TIDUF14 October   2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ76952
      2. 2.3.2 LM5163
      3. 2.3.3 MSP430FR2155
      4. 2.3.4 ISO1042
      5. 2.3.5 TPS54308
      6. 2.3.6 ISO7731
      7. 2.3.7 THVD1400
      8. 2.3.8 UCC27524
      9. 2.3.9 TMP61
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Cell Voltage Accuracy
      2. 3.3.2 Pack Current Accuracy
      3. 3.3.3 Auxiliary Power and System Current Consumption
      4. 3.3.4 Cell Balancing
      5. 3.3.5 Protection
      6. 3.3.6 Working Modes Transition
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  10. 5About the Author

3.3.3 Auxiliary Power and System Current Consumption

Due to the auxiliary power strategy, this design has very low current consumption, especially when in standby mode and ship mode. System-level current consumption contains three parts: (1) DC/DC current, (2) BQ76952 current (current into BQ76952 BAT pin), and (3) LDO current (current into BQ76952 REGIN pin). This current can be measured from the voltage across (1) R78, (2) R54, and (3) R78. Table 3-3 shows the test results of current consumption.

Table 3-3 Current Consumption
MODE DESCRIPTION R79 (100 Ω) R54 (100 Ω) R78 (309 Ω) TOTAL CURRENT (μA)
Standby (MOSFET off) Voltage (mV) 0.64 32 9.9 70.6
Current (μA) 6.6 32 32
Standby (MOSFET on) Voltage (mV) 31 32 9.9 374
Current (μA) 310 32 32
Ship Voltage (mV) 0.66 0 0 6.6
Current (μA) 6.6 0 0

Total current consumption is less than 100-μA in standby mode with both charge and discharge MOSFETs off. If both charge and discharge MOSFETs are required on in standby mode to secure zero discharge delay, the total current consumption is larger since driver circuit require several mA current. This design has about 400-μA total input current with both MOSFETs on. One way to decrease DC/DC input current is to decrease DC/DC switching frequency, circuits are reserved in this design. More drive circuit information is available in the Using Low-Side FETs with the BQ769x2 Battery Monitor Family application note.

Figure 3-4, Figure 3-5, and Figure 3-6 show the auxiliary circuit start-up and output ripple for both 12 V and
3.3 V.

Figure 3-4 Auxiliary Start-Up
Figure 3-6 3.3-V Ripple
Figure 3-5 12-V Ripple