LM6685IM

Overview

The LM6685IM is a dual step-down controller designed for high-efficiency power conversion. It features an embedded integrator control loop to compensate DC voltage error from output ripple and utilizes pulse skipping for light load efficiency. The device supports selectable switching frequencies of 200 kHz/300 kHz, 300 kHz/400 kHz, or 400 kHz/500 kHz for its 5 V and 3.3 V sections. It operates with a 6 V to 28 V input range and provides fixed 5 V and 3.3 V outputs capable of delivering 100 mA peak current. Key electrical parameters include a 1.230 V ±1% reference voltage, a maximum quiescent power of 4 mW, and an internally fixed soft-start time of 2 ms.

Feature Summary

• Lossless current sensing using low-side MOSFETs' RDS(on) for accurate regulation
• Constant on-time architecture ensuring fast load transient response
• Embedded voltage feed-forward providing nearly constant switching frequency operation
• Negative current limit and soft output discharge capabilities

Applications

• High efficiency DC-DC power conversion systems
• Applications requiring lossless current sensing techniques
• Systems needing selectable switching frequencies to avoid audio noise

Procurement Notes

Verify the specific manufacturer source, as National Semiconductor is now part of onsemi. Confirm that the LM6685IM designation aligns with the PM6685 functional description provided in available documentation. Ensure the component matches the required pinout and package specifications for your design integration.

Selection Notes

Select this component when designing dual-output buck converters requiring precise ripple compensation and high efficiency at light loads. The availability of multiple selectable switching frequency options allows optimization for EMI performance and external component size. Consider the integrated protection features such as latched OVP/UVP and negative current limit for robust system reliability.

Part Context

This component belongs to the family of dual step-down controllers utilizing constant on-time architecture. It is engineered to provide extremely high efficiency conversion through lossless current sensing. The design integrates features like output voltage ripple compensation and independent power good signals to support complex power management requirements in modern electronic devices.

Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. Verify compatibility with the PM6685 if cross-referencing functional descriptions, but do not assume direct interchangeability without official datasheet confirmation.