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

2.2.2 Connecting VCC to VBAT Through a Switch

In systems where the CO amplifier, MCU LDO, 300-mV reference, VCCLOW monitor, interconnect, and sleep timer do not need to be continuously powered, the TPS8802 can be unpowered in between smoke measurements to reduce the system standby current. To achieve this, the MCU controls a load switch between VBAT and VCC to disconnect the TPS8802 in between smoke measurements. This allows the smoke alarm to achieve an idle current less than the TPS8802 typical 3.8-μA standby current. This configuration provides the best power savings in smoke-only alarms where the CO amplifier is not used. The battery voltage must be above 2.6 V for parametric performance and above 2.4 V for functional performance. While this configuration has a tighter battery voltage range and cannot use the full capacity of the battery, the lower power consumption of this configuration gives it a longer battery life. VCC and PLDO are shorted together to remove the voltage drop caused by the internal PLDO block.

Figure 2-2 TPS8802 Power Connections with VCC Connected to VBAT Through a Switch
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