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Analog Devices Inc. LT3505IDD#TRPBF
- Part No.:
- LT3505IDD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-WFDFN Exposed Pad
- Datasheet:
-
LT3505IDD#TRPBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 8DFN
- Quantity:
- Payment:
- Shipping:
Inventory:400
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Product details
Overview
LT3505IDD#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode PWM step-down DC/DC converter with integrated 1.4A bipolar NPN power switch, operating from 3.6V to 36V input and delivering up to 1.2A output current at adjustable voltages down to 780mV. It features resistor-programmable switching frequency (200kHz–3MHz), soft-start, <2µA shutdown current, and thermally enhanced 3mm × 3mm DFN-8 package. It is used in automotive battery regulation, industrial control supplies, and wall transformer-derived power rails.
For engineers reviewing the LT3505IDD#TRPBF datasheet, LT3505IDD#TRPBF pinout, LT3505IDD#TRPBF application, or LT3505IDD#TRPBF equivalent, key selection criteria include input voltage range (3.6–36V), output current capability (1.2A), programmable frequency (200kHz–3MHz), feedback reference (780mV), and thermal performance in the DFN-8 package with exposed pad.
Technical Context
The LT3505IDD#TRPBF 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 pin bootstrapping for full saturation, enabling low VCE(SAT) (350mV at 1A) and high efficiency across wide input ranges.
It integrates undervoltage lockout (~3.35V), cycle-by-cycle current limiting (1.4–2.2A), active VC node clamping for current limit, and frequency foldback during overload or startup. The SHDN pin enables <2µA shutdown and provides soft-start via external RC ramping.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V operating; supports unregulated 24V industrial rails and automotive batteries (40V absolute max). |
| Output Current | Up to 1.2A continuous; validated at VIN > 8V, VOUT = 3.3V, fSW = 750kHz per datasheet graphs. |
| Switching Frequency | Resistor-programmable 200kHz to 3MHz; RT pin bias enables precise frequency setting without external clock. |
| Feedback Reference | 780mV ±15mV; sets output voltage via external resistor divider; enables low-VOUT designs (e.g., 0.78V core supplies). |
| Shutdown Current | <2µA; disconnects output and minimizes quiescent drain in battery-powered systems during sleep. |
| Switch VCE(SAT) | 350mV at 1A; reduces conduction loss and improves efficiency, especially at high load currents and low duty cycles. |
| Operating Temp Range | –40°C to +125°C junction; qualified for automotive and industrial environments per LT3505IDD grade. |
Pinout & Package
The LT3505IDD#TRPBF is housed in an 8-lead, 3mm × 3mm plastic DFN package (DD) with exposed thermal pad (Pin 9), which must be soldered to PCB ground for thermal and electrical integrity. θJA = 43°C/W, θJC = 5°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOST (1) | Bootstrap drive supply | Provides elevated gate drive voltage (>VIN) to fully saturate internal bipolar NPN switch; requires external diode + capacitor. |
| SW (2) | Switch node | Connects to inductor, catch diode cathode, and boost capacitor; carries high di/dt switching current and must be routed with minimal loop area. |
| VIN (3) | Main power input | Supplies internal regulator and power switch; requires local ceramic bypass (≥1µF) close to pin. |
| SHDN (4) | Enable/soft-start control | Logic-high (>2.3V) enables operation; grounded disables output and reduces IQ to <2µA; external RC on this pin implements controlled soft-start. |
| GND (5) | Power and signal reference | Return path for internal circuits and feedback divider; must connect to large ground plane and thermal vias under exposed pad. |
| RT (6) | Oscillator programming | Resistor-to-ground sets switching frequency (200kHz–3MHz); sensitive to stray capacitance-keep trace short and guard. |
| FB (7) | Voltage feedback input | Regulated to 780mV; connects to resistor divider tap; determines output voltage; bias current ≤150nA affects high-R divider accuracy. |
| VC (8) | Compensation node | Internal error amplifier output; connect external RC network here to stabilize control loop and set phase margin. |
Key Features
| Feature | Design Value |
|---|---|
| Wide input voltage range | 3.6V–36V operation enables direct regulation from 24V industrial buses and 12V/24V automotive systems without pre-regulation. |
| Integrated 1.4A bipolar switch | Eliminates external MOSFET and driver; low 350mV VCE(SAT) at 1A reduces conduction loss and simplifies thermal design. |
| Resistor-programmable frequency | 200kHz–3MHz tuning allows optimization of size (high-freq → smaller L/C) vs. efficiency (low-freq → lower switching loss). |
| Short-circuit robustness | Cycle-by-cycle current limit (1.4–2.2A) and frequency foldback protect against sustained overloads and output shorts without latch-off. |
| Thermally enhanced DFN | 3mm × 3mm DFN-8 with exposed GND pad achieves θJC = 5°C/W, supporting 1.2A continuous output in compact layouts. |
Applications
| Automotive Battery Regulation | Industrial Control Supply |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery (with load dump transients up to 40V) to stable 3.3V or 5V for microcontrollers and sensors. IC Role / Device Role / Timing Role: Primary buck regulator providing isolated, efficient, and transient-robust power domain for ADAS ECUs and body control modules. Use Value: Operates across –40°C to +125°C ambient; withstands 40V transients; <2µA shutdown extends battery life in parked mode. | Use Scenario: Converting unregulated 24V factory floor supply to 5V for PLC I/O modules and fieldbus interface ICs. IC Role / Device Role / Timing Role: Point-of-load (POL) DC/DC converter delivering clean, regulated power with high PSRR and low noise for analog front-ends. Use Value: Wide 3.6–36V input accommodates brownouts and surges; 1.2A output supports multiple downstream rails; DFN package saves board space. |
| Wall Transformer Regulation | Battery-Powered Equipment |
