R and C values for a bldc card

[jmx66]

Hi all,

Last query before, - i hope - etching and drilling the board.

In fact , on my burnt bldcd card, there's a part with C and R.

Schematic is my true card.

After reading MC33035 and 33039, then AN 1046D , i don't understand purpose of these components.

If someone could give me the answer,and also how to compute them, would be great.

Thanks a lot.

jm

 

[FvM]

You mean the R and C connected through JP1? They set the output current limit and this way adjsut the PWM setpoint. The limit comparator has a threshold of about 100 mV, the sense resistor is shown with a 0.012 ohm value. So without a resistor connected to JP1, the current limit is set to about 8.3 A. Connecting R35 creates a 1:1 divider and doubles the current threshold. The capacitors are used to prevent current spikes to trigger the comparator.

 

[jmx66]

Hi FvM,

Thanks for your really fast reply - about less than 5 minutes after post !!!!! -, in fact, my query is about R6 to R11 with their capacitors.( see num-risation0003-modif-1-png )

I draw a schematic - black scheme - and their labels are R1 -> R6 and C1 - > C6 .

And i don't know how to math R and C values...

Thanks a lot.

jm

 

[FvM]

Do you know the expected maximum output currents? As far as I understand, the current will be normally ruled by the PWM according to the speed setpoint. The current limit should only trigger in abnormal situations, e.g. a blocked motor. The capacitor dimensioning is discussed in datasheet Fig. 26. The actual current threshold is defined by 100 mV/0.012 ohm * (Rx+R35)/R35, where Rx is the resistor connected by JP1.

 

[jmx66]

Hi FvM,

Thanks a lot for your quick replies.

In fact , i 've just modified the original scheme , because i didn't ask question very clearly, with right scheme... Apologies.

So my query is about R6 to R11 and C11 to C16 see grey box with inside

" Values for R6 to R11

C11 to C16 "

Middle left side

I really read datasheet and AN, but with my mechanical background, didn't really how to math these values, hence my answer!!!!!


Thanks a lot.

jm

Ps: Now going to bed, tomorrow five o' clock in the morning.....

 

[FvM]

O.K., I didn't notice this additional point. That's more easy. The resistors are simply pull-ups to be used with input switches and the open collector hall-effect sensor outputs. There are already pull-ups inside the IC (20k and 40k according to the datasheet). I would e.g. place 10 k for each external resistors, and a capacitor around 1 nF to filter possible spikes. But I'm not sure, if they are needed. You should also check the halls sensor specification for the specified ouput load.

 

[jmx66]

Thanks a lot FvM for your clear replies.

Really great .

jm