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Analog Devices Inc. LT3973IDD-3.3#PBF
- Part No.:
- LT3973IDD-3.3#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3973IDD-3.3#PBF.pdf
- Description:
- IC REG BUCK 3.3V 750MA 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:111
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Product details
Overview
LT3973IDD-3.3#PBF from Analog Devices (formerly Linear Technology) is a 42V, 750mA monolithic step-down regulator with fixed 3.3V output, integrated boost and catch diodes, 2.5µA quiescent current at 12VIN, and low-ripple Burst Mode™ operation. It delivers automotive-grade performance in cold-crank scenarios with 530mV minimum dropout voltage and operates across –40°C to 125°C.
For engineers reviewing the LT3973IDD-3.3#PBF datasheet, LT3973IDD-3.3#PBF pinout, LT3973IDD-3.3#PBF application, or LT3973IDD-3.3#PBF equivalent, key selection criteria include its fixed 3.3V output accuracy (±1.2% over temperature), 10-lead 3mm × 3mm DFN package with exposed thermal pad, programmable UVLO, and power-good flag for system sequencing.
Technical Context
The LT3973IDD-3.3#PBF uses current-mode control for fast transient response and stable loop behavior across wide input ranges (4.2V–42V). Its internal bipolar NPN switch is driven by a charge-pump boosted gate voltage, enabling full saturation even during automotive dropout conditions.
Burst Mode operation reduces no-load supply current to 1.8µA while maintaining <10mVP-P output ripple; the power-good flag asserts when VOUT reaches 90% of nominal 3.3V, and an internal catch-diode current limit (1.15A typ.) provides short-circuit protection without external components.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 3.3V ±1.2% over –40°C to 125°C; eliminates external feedback resistors and improves regulation stability. |
| Input Voltage Range | 4.2V to 42V; supports 12V/24V/36V automotive and industrial rails, including cold-crank down to 4.2V. |
| Quiescent Current | 2.5µA at 12VIN → 3.3VOUT; enables always-on systems with multi-year battery life in portable applications. |
| Switching Frequency | 200kHz to 2.2MHz (RT-programmable); allows optimization of inductor size vs. EMI vs. efficiency for specific PCB layouts. |
| Output Current | 750mA continuous; sufficient for powering microcontrollers, sensors, and interface ICs in space-constrained designs. |
| Dropout Voltage | 530mV minimum; maintains regulation when input drops near output, critical for automotive start-stop and battery-depleted conditions. |
| Package | 10-lead 3mm × 3mm DFN with exposed thermal pad; achieves θJA = 40°C/W for high-power-density thermal management. |
Pinout & Package
LT3973IDD-3.3#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.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VOUT (Pin 1) | Fixed-output regulation node | Internally connected to precision 3.3V feedback divider; connects directly to output capacitor and load. |
| OUT (Pin 2) | Dropout regulation & boost capacitor charging node | Tied to VOUT to enable minimum-dropout mode; supplies current to charge boost capacitor during light loads. |
| EN/UVLO (Pin 3) | Enable and programmable undervoltage lockout input | Active-high logic with 1.19V threshold and 30mV hysteresis; enables system-level brownout protection and shutdown control. |
| VIN (Pin 4) | Main power input | Supplies internal circuitry and switch driver; requires local 4.7µF ceramic bypass capacitor. |
| GND (Pin 5 & 11) | Power and signal reference | Pin 5 is signal GND; Pin 11 is exposed thermal pad-must be soldered to large PCB copper area for thermal conduction. |
| SW (Pin 6) | Switch node | Connects to inductor; carries high dI/dt switching current-requires tight layout and Kelvin connection to minimize noise. |
| BOOST (Pin 7) | Charge-pump drive node | Drives external bootstrap capacitor to generate >VIN gate drive for internal bipolar switch; must be decoupled with 0.47µF ceramic. |
| BD (Pin 8) | Bias diode anode | Accepts external bias voltage ≥3.2V (e.g., from VOUT) to improve efficiency by powering internal regulator from regulated rail. |
