Synchronous buck converters reduce a DC input to a lower supply voltage for applications such as industrial controls, battery-powered equipment, and communications systems. These three TI devices integrate both power MOSFETs and require external magnetics and capacitors. The LM5164DDAR combines a 100 V input rating with a 1 A current class. The LM5165DRCR serves smaller loads, while the LM5161PWPR also supports isolated Fly-Buck supplies.

Parameter Comparison

Application Fit

• LM5164DDAR

Consider this device for auxiliary rails supplied from a higher-voltage DC bus with loads in the 1 A class, including industrial battery equipment, motor-control boards, and communications equipment. Its 100 V input limit and light-load diode emulation suit systems with a wide input range and substantial differences between active and standby loads. PGOOD supports output-status monitoring.

• LM5165DRCR

Consider this device for sensors, low-power control nodes, and low-current bias supplies. Select PFM or COT according to load and ripple requirements, while observing the mode-dependent current limits and choosing the current-limit setting and inductor accordingly. LM5165DRCR is the adjustable-output version; fixed 5 V and 3.3 V versions carry the X and Y suffixes, respectively.

• LM5161PWPR

Consider this device for a conventional buck rail or an isolated Fly-Buck bias supply. Fly-Buck operation requires forced continuous conduction mode, an external transformer, secondary rectification, and a ripple network. Available secondary current depends on turns ratio, primary and secondary loading, magnetics, and current limits; the 1 A buck rating is not a secondary-output rating.

Design Considerations

• Check input limits and output requirements first

Account for minimum input voltage, maximum input voltage, and transient spikes, rather than selecting from a nominal 24 V or 48 V bus alone. The LM5165 cannot be used directly if the input can exceed 65 V. All three devices are step-down converters; check dropout and regulation as the input approaches the desired output.

• Compare supply current in the relevant operating state

The LM5164 and LM5165 both specify 10.5 µA typical sleep current, measured at 24 V and 12 V input, respectively. At 48 V input, the LM5161 specifies typical shutdown current of 50 µA and typical non-switching operating current of 2.3 mA. These different test states do not support a direct ranking. Total no-load power consumption also depends on external networks and losses associated with intermittent switching.

Both sleep-current tests use FB = 1.5 V. The LM5164 test uses EN = 2.5 V and TJ = 25°C; the LM5165 test specifies TA = 25°C. For the LM5161, shutdown uses EN/UVLO = 0 V and non-switching operation uses FB = 3 V; typical values correspond to TJ = 25°C.

• Match the control mode and external components

COT control generally provides a nearly constant switching frequency, but frequency changes during light-load pulse skipping. Select the inductor, output capacitor, and feedback ripple network for the intended mode. LM5161 Fly-Buck operation requires a Type-3 ripple network. A statement that external loop compensation is unnecessary does not remove the need for specified components such as a soft-start capacitor.

• Verify current capability against temperature rise

The packages, pinouts, and external circuits differ, so these devices are not drop-in replacements. Check usable output current against inductor saturation, switching losses, PCB heat dissipation, and maximum ambient temperature. The listed temperature ranges are junction temperatures, not permissible system ambient temperatures.

Product Summary

Define the input range and load first, then evaluate light-load power consumption, isolation requirements, and the external circuit. Visit WIN SOURCE to check current inventory and pricing for these parts.