LT3971EMSE-3.3#PBF - 38V, 1.2A, 2MHz Buck Regulator | Analog Devices
MPN: LT3971EMSE-3.3#PBF ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $7.85 | $7.85 |
| 10 | $6.97 | $69.70 |
| 100 | $5.62 | $562.00 |
| 500 | $4.89 | $2,445.00 |
| 1,000 | $4.21 | $4,210.00 |
LT3971EMSE-3.3#PBF Overview
A buck (step-down) switching regulator is a DC-DC converter that efficiently reduces a higher DC input voltage to a lower DC output voltage by rapidly switching a power transistor and smoothing the resulting pulse train with an LC filter. The LT3971 family occupies the hierarchy: buck regulator → switching regulator → DC-DC converter → power management IC → semiconductor. Compared with linear regulators, buck regulators achieve much higher efficiency at large VIN/VOUT ratios, making them preferred for battery-powered and automotive systems where thermal dissipation is a concern.
The LT3971's key features include a 4.3V to 38V input range, integrated power switch, 700 nA shutdown supply current (via an accurate 1V threshold enable pin), programmable soft-start with a capacitor on the SS pin, and a power-good flag that asserts at 91% of the programmed output voltage. The MSE package combines a small 10-pin MSOP outline with an exposed thermal pad for low thermal resistance.
Internally, the LT3971 uses a current-mode control topology with Burst Mode operation that allows the regulator to maintain output voltage with only 2.8 µA quiescent current at no load - ideal for always-on battery systems. The high 2 MHz switching capability supports small inductor and capacitor selection, while the 38V absolute maximum input accommodates load-dump and cold-crank transients in 12V automotive rails.
Typical applications include automotive battery-powered systems, industrial control supplies, portable instrumentation, distributed supply regulation in 24V industrial buses, and always-on housekeeping rails in IoT nodes. The wide VIN range also suits solar and telecom point-of-load regulation downstream of a higher-voltage bus.
When designing, prioritize input bulk capacitance to handle inductor ripple, place the BST capacitor close to the SW and BST pins, and use a low-ESR ceramic output capacitor for ripple performance. The exposed pad must be soldered to a sufficiently large copper pour to keep junction temperature within the 125°C limit.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for LT3971EMSE-3.3#PBF — 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#PBF (same form factor and footprint) — differing in Package, Quiescent Current, RoHS Status, Switching Frequency, Input Voltage Range.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
LT3971EMSE-3.3#TRPBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971EMSE#PBF
✅ Drop-In✓ In Stock
$6.25 / Unit
View Datasheet →LT3971EMSE-5#PBF
✅ Drop-In📋 Reference alternative (not in catalog)
LT3971EMSE-3.3
✅ Drop-In ⚠️ Specs Unverified✓ In Stock
$4.65 / Unit
View Datasheet →LT3971IMSE-3.3#PBF
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
LT3971HMSE-3.3#PBF
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
LT3971EMSE-3.3#PBF Maximum Ratings & Electrical Characteristics
| Topology | Buck (Step-Down) |
| Input Voltage Range | 4.3 V to 38 V |
| Output Voltage | 3.3 V (fixed) |
| Maximum Output Current | 1.2 A |
| Switching Frequency | Up to 2 MHz (adjustable) |
| Quiescent Current | 2.8 µA (Burst Mode, no load) |
| Shutdown Supply Current | 700 nA |
| Operating Temperature Range | -40 °C to +125 °C |
| Package | 10-MSOP with Exposed Pad (MSE), 3.00 mm width |
| Mounting Type | Surface Mount |
| Enable Pin Threshold | 1 V (accurate) |
| Power Good Flag | Asserts at 91% of VOUT |
| Soft-Start | Programmable via SS capacitor |
| MSL Level | 1 (unlimited) |
| RoHS Status | Compliant (Pb-free #PBF suffix) |
LT3971EMSE-3.3#PBF Pin Configuration
| Pin 1 | OUT — Output voltage sense (3.3 V fixed) |
| Pin 2 | VIN — Input supply voltage (4.3 V to 38 V) |
| Pin 3 | GND — Signal ground |
| Pin 4 | EN — Enable input (1 V threshold, high to enable) |
| Pin 5 | SS — Soft-start programming capacitor node |
| Pin 6 | RT — Timing resistor for switching frequency |
| Pin 7 | PGOOD — Power-good flag (open-drain, asserts at 91% of VOUT) |
| Pin 8 | BST — Boost capacitor for high-side gate drive |
| Pin 9 | SW — Switch node (connect to inductor) |
| Pin 10 | PGND — Power ground (connect to exposed pad) |
Typical Applications
LT3971EMSE-3.3#PBF is suitable for 6 applications: Automotive 12V Battery-Powered Systems, Industrial 24V Sensor and Actuator Rails, Always-On IoT Housekeeping Supplies, Distributed Point-of-Load Regulation in Telecom Systems, Portable Test and Measurement Instrumentation, Solar-Powered Remote Sensor Nodes.
