Give you a switched capacitor power supply for high power applications~

The LTC7820 is a fixed ratio, high voltage, high power switched capacitor power supply controller that provides a compact, cost-effective solution with fault protection for high power, non-isolated intermediate bus applications. Features of the LTC7820 include:

Figure 1 shows a voltage divider circuit with 480 W output using the LTC7820. The input voltage is 48 V, the output is 24 V, and the load current is up to 20 A. 16 10 μF ceramic capacitors (1210 size) are used as flying capacitors to transfer power. As shown in Figure 2, the approximate size of the solution is 23 mm × 16.5 mm × 5 mm, while the power density is up to 4000 W/in ³ .

Since no inductor is used in this circuit , all four MOSFETs can achieve soft switching, which greatly reduces the losses caused by switching. As shown in Figure 3, the converter can achieve high efficiency, with a peak efficiency of 99.3% and a full load efficiency of 98.4%. The thermal image in Figure 4 shows a balanced thermal design, with a hot spot temperature of approximately 82.3°C at an ambient temperature of 23°C and without forced air cooling.

In addition to excellent efficiency and thermal performance, the LTC7820 also uses a proprietary pre-balancing method to minimize inrush current in voltage divider applications. Before switching, the LTC7820 controller detects the voltage at the V _{LOW_SENSE} pin and compares it internally to V _{HIGH_SENSE} /2. If the voltage on the V _{LOW_SENSE pin is well below V HIGH_SENSE} /2, a current source injects 93 mA of current on the V _LOW pin to pull V _LOW up. If the voltage on V _{LOW_SENSE} is well above V _{HIGH_SENSE} /2, another current source sinks 50 mA from V _LOW to pull it down. If the voltage on V _{LOW_SENSE is close to V HIGH_SENSE} /2 (i.e., within the preprogrammed window), both current sources are turned off and the LTC7820 begins switching.

Figure 5 shows that without pre-charging, a huge input surge current occurs at startup, which is enough to damage the MOSFET and capacitors. In contrast, after the pre-balancing method is applied, no excessive surge current is observed (as shown in Figure 6).

Although the LTC7820-based voltage divider is an open-loop controlled power supply, good load regulation can still be achieved due to its high efficiency. As shown in Figure 7, the output voltage drops only 1.7% at full load.

The LTC7820 has protection features to ensure high reliability. Overcurrent protection is implemented through a current sampling resistor on the high voltage side. A precision rail-to-rail comparator detects the differential voltage between the _ISENSE+ and _ISENSE– pins, which are connected to the current sampling resistor in a Kelvin manner. When the voltage on _{ISENSE+ is 50 mV higher than ISENSE–} , an overcurrent protection is triggered, the FAULT pin is pulled down to ground, the LTC7820 stops switching and starts a retry mode according to the timer pin setting.

Further protection is provided by the OV/UV window comparator. In normal operation, the voltage on V _{LOW_SENSE should be close to half the V HIGH_SENSE} voltage. The window comparator senses V _{LOW_SENSE} and compares it to V _{HIGH_SENSE} /2. The hysteresis window voltage can be programmed and is equal to the voltage on the HYS_PRGM pin. With a 100 kΩ resistor on the HYS_PRGM pin, the V _{HIGH_SENSE /2 voltage must be within the window of (V LOW_SENSE} ±1 V) during startup and normal operation , otherwise the protection is triggered and the LTC7820 stops switching.

The LTC7820 is a fixed ratio, high voltage, high power switched capacitor controller that meets the power density requirements of bus converters, high power distributed power systems, communications systems and industrial applications. No inductor is required.