TIDUEO0C July   2019  – March 2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS63900: 1.8V-5.5 VIN Buck-Boost Converter With 75-nA Ultra-low Quiescent Current and 400-mA Output Current
      2. 2.3.2 TPS610995: 0.7 VIN Synchronous Boost Converter With 400-nA Ultra-low Quiescent Current and 1-A Peak Current
      3. 2.3.3 TPS62840: 750-mA Synchronous Step-Down Converter With Ultra-low Quiescent Current Consumption
    4. 2.4 System Design Theory
      1. 2.4.1 Battery Gauge BQ35100
      2. 2.4.2 In-System Current Monitoring
        1. 2.4.2.1 Resistor Values Calculation for the two Current Ranges
        2. 2.4.2.2 LPV521 Gain Calculation
        3. 2.4.2.3 Current Ranges Simulation With TINA-TI
        4. 2.4.2.4 Key ADS7142 Register Settings in TIDA-01546 Firmware
          1. 2.4.2.4.1 ADS7142 Sampling Rate
      3. 2.4.3 NB-IoT Module From u-blox
      4. 2.4.4 NB-IoT Module From Quectel
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
      1. 3.1.1 Testing TIDA-010053
      2. 3.1.2 TPS62840 Subsystem
      3. 3.1.3 TPS610995 Subsystem
      4. 3.1.4 Software
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Test Results With the TPS62840 Buck Converter
        2. 3.2.2.2 Test Results With the TPS610995 Boost Converter
        3. 3.2.2.3 Test Results With the TPS63900 Buck-Boost Converter NB
        4. 3.2.2.4 Summary
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7Terminology
  13. 8About the Author
  14. 9Revision History

2.4.2.4 Key ADS7142 Register Settings in TIDA-01546 Firmware

The TIDA-01546 software implements the logic for the system monitoring and battery gauge functions under the assumption that the load profile is a square wave. This square wave alternates between above the window comparator high and below the window comparator low thresholds of the ADS7142, both of which are user programmable.

There is only one set of high- and low-threshold registers in the ADS7142 device, which means that the user-defined threshold values represent different current values, depending on which current range (or resistor) is active. In other words, the ADS7142 threshold settings are used to detect the rising and falling edges of the load profile and respectively switch the 0.1-Ω resistor on and off.

Using the 10.47 µA and 475.86 mA from the list in Section 2.4.2.2, calculate and program the threshold current values as appropriate. The conversion output by the ADS7142 device at 3.3 V is equal to 0xFFF (this is a 12-bit SAR ADC). The default firmware settings for the high- and low-threshold are 0x998 and 0x028 respectively, and correspond to the following:

  1. 0x998/0xFFF = 2456/4096 = 0.5996 = 0.6 for the low-current range
  2. 0x028/0xFFF = 40/4096 = 0.00976 = 0.01 for the high-current range

Table 2-1 shows the conversion of these threshold values into a current value.

Table 2-1 Threshold Settings in Firmware for the two Current Ranges
LOAD PROFILETHRESHOLD (ADS
REGISTER VALUE)		THRESHOLD CURRENT (A)SHUNT RESISTANCE
(Ω) IN USE
Low to High transitionHTRH = 0x9980.6 × 10.47 µA = 6.28 µA6800
High to Low transitionLTHR = 0x0280.01 × 476 mA = 4.76 mA0.1 + 0.045

The stand-by current of the board must be below 6.28 µA, and the active current must stay above
4.76 mA up to 476 mA; otherwise, the 0.1-Ω resistor switches on and off unnecessarily. Modify these settings by changing the values in the high- and low-threshold registers of the ADS7142 device.

Note:

Due to the asymmetric threshold current values when switching from the low-current to the high-current range and back, carefully select the high and low thresholds (including the optional ADS7142 window comparator hysteresis settings) to avoid erroneous changes from one current range to the other.