The TPS54360B-Q1, TPS54560B-Q1, and LMR33630A-Q1 are all automotive-qualified (AEC-Q100) step-down DC-DC converters from TI with an integrated high-side MOSFET, using peak-current-mode control to step 12 V, 24 V, and similar automotive and industrial rails down to a regulated output.

The three parts belong to two platforms: the TPS54360B-Q1 and TPS54560B-Q1 share a 60 V non-synchronous platform, while the LMR33630A-Q1 is a 36 V synchronous-rectification part. The first selection question is therefore the input-voltage platform and rectification method; current is the second step, decided once the platform is fixed.

Parameter Comparison

Application Scenarios

• TPS54360B-Q1

60 V input, 3.5 A, non-synchronous rectification, surviving load-dump pulses up to 65 V per ISO 7637. The switching frequency is set by an external resistor across 100 kHz–2.5 MHz, allowing a trade-off between efficiency and external component size.

The non-synchronous architecture requires an external freewheeling Schottky diode. At full load and high input-output differential, this diode carries the bulk of the low-side conduction loss and is the main constraint on heat and efficiency in a non-synchronous design, so leave a thermal path for it during layout. Its strengths are wide input headroom and a mature reference-design ecosystem, suiting body control, sensor supplies, and industrial 24 V/48 V rail step-down that must ride out automotive bus transients with loads within 3.5 A.

• TPS54560B-Q1

It shares the platform, package, and pinout of the TPS54360B-Q1, the main difference being rated current raised from 3.5 A to 5 A. When the load sits near 3.5 A and needs margin, or when one PCB layout should accommodate two current grades, you can upgrade directly from the TPS54360B-Q1 with no redesign. Under the same thermal conditions, the 5 A part has more junction-temperature margin at a 3.5 A load, helping extend the life of the device and external capacitors. Its target applications match the TPS54360B-Q1, mainly 60 V rail step-down designs with loads of 3.5–5 A that need current margin.

• LMR33630A-Q1

36 V input, 3 A, synchronous rectification with integrated high- and low-side MOSFETs, requiring no external Schottky diode. Synchronous rectification replaces the freewheeling diode with an internal low-side MOSFET, removing that diode’s conduction loss and board area—the main reason peak efficiency reaches above 95% and the design suits miniaturization. It uses a 3×2 mm HotRod package.

Its no-load quiescent current is about 24 µA, roughly one-sixth of the TPS54x60B family (146 µA). For always-on ECUs that stay connected to the battery in standby or light load, this difference flows directly into the vehicle’s quiescent (dark) current budget, making the LMR33630A-Q1 better suited to standby-sensitive modules such as infotainment and telematics; it also offers Functional-Safety-Capable documentation.

• • Two points to note. First, its VIN absolute maximum is 38 V, so it cannot directly absorb a 60 V-class load dump; on a 12 V automotive rail, the front end needs a TVS or clamp to hold the transient within 38 V. Second, its undervoltage lockout acts on the internal LDO output rather than monitoring VIN directly—unlike the VIN-sensed UVLO of the TPS54x60B—so a driver ported from a TPS54x60B needs its power-up logic adjusted accordingly.

Design Considerations

• Non-synchronous efficiency is tied to the chosen Schottky diode

The datasheet efficiency curves for the TPS54360B-Q1 and TPS54560B-Q1 are measured with a specific external Schottky diode. Actual efficiency is significantly affected by the selected diode’s forward voltage VF and reverse leakage: a higher VF raises full-load conduction loss, while increased reverse leakage at high temperature adds further loss. Actual efficiency for these two parts should therefore not be read straight off the datasheet curves; recompute it for the actual diode chosen, especially at high input-output differential and high duty cycle.

• The quiescent-current (IQ) figure is not system standby power

The 146 µA / 24 µA values are the device’s own non-switching consumption and exclude the feedback divider, enable circuit, and other external leakage. In an always-on ECU, the feedback divider current can be on the same order as the device IQ, depending on the divider resistor values. When estimating the vehicle dark-current budget, include the external circuitry rather than the device IQ alone.

• Load-dump capability must be assessed together with front-end protection

The TPS54x60B rating of 65 V (ISO 7637) is the device’s own capability; the system’s actual transient immunity also depends on input-capacitor voltage rating, PCB routing, and front-end protection devices. The LMR33630A-Q1 has a VIN absolute maximum of 38 V, so on a 12 V automotive rail it generally needs a front-end TVS or clamp, with the protection device rated by transient energy rather than peak voltage alone.

• Switching frequency is a three-way trade-off of efficiency, size, and EMI

The TPS54x60B’s 100 kHz–2.5 MHz adjustable range offers flexibility, but higher is not always better: a higher frequency shrinks the inductor and output capacitor but generally increases switching loss, requiring a trade-off between efficiency and size, and it shifts the EMI spectrum. The fixed-frequency LMR33630A-Q1 (A version, 400 kHz) removes the frequency-setting resistor but is not adjustable; if the system has a specific EMI-sensitive band to avoid, confirm during selection whether its fixed frequency and harmonics fall within that window.

• Thermal design should rely on the actual PCB, not datasheet thermal resistance

The datasheet thermal resistance (θJA) for all three is measured on a standard JEDEC board and can differ considerably from a real multilayer board’s copper area, via count, and component layout, so it should not be used directly for junction-temperature estimates. Heat dissipation in both the HotRod and PowerPAD packages depends on the vias and copper under the bottom thermal pad; leave an adequate thermal path during layout and verify with full-load temperature rise on actual hardware.

Product Summary

WIN SOURCE supplies TI automotive-grade step-down DC-DC converters and related power-management devices for automotive electronics, industrial control, infotainment, and embedded power designs. Visit WIN SOURCE to check real-time stock and availability for the TPS54360B-Q1, TPS54560B-Q1, and LMR33630A-Q1.