[Original] An efficient power management solution for handheld devices

Document directory

• 1.1.1 solution Selection
• 1.1.2 Analysis of Total Power Supply Control Scheme

1.1 power management circuit 1.1.1 solution Selection

When using the power generator, the power supply must be effectively managed to save power, reduce power consumption, and prolong the life of the battery. Common Power management solutions include low power consumption management solutions and system power failure management solutions.

1. Low-Power Management Solution

The low-power solution is to put the MCU in deep sleep when the system does not need to measure, disable the fpga pll clock output, and use a transistor to close the power of the liquid crystal and some peripheral circuits, in this way, the total current of the system is less than 1mA theoretically. However, the laser range finder is not measured for a long time. Even if the current is very small, the accumulated time will consume a lot of current, which will shorten the battery time. This method is obviously not the best.

2. system power-off Management Plan

The system power failure management solution automatically controls the power supply of the entire system. When the system has not been measured for more than 10 s, the power supply system of the entire system will be closed, in this way, the system consumes almost 0mA of the current (the Power Management Switch MOS tube consumes a small amount of static current ).

Based on the above two factors, the system power-off management solution is more energy-saving, and is more suitable for laser range finder hosts.

1.1.2 Analysis of Total Power Supply Control Scheme

The entire power supply management circuit consists of the core power supply switch circuit and power supply switch circuit, as shown in Figure 3.1. It is mainly responsible for enabling and shutting down the total power supply. The entire circuit controls the power supply through the external buttons K3 and MCU pins.

The circuit analysis mainly analyzes the work flow of the entire circuit, as well as pressing and popping each circuit by pressing the K3 button. And device selection methods.

Figure 3.1 9 V power supply management Circuit

The entire circuit is divided into four stages: K3 button is not pressed, K3 button is pressed, K3 button is popped up, MCU power-on 10 s.

1. The K3 button is not pressed.

When K3 is not pressed, the battery power supply is not turned on. As shown in Figure 3.1, the voltage of point 2 is marked in the figure. Due to the drop-down of the Resistance R17, the voltage of point 2 is low. Therefore, the n MOS Q2 is turned off, at this time, the voltage marked at point 3 is pulled up by the resistance R14, which is 9 V high at this time. The P-Channel MOS Q1 is in the off state, so the total power supply sw_9v is 0 V at this time, the entire system is powered off.

2. Press K3

When the K3 button is pressed, the battery power is turned on and the voltage of point 2 is marked as 4.5 V due to the partial pressure of R16 and R17. The vgs = V meets the on-voltage of Q2 tube, after the Q2 pipe is turned on, the mark point 3 is equivalent to grounding, and the voltage is 0. The vgs =-9v satisfies the turn-on voltage of Q1 pipe. Therefore, when the q1 tube is turned on, sw_9v obtains the 9 V voltage of the battery power, and the entire system is powered on.

3. Press K3 to pop up

After the system is powered on, after the MCU Initialization is complete, the circuit is resumed immediately, that is, the MCU output pwr_ctl is high. When K3 is started, the Battery Path is disconnected because pwr_ctl is high, vgs = 3v, so the Q2 tube is still in the on-going state, and Q1 tube is also in the on-going State. Therefore, the entire system enters the MCU power-on state.

4. MCU power-on for 10 s

During the MCU power-on process, the measurement key is used to continuously check if K3 is pressed. If K3 is pressed, a new measurement is enabled, and the 10 s shutdown time is reset and the 10 s is scheduled again. If you do not press K3 again within 10 s, the MCU outputs pwr_ctl to a low level. The vgs of the Q2 tube is 0 V, and the Q2 tube is shut down. At this time, note 3 is pulled back to 9 V due to the uplink, the vgs of the Q3 tube is 0 V, and the Q3 tube is also shut down. The sw_9v is 0 V, and the entire system is powered off.

The preceding four steps are used to intelligently manage the total power supply. When the entire system is powered off, only the mos Q1 and 9v are connected, the power consumption of the entire system is equal to the static power-off current at this time. According to the 2sj355 Data Manual, the current consumption is less than 10ua. Therefore, the current consumption of the entire system is very small, it implements an ultra-low power management solution.

5. Selection of key devices

In the switch circuit of the total power supply, the most important choice is the selection of diode D3 and MOS tube Q2. In this design, the MCU outputs a high level to continue the power supply of the Q2 tube, in order to prevent damage to the mcu I/O port from the 4.5v high level when the K3 button is pressed, the diode D3 must be added. When the MCU needs to output the High Level 3.3v for Q2 power-on, if a common diode is used and the voltage drop after passing through the diode is 0.7 V, the vgs is 2.6 V, and the general MOS tube cannot be fully opened. Therefore, in this design, the diode mbr0520 with a low voltage of 0.3v and the mos 2n7002 with a vgs = 2.5v conduction mode are used.