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

4.2.3 Smoke-Only System Measurements

GUID-20200904-CA0I-5NFF-F3HZ-ZWX0FB8L87XK-low.png Figure 4-12 Energia Code Excerpt for Taking Smoke and CO Measurements

The smoke-only smoke measurement subroutine controls the TPS8802 and collects the data required to determine the smoke concentration in the chamber. The waveforms verify that the Energia code is correctly written.

GUID-20200904-CA0I-8308-JSDK-HJS55JQ6GP31-low.gifFigure 4-13 Smoke Measurement Waveforms in the Smoke-Only System
GUID-20200904-CA0I-8PCB-NB0F-RRTKM0X0VQTL-low.pngFigure 4-15 Multiple Smoke Measurements Waveforms with VBAT=2.6 V
GUID-20200908-CA0I-25VC-HXZG-FFFCBNLPKQ9C-low.pngFigure 4-14 Power and Signal Waveforms in the Smoke-Only System

The supply current with the LED connected and disconnected is measured at two voltages, shown in Table 4-2. Four sets of measurements are taken at each condition, making the total measurement time 40 seconds for each condition. For this calculation, the MCU standby, MCU active, battery test, and user alarm test currents are set to zero because they are not implemented in the Energia code. The measurement matches the calculation within 100 nA.

The calculation accuracy verifies that the calculation can be modified to estimate the power consumption with different system specifications. The result of the power calculation with MCU currents, battery test currents, and user alarm test currents added is shown in Figure 4-1.

Table 4-2 Smoke-Only System Current Consumption
Supply Voltage VBAT=3.0V VBAT=2.6V
Condition LED on LED off LED on LED off
Measurement 5.21 µA 2.92 µA 5.03 µA 2.78 µA
Calculation 5.11 µA 2.86 µA 5.02 µA 2.77 µA