The water meter is composed of a wireless communication module and a base meter, which has the functions of metering, calculation, storage, diagnosis, wireless remote transmission, etc., so it has strict requirements for the power consumption, volume and cost of the internal power supply device. CN8911B is a 4-in-1 power management unit, including a high-voltage fixed output synchronous buck, a high-voltage adjustable output synchronous buck, an asynchronous boost, and a supercapacitor charger, which can meet the complex power requirements of highly integrated instruments.
Functional block diagram of the CN8911B.
The key technologies and innovations of CN8911B lie in the following aspects:
1. High integration: 4 power supplies are integrated on a die, which greatly simplifies the design of the PCB board;
2. Intelligent switching: After the system is powered off, the chip will automatically switch from Charger mode to Boost mode, and the energy of the supercapacitor will be transferred to VIN through Boost to ensure that the two bucks remain normal for a certain period of time;
3. Multi-mode control: Both bucks adopt a hybrid control mode combining PMW and PSM to ensure the best efficiency in the full load range.
The main performance and technical specifications of CN8911B are as follows:
1. 4-in-1 PMU, 2-way high-voltage buck, 1-way boost, 1-way charger
2. Input working voltage range: 65v-24v
3. The fixed output buck drive capacity can reach 500mA
4. The adjustable buck output voltage is adjusted by an external resistor, and the driving capacity is up to 800ma@vout=12v
5. The boost driving capacity can reach 300ma@vin=25v
6. The charging current of the charger is 60ma@cc, and the accuracy is 3% @cv
7. Power-down indication function, power-down voltage threshold can be set externally.
8. Perfect protection functions, including OCP, OTP, input OVP and UVLO
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