Figure 4 shows a typical operating circuit for low-side current sensing. A sense resistor is typically used. Alternatively, a PCB trace can be used for high-current or small-form-factor applications. For better measurement, place the sensing element as close as possible to the CSN and GND pin. The IC automatically compensates for the effect of environmental temperature and trace heating on trace resistance.
Figure 5 shows a typical application circuit for multiple-series cells. An external 3V to 5V regulator is required to provide regulated output within BATT pin supply range. Multiple-series-cells measurement requires external voltage divider circuit. The resistor divider should be configured so that 40% of one-cell voltage is measured at analog measurement pin CELLX. As it is configured in Figure 5, the resistor divider ratio is R2/R1 = 5/2 x (N-1) + 3/2, where R2 is the resistance between CELLX pin and the battery pack positive terminal, R1 is the resistance between the CELLX pin and the GND pin, and N is the number of cells. For additional power savings, in trade-off with BOM cost, add a N-channel MOSFET as shown in Figure 5. The gate of the FET is controlled by the SW pin. The SW pin only turns on the resistor divider for a short period of time every time ADC measurement occurs. Higher resistance value for the divider circuit degrades the accuracy of analog measurement, while lower resistance causes more power consumption. The suggested R1 value is 200kΩ. Typical consumption without NMOS is 8μA. For the accuracy of the voltage measurement, use 0.1% resistors.
Figure 4. Low-Side Current Measurement Typical Applications Circuit
