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Analog Devices Inc. LT3991EMSE#PBF
- Part No.:
- LT3991EMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-TFSOP, 10-MSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3991EMSE#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 10MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,320
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Product details
Overview
LT3991EMSE#PBF from Analog Devices (formerly Linear Technology) is a 55V, 1.2A monolithic step-down DC/DC regulator with ultralow 2.8µA quiescent current in regulation, internal 0.44Ω NPN switch, and adjustable switching frequency from 200kHz to 2MHz. It delivers fixed 3.3V output in MSOP-10 package and is used in automotive battery regulation and portable power supplies where low standby power is critical.
For engineers reviewing the LT3991EMSE#PBF datasheet, LT3991EMSE#PBF pinout, LT3991EMSE#PBF application, or LT3991EMSE#PBF equivalent, key selection criteria include input voltage range (4.3V–55V), Burst Mode ripple (<15mVP-P), power good flag accuracy (±9% of VOUT), soft-start control via SS pin, and thermal performance enabled by exposed pad GND.
Technical Context
The LT3991EMSE#PBF implements constant-frequency current-mode control with internal compensation, enabling fast transient response and stable loop behavior across wide VIN/VOUT ratios. Its bipolar NPN switch-driven by BOOST pin voltage-achieves 0.44Ω on-resistance and supports duty cycles up to ~90% at low frequencies.
Burst Mode operation reduces no-load supply current to 2.8µA while maintaining output ripple below 15mVP-P; synchronization via SYNC pin disables Burst Mode and enables pulse-skipping at light loads. The 1V enable threshold with 30mV hysteresis and 700nA shutdown current support precise system-level power sequencing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.3V to 55V - supports direct connection to 12V/24V/48V automotive and industrial rails without pre-regulation |
| Output Current | 1.2A max - sufficient for powering microcontrollers, sensors, and RF modules in space-constrained designs |
| Quiescent Current | 2.8µA at no load - enables >10-year battery life in always-on IoT nodes powered by coin cells or LiSOCl₂ |
| Switching Frequency | 200kHz to 2MHz - selectable via RT resistor; higher frequencies allow smaller magnetics but reduce max VIN capability |
| Feedback Reference | 1.19V - sets output voltage via external resistor divider; enables adjustable outputs from 1.19V to 30V |
| Power Good Threshold | VOUT ≥ 91% of regulation - open-drain PG signal asserts high only when output is within tight tolerance |
| Enable Threshold | 1.01V rising / 0.975V falling - accurate hysteresis prevents chatter during slow-rising supply ramps |
| Thermal Package | 10-pin MSOP with exposed pad - θJA = 45°C/W enables 1.2A operation at +85°C ambient without heatsink |
Pinout & Package
LT3991EMSE#PBF is housed in a thermally enhanced 10-lead plastic MSOP package with exposed pad (Pin 11) soldered to PCB ground for optimal thermal dissipation. Pin numbering follows standard MSOP top-view orientation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost diode anode connection | Connects to cathode of external Schottky; forms charge pump path for BOOST drive |
| BOOST (2) | Internal switch gate drive supply | Must be biased >VIN via external capacitor; enables full saturation of NPN switch |
| SW (3) | Switch node | Drives inductor; connects to catch diode cathode and BOOST capacitor |
| VIN (4) | Main power input | Supplies IC bias and switch current; requires local ceramic bypass (≥1µF) |
| EN (5) | Enable control input | Hysteretic 1V threshold; pulls VIN current to 700nA in shutdown |
| VOUT (6) | Fixed-output voltage sense | Internally regulated to 3.3V; connects to feedback divider tap in adjustable versions |
| SS (7) | Soft-start ramp control | Capacitor-to-ground sets inrush current limit; discharged only during EN low |
| RT (8) | Frequency programming | Resistor-to-ground sets switching frequency from 200kHz to 2MHz |
| PG (9) | Power good flag | Open-drain output active high when VOUT ≥ 91% of target; requires pull-up |
| SYNC (10) | External clock input | Ground for Burst Mode; tie to external clock for synchronized pulse-skipping |
Key Features
| Feature | Design Value |
|---|---|
| Ultralow quiescent current | 2.8µA IQ in regulation enables multi-year operation from primary batteries in remote sensors |
| Low-ripple Burst Mode | Maintains <15mVP-P output ripple at light loads while sustaining >85% efficiency down to 100µA output current |
| Integrated boost diode driver | Eliminates need for external bootstrap circuitry; supports efficient NPN switch operation up to 55V input |
| Accurate power good flag | PG asserts only when output reaches 91% of final value, with 20mV hysteresis - ensures reliable system boot sequencing |
| Thermally optimized MSOP | Exposed pad GND reduces θJA to 45°C/W - sustains 1.2A continuous output at +85°C ambient |
| Internal compensation | Reduces external component count; eliminates stability tuning for standard inductor/capacitor combinations |
Applications
| Automotive Battery Regulation | Portable Medical Sensors |
|---|---|
Use Scenario: Powering CAN transceivers and microcontrollers directly from 12V vehicle battery with cold-crank tolerance down to 4.3V. IC Role / Device Role / Timing Role: Primary buck regulator providing clean, regulated 3.3V rail with ultra-low sleep current to extend ECU battery backup life. Use Value: 2.8µA quiescent current prevents parasitic drain during vehicle off-state; 55V absolute max rating withstands load-dump transients. | Use Scenario: Long-life wearable glucose monitors powered by CR2032 coin cell requiring >5-year shelf life and sub-100µA average system current. IC Role / Device Role / Timing Role: System power manager delivering regulated 3.3V to ADC, BLE radio, and sensor interface during intermittent wake cycles. Use Value: Burst Mode maintains <15mV ripple while drawing only 2.8µA between measurements - maximizes battery energy utilization. |
