Battery powered portable system circuit diagram

Photocoupler

Although voltage measurements have been used alone in many portable products to estimate the remaining battery capacity, this approach can have up to 50% error. The relationship between battery voltage and battery will vary with discharge rate, temperature, and battery age. For example, a high discharge rate results in a larger pressure drop than a low discharge rate of the same charge loss. When the battery is discharged at different temperatures, we will notice some similar features. As the demand for long-running products continues to grow, system designers need a more accurate solution. In a wide range of application power levels, using a battery fuel gauge IC to measure the charge flowing into or out of the battery will result in a better battery power estimation method.
Battery Pack Circuit Design Figure 1 depicts the application circuit in the battery pack. The battery pack will have at least three to four available external terminals, depending on the battery fuel gauge IC used. The VCC and BAT pins are connected to the battery voltage for measurement of IC power and battery voltage. A low-resistance sense resistor is placed on the ground of the battery so that the voltage across the sense resistor can be monitored by the high-impedance SRP and SRN inputs of the battery gauge. The current flowing through the sense resistor helps us determine the amount of charge or discharge that has been discharged. When choosing the value of the sense resistor, the designer must consider that the voltage across it should not exceed 100 mV. Too small a resistance value may cause an error under low current conditions. The board layout must ensure that the SRP and SRN connections to the sense resistor are as close as possible to each end of the sense resistor; that is, Kelvin connection measurements. The HDQ/SDA and SCL pins are open-drain devices, both of which require an external pull-up resistor. This resistor should be located on the host side or on the main application side so that the sleep function of the battery fuel gauge can be activated after the battery pack is disconnected from the portable device. The recommended pull-up resistor value is 10 kΩ.

Figure 2 Circuit with BQ27000 and Verification IC Once the battery is verified, the bq26150 will receive a command to ensure that all communication through the data line is transferred between the host and the battery fuel gauge. In this regard, the host can continue to take advantage of the battery gauge. The entire verification process must be repeated when the battery is disconnected and reconnected to the battery.
Two-Cell Application Circuit Design Figure 3 shows a typical application circuit with a bq26500 supporting two-cell Li-Ion batteries. An adjustable voltage regulator is added to the system for multi-cell support. The BAT pin of the battery fuel gauge is connected to the positive terminal of the bottom battery to achieve regulated voltage measurement of the battery pack. Figure 3 The two-cell battery application host with the bq26500 needs to interpret the battery pack regulation voltage measured by the battery fuel gauge to determine the discharge end threshold and charge termination time. We can use information such as "remaining battery status" as reported by the battery fuel gauge.