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Analog Devices Inc. LT3991EDD#PBF
- Part No.:
- LT3991EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3991EDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:13,132
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Product details
Overview
LT3991EDD#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 DFN-10 package and targets automotive battery regulation and portable power systems requiring long standby life.
For engineers reviewing the LT3991EDD#PBF datasheet, LT3991EDD#PBF pinout, LT3991EDD#PBF application, or LT3991EDD#PBF equivalent, key selection criteria include its 4.3V–55V input range, 700nA shutdown current, Power Good flag, soft-start capability via SS pin, and Burst Mode operation maintaining <15mV output ripple at light loads.
Technical Context
The LT3991EDD#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-driven by BOOST voltage-achieves 0.44Ω on-resistance and supports high-voltage operation up to 55V VIN.
Burst Mode operation reduces no-load supply current to 2.8µA while holding output ripple below 15mVP-P; frequency foldback protects during startup and overload. The EN pin features 1.01V rising threshold with 30mV hysteresis, and PG asserts when FB reaches 91% of regulation voltage.
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 maximum - sufficient for powering microcontrollers, sensors, and interface ICs in compact systems. |
| Quiescent Current | 2.8µA at no load - enables multi-year battery life in always-on IoT and telematics applications. |
| Switching Frequency | 200kHz to 2MHz (adjustable via RT resistor) - allows tradeoff between inductor size and efficiency in space-constrained designs. |
| Feedback Reference | 1.19V (internal) - sets precise output voltage with external resistor divider; LT3991EDD#PBF is the adjustable version, not fixed-output. |
| Power Good Threshold | 91% of regulated VOUT - provides reliable system-level power sequencing and fault detection. |
| Shutdown Current | 700nA - ensures minimal battery drain during deep sleep or system off-states. |
Pinout & Package
LT3991EDD#PBF is housed in a thermally enhanced 10-lead (3mm × 3mm) plastic DFN package with exposed pad (Pin 11 = GND), optimized for low θJA (45°C/W) and high-power density layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Connection | Connects externally to Schottky diode anode; forms charge pump path for BOOST voltage generation. |
| BOOST (2) | Switch Driver Supply | Provides >VIN voltage to fully saturate internal NPN switch; requires external boost capacitor between BOOST and SW. |
| SW (3) | Switch Node | Drives external inductor and catch diode; carries high di/dt switching current - requires tight layout and low-inductance routing. |
| VIN (4) | Main Input Supply | Supplies internal circuitry and switch; must be locally bypassed with low-ESR ceramic capacitor near pin. |
| EN (5) | Enable Control | Hysteretic 1.01V enable threshold; pulls device into 700nA shutdown state when low - critical for system power gating. |
| FB (6) | Feedback Input | Senses output via resistor divider; regulated to 1.19V - determines output voltage in adjustable configuration (LT3991EDD#PBF). |
| SS (7) | Soft-Start Control | Controls inrush current ramp rate via external RC; prevents input voltage sag and output overshoot at startup. |
| RT (8) | Frequency Set | Resistor-to-ground sets switching frequency from 200kHz to 2MHz - enables optimization for EMI, size, or efficiency. |
| PG (9) | Power Good Flag | Open-drain output signals valid regulation (FB ≥91% target); requires external pull-up for host processor monitoring. |
| SYNC (10) | External Clock Input | Accepts 250kHz–2MHz clock for synchronization; grounding enables low-ripple Burst Mode; floating or high disables sync. |
Key Features
| Feature | Design Value |
|---|---|
| Ultralow Quiescent Current | 2.8µA IQ in regulation enables >10-year battery life in always-on sensor nodes powered from coin cells or LiSOCl₂. |
| Internal Compensation | Eliminates need for external compensation network - reduces BOM count and design iteration time for stable operation. |
| Low Ripple Burst Mode | Maintains <15mVP-P output ripple at light loads while sustaining 2.8µA IQ - avoids audible noise and EMI spikes common in standard burst schemes. |
| Thermally Enhanced DFN | 3mm × 3mm DFN with exposed GND pad achieves θJC = 10°C/W - supports 1.2A continuous output without heatsink in ambient ≤85°C. |
| Accurate Enable Threshold | 1.01V EN rising threshold with 30mV hysteresis ensures clean, jitter-free power-up sequencing across temperature (–40°C to 125°C). |
Applications
| Automotive Body Control Module | Industrial IoT Sensor Node |
|---|---|
|
Use Scenario: Powering CAN transceiver, microcontroller, and environmental sensors from 12V battery with cold-crank tolerance down to 4.3V. IC Role / Device Role / Timing Role: Primary 3.3V buck regulator delivering regulated supply under wide-input, high-temperature conditions. Use Value: 2.8µA quiescent current extends battery life during vehicle sleep mode; 55V rating withstands load-dump transients. |
Use Scenario: Long-life remote monitoring node powered by primary lithium battery, requiring years of operation with periodic wake-ups. IC Role / Device Role / Timing Role: System power manager providing stable 3.3V rail to MCU and RF transceiver during ultra-low-duty-cycle operation. Use Value: 700nA shutdown current minimizes self-discharge; Burst Mode maintains regulation without compromising standby efficiency. |
| Portable Medical Diagnostic Device | Railway Signaling Interface |
|
