A typical application circuit diagram of PS61040

The TPS61040/41 internal MOSFET switch Q1 conducts and gradually increases the amount of current from VIN through L1, Q1, and the internal current sense resistor RSENSE. The FB (feedback) pin of TPS61040/41 detects the output voltage. As long as the feedback voltage is lower than the reference voltage (typical value 1.233V), the internal Q1 is turned on and the current increases; when the inductor L1 current reaches the internally set peak current ILM (TPS61040 is Q1 is cut off at 400mA (or 250mA for TPS61041). In addition, in order to cope with extreme conditions to limit the maximum conduction time, Q1 will also be cut off when the maximum conduction time exceeds 6μs (typical value). TPS61040/41 external components determine the off time of Q1.

To maintain operation and set the off-time of Q1, the TPS61040/41 internal controller must monitor the current through L1 using Q1 and RSENSE. When Q1 is turned off, the interruption of the current flowing through L1 will increase the voltage on the inductor, causing the external Schottky diode D1 to be forward biased and turned on. D1 acts as a freewheeling diode to ensure current output and charges the output capacitor C1 to a Higher voltage, this voltage is higher than the separate input voltage VIN. The switch tube must be turned off for at least 400ns (typical value), or the feedback voltage is lower than the reference voltage before it is turned on. The input voltage, L1, and the preset peak current through RSENSE all affect the on-time of Q1. As shown below.