LT3971EMSE-3.3 - 38V, 1.2A, 2MHz Buck Regulator | Analog Devices
MPN: LT3971EMSE-3.3 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $8.6 | $8.60 |
| 10 | $7.74 | $77.40 |
| 100 | $6.88 | $688.00 |
| 500 | $6.05 | $3,025.00 |
| 1,000 | $5.18 | $5,180.00 |
| 2,500 | $4.65 | $11,625.00 |
LT3971EMSE-3.3 Overview
A buck (step-down) switching regulator is a DC-DC converter that produces a lower output voltage than its input by rapidly switching an inductor and storing energy in that inductor, then releasing it through a rectifier into an output capacitor. Buck regulators sit within the power management IC hierarchy (buck -> DC-DC converter -> voltage regulator -> power management IC) and are favored over linear regulators for their high efficiency, especially when VIN significantly exceeds VOUT. The LT3971 family is purpose-built for automotive and industrial applications where high input transients and very low standby drain matter.
Key features include a programmable switching frequency from 200 kHz to 2 MHz, internal 1.2A switch, 2.8 µA Iq with output regulating at no load, fixed 3.3V or 5V and adjustable versions, internal compensation, and internal boost diode. The 10-lead MSOP-EP package offers a thermal resistance suitable for sustained 1.2A operation when properly footprinted, and the exposed pad must be soldered to a sufficiently large copper pour.
Architecturally the LT3971 uses a current-mode control loop with a precision reference and an integrated power switch. The very low IQ allows it to maintain output regulation while drawing only micro-amps from the battery, and Burst Mode operation skips switching cycles at light load to keep efficiency high and output ripple low. Programmable frequency up to 2 MHz enables designers to choose frequencies above the AM band or outside sensitive IF bands, and to use small ceramic capacitors and inductors.
Typical applications include automotive battery-powered systems, portable instruments, industrial control loops, and any 12V/24V supply rail that must deliver 3.3V with high efficiency. Its wide input range also makes it ideal for load-dump tolerant designs and battery-powered equipment that must operate down to deeply discharged battery voltages.
When designing with this part, ensure the exposed pad is soldered over adequate copper (typically >=1 square inch) to keep junction temperature within ratings. Keep the input capacitor loop short to minimize ringing on the SW node, and choose an inductor with low DCR to preserve efficiency.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes that are not found in the manufacturer datasheet alone, accelerating component selection.
Drop-in alternatives for LT3971EMSE-3.3 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with LT3971EMSE-3.3 (same form factor and footprint) — differing in Package, Quiescent Current, Switching Frequency, Topology, Operating Temperature Range.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
LT3971EMSE-3.3#TRPBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971EMSE-3.3
✅ Drop-In✓ In Stock
$4.65 / Unit
View Datasheet →LT3971EMSE#PBF
✅ Drop-In✓ In Stock
$6.25 / Unit
View Datasheet →LT3971EMSE-5#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971AEMSE#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971AEMSE-5#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971EMSE-3.3 Maximum Ratings & Electrical Characteristics
| Topology | Buck (Step-Down) Switching Regulator |
| Input Voltage Range | 4.3 V to 38 V |
| Output Voltage | 3.3 V (fixed) |
| Maximum Output Current | 1.2 A |
| Switching Frequency | 200 kHz to 2 MHz (programmable) |
| Quiescent Current | 2.8 µA (typ, no load, output regulating) |
| Efficiency | Up to ~90% (application dependent, Burst Mode at light load) |
| Internal Switch Current | 1.2 A |
| Light-Load Operation | Burst Mode (low ripple) |
| Feedback Reference / Internal Divider | 10 MΩ (fixed-output versions) |
| Operating Temperature Range | -40 °C to +125 °C (E-grade) |
| Package | 10-TFSOP, 10-MSOP (0.118" / 3.00 mm width) Exposed Pad |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant (PBF suffix) |
| Lead-Free | Yes (Pb-free PBF finish) |
LT3971EMSE-3.3 Pin Configuration
| Pin 1 | VIN — Input supply, 4.3V to 38V |
| Pin 2 | RT — Timing resistor to GND sets switching frequency |
| Pin 3 | EN/UVLO — Enable/undervoltage lockout threshold |
| Pin 4 | BST — Boost flying capacitor for internal driver |
| Pin 5 | GND — Signal ground |
| Pin 6 | VOUT — Output voltage sense (3.3V fixed) |
| Pin 7 | NC — Not connected (per datasheet) |
| Pin 8 | SW — Switch node to external inductor |
| Pin 9 | PGND — Power ground (return for SW) |
| Pin 10 | PGND — Power ground (return for SW) |
Typical Applications
LT3971EMSE-3.3 is suitable for 6 applications: Automotive 12V Battery-Powered Systems, Industrial 24V Bus Point-of-Load Regulation, Portable Battery-Powered Instruments, Load-Dump Tolerant Industrial Sensors, Always-On LED Driver Supplies, USB-Powered Device Side Rails.
Automotive 12V Battery-Powered Systems
The LT3971EMSE-3.3 is a strong fit for 12V automotive rails because it accepts 4.3V to 38V on VIN, tolerating cold-crank dips and load-dump transients without external protection. Its 2.8 µA quiescent current preserves battery life in always-on modules such as body controllers and tire-pressure monitors that spend most of their life in standby. The 1.2A output comfortably powers sensors, CAN transceivers, and small MCUs from a 3.3V rail. Using Burst Mode at light loads keeps efficiency above 80% at 10 mA, which is critical when the vehicle is parked.