Use Scenario: Handheld ultrasound or glucose meter using rechargeable Li-ion, needing clean, low-noise 3.3V supply for analog front-end and display. IC Role / Device Role / Timing Role: Main DC/DC converter supplying precision analog and digital subsystems with tightly regulated output. Use Value: <15mVP-P ripple in Burst Mode eliminates switching artifacts in sensitive ADC measurements; soft-start prevents inrush-induced reset. |
Use Scenario: DIN-rail mounted signaling controller operating from 24V–72V DC railway supply with strict EMC and reliability requirements. IC Role / Device Role / Timing Role: Input-stage buck converter stepping down variable traction power to isolated 3.3V logic supply. Use Value: 55V absolute max rating and –40°C to 125°C junction range ensure robustness across rail voltage surges and ambient extremes. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8609SIS8#PBF | 42V max input, 2A output, 2.5µA IQ, integrated MOSFETs (no external diode), synchronous rectification. | Better efficiency above 100mA; requires no external catch diode; smaller solution size but higher cost. | Select LT8609SIS8#PBF when higher output current, synchronous operation, or reduced component count outweighs 55V rating requirement. |
| TPS54202DRCT | 48V max input, 2A output, 2µA IQ (shutdown), 100kHz–2.5MHz sync, integrated FETs, thermal shutdown. | Lower quiescent current in shutdown (2µA vs 700nA), wider frequency range, but lacks Power Good flag and fixed 3.3V option. | Choose TPS54202DRCT for cost-sensitive industrial supplies where PG flag is non-critical and thermal protection is prioritized. |
Compared with LT3991EDD#PBF, LT8609SIS8#PBF offers higher current and synchronous efficiency but sacrifices 55V tolerance; TPS54202DRCT provides lower shutdown IQ and broader sync range but omits PG signaling and requires external feedback for 3.3V output.
Availability
LT3991EDD#PBF is available at Aetrix Electronics and suitable for automotive body electronics, industrial IoT sensor nodes, and portable medical devices requiring stable component supply with extended temperature support and low-power performance.
Supply support for LT3991EDD#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 Linear power ICs.
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 and standby efficiency are critical.
FAQ
What is the function of the BD pin on the LT3991EDD#PBF?
The BD (Boost Diode) pin on the LT3991EDD#PBF connects to the anode of the external Schottky diode used in the bootstrap circuit. It forms part of the charge pump that generates the BOOST voltage required to fully saturate the internal bipolar NPN switch. Correct BD connection is essential for achieving the specified 0.44Ω on-resistance and 1.2A output capability across temperature.
Does the LT3991EDD#PBF support fixed 3.3V output, or is it adjustable only?
The LT3991EDD#PBF is the adjustable version of the LT3991 family and does not have a fixed 3.3V output. It regulates the FB pin to 1.19V and requires an external resistor divider to set the output voltage. Fixed-output variants (e.g., LT3991EMSE-3.3#PBF) integrate the feedback divider internally; LT3991EDD#PBF retains full adjustability from 1.19V to 30V.
How does the LT3991EDD#PBF achieve 2.8µA quiescent current while maintaining regulation?
The LT3991EDD#PBF achieves 2.8µA quiescent current through Low Ripple Burst Mode operation: it delivers discrete current pulses to the output capacitor, then enters deep sleep between bursts, reducing circuit activity. During sleep, only essential bias currents remain active. This preserves output voltage accuracy and ripple (<15mVP-P) while minimizing average input current - confirmed across –40°C to 125°C.
Can the LT3991EDD#PBF be synchronized to an external clock, and what is the impact on efficiency?
Yes, the LT3991EDD#PBF accepts external synchronization on the SYNC pin across 250kHz–2MHz. However, synchronizing forces pulse-skipping instead of Burst Mode at light loads, increasing quiescent current from 2.8µA to ~1.5mA. For best light-load efficiency, SYNC should be grounded; use synchronization only when EMI control or channel interleaving is required.
What thermal considerations apply to the LT3991EDD#PBF in its 3mm × 3mm DFN package?
The LT3991EDD#PBF's DFN package features an exposed GND pad (Pin 11) that must be soldered to a PCB copper pour for effective heat dissipation. With θJC = 10°C/W and θJA = 45°C/W, it sustains 1.2A continuous output at TA ≤ 85°C when using ≥2 cm² of 2-oz copper connected to the pad. Insufficient thermal relief causes junction temperatures to exceed 125°C, triggering thermal shutdown.
LT3991EDD#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)
LT3991EDD#PBF FAQ
1.How can I place an order for LT3991EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3991EDD#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 LT3991EDD#PBF reliable?
The price and inventory of LT3991EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3991EDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3991EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3991EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3991EDD#PBF?
LT3991EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3991EDD#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 LT3991EDD#PBF?
For technical support, including LT3991EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3991EDD#PBF requirements.
6.How does Aetrix verify that LT3991EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3991EDD#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 LT3991EDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3991EDD#PBF?
All LT3991EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3991EDD#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 LT3991EDD#PBF part is unused and in its original packaging.
Return procedure for LT3991EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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