SLAAEI3 February   2024 MSPM0C1104 , MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G3105 , MSPM0G3106 , MSPM0G3107 , MSPM0G3107-Q1 , MSPM0G3505 , MSPM0G3506 , MSPM0G3507 , MSPM0G3507-Q1 , MSPM0L1105 , MSPM0L1106 , MSPM0L1228 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2228

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Relationship Between I, C and t
  5. 2Application Scenarios
  6. 3Derivation of Formulas
  7. 4Experimental Verification
    1. 4.1 Test Environment Setup
    2. 4.2 The Result of Experiment
  8. 5Notes

5 Notes

The selection of capacitors requires attention to the following points.

  1. Pay attention to the error of the capacitor's own capacitance.

    Capacitor material. Here is the example of GRM188R60J106ME47(muRata, MLCC, X5R)’s DC Bias characteristics. When DC increases, the capacitance of the ceramic capacitor has a large error. In this example, when the dc bias voltage is 3.3 V, the capacitance error can reach 50%.

    GUID-2F908BCB-AD6C-430A-8ECA-330B5DCFAAD5-low.png Figure 5-1 GRM188R60J106ME47's DC Bias Characteristics.

    For further validation, the capacitor was used to test the power supply of the MCU. The result is shown in Figure 5-2. The operating current is 1.5 mA, and the supply capacitance is 41.1 μF. But the operating time is 29.95 ms, which is far lower than the theoretical calculation of 45.76 ms.

    As a result, when using capacitors, it's necessary to pay attention to the characteristics of the capacitor itself.

    GUID-165D8534-C721-403B-914E-74ACACDC6EDE-low.png Figure 5-2 The Operating Time of MCU Powered by GRM188R60J106ME47

    Size of capacitor. The size of the package affects the thickness of the dielectric, and in the case of applying the same voltage, especially for ceramic capacitors with ferroelectric materials as dielectric materials, the smaller the thickness of the dielectric, the greater the internal electric field stress, which can lead to the large error of capacity. As a result, capacitors with stable capacitance values are preferred in this model. Therefore, please test the capacitance value with a tool such as a multimeter between uses

  2. Pay attention to the effect of leakage.

    Capacitor material. Compared to capacitors of other materials, electrolytic capacitors have a larger leakage current. When the MCU is in standby0 mode, that is, the operating current is close to 1.5μA, the effect of leakage current becomes obvious. Therefore, when the operating current is small, the leakage current needs to be considered.

    PCB layout. It should be noted that there will be equivalent resistance in the trace between the power supply capacitor and the MCU power pin, which will lose the energy of part of the capacitor, so this factor needs to be taken into account when the capacitor selection capacity is small.