SLVAFK1 January   2025 INA228 , INA232 , INA234 , INA236 , INA237 , INA238 , MSPM0C1103 , MSPM0C1103-Q1 , MSPM0C1104 , MSPM0C1104-Q1 , MSPM0C1105 , MSPM0C1106 , MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G1518 , MSPM0G1519 , MSPM0G3105 , MSPM0G3105-Q1 , MSPM0G3106 , MSPM0G3106-Q1 , MSPM0G3107 , MSPM0G3107-Q1 , MSPM0G3505 , MSPM0G3505-Q1 , MSPM0G3506 , MSPM0G3506-Q1 , MSPM0G3507 , MSPM0G3507-Q1 , MSPM0G3518 , MSPM0G3518-Q1 , MSPM0G3519 , MSPM0G3519-Q1 , MSPM0H3216 , MSPM0L1105 , MSPM0L1106 , MSPM0L1117 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-Q1 , TPS62866 , TPS62868 , TPS62869 , TPS6286A06 , TPS6286A08 , TPS6286A10 , TPS6286B08 , TPS6286B10

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Traditional Heater Control
  5. 2Constant Power Heater Control
  6. 3Hardware Implementation
  7. 4Software Implementation
  8. 5Software Algorithm Flow Chart
  9. 6Results
  10. 7Summary and Adaptations
  11. 8References

3 Hardware Implementation

The constant power drive design requires hardware to measure the voltage across the heating element and the current through the heating element to calculate the power. This is achieved using the INA234 which is a 28V, 12bit, I2C output current/voltage/power monitor. In this design the device measures the voltage directly across the heating element and the current through a high-side 10mΩ, ± 1%, 1W sense resistor. The devices then calculates the power and reports values for voltage, current and power via I2C.

For this example, we assume a 1Ω heating element that can vary by ± 20% across temperature and batch range. Table 3-1 shows the required voltage and current for different power levels across the resistance range. The input voltage is 3.3V to 5.0V. This means a buck or step-down dc/dc regulator can be used for the whole range required. The applied voltage is controlled using the TPS62868 which is a 2.4V to 5.5V input, synchronous buck converter with 4A output capability. Importantly, this device is I2C controlled which allows the output voltage to be easily adjusted.

Table 3-1 Voltage and Current for Different Power Levels and Different Resistances
Power (W)Current (A) at 0.8ΩVoltage (V) at 0.8ΩCurrent (A) at 1.0ΩVoltage (V) at 1.0ΩCurrent (A) at 1.2ΩVoltage (V) at 1.2Ω
4.02.241.792.002.001.832.19
5.02.502.002.242.242.042.45
6.02.742.192.452.452.242.68
7.02.962.372.652.652.422.90
8.03.162.532.832.832.583.10
9.03.352.683.003.002.743.29

The voltage, current and power is read from the INA234 via I2C using an MSPM0L1306. This low cost microprocessor is also responsible for adjusting the output voltage of the TPS62868 via I2C. The simplified and full circuit schematic can be seen respectively in Figure 3-2 and Figure 3-3.

Simplified Constant Power Control SchematicFigure 3-1 Simplified Constant Power Control Schematic
Constant Power Control SchematicFigure 3-2 Constant Power Control Schematic
Constant Power Control PCBAFigure 3-3 Constant Power Control PCBA