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Analog Devices Inc. LT3991IMSE#PBF
- Part No.:
- LT3991IMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-TFSOP, 10-MSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3991IMSE#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 10MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:778
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Product details
Overview
LT3991IMSE#PBF from Analog Devices (formerly Linear Technology) is a 55V, 1.2A monolithic step-down switching regulator with ultralow 2.8µA quiescent current in regulation, internal compensation, and a 0.44Ω NPN switch. It operates from 4.3V to 55V input, delivers fixed 3.3V output, and integrates power good flag, soft-start, and Burst Mode® for <15mV ripple at light loads - used in automotive battery regulation and portable power supplies.
For engineers reviewing the LT3991IMSE#PBF datasheet, LT3991IMSE#PBF pinout, LT3991IMSE#PBF application, or LT3991IMSE#PBF equivalent, key selection criteria include its 3.3V fixed output, 10-pin MSOP package with exposed pad, 700nA shutdown current, 1V enable threshold, and compatibility with 200kHz–2MHz frequency programming via RT pin.
Technical Context
The LT3991IMSE#PBF implements constant-frequency current-mode control with an internally compensated error amplifier and slope-compensated PWM. Its bipolar NPN switch is driven by a BOOST pin voltage higher than VIN, enabling full saturation and low 0.44Ω on-resistance.
Burst Mode® operation shuts down control circuitry between pulses to achieve 2.8µA no-load IQ, while maintaining output regulation and <15mVP-P ripple. The power good (PG) comparator asserts when FB reaches 91% of 1.19V reference (i.e., ~1.083V), and EN pin hysteresis ensures clean startup at 1.005V rising / 0.975V falling thresholds.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.3V to 55V - supports wide automotive and industrial supply rails without external pre-regulation. |
| Output Voltage | Fixed 3.3V ±1.5% - internally trimmed; eliminates external feedback resistors and improves accuracy over temperature. |
| Max Output Current | 1.2A continuous - sufficient for microcontrollers, sensors, and communication ICs in space-constrained designs. |
| Quiescent Current | 2.8µA at no load - enables multi-year battery life in always-on IoT and telematics applications. |
| Shutdown Current | 700nA - reduces system standby power to negligible levels when EN is pulled low. |
| Switch On-Resistance | 0.44Ω - minimizes conduction loss and thermal rise at full load in compact MSOP package. |
| Switching Frequency | 200kHz to 2MHz - adjustable via RT pin resistor; allows optimization of inductor size vs. efficiency tradeoff. |
| Power Good Threshold | 91% of regulated output - provides reliable sequencing signal for downstream logic without external comparators. |
Pinout & Package
LT3991IMSE#PBF is housed in a thermally enhanced 10-lead plastic MSOP package with exposed pad (Pin 11 = GND), θJA = 45°C/W, θJC = 10°C/W. The exposed pad must be soldered to PCB for optimal thermal performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Connection | Connects to cathode of external Schottky diode; forms charge pump path for BOOST drive voltage. |
| BOOST (2) | Internal Switch Drive Supply | Provides >VIN voltage to fully saturate NPN switch; requires external capacitor to VOUT. |
| SW (3) | Switch Node | Drives inductor and catch diode; high dv/dt node requiring careful layout and snubbing. |
| VIN (4) | Main Power Input | Supplies internal circuitry and switch; requires local 1µF ceramic bypass capacitor. |
| EN (5) | Enable Control Input | Hysteretic 1V threshold (±30mV); pulls low to reduce supply current to 700nA. |
| VOUT (6) | Fixed 3.3V Output | Internally regulated node; connects to output capacitor and load; also serves as feedback reference. |
| SS (7) | Soft-Start Control | Controls inrush current ramp via external RC; disables soft-start if left floating. |
| RT (8) | Frequency Set Resistor | Resistor to GND sets switching frequency from 200kHz to 2MHz per datasheet table. |
| PG (9) | Power Good Flag | Open-drain output; pulled high externally when VOUT reaches 91% of target (≈3.003V). |
| SYNC (10) | External Clock Input | Ground for Burst Mode; tie to external clock for synchronization (increases IQ to 1.5mA). |
Key Features
| Feature | Design Value |
|---|---|
| Ultralow Quiescent Current | 2.8µA IQ in regulation enables >10-year battery life in always-on sensor nodes. |
| Low-Ripple Burst Mode® | Maintains <15mVP-P output ripple at light loads while preserving high efficiency. |
| Integrated Power Good Flag | Eliminates need for external supervisor IC; provides precise 91% output validation. |
| Thermally Enhanced MSOP | 10-pin MSOP with exposed pad delivers θJC = 10°C/W for reliable 1.2A operation without heatsink. |
| Internal Compensation | Reduces BOM count and design risk - no external compensation network required. |
| Accurate Enable Threshold | 1.005V rising / 0.975V falling hysteresis prevents chatter during brown-in/brown-out conditions. |
Applications
| Automotive Battery Regulation | Portable Medical Device Power |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery to stable 3.3V for CAN transceivers and microcontrollers under cold-crank (4.3V min) and load-dump (55V max) conditions. IC Role / Device Role / Timing Role: Primary buck regulator providing isolated, low-noise 3.3V rail with fast transient response to engine start-stop events. Use Value: 2.8µA quiescent current prevents battery drain during extended parking; PG flag enables safe MCU wake-up sequencing. | Use Scenario: Powering handheld ECG monitors and glucose meters from single-cell Li-ion (3.0–4.2V) or dual-cell alkaline (1.8–3.2V) batteries. IC Role / Device Role / Timing Role: Step-down converter delivering regulated 3.3V to low-power ARM Cortex-M0+ MCU and analog front-end. Use Value: 700nA shutdown current extends shelf life; Burst Mode maintains <15mV ripple during sensor sampling bursts. |
