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Analog Devices Inc. LT3991IMSE-3.3#PBF
- Part No.:
- LT3991IMSE-3.3#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-TFSOP, 10-MSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3991IMSE-3.3#PBF.pdf
- Description:
- IC REG BUCK 3.3V 1.2A 10MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:207
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Product details
Overview
LT3991IMSE-3.3#PBF from Analog Devices (formerly Linear Technology) is a 55V input, 1.2A fixed-output step-down regulator in thermally enhanced 10-pin MSOP package, featuring 2.8µA quiescent current in regulation, low-ripple Burst Mode operation (<15mVP-P), and integrated 0.44Ω NPN switch with internal boost Schottky diode drive. It delivers stable 3.3V output for automotive battery-powered systems requiring ultra-low standby power.
For engineers reviewing the LT3991IMSE-3.3#PBF datasheet, LT3991IMSE-3.3#PBF pinout, LT3991IMSE-3.3#PBF application, or LT3991IMSE-3.3#PBF equivalent, key selection criteria include its 4.3V–55V input range, 3.3V ±1.5% output accuracy over –40°C to 125°C, 700nA shutdown current, power good flag, and soft-start capability via SS pin - all critical for reliable cold-cranking and long-life battery operation.
Technical Context
The LT3991IMSE-3.3#PBF implements constant-frequency current-mode control with internal compensation, enabling fast transient response and stable loop behavior across wide input/output conditions. Its bipolar NPN switch is driven by an on-chip BOOST circuit that elevates gate voltage above VIN using an external capacitor and BD-connected Schottky diode.
Burst Mode operation reduces no-load supply current to 2.8µA while maintaining output ripple below 15mVP-P; frequency foldback during startup and overload protects against excessive peak inductor current. The device integrates a 1V-threshold enable pin with 30mV hysteresis and open-drain PG output asserting at 91% of regulated output.
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 Voltage | 3.3V ±1.5% (–40°C to 125°C) - factory-trimmed fixed output eliminates external feedback resistors and improves accuracy vs adjustable variants. |
| Quiescent Current | 2.8µA at no load - enables >10-year battery life in always-on telematics and ECU sleep modes. |
| Max Output Current | 1.2A continuous - sufficient for powering microcontrollers, CAN transceivers, and sensor interfaces from single-stage conversion. |
| Switch On-Resistance | 0.44Ω - minimizes conduction loss at high duty cycles; enables >90% efficiency at 1A with 12VIN/3.3VOUT. |
| Shutdown Current | 700nA - ensures negligible drain during system deep-sleep states. |
| Power Good Threshold | 91% of VOUT (±1.3%) - provides precise, temperature-stable sequencing signal for downstream logic reset. |
Pinout & Package
LT3991IMSE-3.3#PBF is housed in a 10-lead plastic MSOP package with exposed thermal pad (Pin 11 = GND), optimized for low θJA = 45°C/W and θJC = 10°C/W. The exposed pad must be soldered to PCB for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Connection | Connects to Schottky diode anode; forms charge pump path to elevate BOOST voltage above VIN for NPN saturation. |
| BOOST (2) | Internal Switch Drive Supply | Provides elevated voltage to base of internal NPN switch; requires external capacitor between BOOST and SW pins. |
| SW (3) | Switch Node | Drives inductor and catch diode; connects to BOOST capacitor and BD diode cathode; carries high di/dt switching current. |
| VIN (4) | Main Power Input | Supplies internal bias and switch current; must be locally bypassed with low-ESR ceramic capacitor near package. |
| EN (5) | Enable Control Input | Hysteretic 1.01V rising / 0.975V falling threshold; pulls to GND for shutdown (700nA IQ); tie to VIN if unused. |
| VOUT (6) | Fixed Output Voltage Reference | Internally regulated 3.3V output node; connects to internal 10MΩ feedback divider - no external resistors required. |
| SS (7) | Soft-Start Control | Controls ramp rate of peak current limit; external RC network sets inrush current profile and prevents output overshoot. |
| RT (8) | Frequency Setting Input | Resistor-to-GND sets switching frequency from 200kHz to 2MHz; enables optimization of size vs efficiency tradeoffs. |
