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Analog Devices Inc. LT3991IDD#PBF
- Part No.:
- LT3991IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3991IDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:509
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Product details
Overview
LT3991IDD#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 and 700nA shutdown current. It features internal compensation, 0.44Ω NPN switch, integrated boost Schottky diode driver, and power good flag. Designed for automotive battery regulation and portable power supplies where low standby power is critical.
For engineers reviewing the LT3991IDD#PBF datasheet, LT3991IDD#PBF pinout, LT3991IDD#PBF application, or LT3991IDD#PBF equivalent, key selection criteria include input voltage range (4.3V–55V), adjustable frequency (200kHz–2MHz), Burst Mode ripple control (<15mVP-P), soft-start capability, and thermal performance in the 3mm × 3mm DFN package with exposed pad.
Technical Context
The LT3991IDD#PBF implements constant-frequency current-mode control with internal slope compensation and an actively clamped VC node for fast transient response and loop stability. Its bipolar NPN switch is driven via an external BOOST capacitor to ensure saturation across the full input range up to 55V.
Burst Mode operation reduces no-load supply current to 2.8µA while maintaining output ripple below 15mVP-P; synchronization via the SYNC pin enables pulse-skipping at light loads but increases quiescent current to 1.5mA. The EN pin provides accurate 1.01V rising threshold with 30mV hysteresis and supports UVLO behavior below 4.3V VIN.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.3V to 55V - supports wide automotive and industrial input rails without external pre-regulation |
| Max Output Current | 1.2A - sustained DC load capability with internal 2.3A typical switch current limit |
| Quiescent Current | 2.8µA at no load - enables >10-year battery life in always-on monitoring systems |
| Switch On-Resistance | 0.44Ω - minimizes conduction loss and thermal rise at full load |
| Switching Frequency | 200kHz to 2MHz - adjustable via RT resistor; enables optimization of size vs. efficiency |
| Feedback Reference | 1.19V - precise internal reference enabling accurate output programming from 1.19V to 30V |
| Power Good Threshold | 91% of VOUT - open-drain PG flag asserts when output reaches regulation tolerance |
Pinout & Package
LT3991IDD#PBF is housed in a thermally enhanced 10-lead (3mm × 3mm) plastic DFN package with exposed GND pad (Pin 11) requiring PCB soldering for optimal thermal performance (θJA = 45°C/W, θJC = 10°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Connection | Connects to cathode of external Schottky diode; forms bootstrap path for switch drive |
| BOOST (2) | Bootstrap Voltage Supply | Drives internal NPN switch base above VIN; requires external capacitor to SW |
| SW (3) | Switch Node | High-side bipolar NPN collector output; connects to inductor, catch diode, and BOOST cap |
| VIN (4) | Main Power Input | Supplies internal circuitry and switch; must be locally bypassed with low-ESR capacitor |
| EN (5) | Enable/UVLO Input | Hysteretic 1.01V enable threshold; pulls device into 700nA shutdown when low |
| FB (6) | Feedback Input | Regulated to 1.19V; connects to resistor divider tap for adjustable output voltage |
| SS (7) | Soft-Start Control | Controls inrush current via external RC ramp; discharged only during EN low |
| RT (8) | Frequency Set Input | Resistor-to-GND sets switching frequency from 200kHz to 2MHz |
| PG (9) | Power Good Flag | Open-drain output active high when FB reaches 91% of target; valid only if VIN > 4.3V |
| SYNC (10) | External Clock Input | Ground for Burst Mode; accept 250kHz–2MHz clock for synchronized pulse-skipping |
Key Features
| Feature | Design Value |
|---|---|
| Ultralow Quiescent Current | 2.8µA regulating - extends battery runtime in always-on telematics and sensor nodes |
| Low Ripple Burst Mode | <15mVP-P output ripple - eliminates need for post-regulation LDO in noise-sensitive analog circuits |
| Internal Compensation | No external compensation components required - reduces BOM count and layout sensitivity |
| Saturating Switch Design | 0.44Ω on-resistance - delivers >90% efficiency at 1A with 12V→3.3V conversion |
| Thermally Enhanced DFN | Exposed GND pad + 10°C/W θJC - enables 1.2A continuous operation without heatsink at 70°C ambient |
Applications
| Automotive Battery Regulation | Portable Medical Instrumentation |
|---|---|
Use Scenario: Powering CAN transceivers and microcontrollers from 12V/24V vehicle batteries with cold-crank survivability down to 4.3V. IC Role / Device Role / Timing Role: Primary buck regulator providing stable 3.3V or 5V rail with ultralow IQ to maintain ECU wake-up logic during engine-off periods. Use Value: 2.8µA no-load current enables >15-year battery backup for event-triggered logging without parasitic drain. |
Use Scenario: Powering handheld glucose meters and pulse oximeters operating from single-cell Li-ion or alkaline batteries. IC Role / Device Role / Timing Role: Main system regulator delivering regulated 3.3V to MCU, ADC, and display with soft-start to prevent brownout during battery insertion. Use Value: Internal 10MΩ feedback divider (in fixed variants) and 700nA shutdown reduce sleep-mode current to sub-µA levels. |
| Industrial IoT Sensor Nodes | Railway Signaling Power |