| PG (Pin 9) | Open-drain power-good flag | Asserts high (via external pull-up) when VOUT reaches 90% of 3.3V; used for system reset sequencing and fault monitoring. |
| RT (Pin 10) | Frequency-setting resistor node | Connects to ground via resistor (e.g., 215kΩ for 600kHz); sets oscillator frequency and influences minimum on-time constraints. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated boost and catch diodes | Eliminates four external diodes, reducing BOM count, board area, and forward-voltage losses in compact designs. |
| Low-ripple Burst Mode™ operation | Maintains <10mVP-P output ripple at light loads while achieving 1.8µA no-load IQ-critical for noise-sensitive analog circuits. |
| Accurate programmable UVLO | EN/UVLO pin allows custom brownout thresholds (e.g., 9V startup for 12V automotive) with 30mV hysteresis to prevent chatter. |
| Thermal shutdown and current limiting | Combines catch-diode valley-current limit (1.15A typ.) and thermal shutdown to protect against sustained shorts and overload without external sensing. |
| Power-good flag with 90% threshold | PG output signals valid regulation before full settling, enabling precise power-rail sequencing in multi-rail systems. |
Applications
| Automotive Body Control Module | Industrial Sensor Node |
|---|---|
Use Scenario: Powering MCU, CAN transceiver, and LIN interface in under-hood ECUs exposed to 4.5V–42V battery transients and –40°C to 125°C ambient. IC Role / Device Role / Timing Role: Primary 3.3V buck regulator providing stable, low-noise supply with cold-crank support and system sequencing via PG flag. Use Value: 530mV dropout ensures uninterrupted operation during engine cranking; 2.5µA IQ extends battery backup time in sleep modes. | Use Scenario: Supplying low-power wireless sensor nodes (e.g., LoRaWAN, NB-IoT) deployed in remote industrial environments with wide-temperature and long-life requirements. IC Role / Device Role / Timing Role: Fixed-output DC-DC converter delivering regulated 3.3V to RF SoC and analog front-end, synchronized to wake-up events. Use Value: 1.8µA Burst Mode IQ enables multi-year operation on primary lithium batteries; integrated diodes reduce component count and failure points. |
| Portable Medical Instrument | Test & Measurement Front-End |
Use Scenario: Powering precision ADCs, op-amps, and microcontrollers in handheld diagnostic devices operating from single-cell Li-ion (3.0V–4.2V) or dual-cell configurations. IC Role / Device Role / Timing Role: Step-down regulator converting variable battery voltage to clean, low-noise 3.3V rail for analog signal chain and digital logic. Use Value: <10mVP-P ripple prevents SNR degradation in 16-bit+ data converters; 4.2V minimum input enables usable battery range extension. | Use Scenario: Providing isolated, low-noise 3.3V supply for high-speed ADC drivers and FPGA configuration in benchtop test equipment with strict EMI limits. IC Role / Device Role / Timing Role: Main system regulator with programmable frequency (600kHz typical) to avoid sensitive measurement bands and simplify EMI filtering. Use Value: RT-programmable switching frequency enables layout-specific EMI mitigation; exposed thermal pad supports continuous 750mA output in compact enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3973EMSE-3.3#PBF | Same electrical specs but in 10-lead MSOP package (θJA = 45°C/W); no exposed thermal pad. | Suitable for lower-power or less thermally constrained layouts where DFN assembly is not available. | Select when board assembly process favors MSOP or when thermal demand is ≤500mA continuous. |
| LMR36503DQDRRR | 3.3V fixed-output buck (65V max, 300mA); 2.5µA IQ; different pinout, no integrated catch diode, no PG flag. | Lacks power-good signaling and automotive dropout robustness; requires external catch diode and UVLO network. | Choose only for cost-sensitive, non-automotive applications where 300mA output suffices and sequencing is handled externally. |
Compared with LT3973EMSE-3.3#PBF, the LT3973IDD-3.3#PBF offers superior thermal performance (θJA = 40°C/W vs. 45°C/W) and smaller footprint; versus LMR36503DQDRRR, it delivers higher current, integrated protection features, and automotive-ready regulation-but at higher BOM cost and complexity.