| PG (9) | Power Good Flag | Open-drain output active low until VOUT reaches 91% of regulation; requires external pull-up for system monitoring. |
| SYNC (10) | External Clock Synchronization | Ground for Burst Mode; accept external clock (250kHz–2MHz) for deterministic timing; disables Burst Mode when driven. |
Key Features
| Feature | Design Value |
|---|---|
| Ultralow Quiescent Current | 2.8µA regulating 12VIN to 3.3VOUT - extends battery runtime in always-on vehicle modules without compromising regulation stability. |
| Low-Ripple Burst Mode | Output ripple <15mVP-P at light loads - avoids audible noise and EMI issues common in traditional pulse-skipping regulators. |
| Integrated Boost Circuitry | On-die BOOST driver + BD pin - eliminates need for external charge pump IC or discrete transistor, reducing BOM count and layout area. |
| Accurate Power Good Flag | PG asserts at 91% of VOUT with 1.3% hysteresis - enables reliable power sequencing and fault detection in multi-rail systems. |
| Thermally Enhanced Package | MSOP with exposed GND pad - achieves θJC = 10°C/W, allowing 1.2A operation up to 125°C junction temperature with minimal heatsinking. |
Applications
| Automotive Body Control Module (BCM) | Industrial IoT Sensor Node |
|---|---|
Use Scenario: Powering microcontroller, LIN transceiver, and door-lock actuator drivers from 12V battery with cold-crank tolerance down to 4.3V. IC Role / Device Role / Timing Role: Primary 3.3V system rail regulator with ultralow IQ, PG signaling, and robust input transient handling. Use Value: Enables >15-year battery life in parked vehicle mode while maintaining immediate wake-up capability and ASIL-B compatible power sequencing. |
Use Scenario: Supplying 3.3V to ARM Cortex-M based edge node with LoRaWAN radio, environmental sensors, and EEPROM under intermittent solar/battery power. IC Role / Device Role / Timing Role: Main DC-DC converter delivering regulated 3.3V with minimal self-consumption during multi-day sleep cycles. Use Value: Reduces average system IQ to sub-µA level, extending field deployment interval from months to years without maintenance. |
| Railway Onboard Telematics Unit | Medical Portable Diagnostic Device |
Use Scenario: Converting 72V nominal railway battery (range: 45V–100V) to isolated 3.3V logic supply for GPS/GSM module and data logger. IC Role / Device Role / Timing Role: Front-end buck regulator accepting wide input range and providing clean, sequenced 3.3V output with PG confirmation. Use Value: Eliminates need for intermediate 24V stage, simplifying architecture and improving overall efficiency by >8% vs two-stage conversion. |
Use Scenario: Powering clinical-grade ADC, OLED display controller, and Bluetooth LE SoC from single-cell Li-ion (3.0V–4.2V) with backup coin cell. IC Role / Device Role / Timing Role: High-efficiency 3.3V regulator operating down to 4.3V input, supporting seamless switchover between main and backup sources. Use Value: Maintains full functionality during brownout events and extends usable battery capacity by minimizing no-load losses. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar fixed-output buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8609SIV#PBF | 42V max input, 2A output, 2.5µA IQ, synchronous rectification, 3mm × 4mm LQFN | Higher current, lower IQ, but lacks integrated boost diode drive and fixed 3.3V option - requires external feedback network. | Choose for higher output current and synchronous efficiency where board space allows LQFN and design tolerates external resistor network. |
| TPS54332DDAR | 28V max input, 3.5A output, 26µA IQ, adjustable only, SOIC-8 | Lower input voltage rating, significantly higher quiescent current, no PG flag or soft-start pin - less suitable for automotive battery systems. | Choose for cost-sensitive industrial supplies where 28V input ceiling and higher IQ are acceptable, and PG/soft-start are not required. |
Compared with LT3991IMSE-3.3#PBF, LT8609SIV#PBF offers higher current and lower IQ but requires external feedback and lacks integrated boost drive, while TPS54332DDAR trades off input range and ultra-low IQ for cost and availability in non-automotive contexts.
