC to DC?  

Same as above just depend on how Vboost genration is done

To avoid regulation disturbances, the boost voltage regulation is stopped by the mean of the internal flag 0 when an injection phase starts. From AN4849 But why is it disturbed, when in switching? Is it only the negative overcurrent detection disturbed?

In AN we have Vboost cap connected to shunt so we disable the regulation to avoid wrong measurement of Vboost current

I hope this information helps.

Regards,

David

[Fast]

Thank you David. That makes complete sense. Wish it had been described in documentation. But one more question please; what is the advantage of measuring, the current to injector thru shunt to cap to injector? HS Vboost pass MOSFET is protected with Vds monitoring. I note the only other ASIC on the open market has the "Vtank" capacitor grounded directly, so not thru current sense.

[diazmarin09]

Hello Fast, 

I am pleased to know that the information provided was useful for you.

Please review the response from our specialist below:

This is explained in AN4849.

If you connect Boost cap to shunt then you can control the boost in current with two threshold high and low.

If you don't then you can only monitor the current when Low side is ON and used a fixed turn OFF duration before restarting LS7

But customer can do the way they want both options works well.

Regards,

David

[Fast]

David thanks for interceding with specialist.

If I take capacitor to ground, avoiding current shunt; must I change PT2001 code?

[diazmarin09]

Hello Fast,

I'm glad to know that you found the AN4849 useful.

In regard to your question, I would need to consult the designer. I´ll keep you updated in case I have further information.

Regards,

David

[diazmarin09]

Hello Fast,

I hope all is great with you. Thank you for using the NXP communities.

“During the boost phase, the corresponding low-side driver is simultaneously switched on with the high-side switch connected to the Vboost voltage. If the boost current target Iboost is reached, the high-side driver is switched off and the current recirculates for a fixed time (tpeak_off) through the diode connected to ground. Then the peak phase starts”.

You may find further information at the Application Note AN4849 (attached).

I hope this information helps.

Regards,

David