SNVSBJ0A December 2019 – June 2020 LM5170
The LM5170 has a built-in diode emulation function. Each channel has a real time current zero crossing detector to monitor instantaneous VCS. When VCS is detected to cross zero, the LM5170 turns off the gate drive of the synchronous rectifier to prevent negative current. In this way, the negative current is prevented and the light load efficiency is improved. Figure 32 shows key waveforms of a typical operation transiting into the diode emulation mode.
To obtain optimal diode emulation performance, it requires the VCS signal to be accurate in real time. Any signal distortion caused by parasitic inductances in the current sense resistor or sensing traces may lead to erroneous zero crossing detection and cause non-optimal diode emulation operation, and the sync FET may be turned off while the current is still high in the positive direction. See the Application Information section for coping with current sense parasitic inductances for optimal diode emulation operation.