SNVSCU4 October 2025 LM25137
PRODMIX
The LM25137 contains MOSFET gate drivers and associated high-side level shifters to drive the external N-channel power MOSFETs. The high-side gate driver works in conjunction with the integrated bootstrap diode and external bootstrap capacitor CBOOT. During the conduction interval of the low-side MOSFET, the SW voltage is approximately 0V and CBOOT charges from VCC through the diode.
The LM25137 controls the HO and LO outputs with an adaptive dead-time methodology such that both outputs (HO and LO) are never enabled at the same time, preventing cross conduction. When the controller commands LO to be enabled, the adaptive dead-time logic first disables HO and waits for the HO-to-GND voltage to drop below 2V (typical). LO is then enabled after a small delay (HO falling to LO rising delay). Similarly, the HO turn-on is delayed until the LO voltage has dropped below 2V. HO is then enabled after a small delay (LO falling to HO rising delay). This technique provides adequate dead-time for any size N-channel MOSFET component or parallel MOSFET configurations. Caution is advised when adding series gate resistors, as series gate resistors can decrease the effective dead-time. The selected high-side power MOSFET determines the appropriate bootstrap capacitance value CBOOT in accordance with Equation 10.
where
To determine CBOOT, choose ΔVCBOOT so that the available gate drive voltage is not significantly impacted. An acceptable range of ΔVCBOOT is 100mV to 200mV. The bootstrap capacitor must be a low-ESR ceramic capacitor, typically 0.1μF. Given the nominal VCC voltage of 5V, using logic-level power MOSFETs with RDS(on) rated at VGS = 4.5V is imperative.