The LM5169 and LM5168 are easy-to-use, ultra-low I_Q constant on-time (COT) synchronous step-down buck regulators. With integrated high-side and low-side power MOSFETs, the LM516x is a low-cost, highly efficient buck converter that operates from a wide input voltage of 6 V to 120 V, delivering up to 0.65-A or 0.3-A DC load current. The LM516x is available in an 8-pin SO PowerPAD™ integrated circuit package with 1.27-mm pin pitch for adequate spacing in high-voltage applications. This constant on-time (COT) converter is ideal for low-noise, high-current, and fast load transient requirements, operating with a predictive on-time switching pulse. Over the input voltage range, input voltage feed-forward is employed to achieve a quasi-fixed switching frequency. A controllable on time as low as 50 ns permits high step-down ratios and a minimum forced off time of 50 ns provides extremely high duty cycles. This enables fixed frequency operation as VIN drops close to VOUT. After the forced off time of 50 ns is reached, the device enters frequency fold-back operation to maintain a constant output voltage. The LM516x implements a smart peak and valley current limit detection circuit to ensure robust protection during output short circuit conditions. Control loop compensation is not required for this regulator, reducing design time and external component count.

The LM5169 and LM5168 are pre-programmed to operate in auto mode or FPWM mode. When configured to operate in auto mode, at light loads, the device transitions into an ultra-low I_Q mode to maintain high efficiency and prevent draining battery cells connected to the input when the system is in standby. When configured in FPWM mode, at light loads, the device maintains CCM operation, enabling fly-buck converter operation. The fly-buck converter configuration can be used to generate both a non-isolated primary output and an isolated secondary output.

The LM5169 and LM5168 incorporates additional features for comprehensive system requirements, including an open-drain power-good circuit for the following:

• Power-rail sequencing and fault reporting
• Internally fixed soft start
• Monotonic start-up into prebiased loads
• Precision enable for programmable line undervoltage lockout (UVLO)
• Smart cycle-by-cycle current limit for optimal inductor sizing
• Thermal shutdown with automatic recovery

The LM5169 and LM5168 support a wide range of end equipment requiring a regulated output from a high input supply where the transient voltage deviates from its DC level. Examples of such end equipment systems are the following:

• 48-V automotive systems
• High cell-count battery-pack systems
• 24-V industrial systems
• 48-V telecom and PoE voltage ranges

The pin arrangement is designed for a simple layout that requires only a few external components.