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Analog Devices Inc. LT3505IDD#PBF
- Part No.:
- LT3505IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LT3505IDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 8DFN
- Quantity:
- Payment:
- Shipping:
Inventory:166
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Product details
Overview
LT3505IDD#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, <2µA shutdown current, and thermal protection in a 3mm × 3mm DFN-8 package - ideal for automotive battery regulation and industrial control supplies.
For engineers reviewing the LT3505IDD#PBF datasheet, LT3505IDD#PBF pinout, LT3505IDD#PBF application, or LT3505IDD#PBF equivalent, this page delivers verified electrical parameters, validated DFN-8 pin functions, confirmed thermal performance (θJA = 43°C/W), and real-world design constraints including minimum on-time (130ns), VIN(PS) limits, and frequency foldback behavior under overload.
Technical Context
The LT3505IDD#PBF implements constant-frequency current-mode control using an RS flip-flop driven by a resistor-programmed oscillator and slope-compensated current sensing. Its internal bipolar NPN switch requires BOOST voltage > VIN to achieve low VCE(SAT) (350mV @ 1A), enabling high efficiency across wide input ranges.
Operation includes cycle-by-cycle current limiting, UVLO (3.35V typ), active VC-clamp-based current limit, and frequency foldback triggered when FB < 600mV - critical for safe start-up into heavy loads or short-circuit conditions without exceeding 1.75A switch current limit.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V operating; 40V absolute max - supports 24V industrial rails and automotive cold-crank (6V) to load-dump (36V) transients. |
| Output Current | Up to 1.2A continuous (VIN > 8V); derates to 1.1A at VIN > 5V - defined by thermal limits in DFN-8 package with exposed pad soldered to PCB ground. |
| Switching Frequency | 200kHz to 3MHz, resistor-programmed via RT pin - enables trade-off between small magnetics (high-freq) and peak efficiency (750kHz typical). |
| Feedback Reference | 780mV ±15mV over –40°C to 125°C - sets output voltage accuracy; R1/R2 divider must use ≤20kΩ R2 to minimize bias current error. |
| Shutdown Current | <2µA - enables true output disconnect and ultra-low quiescent power in battery-powered systems during sleep mode. |
| Switch VCE(SAT) | 350mV @ 1A - ensures low conduction loss and high efficiency at full load, especially critical in 12V→3.3V/5V conversion. |
| Min On-Time | 130ns (typ, worst-case) - determines maximum input voltage for constant-frequency operation (VIN(PS)) and pulse-skipping onset. |
Pinout & Package
LT3505IDD#PBF is housed in an 8-lead, 3mm × 3mm plastic DFN package with exposed thermal pad (Pin 9) that must be soldered to PCB ground for thermal management (θJA = 43°C/W, θJC = 5°C/W). The device operates over –40°C to +125°C junction temperature.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOST (1) | Charge pump drive node | Must be connected to SW via external diode/capacitor to generate >VIN gate drive for bipolar switch; max 50V rating. |
| SW (2) | Switch collector output | Connects to inductor, catch diode cathode, and BOOST capacitor; carries full switched current and high dv/dt. |
| VIN (3) | Main power input | Supplies internal regulator and switch; requires local 1µF ceramic bypass; 40V absolute max rating. |
| SHDN (4) | Enable/soft-start control | Logic-high (>2.3V) enables operation; tied to VIN if unused; internal ramp provides controlled soft-start. |
| GND (5) | Analog/digital reference | Return path for feedback divider and internal circuits; must connect to low-impedance ground plane under exposed pad. |
| RT (6) | Oscillator programming | Resistor to GND sets switching frequency (200kHz–3MHz); sensitive to stray capacitance - keep trace short. |
| FB (7) | Voltage feedback input | Regulated to 780mV; connects to resistor divider tap; bias current ≤150nA affects high-R divider accuracy. |
| VC (8) | Compensation node | Connect external RC network to GND for loop stability; clamped to SHDN during soft-start and current limit. |
Key Features
| Feature | Design Value |
|---|---|
| Wide input range support | 3.6V–36V operation enables direct regulation from unregulated wall adapters, 24V industrial buses, and automotive batteries (including cold-crank and load-dump). |
| Robust short-circuit protection | Cycle-by-cycle current limit (1.4A typ, 1.75A min) combined with frequency foldback prevents thermal runaway during output shorts or heavy overload. |
| Thermally enhanced packaging | 3mm × 3mm DFN-8 with soldered exposed pad achieves θJA = 43°C/W - allows 1.2A continuous output at +85°C ambient without heatsink. |
| Low-power shutdown | <2µA shutdown current enables true output disconnect and extends battery life in portable equipment with deep-sleep modes. |
| Programmable high-frequency operation | Up to 3MHz switching enables use of sub-5mm inductors and 1µF ceramic input caps - reduces board area and cost in space-constrained designs. |
Applications
| Automotive Battery Regulation | Industrial Control Supplies |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery to stable 3.3V or 5V for microcontrollers, CAN transceivers, and sensors under cold-crank (6V) and load-dump (36V) conditions. IC Role / Device Role / Timing Role: Primary buck regulator providing isolated, ripple-controlled power with UVLO and thermal protection. Use Value: Maintains regulation across automotive transients without external supervision; 1.2A output supports multi-rail SoC power domains. | Use Scenario: Powering PLC I/O modules, fieldbus interfaces (RS-485, Profibus), and sensor signal conditioning circuits from 24V industrial supply rails. IC Role / Device Role / Timing Role: High-reliability DC/DC converter delivering clean, regulated voltage in electrically noisy factory environments. Use Value: Wide input range eliminates need for pre-regulators; DFN-8 package withstands vibration and thermal cycling per AEC-Q200 stress profiles. |
| Wall Transformer Regulation | Battery-Powered Equipment |
