SNVSCU2A August 2024 – August 2024 LM5137-Q1
ADVANCE INFORMATION
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-Q1 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 at light-load conditions; the disadvantage being slower light-load transient response.
The diode emulation feature is configured with the PFM/SYNCIN pin. To enable diode emulation and thus achieve discontinuous conduction mode (DCM) operation at light loads, connect PFM/SYNCIN to VDDA. If FPWM or continuous conduction mode (CCM) operation is desired, tie PFM/SYNCIN to AGND. See Table 7-8. 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.
PFM/SYNCIN | FPWM / PFM |
---|---|
VDDA | PFM |
AGND | FPWM |
External clock | FPWM |
ITEM | OBSERVED BEHAVIOR | COMMENTS |
---|---|---|
1 | LO on one channel can be deactivated when the SW voltage on the other channel transitions high. This event only occurs in PFM mode. | This event can decrease the efficiency in PFM. |