SLVAET3 October   2021 TPS8802

 

  1.   Trademarks
  2. 1Introduction
  3. 2System Architecture
    1. 2.1 Battery Voltage
    2. 2.2 VCC Supply
      1. 2.2.1 Connecting VCC to VBST
      2. 2.2.2 Connecting VCC to VBAT Through a Switch
    3. 2.3 MCU Supply
      1. 2.3.1 MCU Connected to VBAT
      2. 2.3.2 MCU Connected to MCU LDO
      3. 2.3.3 MCU with VCC Connected to VBAT Through a Switch
    4. 2.4 Photoelectric Smoke Sensor LED Supply
      1. 2.4.1 LED Connected to VBAT
      2. 2.4.2 LED Connected to PLDO
      3. 2.4.3 LED Connected to LEDLDO
    5. 2.5 Example Schematics
      1. 2.5.1 Smoke and CO Schematics
      2. 2.5.2 Smoke-Only Schematics
  4. 3Current Consumption
    1. 3.1 Standby Current
      1. 3.1.1 TPS8802 Standby Current
      2. 3.1.2 Microcontroller Standby Current
    2. 3.2 Measurement Current
      1. 3.2.1 Smoke Measurement Current
      2. 3.2.2 CO Measurement Current
      3. 3.2.3 Battery Test Current
      4. 3.2.4 User Alarm Test Current
    3. 3.3 Other Current Consumption
      1. 3.3.1 Boost Charge Current
      2. 3.3.2 Initialization Current
  5. 4System Power Calculation and Measurements
    1. 4.1 Power Calculation Spreadsheet
      1. 4.1.1 Power Consumption Overview Page
      2. 4.1.2 Detailed Calculation Pages
    2. 4.2 Power Consumption Measurements
      1. 4.2.1 Power Measurement Method
      2. 4.2.2 Smoke and CO System Measurements
      3. 4.2.3 Smoke-Only System Measurements
  6. 5Summary
  7. 6References

2.1 Battery Voltage

The TPS8802 operates with a battery voltage between 2.0 V and 15.6 V and a VCC voltage between 2.6 V and 15.6 V. When the battery voltage is less than 2.6 V, the boost converter increases the voltage to adequately supply VCC. This allows the TPS8802 to be powered from a variety of batteries, including 3-V lithium, series-connected 1.5-V alkaline, and 9-V alkaline or lithium. Alkaline batteries typically have a shorter shelf life than lithium batteries, making lithium batteries more viable for 10-year smoke alarms. The VCC voltage must be at least 2.6 V for the internal amplifiers to function properly, making the system most efficient when VCC is close to 2.6 V. Therefore, 3-V lithium manganese dioxide (LiMnO2) batteries and two series-connected 1.5-V lithium iron disulfide (LiFeS2) batteries provide the best capacity per cost in this application. Other lithium battery chemistries such as lithium ion and lithium thionyl chloride are not considered due to their higher cost. With the battery voltage selected, the system architecture can be designed and current consumption can be calculated. A specific battery size is selected after the capacity requirement is calculated.