Use Scenario: Converting unregulated 9–24V AC/DC wall adapter outputs to precise 3.3V for embedded networking devices (Wi-Fi, Ethernet PHYs) and IoT gateways. IC Role / Device Role / Timing Role: Efficient step-down regulator compensating for poor line regulation and wide adapter tolerance (±20%). Use Value: Resistor-programmable frequency allows optimization for lowest EMI in EMC-sensitive applications (e.g., FCC Class B). | Use Scenario: Supplying 5V/3.3V to portable medical monitors, handheld test equipment, and wireless sensors powered by Li-ion or alkaline batteries. IC Role / Device Role / Timing Role: Low-quiescent buck converter enabling long standby time and fast wake-up from shutdown. Use Value: <2µA shutdown current extends battery shelf life; soft-start prevents inrush into large capacitive loads during power-on. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3605EDE#PBF | Monolithic synchronous buck; 3.6V–32V input; 1.5A output; 3mm × 3mm DFN; no BOOST pin required. | Higher efficiency (no external diode), lower quiescent current (25µA), but lacks frequency foldback and has different compensation structure. | Select for new designs prioritizing efficiency and simplicity; not drop-in due to different pinout and control architecture. |
| LM5164QDDARQ1 | Automotive-grade (AEC-Q100 Grade 1); 3.5V–65V input; 1A output; integrated MOSFETs; 8-pin SO PowerPAD. | Wider VIN range and automotive qualification; higher max input but lower output current and larger SO package (5mm × 6mm). | Select when AEC-Q100 compliance or >36V transient tolerance is mandatory; layout change required due to SO package and thermal pad location. |
Compared with LTC3605EDE#PBF and LM5164QDDARQ1, the LT3505IDD#PBF offers unique bipolar-switch robustness for high-voltage transients, proven frequency foldback for short-circuit resilience, and identical DFN-8 footprint - making it preferred for legacy industrial and automotive designs where bipolar switch ruggedness and known failure modes are valued over synchronous efficiency gains.
Availability
LT3505IDD#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 ranges and long production lifecycles.
Supply support for LT3505IDD#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) is a global leader in high-performance analog, mixed-signal, and power management ICs, serving precision instrumentation, industrial automation, and automotive markets.
The LT3505IDD#PBF belongs to Linear's legacy high-voltage monolithic buck regulator family, designed specifically for rugged, wide-input industrial and automotive power conversion where bipolar switch reliability, transient immunity, and predictable fault behavior are prioritized over peak efficiency.
FAQ
What is the maximum input voltage the LT3505IDD#PBF can safely handle?
The LT3505IDD#PBF has an absolute maximum VIN rating of 40V, but its recommended operating range is 3.6V to 36V. Operation above 36V risks permanent damage. For constant-frequency operation, the practical maximum input depends on output voltage, switching frequency, and inductor selection - defined by VIN(PS), the point where minimum on-time (130ns) forces pulse-skipping. At 750kHz and 3.3V output, VIN(PS) ≈ 33V; exceeding it increases ripple but remains safe if peak inductor current stays below 2.2A.
Does the LT3505IDD#PBF require an external catch diode?
Yes, the LT3505IDD#PBF requires an external Schottky catch diode (e.g., MBRM140) connected from SW to GND. Unlike synchronous buck regulators, it uses an internal bipolar NPN switch and external diode for freewheeling. The diode must have ≥40V reverse voltage rating and ≥1A average forward current capability. Omitting it will cause catastrophic failure due to lack of current path during switch-off.
How does the BOOST pin function on the LT3505IDD#PBF?
The BOOST pin on the LT3505IDD#PBF supplies gate drive voltage higher than VIN to fully saturate the internal bipolar NPN power switch. It must be connected to SW through an external diode and capacitor (e.g., 10nF ceramic). During switch turn-on, the capacitor charges to VIN + Vf(diode); during turn-off, it provides ~VIN + 0.4V to the base, ensuring low VCE(SAT) (350mV @ 1A) and high efficiency. BOOST voltage must not exceed 50V.
What is the purpose of frequency foldback in the LT3505IDD#PBF?
Frequency foldback in the LT3505IDD#PBF reduces switching frequency when FB voltage drops below 600mV - occurring during start-up into heavy loads or output shorts. This lowers peak switch current and die temperature, preventing thermal runaway. It is implemented by reducing RT pin bias current, which decreases oscillator frequency. Foldback is automatic and does not require external circuitry, though optional zener-based foldback (e.g., BZT52C16T) extends protection at high VIN.
Can the LT3505IDD#PBF operate in discontinuous conduction mode (DCM)?
Yes, the LT3505IDD#PBF naturally operates in DCM at light loads or with small inductors. Its current-mode architecture maintains stability without external compensation in DCM. However, maximum output current is reduced in DCM - e.g., with 4.7µH inductor at 2.2MHz, max load drops to ~0.9A at 3.3V. DCM increases output voltage ripple and reduces efficiency at light loads but does not affect reliability or regulation accuracy.
LT3505IDD#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 ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-DFN (3x3)
LT3505IDD#PBF FAQ
1.How can I place an order for LT3505IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3505IDD#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 LT3505IDD#PBF reliable?
The price and inventory of LT3505IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3505IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3505IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3505IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3505IDD#PBF?
LT3505IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3505IDD#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 LT3505IDD#PBF?
For technical support, including LT3505IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3505IDD#PBF requirements.
6.How does Aetrix verify that LT3505IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3505IDD#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 LT3505IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3505IDD#PBF?
All LT3505IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3505IDD#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 LT3505IDD#PBF part is unused and in its original packaging.
Return procedure for LT3505IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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