7.1 Overview

The LMR10530 is a constant frequency PWM buck regulator IC that delivers a 3-A load current. The regulator is available in preset switching frequencies of 1.5 MHz or 3 MHz. This high frequency allows the LMR10530 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LMR10530 is internally compensated, therefore it is simple to use and requires few external components. The LMR10530 uses peak current-mode control to regulate the output voltage. The following description of operation of the LMR10530 will refer to the Figure 30, to the waveforms in Figure 20 and simplified block diagram in Functional Block Diagram. The LMR10530 supplies a regulated output voltage by switching the internal PMOS power switch at a constant frequency and variable duty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal PMOS power switch. During this on-time, the SW pin voltage (V_SW) swings up to approximately V_IN, and the inductor current (I_L) increases with a linear slope. I_L is measured by the current sense amplifier, which generates an output proportional to the switch current. The sense signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference between the feedback voltage and V_REF. When the PWM comparator output goes high, the internal power switch turns off until the next switching cycle begins. During the switch off-time, the inductor current discharges through the catch diode D1, which forces the SW pin to swing below ground by the forward voltage (V_D) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage.

Figure 20. Typical Waveforms