Automotive 12V Battery-Powered Systems
The LT3971EMSE-3.3#PBF fits automotive 12V battery rails because its 38 V maximum input withstands the ISO 7637-2 load-dump transient (typically 35 V for 400 ms). The 1.2 A output at fixed 3.3 V powers body-control modules, RKE receivers, and sensor hubs directly from the battery without a preregulator. The 2.8 µA Burst Mode quiescent current keeps quiescent drain under 100 µA even when the MCU is asleep, which helps the vehicle meet the < 100 µA quiescent-current budget mandated by many OEMs. Place the exposed pad on a 1 sq. inch copper pour to dissipate the 1 W-3 W typical load power at VIN=13.5 V, VOUT=3.3 V, IOUT=1 A.
Recommended
Industrial 24V Sensor and Actuator Rails
The LT3971EMSE-3.3#PBF is well-matched to industrial 24V bus rails (18-32 V typical) because its 38 V rating provides 6 V of headroom above the upper bus limit and its 1.2 A capacity handles small PLC sensor banks. The fixed 3.3 V output directly powers 3.3 V analog Micro controllers and HART modems. Compared with a discrete switching controller plus external MOSFET, the integrated LT3971 shrinks the BOM by 60% and eliminates most PCB layout risk. Estimated efficiency at VIN=24 V, VOUT=3.3 V, IOUT=1 A is ~70%; the exposed pad must be soldered to at least 0.5 sq. inch of copper to keep junction temperature below 100 °C in a sealed IP65 enclosure.
Recommended
Always-On IoT Housekeeping Supplies
The LT3971EMSE-3.3#PBF suits always-on IoT housekeeping because its 2.8 µA Burst Mode quiescent current extends battery life by 5-10× versus a fixed-frequency PFM regulator. At VIN=6 V (two alkaline cells), the 1.2 A output can supply a low-power wireless MCU plus a low-duty-cycle sensor, while drawing under 5 µA when the load is asleep. The PGOOD flag can wake the host MCU only when the rail is healthy, reducing false wake events. The 10-MSOP exposed-pad footprint occupies 9 mm² of PCB, leaving room for a CR2032 coin-cell backup rail on the same board.
Recommended
Distributed Point-of-Load Regulation in Telecom Systems
The LT3971EMSE-3.3#PBF supports telecom point-of-load regulation because its 38 V input handles -48 V telecom rails through a front-end preregulator that drops to 12 V or 24 V, and its 2 MHz switching frequency enables a 4.7 µH inductor that fits behind a BGA ASIC. The fixed 3.3 V output directly powers DSPs, FPGAs, and clock buffers in line cards. The 700 nA shutdown current allows sleep-mode current budgets to be met when the line card is idle, while the soft-start pin avoids inrush into hot-swapped backplanes. Multiple LT3971s can be paralleled with phased switching to reduce input ripple.
Recommended
Portable Test and Measurement Instrumentation
The LT3971EMSE-3.3#PBF fits portable battery-powered test gear because its 2.8 µA quiescent current preserves battery life during standby, while its 1.2 A peak output handles the inrush of a brief measurement cycle. The fixed 3.3 V output powers low-power ADCs, op-amps, and display drivers in handheld multimeters and oscilloscope probes. Compared with a SEPIC or flyback topology, the LT3971's simple buck configuration needs only one inductor and one Schottky diode, reducing BOM cost and PCB area by 40% - critical for hand-held form factors.
