The LM73605-Q1/6-Q1 synchronous buck with both power MOSFETs integrated in the device. Figure 8-1 shows a simplified schematic for synchronous and non-synchronous buck converters. The synchronous buck integrates both high-side (HS) and low-side (LS) power MOSFETs. The non-synchronous buck integrates HS MOSFET and works with a discrete power diode as LS rectifier.

Figure 8-1 Simplified Synchronous versus Non-synchronous Buck Converters

A synchronous converter with integrated HS and LS MOSFETs offers benefits such as the following:

• Less design effort
• Lower external component count
• Reduced total solution size
• Higher efficiency at heavier load
• Easier PCB design
• More control flexibility

The main advantage of a synchronous converter is that the voltage drop across the LS MOSFET is lower than the voltage drop across the power diode of a non-synchronous converter. Lower voltage drop translates into less power dissipation and higher efficiency. The LM73605-Q1/6-Q1 HS and LS MOSFETs with very low on-time resistance to improve efficiency. It is especially beneficial when the output voltage is low. Because the LS MOSFET is integrated into these devices, at light loads a synchronous converter has the flexibility to operate in either discontinuous or continuous conduction mode.

An integrated LS MOSFET also allows the controller to obtain inductor current information when the LS switch is on. It allows the control loop to make more complex decisions based on HS and LS currents. It allows the LM73605-Q1/6-Q1 to have peak and valley cycle-by-cycle current limiting for more robust protection.