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

2.2 Design Considerations

An important design consideration is the use of auxiliary power. With the need for low current consumption in standby mode and ship mode, and good thermal performance in normal mode, this design uses the auxiliary power strategy shown in Figure 2-2.

Figure 2-2 Auxiliary Power Architecture

When the system is working in normal mode, the LM5163 buck DC/DC converter steps down the total battery voltage to 12 V to power the low-side MOSFET drivers – UCC27524 and UCC27517. A fly-buck converter generates a non-isolated 3.3 V to power the MCU and an isolated 5 V is available for isolated communications with the TPS54308 from 12 V. The TPS7A24, a low IQ LDO, regulates isolated rail output of the fly-buck to a stable 5 V to power isolated transceivers. In standby mode, the MOSFETs are in off state, isolated communications are not available.

The LM5163 is disabled through the EN pin and the TPS54308, UCC27524, UCC27517 devices are powered off to save energy. The bq76952 device outputs 3.3 V through one regulator to power the MCU which is in lower power mode. If MOSFETs are required to be on in standby mode to enable a fast discharge response, the LM5163 device is still enabled to power 12 V for the driver IC. At this time the TPS54308 is disabled through the EN pin to power off isolated communications to save power. If further lower standby current is needed, a lower current consumption driving circuit can be used. For more information, see the Using Low-Side FETs with the BQ769x2 Battery Monitor Family application note.

The series diode on the BQ76952 regulator output makes sure that all power is from the DC/DC converter in normal mode preventing the BQ76952 regulator circuits from overheating. Therefore, design the DC/DC output a little higher than the 3.3 V BQ76952 regulator output. Detailed component design guidance is available from the LM5163 and LM5164 converter quickstart design tool. When the system experiences a serious cell undervoltage and must enter ship mode, the MCU configures the BQ76952 device to enter shutdown mode through an I2C command or RST_SHUT pin and disables LM5163 output through the EN pin. This configures the system to very low current consumption mode. This design supports the charger attach wake up function. When charger is attached, the BQ76952 wakes up and enables normal 5-V regulator output. The MCU is then powered on and enables the LM5163 through the EN pin. The whole system then returns to normal mode.