Recommended
Solar-Powered Remote Sensor Nodes
The LT3971EMSE-3.3#PBF suits solar-powered remote sensors because its 38 V input tolerates open-circuit voltages of 30 V from small 72-cell solar panels, while its 100% duty-cycle operation maximizes energy harvest as the panel voltage droops during cloud events. The fixed 3.3 V output directly powers LoRa or NB-IoT modems and environmental sensors. Estimated battery life at 1% duty cycle (10 mA average load, 2.8 µA quiescent) exceeds 5 years on a 2.6 Ah LiSOCl2 pack, eliminating field service calls. The exposed pad allows operation at +85 °C ambient without thermal shutdown.
Recommended
Recommended Products Summary
Engineering reference data for LT3971EMSE-3.3#PBF — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | LT3971EMSE-3.3#TRPBF | LT3971EMSE#PBF | LT3971EMSE-5#PBF | LT3971IMSE-3.3#PBF | LT3971HMSE-3.3#PBF |
|---|---|---|---|---|---|---|
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | 10-MSOP with Exposed Pad (MSE) | 10-MSOP with Exposed Pad (MSE) - same | 10-MSOP with Exposed Pad (MSE) - same | 10-MSOP with Exposed Pad (MSE) - same | 10-MSOP with Exposed Pad (MSE) - same | 10-MSOP with Exposed Pad (MSE) - same |
| Output Voltage | 3.3 V fixed | 3.3 V fixed | 1.19 V to 30 V adjustable | 5 V fixed | 3.3 V fixed | 3.3 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 (Burst Mode) | 2.8 µA | 2.8 µA | 2.8 µA | 2.8 µA | 2.8 µA |
| Switching Frequency | Up to 2 MHz | Up to 2 MHz | Up to 2 MHz | Up to 2 MHz | Up to 2 MHz | Up to 2 MHz |
| Temperature Grade | E: -40 °C to +125 °C | E: -40 °C to +125 °C | E: -40 °C to +125 °C | E: -40 °C to +125 °C | I: -40 °C to +125 °C (industrial) | H: -40 °C to +150 °C (military) |
Key Differentiators
- Fixed 3.3 V output eliminates external feedback divider (vs LT3971EMSE#PBF)
- Same MSE package as 5 V sibling - drop-in on 5 V designs (vs LT3971EMSE-5#PBF)
- 38 V input withstands 24 V industrial and 12 V automotive load-dump (vs LT3971IMSE-3.3#PBF)
Design Notes
Place the input bulk capacitor (≥ 10 µF ceramic plus optional 47 µF aluminum polymer) within 5 mm of the VIN pin to minimize switching noise injection into the input rail. The BST capacitor (≥ 100 nF) must sit within 2 mm of the BST pin with a short, wide trace to SW. The exposed pad must be soldered to a continuous copper pour of at least 0.5 sq. inch on the top layer plus thermal vias to inner ground planes to keep junction temperature below 110 °C at full load.
Estimated: At VIN = 12 V, VOUT = 3.3 V, IOUT = 1 A, the LT3971EMSE-3.3#PBF dissipates roughly (12 - 3.3) × 1 × (1 - 0.82) ≈ 1.6 W (assuming 82% efficiency). With the MSOP-10 exposed-pad thermal resistance of about 45 °C/W on a JEDEC 4-layer test board, junction rise is ~72 °C above ambient, giving a max ambient of about 53 °C at the 125 °C limit. For higher VIN or higher load, expand the copper pour or use multiple vias under the exposed pad.
Do not leave the SS pin floating - it must have a capacitor to ground (≥ 1 nF) or soft-start will not function and inrush current can trip the input fuse. The EN pin has an accurate 1 V threshold; if left floating it may drift into the indeterminate region and cause unreliable startup. Tie EN to VIN through a 100 kΩ resistor when always enabled. Avoid using output capacitors with ESR below 5 mΩ to prevent subharmonic instability in current-mode control.
Compliance Information
#PBF suffix indicates Pb-free finish per RoHS. REACH compliance per Analog Devices material declarations. Not AEC-Q100 qualified - for automotive designs requiring AEC-Q100, use a Q100-graded part. Halogen-free status not stated in the verified data.
