7.3.1 Accurate Current Sense

For version B, the high-accuracy current-sense function is internally implemented, which allows a better real-time monitoring effect and more-accurate diagnostics without further calibration. A current mirror is used to source 1 / K of the load current, flowing out to the external resistor between the CS pin and GND, and reflected as voltage on the CS pin.

K is the ratio of the output current and the sense current. It is a constant value across the temperature and supply voltage. Each device was internally calibrated while in production, so post-calibration by users is not required in most cases.

Figure 29. Current-Sense Accuracy

Ensure the CS voltage is in the linear region (0 to 4 V) during normal operation. Calculate R_CS with Equation 1.

Equation 1.

Also, when a fault condition occurs, CS works as a diagnostics report pin. When an open load or short to battery occurs in the on-state, V_CS almost equals 0. When current limit, thermal shutdown/swing, open load, or short to battery in the off-state occurs, the voltage is pulled up to V_CS,h. Figure 30 shows a typical current-sense voltage according to the operating conditions, including fault conditions.

Figure 30. Voltage Indication on the Current-Sense Pin

Figure 31. Current-Sense and Current-Limit Block Diagram