Recommended
Industrial 24V Bus Point-of-Load Regulation
Industrial PLCs and sensor backplanes often run on a 24V nominal bus that can swing from 18V to 36V. The LT3971EMSE-3.3 handles this full range with a single part and delivers a clean 3.3V at 1.2A for digital logic, microcontrollers, and isolated transceivers. Its 2 MHz switching frequency allows use of small ceramic output capacitors, which simplifies PCB layout and reduces BOM cost in space-constrained DIN-rail modules. The 10-MSOP exposed pad footprint is well-suited to high-density backplane designs.
Recommended
Portable Battery-Powered Instruments
Handheld measurement tools and field instruments demand long battery life and wide operating voltage range. The LT3971EMSE-3.3 operates from as low as 4.3V, allowing use with 4-cell NiMH or 1S Li-ion packs down to deeply discharged states. Its 2.8 µA Iq keeps standby drain negligible when the instrument is off but the battery remains connected. The fixed 3.3V output is convenient for low-power MCUs, BLE modules, and analog front ends without needing external feedback parts.
Recommended
Load-Dump Tolerant Industrial Sensors
Sensors mounted near motors, solenoids, or relays experience large transient voltages on the supply rail. The LT3971EMSE-3.3's 38V absolute-maximum input and 4.3V minimum make it tolerant of these swings without requiring bulky TVS components. With its fixed 3.3V output it powers analog sensors, op-amps, and ADCs directly. Burst Mode operation prevents audible switching noise from coupling into sensitive measurement channels, an advantage over fixed-frequency regulators at light load.
Recommended
Always-On LED Driver Supplies
Indicator LEDs and small LED strings in industrial panels need efficient 3.3V rails that draw minimal current when the LED is off. The LT3971EMSE-3.3 maintains regulation with only 2.8 µA Iq, eliminating the need for a separate always-on LDO. Its 2 MHz switching frequency keeps the converter footprint small, ideal for backplanes with hundreds of indicator LEDs that must each have isolated supplies. Burst Mode keeps light-load ripple below levels that would cause visible LED flicker.
Recommended
USB-Powered Device Side Rails
When a device is bus-powered from USB but needs a clean internal 3.3V rail, the LT3971EMSE-3.3 can be fed from the 5V USB rail (well within its 4.3-38V window). It provides a more efficient and lower-noise 3.3V than a simple LDO when the current demand approaches 1A. Burst Mode operation eliminates audible noise during USB suspend states. The exposed pad MSOP-EP footprint is also used by the LT3971A series for higher-accuracy USB reference designs.
Recommended
Recommended Products Summary
Engineering reference data for LT3971EMSE-3.3 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LT3971EMSE-3.3#TRPBF | LT3971EMSE#PBF | LT3971EMSE-5#PBF | LT3971AEMSE#PBF | LT3971AEMSE-5#PBF |
|---|---|---|---|---|---|---|
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | 10-MSOP (Exposed Pad) | 10-MSOP (Exposed Pad) | 10-MSOP (Exposed Pad) | 10-MSOP (Exposed Pad) | 10-MSOP (Exposed Pad) | 10-MSOP (Exposed Pad) |
| Output Voltage | 3.3 V (fixed) | 3.3 V (fixed) | 1.19 V to 30 V (adjustable) | 5 V (fixed) | 1.19 V to 30 V (adjustable) | 5 V (fixed) |
| Maximum Output Current | 1.2 A | 1.2 A | 1.2 A | 1.2 A | 1.2 A | 1.2 A |
| Input Voltage Range | 4.3 V to 38 V | 4.3 V to 38 V | 4.3 V to 38 V | 4.3 V to 38 V | 4.3 V to 38 V | 4.3 V to 38 V |
| Quiescent Current | 2.8 µA | 2.8 µA | 2.8 µA | 2.8 µA | 2.8 µA | 2.8 µA |
| Switching Frequency Range | 200 kHz to 2 MHz | 200 kHz to 2 MHz | 200 kHz to 2 MHz | 200 kHz to 2 MHz | 200 kHz to 2 MHz | 200 kHz to 2 MHz |
| Reference Accuracy | Standard (LT3971 family) | Standard | Standard | Standard | Tighter (LT3971A series) | Tighter (LT3971A series) |
Key Differentiators
- Fixed 3.3V output without external feedback resistors (vs LT3971EMSE#PBF)
- 2.8 µA quiescent current with output regulating (vs LM25010SD/NOPB)
- Higher reference accuracy option within same footprint (vs LT3971AEMSE#PBF)
Design Notes
Estimated: At VIN=24V, VOUT=3.3V, IOUT=1.0A, the LT3971EMSE-3.3 dissipates approximately (24-3.3)*1.0 = 20.7 W minus switching losses (rough practical loss is ~15-17 W in worst-case conditions). With theta_JA ~40 C/W on a 1 sq. inch copper pour, junction temperature rise is ~600 C above ambient, well above the 125 C rating. For full 1.2A output at high VIN, a much larger copper pour (>=4 sq. inches) or forced-air cooling is required; at lower VIN=12V the dissipation is ~10 W and the design is more feasible with standard PCB cooling.
Solder the exposed pad to a continuous ground plane with thermal vias for heat removal. Keep the input capacitor, SW trace, and output loop areas small to minimize EMI. Place the RT resistor close to Pin 2 with a short ground return, since stray capacitance shifts the programmed switching frequency.
Do not exceed the absolute maximum VIN of 38V; load-dump transients on automotive 24V systems can briefly exceed this. Place a TVS diode rated above 38V if load-dump is expected. Avoid leaving the BST floating - the BST pin must have a flying capacitor (~10 nF) to the SW node for the high-side gate drive to work. Using the wrong output inductor value can cause subharmonic instability in current-mode control at duty cycles above 50%.
Compliance Information
RoHS compliant per #PBF suffix on the official part number. AEC-Q100 not explicitly qualified in available data. Halogen-free and conflict-minerals status not stated in the provided sources.
