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Analog Devices Inc. LT3505EDD#PBF
- Part No.:
- LT3505EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LT3505EDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 8DFN
- Quantity:
- Payment:
- Shipping:
Inventory:5,790
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Product details
Overview
LT3505EDD#PBF from Analog Devices (formerly Linear Technology) is a current-mode PWM step-down DC/DC converter with an integrated 1.4A bipolar NPN power switch, operating from 3.6V to 36V input and delivering up to 1.2A output at adjustable voltages down to 780mV. It features resistor-programmable switching frequency (200kHz–3MHz), soft-start, cycle-by-cycle current limiting, and <2µA shutdown current-ideal for automotive battery regulation and industrial control supplies.
For engineers reviewing the LT3505EDD#PBF datasheet, LT3505EDD#PBF pinout, LT3505EDD#PBF application, or LT3505EDD#PBF equivalent, key selection considerations include its 3mm × 3mm DFN-8 package with exposed thermal pad, 780mV feedback reference, 350mV VCE(SAT) at 1A, and robust short-circuit protection in high-input-voltage environments.
Technical Context
The LT3505EDD#PBF implements constant-frequency current-mode control using an RS flip-flop driven by a resistor-programmed oscillator. Its internal bipolar NPN switch is driven via the BOOST pin, requiring an external bootstrap capacitor and diode to achieve full saturation and low conduction loss (350mV at 1A).
Cycle-by-cycle current sensing monitors VIN-to-SW current, while the error amplifier servo-controls the VC node to regulate FB at 780mV. Frequency foldback activates when FB drops below 600mV-e.g., during overload-to reduce switching frequency and limit peak switch current.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V operating; supports unregulated wall transformers, 24V industrial rails, and automotive batteries (40V absolute max). |
| Output Current | Up to 1.2A continuous (1.1A at VIN > 5V); limited by thermal performance and inductor saturation. |
| Feedback Reference | 780mV ±15mV; enables precise output voltage setting via external resistor divider (e.g., 3.3V with 69.8k/11.3k). |
| Switch VCE(SAT) | 350mV at 1A; minimizes conduction loss and improves efficiency in high-current, low-VOUT applications. |
| Shutdown Current | <2µA; enables true output disconnect and ultra-low quiescent power in battery-powered systems. |
| Switching Frequency | 200kHz to 3MHz, resistor-programmable via RT pin; allows trade-off between component size (high-freq) and efficiency (low-freq). |
| Thermal Package | 3mm × 3mm DFN-8 with exposed GND pad; θJA = 43°C/W enables 1.2A operation without forced air in typical PCB layouts. |
Pinout & Package
LT3505EDD#PBF is housed in an 8-lead, 3mm × 3mm plastic DFN package with exposed thermal pad (Pin 9), which must be soldered to PCB ground for thermal and electrical integrity. The package supports –40°C to +85°C operating temperature range (E-grade).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOST (1) | Bootstrap drive supply | Provides >VIN gate drive to internal bipolar NPN switch; requires external capacitor + Schottky diode from SW. |
| SW (2) | Switch node | Connects to inductor, catch diode cathode, and BOOST capacitor; carries high di/dt switching current. |
| VIN (3) | Main power input | Supplies internal regulator and power switch; requires local 1µF ceramic bypass near pin. |
| SHDN (4) | Enable/shutdown control | Logic-high ≥2.3V enables operation; tied to VIN for always-on; also provides soft-start ramp when RC-filtered. |
| GND (5) | Power and signal ground | Reference for FB, VC, RT; must connect to large PCB ground plane with thermal vias under exposed pad. |
| RT (6) | Frequency programming | Resistor to GND sets oscillator frequency (200kHz–3MHz); sensitive to stray capacitance. |
| FB (7) | Feedback input | Regulated to 780mV; connects to resistor divider tap; bias current ≤150nA minimizes divider error. |
| VC (8) | Compensation node | Connects external RC network to GND for loop stability; clamped to SHDN during soft-start. |
Key Features
| Feature | Design Value |
|---|---|
| Wide input range support | 3.6V–36V operation enables direct regulation from 24V industrial buses and automotive batteries without pre-regulation. |
| Integrated power switch | 1.4A bipolar NPN switch with 350mV VCE(SAT) eliminates need for external MOSFET and driver, reducing BOM count and layout complexity. |
| Programmable high-frequency operation | Up to 3MHz switching allows use of sub-5mm inductors and 1µF ceramic output capacitors, minimizing solution footprint. |
| Robust fault protection | Cycle-by-cycle current limit, undervoltage lockout (~3.35V), and thermal shutdown prevent damage during short-circuit or startup overload. |
| Low-power shutdown mode | <2µA quiescent current enables long-term battery operation in portable or remote-sensor applications. |
Applications
| Automotive Battery Regulation | Industrial Control Supply |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery to 3.3V or 5V for infotainment microcontrollers and CAN transceivers under load-dump conditions. IC Role / Device Role / Timing Role: Primary buck converter providing stable, ripple-controlled power with input transient tolerance up to 40V. Use Value: Eliminates need for external TVS or pre-regulator; 1.2A output sustains peak MCU + sensor loads; frequency foldback prevents thermal runaway during overvoltage events. | Use Scenario: Powering PLC I/O modules and fieldbus interfaces from 24V DC industrial rails subject to brownouts and surges. IC Role / Device Role / Timing Role: High-reliability step-down regulator with undervoltage lockout and short-circuit robustness for factory-floor equipment. Use Value: 3.6V minimum start-up ensures operation during 24V rail sag; exposed-pad DFN maintains thermal margin at full load in enclosed enclosures. |
| Wall Transformer Regulation | Battery-Powered Equipment |
