Portable devices to accurately measure remaining battery power method

Use of portable electronic products, hoping to always know the battery's remaining power, the working hours that can be sustained, and accordingly adjust the related applications, which will undoubtedly be a very handy thing, especially for business people using smart phones. Battery detection technology has been common in laptops, most laptops have power management options, with different power modes, and battery alarm. But in the more compact portable market, this technology still rare.

Portable product offering more and more numerous, users increasingly need to accurately monitor the battery power, so the flexibility to manage available power, clearly shows that the remaining work time as possible to extend system run time. Most phones now use the power measurement method is relatively simple, the lack of accuracy. Current detection method is simple mainstream measuring the battery voltage to estimate the corresponding remaining battery power. The total power divided by 4 or 5, which is usually on the phone screen to see 4 or 5 grid electricity grid Bar, so the accuracy of each grid that is 25% or 20%, so the accuracy is clearly unable to meet the precision requirements applications.

This method of voltage electricity is usually estimated as follows: a battery discharge when the battery voltage with the loss of battery power gradually declined. This can be a relatively simple and effective correspondence, is the voltage corresponding to the capacity. By normal use the battery (for example, 100mA discharge) discharge curve of the time 4 equal portions, to limit voltage of 4.2V rechargeable lithium battery, for example, can list a corresponding relationship, 4.20V-100%, 3.85V- 75%, 3.75V-50%, 3.60V-25%, 3.40V-5% (because the phone can not be completely run out of battery power and generally lower than 3.40V may automatically shut down when a). Obviously, this precision is only up to 25%. In addition, the battery voltage with the launch power RFPA mutations usually become smaller 0.2V-0.3V. If you blindly use of voltage analog power method, the error will be larger. In order to solve the battery voltage measurement problems suddenly become smaller, the current general engineers is to use software algorithms to mean filter, the time average of the battery voltage, if the time does the average battery voltage down, then the pre- estimated power did become less, or that that power did not change.

Remaining capacity of the battery voltage analog method the existence of a defect, and real-time monitoring through the Coulomb charge and calculate the remaining battery power consumption of the method is very accurate. Fairchild's FAN4010 is a typical device of this application. It is a current detection sensors, portable devices designed to detect the battery charge / current consumption, can detect through the precision resistor converts the current signal to the ADC can detect the voltage signal, within a period of time in order to calculate the real power consumption .

Typical hardware circuit design

In order to meet the needs of high-precision battery monitor, FAN4010 plus the appropriate application circuit and control algorithm with specific software, we can well meet the requirements. Figure 1 is a block diagram of a typical application FAN4010. Requires only two external resistors Rsense, Rout constitute a high-precision amplifier. Figure 2 is a schematic diagram of the internal structure, so there Vsense = I_load * Rsense, Vout = 0.01 * Vsense * Rout, this relationship can wait until two I_load = 100 * Vout / (Rout * Rsense), so long as the monitoring of the ADC Vout on the voltage divided by the known resistance Rout and Rsense, you can get an accurate load current consumption, and current on the time integral, that is, the amount of electricity can achieve an accurate value. With a total power minus the value of accurate power consumption, you can get an accurate remaining capacity. Charging circuit, the same reason.

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