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Analog Devices Inc. LT3505IMS8E#PBF
- Part No.:
- LT3505IMS8E#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-TSSOP, 8-MSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3505IMS8E#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 8MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,004
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Product details
Overview
LT3505IMS8E#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 current at adjustable voltages down to 780mV. It features resistor-programmable switching frequency (200kHz–3MHz), soft-start, <2µA shutdown current, and thermal protection-ideal for automotive battery regulation and industrial control supplies.
For engineers reviewing the LT3505IMS8E#PBF datasheet, LT3505IMS8E#PBF pinout, LT3505IMS8E#PBF application, or LT3505IMS8E#PBF equivalent, key selection criteria include its 8-lead MSOP package with exposed pad, 780mV feedback reference, cycle-by-cycle current limiting, and robust short-circuit operation in harsh environments.
Technical Context
The LT3505IMS8E#PBF implements constant-frequency current-mode control using an internal RS flip-flop and slope-compensated current sensing. Its oscillator is resistor-programmed via the RT pin, enabling precise frequency tuning between 200kHz and 3MHz while maintaining stable loop dynamics across temperature and load.
It integrates undervoltage lockout (~3.35V), BOOST-driven switch gate drive for low VCE(SAT) (350mV @ 1A), and VC-pin-based error amplifier compensation. The device enters pulse-skipping mode above VIN(PS) when minimum on-time limits duty cycle, with frequency foldback support for safe high-input-voltage operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V operating; supports unregulated 24V industrial rails and automotive batteries with 40V absolute max rating. |
| Output Current | Up to 1.2A continuous (at VIN > 8V); limited by thermal performance and inductor saturation in MSOP-8 package. |
| Switching Frequency | 200kHz–3MHz, resistor-programmed via RT pin; enables trade-off between small magnetics (high fSW) and peak efficiency (low fSW). |
| Feedback Reference | 780mV ±15mV; sets output voltage via external resistor divider; enables precise low-VOUT regulation including 3.3V and 5V rails. |
| Shutdown Current | <2µA; disconnects output and minimizes quiescent drain in battery-powered systems during sleep mode. |
| Power Switch | Integrated 1.4A bipolar NPN with 350mV VCE(SAT) @ 1A; requires external BOOST capacitor/diode for full saturation and low conduction loss. |
| Thermal Performance | θJA = 40°C/W (MSOP-8); exposed pad must be soldered to PCB ground plane with thermal vias for reliable 1.2A operation at TA ≤ 125°C. |
Pinout & Package
LT3505IMS8E#PBF uses the 8-lead plastic MSOP package (MS8E) with exposed pad (Pin 9), requiring soldering to PCB ground for thermal and electrical integrity. Package dimensions: 3.0mm × 3.0mm × 1.1mm height.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOST (1) | Charge pump bootstrap supply | Drives internal NPN switch base above VIN; requires external diode + capacitor to generate ~VIN + 2V for full saturation. |
| SW (2) | Switch node | Connects to inductor, catch diode cathode, and BOOST capacitor; carries high di/dt switching current and requires tight layout. |
| VIN (3) | Main power input | Supplies internal regulator and power switch; must be locally bypassed with ≥1µF X7R ceramic capacitor. |
| SHDN (4) | Enable/shutdown control | Logic-high (>2.3V) enables operation; tied to VIN for always-on use; also provides soft-start ramp when driven via RC network. |
| GND (5) | Analog/digital ground | Reference for FB, VC, RT; must connect to low-impedance ground plane; exposed pad is electrically GND and thermally critical. |
| RT (6) | Oscillator programming | Resistor-to-ground sets switching frequency; bias voltage ~0.5V; sensitive to stray capacitance-keep trace short and guard. |
| FB (7) | 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 | Output of error amplifier; connects to external RC network for loop stability; clamped to SHDN during soft-start and overcurrent. |
Key Features
| Feature | Design Value |
|---|---|
| Wide input range (3.6V–36V) | Enables single-supply compatibility across automotive (cold crank to load dump), industrial 24V, and wall adapter inputs without pre-regulation. |
| Cycle-by-cycle current limit | Protects against shorted outputs and inductor saturation by limiting peak switch current to 1.4A–2.2A depending on duty cycle and temperature. |
| Resistor-programmable frequency | Permits optimization of magnetic size vs. efficiency: 2.2MHz allows 2.2µH inductors; 200kHz supports higher-efficiency 22µH designs. |
| Soft-start function | Eliminates input surge during startup by ramping SHDN voltage externally; prevents inrush into bulk output capacitors. |
| Low shutdown current (<2µA) | Extends battery life in portable equipment; enables clean power sequencing in multi-rail systems with independent enable control. |
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 rail with built-in UVLO and short-circuit protection. Use Value: Eliminates need for external TVS or pre-regulator stages; operates continuously up to 36V input and survives 40V transients without latch-off. | Use Scenario: Powering PLC I/O modules, fieldbus interfaces, or analog sensor front-ends from noisy 24V DC industrial bus. IC Role / Device Role / Timing Role: Immune step-down converter delivering clean, regulated output despite wide input variation and EMI-rich environment. Use Value: Maintains regulation under 3.6V–36V input swing; low 2µA shutdown enables remote wake-up; MSOP package fits dense control board layouts. |
