Abstract: Some systems require measuring the power output to the load, which is more important than simply measuring current through a conventional current sense amplifier. Load power measurement accurately manages the power of the battery or AC adapter powered device. This application note shows the creation of a simple analog multiplier (using the MAX4210D/E/F) that multiplies two 0 to 1V input signals for accurate load power measurement. Importance of load power measurement In notebook applications, measurement of load power is often important. In such applications, the entire circuit (load) is powered by a Li-Ion (Li+) battery or by an AC adapter that simultaneously charges the battery. Because the output voltage of each power supply is different, the load current is different. Normally, the AC adapter outputs 16V, and the battery pack consists of three Li-ion batteries. The voltage is about 12.6V when fully charged and about 9V when fully charged. To accurately manage the power in the circuit, it is not enough to measure the load current because it does not give information on which type of voltage source is being used. In addition, microcontrollers in some portable applications have limited pins, so you need to measure power directly, rather than measuring voltage and current separately, and then multiplying them in firmware. Building a 0 to 1V Analog Multiplier with the MAX4210D/E/F The MAX4210D/MAX4210E/MAX4210F are high-side current and power monitors with an internal true analog multiplier. These devices directly multiply the battery current by an input voltage of 0 to 1V. However, if you simply multiply two 0 to 1V signals, the input common-mode voltage threshold (4.5V minimum) will make the circuit inoperable. Figure 1 shows a circuit for building a 0 to 1V analog multiplier with the MAX4210D/E/F and a MAX4477 op amp and n-channel MOSFET. This circuit can multiply two independent input voltages up to 1V. Figure 1: Building a general-purpose 1V analog multiplier with the MAX4210D/E/F and MAX4477. This application note uses the MAX4210E as an example; the MAX4210D and MAX4210F can also be used to build general-purpose analog multipliers. In the circuit of Figure 1, the input voltage V1 is converted to current by an op amp, MOSFET, and R1 resistor; the R2 resistor then converts it to a smaller voltage. This small voltage is connected to the differential input of the MAX4210E. The MAX4210E allows a maximum input detection voltage of 150mV. Accordingly, the values ​​of R1 and R2 are selected: R1 = 1kΩ and R2 = 150Ω. The power supply VCC of the entire circuit is 5V; the MAX4210E has a gain of 25V/V. Therefore, the full-scale output voltage is 3.75V. The op amp with an input common-mode voltage range of ground and a precision better than the MAX4210E should be selected in the circuit. At 25°C, the MAX4210E's total output error is less than ±1.5% of the full-scale output (FSO) range. The MAX4477 features an ultra-small bias current of pA, an input voltage bias of less than 350μV, and a CMRR of at least 90dB; therefore, the introduced error is negligible compared to the MAX4210E. Lithium Battery Crv3,Lithium Battery Camera,Camera Lithium Battery,Lithium Photo Battery Jiangmen Hongli Energy Co.ltd , https://www.honglienergy.com