| Industrial Sensor Node Supply | Railway Signaling Interface Power |
Use Scenario: Converting 24V DC industrial bus to 3.3V for wireless LoRaWAN or NB-IoT sensor modules operating in unattended field deployments. IC Role / Device Role / Timing Role: Primary DC/DC converter supplying power to RF SoC, temperature/humidity sensors, and EEPROM. Use Value: Wide 4.3–55V input range accommodates 24V nominal systems with long cable drops and surges; MSOP package fits tight PCB footprints. | Use Scenario: Providing isolated 3.3V logic supply for train-mounted signaling interface boards exposed to 72V–110V DC traction power with EMI and surge stress. IC Role / Device Role / Timing Role: Secondary buck regulator deriving clean 3.3V from intermediate 24V rail generated from high-voltage input. Use Value: Internal 0.44Ω switch and thermal pad sustain 1.2A load at 70°C ambient; PG flag validates rail before enabling safety-critical I/O. |
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; 1.5A output; 3.5µA IQ; no fixed 3.3V option - requires external feedback. | Supports wider input range and higher current but lacks integrated 3.3V reference and PG flag. | Choose LTC3639EMSE#PBF only if >55V input or >1.2A load is required; adds two resistors and loses PG functionality. |
| TPS63036DSKR | Buck-boost topology; 1.8–5.5V input; 3.3V fixed; 25µA IQ; 1A output; no PG or SYNC. | Operates below 4.3V input (e.g., single Li-ion), but cannot handle >5.5V - unsuitable for automotive or industrial 12V/24V rails. | Select TPS63036DSKR only for sub-5.5V battery-powered devices needing buck-boost; not a drop-in replacement for LT3991IMSE#PBF. |
Compared with LTC3639EMSE#PBF and TPS63036DSKR, the LT3991IMSE#PBF uniquely combines 55V input capability, fixed 3.3V output, 2.8µA IQ, and integrated PG flag in a 10-pin MSOP - making it optimal for automotive and industrial 12V/24V systems where simplicity, low standby power, and rail validation are critical.
Availability
LT3991IMSE#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable medical device power, industrial sensor node supply, and railway signaling interface power requiring stable component supply across extended temperature ranges.
Supply support for LT3991IMSE#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 qualification standards.
The LT3991 product line was designed specifically for ultralow-power, wide-input-voltage DC/DC conversion in harsh environments - targeting automotive, industrial, and portable electronics where quiescent current, thermal robustness, and functional integration are paramount.
FAQ
What is the guaranteed operating temperature range for LT3991IMSE#PBF?
The LT3991IMSE#PBF is specified for –40°C to 125°C junction temperature. This "I" grade rating ensures full electrical performance across automotive under-hood and industrial control cabinet environments without derating. All parameters in the Electrical Characteristics table marked with "l" apply over this full range, including feedback voltage (1.175V to 1.205V), EN threshold (0.95V to 1.07V), and PG hysteresis (20mV).
Does LT3991IMSE#PBF require external compensation components?
No, the LT3991IMSE#PBF features internal compensation for its current-mode control loop. This eliminates the need for external Type II or Type III compensation networks, reducing BOM count, board area, and design iteration time. The internal compensation is optimized for stability with standard output capacitor ESR values and typical inductor selections cited in the datasheet.
Can LT3991IMSE#PBF be synchronized to an external clock?
Yes, the LT3991IMSE#PBF supports external synchronization via the SYNC pin (Pin 10). When driven with a TTL/CMOS clock between 250kHz and 2MHz, the regulator locks to the external frequency. However, synchronizing disables Burst Mode® and increases no-load quiescent current from 2.8µA to 1.5mA - a critical trade-off for battery-sensitive applications.
What is the function of the BD pin on LT3991IMSE#PBF?
The BD (Boost Diode) pin on LT3991IMSE#PBF connects to the anode of an external Schottky diode whose cathode ties to VOUT. This forms a charge pump that generates the BOOST voltage needed to fully saturate the internal bipolar NPN switch. Proper BD connection is essential for achieving the specified 0.44Ω RCE(SAT) and high efficiency across the full input range.
How does the power good (PG) flag behave on LT3991IMSE#PBF?
The PG pin on LT3991IMSE#PBF is an open-drain output that remains low until the VOUT pin reaches 91% of its final regulated value (≈3.003V for LT3991IMSE#PBF). It is valid only when EN is high and VIN exceeds 4.3V. An external pull-up resistor (typically 10kΩ to 3.3V) is required to generate a logic-high signal indicating stable regulation.
LT3991IMSE#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
LT3991IMSE#PBF FAQ
1.How can I place an order for LT3991IMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3991IMSE#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#PBF reliable?
The price and inventory of LT3991IMSE#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#PBF is usually 5 days.
3.What payment methods are accepted for LT3991IMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3991IMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3991IMSE#PBF?
LT3991IMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3991IMSE#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#PBF?
For technical support, including LT3991IMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3991IMSE#PBF requirements.
6.How does Aetrix verify that LT3991IMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3991IMSE#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#PBF meets industry standards.
7.What is the process for return or replacement of LT3991IMSE#PBF?
All LT3991IMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3991IMSE#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#PBF part is unused and in its original packaging.
Return procedure for LT3991IMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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