5s supercapacitor design can provide more energy, so it is mainly used in centralized architecture. The following section shows three different power management designs for 5s supercapacitors.

• Buck-boost charge + Diode discharge

Buck-boost converter is used to charge supercapacitor. Diode is used to discharge the energy of supercapacitor to motor driver. Taking a 5s, 2.7V, 25F supercapacitor as an example, the rated voltage of the supercapacitor is 13.5V. The operating voltage range of a car's 12V main battery is 9V-16V, so a buck-boost charger is needed, such as TPS552892-Q1. A diode LM74700-Q1 is used as discharge to power the motor. Since the operating range of the motor is 9V to 16V, the supercapacitor can only discharge down to 9V, and energy below 9V cannot be utilized. Due to differences in supercapacitor production and manufacturing, when supercapacitors are connected in series, the voltage across each series may become unbalanced. Therefore, a cell balance IC such as BQ79607-Q1 / BQ78709-Q1(ASIL-B version) is needed to monitor the voltage of each cell in real time and perform passive discharge to balance the voltage of each cell and extend the life of the supercapacitors.

CPM also needs MCU, SBC and motor driver. MCU operates as the central system controlling the CPM, and it is recommended to use the MSPM0G3107-Q1. SBC can be the TCAN2845-Q1, which integrates a CAN-FD transceiver and a 3.3V LDO, used to power the MCU and communicate with the ZCU. The motor driver is used to drive the motor, such as DRV8244-Q1. The recommended system block diagram is shown in Figure 4-1 .

Figure 4-1 5s Supercapacitor System Block: Buck-Boost Charge and Diode Discharge

Figure 4-2 is the test waveforms of TPS552892-Q1 charging a supercapacitor. Channels 1-3 are the enable pin EN, supercapacitor voltage VOUT, charging current IOUT, respectively. From the waveform, after the enable pin is high, TPS552892-Q1 enters constant current charging phase, charging the supercapacitor with a constant current of 2.5A until the voltage reaches about 12.5V. Then IC enters the constant voltage charging phase, during which the charging current gradually decreases. The entire charging process lasts for 25 seconds. For more detailed application information, please refer to E-latch with 5S SuperCaps Solution Using Buck-Boost Converter.

Figure 4-2 Test Waveform of TPS552892-Q1 for Charging the Supercapacitor

• Buck-boost charge + Boost discharge

During discharging, using a boost controller such as LM5122-Q1 to replace diode can make full use of the energy of the supercapacitor. When the supercapacitor voltage is below 9V, the output can be boosted to 12V through a boost controller to drive the motor. The system block diagram is shown in Figure 4-3.

Figure 4-3 5s Supercapacitor System Block: Buck-Boost Charge + Boost Discharge

• Bi-directional buck-boost controller to charge and discharge

In the below design, it needs a buck-boost charger and a boost controller to discharge. TI launched a bi-directional buck-boost controller LM51772-Q1, which uses the same circuit for charging and discharging. It has higher integration and can significantly reduce system costs. The system block diagram is shown in Figure 4-4. The detailed application note is Battery or Capacitor Backup Operation with the LM51772.

Figure 4-4 5s Supercapacitor System Block: Bi-directional Buck-Boost Controller to Charge and Discharge