我查了手册：
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The charge pump circuitry generates a voltage to drive the NMOS of the linear regulator. The voltage across the charge pump capacitor between VLNB and VCP is about 5.4 V, so the absolute value of the VCP voltage will be VLNB + 5.4 V
也就是说Q1是确保输出电压为5.4V的
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7.3.6 Short Circuit Protection, Hiccup and Overtemperature Protection
The LNB output current limit can be set by an external resistor. When short circuit conditions occur or current limit is triggered, the output current is clamped at the current limit for 4 ms with LDO on. If the condition retains, the converter will shut down for 128 ms and then restart. This hiccup behavior prevents IC from being overheat. The hiccup ON/OFF time can be set by I2C register. Refer to Control Register 1 for detail.

The low side MOSFET of the boost converter has a peak current limit threshold which serves as the secondary protection. If boost converter’s peak current limit is triggered, the peak current will be clamped as high as 3.8 A when setting ISW default and LNB current limit up to 1 A. If loading current continues to increase, output voltage starts to drop and output power drops.

Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the junction temperature exceeds 160°C, the output shuts down. When the die temperature drops below its lower threshold typically 140°C, the output is enabled.

When the chip is in overcurrent protection or thermal shutdown, the I2C interface and logic are still active. The Fault pin is pulled down to signal the processor. The Fault pin signal remains low unless the following action is taken:

If I2C interface is not used to control, EN pin must be recycled in order to pull Fault pin back to high.
If I2C interface is used, the I2C master need to read the status Control Register 2, then the Fault pin will be back to high.

Q2用于短路保护 过热保护时候起作用 正常情况下不用管他