Use Scenario: Converting unregulated 9–24V AC/DC wall adapter outputs to clean 3.3V for embedded networking devices. IC Role / Device Role / Timing Role: Input-flexible buck converter accepting wide-range, poorly regulated inputs without external LDO post-regulation. Use Value: Resistor-programmable frequency allows optimization for low-noise (≤500kHz) or compact (≥2MHz) designs; soft-start prevents inrush into bulk capacitance. | Use Scenario: Power management in handheld test instruments or portable data loggers using Li-ion or alkaline batteries. IC Role / Device Role / Timing Role: Efficient primary regulator with ultra-low shutdown current and output disconnect capability. Use Value: <2µA shutdown current extends shelf life; 780mV feedback reference enables accurate low-VOUT regulation critical for low-power MCU sleep modes. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3605EMSE#PBF | Monolithic 3A synchronous buck; 2.7–5.5V input; no BOOST pin required; higher efficiency but narrower input range. | Suitable only for low-input-voltage systems (e.g., USB-powered); cannot replace LT3505EDD#PBF in 12–36V applications. | Select LTC3605EMSE#PBF only if input is ≤5.5V and 3A output is required; not a drop-in replacement. |
| LM5164QDDARQ1 | 4.5–65V input, 1A synchronous buck; integrated high-side MOSFET; requires external bootstrap capacitor but no BOOST diode. | Supports higher input voltages and automotive AEC-Q100 qualification; lacks frequency foldback and has different compensation architecture. | Choose LM5164QDDARQ1 for AEC-Q100-compliant automotive designs above 36V or where synchronous rectification is mandatory. |
Compared with LTC3605EMSE#PBF and LM5164QDDARQ1, the LT3505EDD#PBF uniquely balances wide 3.6–36V input, integrated bipolar switch with BOOST drive, and programmable frequency foldback-making it optimal for cost-sensitive, non-synchronous, high-input-voltage industrial and automotive applications where 1.2A output suffices.
Availability
LT3505EDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial control supplies, and wall transformer regulation requiring stable component supply across extended temperature and input voltage ranges.
Supply support for LT3505EDD#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 portfolio of high-performance analog and power management ICs with rigorous reliability testing and long-term product support.
The LT3505 belongs to Linear's legacy high-voltage monolithic buck regulator family, designed specifically for rugged, wide-input-voltage DC/DC conversion in automotive, industrial, and telecom infrastructure applications.
FAQ
What is the maximum input voltage rating for the LT3505EDD#PBF?
The LT3505EDD#PBF has an absolute maximum input voltage rating of 40V on the VIN pin, with guaranteed operation from 3.6V to 36V. Exceeding 36V may trigger frequency foldback or pulse-skipping above VIN(PS), but brief transients up to 40V are tolerated if the output remains in regulation and inductor saturation is avoided.
Does the LT3505EDD#PBF require an external catch diode?
Yes, the LT3505EDD#PBF requires an external Schottky catch diode (e.g., MBRM140) connected from SW to GND. Its internal bipolar NPN switch is not synchronous, so the diode provides the return path for inductor current during switch-off time and must withstand the full input voltage.
How is the switching frequency set on the LT3505EDD#PBF?
The switching frequency of the LT3505EDD#PBF is set by connecting a 1% resistor from the RT pin to GND. Values from 13.7kΩ (3MHz) to 357kΩ (200kHz) are supported per the datasheet table; RT pin bias voltage is ~0.5V, and stray capacitance must be minimized to avoid frequency drift.
What is the purpose of the BOOST pin on the LT3505EDD#PBF?
The BOOST pin on the LT3505EDD#PBF supplies a boosted gate drive voltage (>VIN) to fully saturate the internal bipolar NPN power switch, reducing VCE(SAT) to 350mV at 1A. It requires an external capacitor charged via a Schottky diode from the SW node-no connection to external supplies is needed.
Can the LT3505EDD#PBF operate in discontinuous conduction mode (DCM)?
Yes, the LT3505EDD#PBF operates in DCM at light loads or with small inductors. Its current-mode architecture remains stable in DCM, and the datasheet provides graphs of maximum load current vs. input voltage for common inductor values (e.g., 4.7µH, 10µH) to guide design.
LT3505EDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-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):
- 3.6V
- Voltage - Input (Max):
- 36V
- Voltage - Output (Min/Fixed):
- 0.78V
- Voltage - Output (Max):
- 33.84V
- Current - Output:
- 1.2A
- Frequency - Switching:
- 200kHz ~ 3.01MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-DFN (3x3)
LT3505EDD#PBF FAQ
1.How can I place an order for LT3505EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3505EDD#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 LT3505EDD#PBF reliable?
The price and inventory of LT3505EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3505EDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3505EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3505EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3505EDD#PBF?
LT3505EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3505EDD#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 LT3505EDD#PBF?
For technical support, including LT3505EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3505EDD#PBF requirements.
6.How does Aetrix verify that LT3505EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3505EDD#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 LT3505EDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3505EDD#PBF?
All LT3505EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3505EDD#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 LT3505EDD#PBF part is unused and in its original packaging.
Return procedure for LT3505EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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