Availability
LT3991IMSE-3.3#PBF is available at Aetrix Electronics and suitable for automotive body electronics, industrial sensor nodes, railway telematics, and portable medical devices requiring stable component supply across extended temperature ranges and long product lifecycles.
Supply support for LT3991IMSE-3.3#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 its high-reliability analog and power management portfolio with rigorous automotive qualification standards and long-term product support.
The LT3991 family was designed specifically for automotive and industrial applications demanding wide-input, ultralow-quiescent-current DC-DC conversion with integrated protection and sequencing features - targeting cold-crank resilience and multi-year battery operation.
FAQ
What is the guaranteed operating temperature range for LT3991IMSE-3.3#PBF?
The LT3991IMSE-3.3#PBF is specified for –40°C to 125°C junction temperature operation and is tested to meet all electrical characteristics across this full range. The 'I' grade designation confirms industrial/automotive qualification, including thermal cycling and long-term reliability testing per AEC-Q100 stress requirements.
Does LT3991IMSE-3.3#PBF require external feedback resistors to set the 3.3V output?
No. The LT3991IMSE-3.3#PBF integrates an internal 10MΩ feedback resistor divider and precision 1.19V reference, delivering a factory-trimmed 3.3V ±1.5% output directly at the VOUT pin (Pin 6). No external resistors are needed - simplifying layout and improving accuracy versus adjustable variants like the base LT3991.
How does the LT3991IMSE-3.3#PBF achieve 2.8µA quiescent current while maintaining regulation?
The LT3991IMSE-3.3#PBF achieves 2.8µA IQ through proprietary low-ripple Burst Mode operation: it delivers discrete current pulses to the output capacitor, then enters deep sleep (consuming only 1.7µA), minimizing average input current while holding VOUT within regulation. This differs from standard pulse-skipping, which increases ripple and IQ to ~1.5mA.
Can LT3991IMSE-3.3#PBF operate from a 48V input while delivering 3.3V/1.2A?
Yes. The LT3991IMSE-3.3#PBF supports inputs up to 55V and delivers 1.2A continuously at 3.3V with proper thermal design. At 48VIN/3.3VOUT, efficiency exceeds 82% (per Figure G01), and thermal performance remains within spec when the exposed pad is soldered to ≥2 cm² copper area with 4+ thermal vias.
What is the function of the BD pin on LT3991IMSE-3.3#PBF, and what diode is recommended?
The BD (Boost Diode) pin connects to the anode of an external Schottky diode (e.g., DFLS2100), forming a charge pump that generates the BOOST voltage needed to saturate the internal NPN switch. Linear recommends low-leakage Schottky diodes with <1µA reverse current at 25°C - critical for preserving ultralow IQ in battery applications.
LT3991IMSE-3.3#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:
- Fixed
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4.3V
- Voltage - Input (Max):
- 55V
- Voltage - Output (Min/Fixed):
- 3.3V
- Voltage - Output (Max):
- -
- 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
LT3991IMSE-3.3#PBF FAQ
1.How can I place an order for LT3991IMSE-3.3#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3991IMSE-3.3#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 LT3991IMSE-3.3#PBF reliable?
The price and inventory of LT3991IMSE-3.3#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3991IMSE-3.3#PBF is usually 5 days.
3.What payment methods are accepted for LT3991IMSE-3.3#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3991IMSE-3.3#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3991IMSE-3.3#PBF?
LT3991IMSE-3.3#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3991IMSE-3.3#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 LT3991IMSE-3.3#PBF?
For technical support, including LT3991IMSE-3.3#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3991IMSE-3.3#PBF requirements.
6.How does Aetrix verify that LT3991IMSE-3.3#PBF is sourced from the original manufacturer or authorized distributors?
All LT3991IMSE-3.3#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 LT3991IMSE-3.3#PBF meets industry standards.
7.What is the process for return or replacement of LT3991IMSE-3.3#PBF?
All LT3991IMSE-3.3#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3991IMSE-3.3#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 LT3991IMSE-3.3#PBF part is unused and in its original packaging.
Return procedure for LT3991IMSE-3.3#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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