SLVAF41A March   2021  – November 2021 TPS61094


  1.   Trademarks
  2. 1Introduction of the Smart Meter
  3. 2The Traditional Power Solution of the Smart Meter
    1. 2.1 Connecting the Battery Directly
    2. 2.2 The Pure Boost TPS61094 or TPS610995 Solution
  4. 3The TPS61094 with Supercap Solution
    1. 3.1 TPS61094 Description
    2. 3.2 System Operation Description
  5. 4Solution Comparison
  6. 5Supercap Behavior and Design
    1. 5.1 Supercap Life Time
    2. 5.2 Supercap Leakage Currrent
    3. 5.3 Supercap Parameter Design in TPS61094 Solution
  7. 6Test Report Based on TPS61094 Solution
    1. 6.1 Test Waveform
      1. 6.1.1 NB-IoT Data Transmission
      2. 6.1.2 Supercap Charging
    2. 6.2 Efficiency
  8. 7References
  9. 8Revision History

Introduction of the Smart Meter

Smart meters, including gas and water meters need to record information such as gas or water consumption and then communicate this information to a data center. Wireless communication commonly uses methods such as, NB-IoT, LoRa and ZigBee®. Take NB-IoT as an example, the typical range of input voltage of a NB-IoT module (such as the ZTE ZM8300G module) is from 3 V to 4.2 V, with a typical voltage of 3.6 V (reference 1 ). The current consumption is similar to Figure 1-1. The typical peak current is about 250 mA.

GUID-20210201-CA0I-1BL7-ZH4M-WXCRGNR8RXDH-low.gif Figure 1-1 Typical Current Consumption of NB-IoT

Most smart meters are powered by LiMnO2 (lithium manganese dioxide) or LiSOCl2 batteries and need to support 10 years or more of operation. Because the voltage of a LiSOCl2 battery (about 3.6 V) is higher than a LiMnO2 battery (about 2-3 V), a LiSOCl2 battery can better support a 3-V electromagnetic valve, which why it is a more popular choice for smart meter applications. The weakness of a LiSOCl2 battery is that the maximum continuous current and pulse current capability is limited. Take an 8.5 Ah LiSOCl2 battery (Tadiran TL-4920(ER26500)) as an example, the maximum recommended continuous current is 75 mAand the maximum 1 sec. pulse capability is 200 mA (reference 2). Because of this, it is common to parallel the hybrid layer capacitor (HLC) or the supercapacitor with the LiSOCl2 battery to support the high pulse current for data transmission. Another characteristic of the LiSOCl2 battery is that the battery capacity is related to the discharging current and the working temperature as shown in Figure 1-2 (reference 2). The battery capacity is about 8.5 Ah with 3-mA discharging current at 25 °C, which is shown in the ER26500 data sheet. However, the capacity drops to 2 Ah (a 76% reduction) with a 100 mA load. It is better to control the discharge current of a LiSOCl2 battery to get a higher capacity and thus, increase the working lifetime (reference 3).

GUID-20210201-CA0I-M0BW-DG3Z-Q5JDHXFTLRF6-low.gif Figure 1-2 Capacity vs. Discharging Current and Temperature