SNVS397F September 2005 – December 2025 LM5005
PRODUCTION DATA
The LM5005 integrates an N-channel high-side MOSFET and associated floating high-voltage gate driver. This gate driver circuit works in conjunction with an internal bootstrap diode and an external bootstrap capacitor. TI recommends using a 22nF ceramic capacitor that is connected with short traces between the BST and SW pins. During the off time of the buck switch, the SW voltage is approximately –0.5V and the bootstrap capacitor is charged from VCC through the internal bootstrap diode. When operating at a high PWM duty cycle, the buck switch is forced off each cycle for 500ns to verify that the bootstrap capacitor is recharged.
Under light-load conditions or when the output voltage is precharged, the SW voltage may not remain low during the off-time of the buck switch. If the inductor current falls to zero and the SW voltage rises, the bootstrap capacitor may not have sufficient voltage to operate the buck switch gate driver. For these applications, connect the PRE pin to the SW pins to precharge the bootstrap capacitor. The internal precharge MOSFET and diode connected between the PRE and PGND pins turns on each cycle for 250ns just prior to the onset of a new switching cycle. If the SW pin is at a normal negative voltage level (continuous conduction mode), then no current flows through the precharge MOSFET and diode.