Use Scenario: Stepping down noisy, unregulated 9–24V AC/DC wall adapter output to low-noise 3.3V for embedded Wi-Fi modules and IoT gateways. IC Role / Device Role / Timing Role: Input-filtering and regulation stage converting variable adapter voltage into stable system rail with minimal external components. Use Value: Resistor-programmable frequency allows EMI optimization (e.g., 750kHz avoids AM band); soft-start prevents inrush into bulk capacitors. | Use Scenario: Powering portable medical monitors or handheld test equipment from 2-cell Li-ion (6–8.4V) or 3-cell alkaline (3–4.5V) batteries. IC Role / Device Role / Timing Role: Main system regulator enabling deep-sleep modes and dynamic voltage scaling for ultra-low-power operation. Use Value: <2µA shutdown current preserves battery charge; 780mV feedback reference supports low-VOUT logic rails; high efficiency at light loads extends runtime. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3631EMSE#TRPBF | Monolithic 1.5A buck; 3.6–40V input; fixed 750kHz freq; no RT pin; 800mV ref; MSOP-10 package. | Higher current, fixed frequency, no programmability; lacks frequency foldback and BOOST pin flexibility. | Select when simplicity and higher current are prioritized over frequency tuning and bootstrap optimization. |
| MP2451DT-LF-Z | 1.5A buck; 3.3–36V input; 2.2MHz fixed freq; 800mV ref; SOT-23-6; no BOOST pin; MOSFET-based. | Smaller footprint, higher fixed frequency, no external bootstrap required; lower thermal performance (no exposed pad). | Select for space-constrained consumer applications where 2.2MHz operation enables tiny passives and no thermal pad is acceptable. |
Compared with LTC3631EMSE#TRPBF and MP2451DT-LF-Z, the LT3505IDD#TRPBF offers unique programmable frequency, bipolar switch architecture with BOOST-driven saturation, and robust short-circuit handling via frequency foldback-making it preferred for industrial and automotive designs requiring flexibility, thermal resilience, and transient tolerance.
Availability
LT3505IDD#TRPBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial control supplies, and wall transformer-derived power rails requiring stable component supply, extended temperature support, and long-term lifecycle continuity.
Supply support for LT3505IDD#TRPBF 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 semiconductors.
The LT3505IDD#TRPBF belongs to Linear's legacy monolithic buck regulator product line, designed specifically for wide-input industrial and automotive power conversion where reliability, thermal performance, and transient robustness are critical.
FAQ
What is the maximum input voltage rating for the LT3505IDD#TRPBF?
The LT3505IDD#TRPBF has an absolute maximum input voltage rating of 40V on the VIN pin. Its specified operating input range is 3.6V to 36V. Operation at 40V is permitted only for brief transients (e.g., automotive load dump), provided the device remains in regulation and peak inductor current stays below 2.2A. Continuous operation above 36V is not recommended.
Does the LT3505IDD#TRPBF require an external bootstrap capacitor and diode?
Yes, the LT3505IDD#TRPBF requires an external bootstrap capacitor and diode connected between the BOOST and SW pins. This network generates a voltage higher than VIN to fully saturate its internal bipolar NPN power switch. Typical values are a 100nF ceramic capacitor and a Schottky diode (e.g., 1N5817); layout must minimize loop inductance for reliable switching.
What is the feedback reference voltage of the LT3505IDD#TRPBF, and how does it affect output accuracy?
The LT3505IDD#TRPBF regulates its FB pin to a nominal 780mV, with a typical tolerance of ±15mV (765–795mV). This reference directly determines output voltage accuracy when used with a resistor divider. For best accuracy, use 1% resistors and keep R2 ≤20kΩ to minimize error from FB bias current (≤150nA).
Can the LT3505IDD#TRPBF operate in pulse-skipping mode, and when does it occur?
Yes, the LT3505IDD#TRPBF enters pulse-skipping mode when input voltage exceeds VIN(PS)-the calculated threshold where required duty cycle falls below the minimum achievable on-time (130ns typ). This occurs at high VIN and/or high fSW (e.g., >750kHz). Pulse-skipping increases output ripple but does not damage the part if peak inductor current stays ≤2.2A and output remains regulated.
What thermal considerations apply to the LT3505IDD#TRPBF in its DFN-8 package?
The LT3505IDD#TRPBF uses a 3mm × 3mm DFN-8 package with an exposed thermal pad (Pin 9) that must be soldered to a PCB ground plane with ≥4 thermal vias. With proper layout, it achieves θJC = 5°C/W and θJA = 43°C/W. At 1.2A output and 12V input, junction temperature rise is ~45°C above ambient-ensuring safe operation within its –40°C to +125°C rated range.
LT3505IDD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-WFDFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LT3505IDD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3505IDD#TRPBF 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#TRPBF reliable?
The price and inventory of LT3505IDD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3505IDD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3505IDD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3505IDD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3505IDD#TRPBF?
LT3505IDD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3505IDD#TRPBF 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#TRPBF?
For technical support, including LT3505IDD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3505IDD#TRPBF requirements.
6.How does Aetrix verify that LT3505IDD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3505IDD#TRPBF 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#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3505IDD#TRPBF?
All LT3505IDD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3505IDD#TRPBF, 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#TRPBF part is unused and in its original packaging.
Return procedure for LT3505IDD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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