SNVSCU3 October 2025 LM5137
PRODMIX
A synchronous buck regulator implemented with a low-side MOSFET rather than a diode has the capability to sink negative current from the output during light-load, overvoltage, and prebias start-up conditions. The LM5137 provides a diode emulation feature that can be enabled to prevent reverse (drain-to-source) current flow in the low-side MOSFET. When configured for diode emulation (DEM), the low-side MOSFET is switched off when reverse current flow is detected by sensing of the applicable SW voltage using a zero-cross comparator. The benefit of this configuration is lower power loss during light-load conditions; the disadvantage being slower light-load transient response.
| PFM/SYNC | FPWM, PFM |
|---|---|
| VDDA | PFM |
| AGND | FPWM |
| External clock | FPWM |
Configure the diode emulation feature using the PFM/SYNC pin. To enable diode emulation and thus achieve discontinuous conduction mode (DCM) operation at light loads, connect PFM/SYNC to VDDA. If FPWM or continuous conduction mode (CCM) operation is desired, tie PFM/SYNC to AGND. See Table 7-6. Note that diode emulation is automatically engaged (in both PFM and FPWM modes) to prevent reverse current flow during a prebias start-up. A gradual change from DCM to CCM operation provides monotonic start-up performance.