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Original question:

DRV8312: DRV8312, DRV8332 Power up and down sequence

DRV8312: VDD to GND capacitor of DRV8312 & DRV8332

Naoki.N
Intellectual 515 points
Part Number: DRV8312

Hi

According to the DRV8312's datasheet, in 10.3.2 VDD Pin mentioned that "A 22-μF to 47-μF capacitor should be placed on VDD pin."

Is this capacitor mean electrolytic capacitor? 

Parts supplier supply this capacity's ceramic capacitor.

Could you give me some advice on whether ceramic capacitors are okay?

Or does it depend on GVDD current?

Best regards

Naoki 

  • 0
    TI__Mastermind 18900 points

    Hello Naoki,

    When it comes to decoupling capacitors, the rule of thumb is a bulk cap (>10uF) and bypass cap (~100nF). Ceramic caps, from a performance standpoint, are always better because the ESR of the caps are low which means charge can more freely leave the cap and be used by the DRVx as opposed to an electrolytic cap. The problem is finding a ceramic cap in the voltage rating and value that are considered larger than 47uF.

    That being said, there's always a chance that there's still supply pumping or voltage ripple by using a 47uF, which means you need to add more capacitance to make it go away. Now, there might be some ceramic caps that are >47uF but I can guarantee that you'll find so electrolytic caps >47uF in the voltage ratings you need. As such, deciding to use a ceramic cap instead of an electrolytic is a sort of assembly, sustainability, and manufacturability risk exercise. 

    Will those ceramic caps always be there? What's their price compared to a electrolytic? Do multiple manufacturers carry an equivalent ceramic cap, or is it just one? If you need more capacitance, can you find another in a similar package? Is an electrolytic too large for the layout?

    These are all the questions you must consider. The safest option is to add a footprint for electrolytic and do not populate it until testing the board. Then you can decide to add it or not.

    I give another explanation about decoupling caps in this thread:  

    Best,

    -Cole

  • 0 in reply to Cole Macias
    Intellectual 515 points

    Thank you for answering question.

    Regarding 12V(GVDD and PVDD) capacitor

    There are 47uF ceramic capacitor such as TMK325ABJ476MM-P(Taiyo Yuden) .

    Maximum voltage value is up to 25V.

    As you guessed, the area is limited and I think I don't want to put an electrolytic cap if possible.

    Regarding 24V(PVDD) capacitor

    Have you ever considered using ceramic capacitors instead of PVDD electrolytic capacitors?

    Are there any advice on converting capacitor to ceramic.

    Of course, I think that multiple ceramic capacitors are necessary connected in parallel.

    Best regards

    Naoki

  • 0 in reply to Naoki.N
    TI__Mastermind 18900 points

    Hello Naoki-san,

    No concerns from me about using a ceramic instead of an electrolytic. I personally prefer them.

    The biggest problem with ceramic is with the voltage derating. I think you mentioned PVDD = 24V in a different post, if I'm not mistaken. That means, you need >48V rated ceramic capacitor (V_expected*2 = V_capVoltageRating) as a rule of thumb. This is mostly in the case of type 2 and type 3 ceramic capacitors, which I'm going to assume this capacitor would fall under. This means, the 25V rated cap might not work for your application. 

    There's are plenty of articles that talk about why (i.e. geometry of capacitor construction is the reason), here's one:  

    I encourage you to take a look at the cap's datasheet and see if the capacitance value changes over the applied voltage range or ask the manufacturer directly.

    If you haven't already, I would highly recommended you read the capacitor section of the Analog Engineer's Pocket Reference, it'll talk about the different types and what they're good for, in reality (in theory, if we could use C0G caps for everything, we would because they have the best performance):  

    Best,

    -Cole