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TLV3491: Layout and Data Sheet Descriptions

Ryu Yamashita
Expert 2680 points
Part Number: TLV3491

Tool/software:

Hi team,

In the datasheet 11.2 Layout Example, 0.01uF and 10uF are connected to the power supply, but in 11.1 Layout Guidelines 2. sentence, it is stated that 0.1uF is connected to the power supply.
Which is correct?
The diagram in 8.2 Functional Block Diagram shows a symbol for Schmitt trigger function.
Does this comparator have a built-in Schmitt trigger function?

Regards,
Ryu.

  • +1
    TI__Expert 6165 points

    Hi Ryu-san,

    The datasheet mentions to use both a 0.1uF and 10uF capacitor to act as decoupling capacitors for the device VCC. Guidelines 2 intends to mention that for the best effect, the decoupling capacitors should be laid out as close to the VCC pin as possible. Ideally, both the 0.1uF and 10uF should be as close to the VCC pin as possible.

    The block diagram in 8-2 is a schematic symbol of a comparator. The TLV3491 does not have internal hysteresis.

  • 0 in reply to HO SIU
    Expert 2680 points

    Hi HO-san,

    Thanks for your reply.
    In 11.1 of the datasheet it states the following.
    “. To minimize supply noise, power supplies must be capacitively decoupled by a 0.01-µF ceramic capacitor in parallel with a 10-µF electrolytic capacitor. Proper grounding (the use of a ground plane) helps to maintain the specified performance of the TLV349x family.
    Are you sure it is 10μF and 0.1μF?
    Also, I understand that these are for noise rejection, but what is the intent of each value?

    Regards,
    Ryu.

  • +1 in reply to Ryu Yamashita
    TI__Expert 6165 points

    Hi Ryu-san,

    The decoupling capacitors serve two purposes:

    One is that it serves as a charge reservoir, which provides charge to the device whenever it suddenly draws more current from the power rail, for example, when the device switches.

    Two, the decoupling capacitors serve as a low pass filter that rejects high frequency noise/ripple such that the voltage at the VCC pin is a clean DC voltage.

    Ryu Yamashita said:

    Also, I understand that these are for noise rejection, but what is the intent of each value?

    The intent for each value is that the lower valued capacitor serves as the "high frequency capacitor," because older through hole capacitors with lower values tended to have lower equivalent series inductance. Having this parallel combination of capacitors decades apart served to lower overall parasitic inductance in the decoupling network. With surface mount MLCCs, equivalent series inductance is not as dependent on the capacitor values, so whether it be 10uF with 0.1uF or 10uF with 0.01uF, the decoupling capacitors would still work. 

    This video actually details an adverse effect on the use of different values, such impedance not being as low in resonant frequencies:

    Decoupling capacitors | Video | TI.com