| Industrial Remote I/O Modules | Smart Utility Meters |
Use Scenario: Field-deployed DIN-rail controllers operating from 24VDC industrial bus with strict EMC and thermal constraints. IC Role / Device Role / Timing Role: Isolated auxiliary supply generating 3.3V for microcontroller and RS-485 transceiver in compact enclosure. Use Value: MSOP-10 exposed pad enables conduction cooling; 200kHz–2MHz frequency adjustability allows EMI optimization around sensitive bands. | Use Scenario: AMI smart meters with lithium-thionyl chloride primary battery and 10+ year deployment requirement. IC Role / Device Role / Timing Role: Main system regulator supporting metering SoC, LCD, and PLC communication during brief daily wake windows. Use Value: 700nA shutdown current preserves battery capacity during 99.9% of operational lifetime; PG flag validates rail integrity before measurement cycle. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3639EMSE#PBF | Higher 60V max input; lower 1.5µA IQ; integrated MOSFETs; no BOOST pin required | Better suited for 48V telecom or PoE-powered systems; lacks BD/BOOST flexibility for ultra-high-efficiency NPN designs | Select LTC3639EMSE#PBF when lowest possible IQ and simplified layout outweigh need for bipolar switch optimization |
| TPS63060DSCR | Buck-boost topology; 3.5V–20V input; 3A output; 25µA IQ; no PG or SYNC | Required where input may drop below output (e.g., single-cell Li-ion); not suitable for 55V automotive or industrial rails | Choose TPS63060DSCR only when input voltage can fall below VOUT - LT3991EMSE#PBF is superior for unidirectional high-VIN step-down |
Compared with LTC3639EMSE#PBF and TPS63060DSCR, LT3991EMSE#PBF uniquely balances 55V input capability, 2.8µA IQ, and bipolar switch efficiency - making it optimal for automotive and long-life industrial battery systems where input never falls below output.
Availability
LT3991EMSE#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable medical sensors, and industrial remote I/O modules requiring stable component supply with guaranteed long-term availability.
Supply support for LT3991EMSE#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for all LT-branded ICs.
The LT3991 product line was designed specifically for high-input-voltage, ultralow-quiescent-current DC/DC conversion in automotive, industrial, and battery-powered applications demanding decades-long reliability.
FAQ
What is the maximum input voltage rating for LT3991EMSE#PBF?
The LT3991EMSE#PBF has an absolute maximum input voltage rating of 55V on the VIN pin, with guaranteed operation from 4.3V to 55V. This enables direct connection to 12V, 24V, and 48V industrial and automotive power rails, including tolerance for load-dump transients up to 55V. Exceeding 55V risks permanent damage per Absolute Maximum Ratings.
Does LT3991EMSE#PBF support adjustable output voltage?
No - LT3991EMSE#PBF is the fixed 3.3V output variant. It uses an internal 10MΩ feedback divider connected to Pin 6 (VOUT), eliminating external resistors. For adjustable output, use LT3991EMSE#PBF's sibling part LT3991EMSE#PBF (no suffix), which exposes FB pin (Pin 6) and requires external resistor divider to set VOUT from 1.19V to 30V.
How does the power good (PG) flag behave on LT3991EMSE#PBF?
The PG pin on LT3991EMSE#PBF is an open-drain output that remains low until VOUT reaches 91% of its nominal 3.3V output (i.e., ≥3.003V). It asserts high only when enabled and VIN >4.3V. PG has 20mV hysteresis and requires an external pull-up resistor; it signals valid regulation to host processors for safe system boot sequencing.
Can LT3991EMSE#PBF operate in Burst Mode when synchronized to an external clock?
No - grounding the SYNC pin is mandatory for Burst Mode operation. When SYNC is tied to an external clock, LT3991EMSE#PBF enters pulse-skipping mode instead, increasing quiescent current to 1.5mA and raising output ripple. For ultralow IQ and low ripple at light loads, SYNC must be grounded; use SYNC only when EMI-sensitive timing alignment is required.
What thermal performance can be expected from LT3991EMSE#PBF in MSOP package?
LT3991EMSE#PBF in 10-lead MSOP with soldered exposed pad achieves θJA = 45°C/W and θJC = 10°C/W. With proper PCB copper area under the exposed pad, it delivers full 1.2A output continuously at +85°C ambient. Derating begins above +100°C junction temperature; maximum rated junction temperature is 125°C.
LT3991EMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 10-TFSOP, 10-MSOP (0.118", 3.00mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4.3V
- Voltage - Input (Max):
- 55V
- Voltage - Output (Min/Fixed):
- 1.19V
- Voltage - Output (Max):
- 30V
- Current - Output:
- 1.2A
- Frequency - Switching:
- 200kHz ~ 2MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-MSOP-EP
LT3991EMSE#PBF FAQ
1.How can I place an order for LT3991EMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3991EMSE#PBF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LT3991EMSE#PBF reliable?
The price and inventory of LT3991EMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3991EMSE#PBF is usually 5 days.
3.What payment methods are accepted for LT3991EMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3991EMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3991EMSE#PBF?
LT3991EMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3991EMSE#PBF order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LT3991EMSE#PBF?
For technical support, including LT3991EMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3991EMSE#PBF requirements.
6.How does Aetrix verify that LT3991EMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3991EMSE#PBF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LT3991EMSE#PBF meets industry standards.
7.What is the process for return or replacement of LT3991EMSE#PBF?
All LT3991EMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3991EMSE#PBF, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LT3991EMSE#PBF part is unused and in its original packaging.
Return procedure for LT3991EMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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