SLVAFC9 August   2022 TPS61094

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction of Solar Cell and MPPT
    1. 1.1 Traditional MPPT Solution
  4. 2Typical System with Solar cell
    1. 2.1 General Introduction
    2. 2.2 Specific End Equipment
      1. 2.2.1 System Requirements
  5. 3TPS61094 Solution
    1. 3.1 Supercap and Battery Design
    2. 3.2 Solar Panel Design
    3. 3.3 TPS61094 Description and Operation
    4. 3.4 System Solution
  6. 4Test Report Based on TPS61094 Solution
    1. 4.1 Test Waveform
  7. 5References

3.4 System Solution

To realize MPPT function and shorten the time of system testing. Auto buck or boost mode is being used in this system. A smaller super cap is used on the testing board. Table 3-1 shows the setting in this test.

Table 3-1 Test Setting on EVM Board
Parameters Values
Solar Panel 5.5 V 100 mW
Super Cap 3 F 2.7 V
Target Voltage 4.8 V
Charge Current 150 mA
Charge Voltage 2.7 V

The realization of the system mainly takes advantage of the characteristic that the voltage of the solar panel will drop when a large current is drawn. Combined with the auto buck-boost spec of TPS61094, the target voltage is 4.8 V and the charging current is 150 mA, which is higher than the Impp. Due to the characteristics of the solar cells, TPS61094 will switch between different modes quickly. This makes the output voltage fluctuate around the target voltage. And the output voltage is stable regardless of the light and the load. This solution realizes MPPT for not only battery charging but also post-stage power supply. The main operation mode of the system shows in Figure 3-3.

Figure 3-3 Main Two Operation States Transition

The TPS61094 works at buck mode first. There is a heavy load transient in the SUP pin and the solar panel cannot hold it, which makes the output voltage lower than the output target voltage (OSEL pin setting). The TPS61094 transfers from buck mode to supplement mode. The solar panel and SUP power source will supply the load together.

In supplement state, the input voltage will rise because the sup is not charged. And the output voltage will be higher than the output target voltage + 100 mV, meaning the solar panel can support the output load, the TPS61094 transfers from supplement to buck mode.

Figure 3-4 shows the waveform of the system. The yellow line shows the terminal voltage of the solar panel, the voltage is kept at around 4.8 V. The purple line shows the output voltage. A 47 uF electrolytic cap is added between the output and ground to filter out a 25 Hz switching ripple. The green line shows the current of the inductor. TPS61094 is in buck mode when the current is positive and in supplement mode when the current is negative. The result shows that this solution can successfully realize MPPT.

Figure 3-4 Typical Waveform to Realize MPPT