SLAAEI3 February   2024 MSPM0C1103 , MSPM0C1103-Q1 , MSPM0C1104 , MSPM0C1104-Q1 , MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G3105 , MSPM0G3105-Q1 , MSPM0G3106 , MSPM0G3106-Q1 , MSPM0G3107 , MSPM0G3107-Q1 , MSPM0G3505 , MSPM0G3505-Q1 , MSPM0G3506 , MSPM0G3506-Q1 , MSPM0G3507 , MSPM0G3507-Q1 , MSPM0G3519 , MSPM0L1105 , MSPM0L1106 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-Q1

 

  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

1 Relationship Between I, C and t

Under certain conditions, capacitors can be used to power the MCU. But how long the capacitor can last, and what factors are related to the maintenance time. Here, the relationship between hold-up time and supply capacitance is given in Equation 2.

Equation 1. t = C × V work 2 - V cutoff 2 I × V work + V cutoff

where,

t is the device operating maintenance time,

C represents the capacitance value, which is chosen by the user,

Vwork is the normal operating voltage of the MCU, that is, the starting voltage of the capacitor power supply,

Vcutoff is the cut-off voltage at which the MCU stops working. As the power supply is below Brown-out reset voltage level 0 (BOR0-), the device will discharge slowly because only Power-on Reset (POR), Bandgap (BG) and BOR are active, which means the MCU can not work normally. According to device-specific data sheet, the maximum of VBOR0- is 1.61V, I is the constant operating current of MCU, which depends on the operating mode of the MCU and the operation of the peripherals. In addition to direct measurement, here we provide two ways. One is to consult the device-specific data sheet, which includes the operating current of different peripherals under different operating conditions. The other is to directly use the EnergyTrace™ provided by TI to calculate the operating current of the device.

According to Equation 2, the correspondence between t and C can be obtained with the known operating current. This provides a reference to select the appropriate capacitor.