Use Scenario: Long-life wireless temperature/humidity sensors deployed in remote infrastructure with 10+ year battery requirements. IC Role / Device Role / Timing Role: Efficient step-down converter supplying 3.3V to ultra-low-power MCU and LoRaWAN transceiver in intermittent transmit mode. Use Value: Burst Mode maintains <15mV ripple while drawing only 2.8µA between transmissions - directly enabling multi-year field deployment. |
Use Scenario: Converting 72V–110V DC traction supply to 5V/3.3V for onboard diagnostics and LED signaling in rolling stock. IC Role / Device Role / Timing Role: High-input-voltage buck controller supporting 55V absolute max with robust thermal design in confined enclosures. Use Value: 55V rating and 45°C/W θJA allow direct regulation from legacy railway bus without intermediate converters or derating. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8610EMSE#PBF | 42V max input, 3.5A output, 2.5µA IQ, synchronous rectification | Higher current, lower IQ, but no internal boost diode driver; requires external MOSFET sync | Choose for higher load current and tighter ripple control where board space allows larger inductor |
| TPS63060DSCR | 18V max input, 2A output, 25µA IQ, buck-boost topology | Supports input voltages below output (e.g., 3.3V out from 2.5V–12V in); higher IQ than LT3991IDD#PBF | Choose when input may dip below output voltage - not suitable for 55V automotive or industrial inputs |
Compared with LT8610EMSE#PBF and TPS63060DSCR, the LT3991IDD#PBF uniquely combines 55V input capability, 2.8µA quiescent current, and integrated boost diode drive in a 3mm × 3mm DFN - making it optimal for space-constrained, high-VIN, ultra-low-power applications where synchronous FETs are unnecessary.
Availability
LT3991IDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, portable medical instrumentation, and industrial IoT sensor nodes requiring stable component supply with long-term lifecycle assurance.
Supply support for LT3991IDD#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 precision power portfolio with rigorous automotive-grade qualification and long-term product longevity commitments.
The LT3991 series was designed specifically for high-input-voltage, ultralow-quiescent-current DC/DC conversion in automotive, industrial, and battery-powered systems where reliability under extreme voltage transients is mandatory.
FAQ
What is the maximum input voltage supported by the LT3991IDD#PBF?
The LT3991IDD#PBF supports an absolute maximum input voltage of 55V on the VIN pin. Its operational input range is specified from 4.3V to 55V, enabling direct connection to 12V, 24V, and 48V industrial and automotive power buses. Exceeding 55V risks permanent damage per Absolute Maximum Ratings.
Does the LT3991IDD#PBF require an external Schottky diode?
Yes - the LT3991IDD#PBF integrates a boost Schottky diode driver (BD pin) but requires an external Schottky diode connected between BD and VOUT. The internal switch is a bipolar NPN transistor, so the external diode provides the catch path during switch-off. Diode reverse leakage must be <1µA to preserve ultralow quiescent current.
How does the LT3991IDD#PBF achieve 2.8µA quiescent current?
The LT3991IDD#PBF achieves 2.8µA quiescent current through low-power circuit design, including a 1µA oscillator bias current, optimized gate drive, and Burst Mode operation that shuts down all non-essential circuitry between output pulses. This value is measured at no load with SYNC grounded and VIN = 12V, VOUT = 3.3V.
Can the LT3991IDD#PBF be synchronized to an external clock?
Yes - the LT3991IDD#PBF accepts an external clock signal on the SYNC pin, supporting frequencies from 250kHz to 2MHz. When synchronized, it operates in pulse-skipping mode at light loads instead of Burst Mode, increasing quiescent current to ~1.5mA but eliminating low-frequency ripple components.
What package type is used for the LT3991IDD#PBF?
The LT3991IDD#PBF uses a 10-lead (3mm × 3mm) plastic DFN package with exposed thermal pad (Pin 11 = GND). This package provides low thermal resistance (θJC = 10°C/W) and is RoHS-compliant with lead-free finish (PBF designation). The exposed pad must be soldered to a thermal plane on the PCB for rated performance.
LT3991IDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 10-WFDFN 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-DFN (3x3)
LT3991IDD#PBF FAQ
1.How can I place an order for LT3991IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3991IDD#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 LT3991IDD#PBF reliable?
The price and inventory of LT3991IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3991IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3991IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3991IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3991IDD#PBF?
LT3991IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3991IDD#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 LT3991IDD#PBF?
For technical support, including LT3991IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3991IDD#PBF requirements.
6.How does Aetrix verify that LT3991IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3991IDD#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 LT3991IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3991IDD#PBF?
All LT3991IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3991IDD#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 LT3991IDD#PBF part is unused and in its original packaging.
Return procedure for LT3991IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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