Availability
LT3973IDD-3.3#PBF is available at Aetrix Electronics and suitable for automotive body electronics, industrial sensor nodes, portable medical instrumentation, and test & measurement front-ends requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT3973IDD-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 continues to manufacture and support its high-performance analog and power management portfolio under the ADI brand.
The LT3973 family was designed specifically for demanding automotive and industrial DC-DC conversion applications requiring ultralow quiescent current, wide input voltage tolerance, and integrated protection-without sacrificing output accuracy or thermal efficiency.
FAQ
What is the guaranteed output voltage accuracy of the LT3973IDD-3.3#PBF over temperature?
The LT3973IDD-3.3#PBF guarantees a 3.3V output with ±1.2% accuracy across its full operating junction temperature range of –40°C to 125°C. This is confirmed in the Electrical Characteristics table (page 3), where min/max values are specified as 3.234V to 3.366V at TJ = –40°C to 125°C. The part achieves this using a trimmed internal feedback divider, eliminating external resistor drift errors.
Does the LT3973IDD-3.3#PBF require external diodes for operation?
No, the LT3973IDD-3.3#PBF does not require external diodes. It integrates both the boost diode (for gate-drive charge pump) and the catch diode (for inductor freewheeling) on-die. This is explicitly stated in the product description ("integrated boost and catch diodes") and confirmed in the Features list and Block Diagram. External diodes would compromise the device's low-component-count advantage and increase power loss.
How does the LT3973IDD-3.3#PBF maintain regulation during automotive cold-crank conditions?
The LT3973IDD-3.3#PBF maintains regulation during cold-crank by enforcing a minimum dropout voltage of 530mV and extending duty cycle up to ~97.5%. When VIN drops near VOUT, it skips switch-off cycles and sustains conduction-keeping the boost capacitor charged and the internal bipolar switch fully saturated. This behavior is detailed in the "Start-Up and Dropout Performance" section and verified in Figure G23 of the datasheet.
Can the LT3973IDD-3.3#PBF be used with input voltages below 4.2V?
The LT3973IDD-3.3#PBF can begin switching at input voltages as low as ~3V, but regulation to 3.3V is not guaranteed below 4.2V. The datasheet specifies 4.2V as the minimum input for accurate FB reference operation (Note 3) and stable 3.3V output. Below this, output voltage droops and feedback accuracy degrades-making it unsuitable for applications requiring tight 3.3V tolerance at low VIN.
What is the purpose of the BD pin on the LT3973IDD-3.3#PBF, and how should it be connected?
The BD pin on the LT3973IDD-3.3#PBF accepts an external bias voltage ≥3.2V (e.g., from VOUT) to power the internal regulator, improving efficiency by reducing VIN current draw. When BD > 3.2V, the IC draws bias current from BD instead of VIN. For standard operation, BD is typically tied to VOUT via a small-signal Schottky diode or directly if VOUT remains above 3.2V during all operating conditions.
LT3973IDD-3.3#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:
- Fixed
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4.2V
- Voltage - Input (Max):
- 42V
- Voltage - Output (Min/Fixed):
- 3.3V
- Voltage - Output (Max):
- -
- Current - Output:
- 750mA
- Frequency - Switching:
- 195kHz ~ 2.15MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT3973IDD-3.3#PBF FAQ
1.How can I place an order for LT3973IDD-3.3#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3973IDD-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 LT3973IDD-3.3#PBF reliable?
The price and inventory of LT3973IDD-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 LT3973IDD-3.3#PBF is usually 5 days.
3.What payment methods are accepted for LT3973IDD-3.3#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3973IDD-3.3#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3973IDD-3.3#PBF?
LT3973IDD-3.3#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3973IDD-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 LT3973IDD-3.3#PBF?
For technical support, including LT3973IDD-3.3#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3973IDD-3.3#PBF requirements.
6.How does Aetrix verify that LT3973IDD-3.3#PBF is sourced from the original manufacturer or authorized distributors?
All LT3973IDD-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 LT3973IDD-3.3#PBF meets industry standards.
7.What is the process for return or replacement of LT3973IDD-3.3#PBF?
All LT3973IDD-3.3#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3973IDD-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 LT3973IDD-3.3#PBF part is unused and in its original packaging.
Return procedure for LT3973IDD-3.3#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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