| Wall Transformer Regulation | Battery-Powered Equipment |
Use Scenario: Converting unregulated 9–24V AC/DC wall adapter output to fixed 3.3V for embedded networking devices. IC Role / Device Role / Timing Role: High-input-range buck controller accepting variable, poorly regulated input while delivering precise, low-noise output. Use Value: No input pre-filtering required; programmable frequency avoids AM band interference; soft-start prevents adapter overload. | Use Scenario: Power management in handheld test instruments or portable data loggers using Li-ion or alkaline primary cells. IC Role / Device Role / Timing Role: Efficient battery discharge regulator with ultra-low quiescent current and output disconnect during shutdown. Use Value: Extends runtime via <2µA shutdown; supports deep-sleep modes; 780mV reference enables low-VOUT rails for modern low-power MCUs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3631EMS8E#PBF | Higher efficiency (95% typical), 3.5A output, but narrower 2.7V–20V input range; requires external MOSFETs. | Better suited for high-current, low-input-voltage applications where 36V capability is unnecessary. | Select LTC3631EMS8E#PBF only if input stays below 20V and >2A output is needed; not drop-in compatible due to different pinout and topology. |
| LM5164QDDARQ1 | Automotive-grade (AEC-Q100), 1.5A, 3V–65V input, but uses external MOSFETs and requires more external components. | Preferred for automotive safety-critical systems requiring qualification and extended input range beyond 36V. | Choose LM5164QDDARQ1 for AEC-Q100 compliance and >36V tolerance; LT3505IMS8E#PBF offers simpler BOM and integrated switch for non-automotive 36V max use cases. |
Compared with LTC3631EMS8E#PBF and LM5164QDDARQ1, the LT3505IMS8E#PBF delivers optimal integration and ruggedness for 3.6V–36V industrial and automotive auxiliary rails where 1.2A output and minimal external parts are priorities-not for >20V input with LTC3631 or AEC-Q100-certified designs requiring LM5164QDDARQ1.
Availability
LT3505IMS8E#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.
Supply support for LT3505IMS8E#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 high-performance analog and power management portfolio with rigorous testing and long-term product support.
The LT3505 belongs to Linear's monolithic current-mode buck regulator family, designed specifically for wide-input industrial and automotive power conversion where reliability, simplicity, and transient robustness are critical.
FAQ
What is the maximum output current of the LT3505IMS8E#PBF?
The LT3505IMS8E#PBF delivers up to 1.2A continuous output current when VIN > 8V and ambient temperature remains within its –40°C to 125°C operating range. Actual achievable current depends on PCB thermal design, inductor DCR, and switching frequency-higher frequencies reduce thermal headroom. The internal 1.4A switch and cycle-by-cycle current limit ensure safe operation up to 2.2A peak under fault conditions.
Does the LT3505IMS8E#PBF require an external catch diode?
Yes, the LT3505IMS8E#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 relies on this external diode for freewheeling current path during switch-off periods. Diode selection must consider 40V reverse voltage rating and ≥1A average current handling.
How is the switching frequency set on the LT3505IMS8E#PBF?
The switching frequency of the LT3505IMS8E#PBF is set by connecting a precision 1% resistor from the RT pin to GND. Values from 13.7kΩ (3MHz) to 357kΩ (200kHz) are supported per the datasheet table. The RT pin bias voltage is ~0.5V, and stray capacitance must be minimized to avoid frequency drift-short, guarded traces are recommended.
What is the purpose of the BOOST pin on the LT3505IMS8E#PBF?
The BOOST pin on the LT3505IMS8E#PBF supplies gate drive voltage to the internal bipolar NPN power switch, enabling full saturation and low VCE(SAT) (350mV @ 1A). It requires an external diode and capacitor to generate a voltage ~2V above VIN. Without proper BOOST circuitry, the switch operates inefficiently with increased conduction loss and thermal stress.
Can the LT3505IMS8E#PBF operate with input voltages above 36V?
No-the LT3505IMS8E#PBF has a maximum rated input voltage of 36V for continuous operation and 40V as absolute maximum. Exceeding 36V risks permanent damage. During transients (e.g., automotive load dump), brief excursions to 40V are tolerated *only if* the output remains regulated and the part does not enter uncontrolled pulse-skipping-designs must include input clamping or filtering to enforce this limit.
LT3505IMS8E#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-TSSOP, 8-MSOP (0.118", 3.00mm Width) 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-MSOP-EP
LT3505IMS8E#PBF FAQ
1.How can I place an order for LT3505IMS8E#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3505IMS8E#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 LT3505IMS8E#PBF reliable?
The price and inventory of LT3505IMS8E#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3505IMS8E#PBF is usually 5 days.
3.What payment methods are accepted for LT3505IMS8E#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3505IMS8E#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3505IMS8E#PBF?
LT3505IMS8E#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3505IMS8E#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 LT3505IMS8E#PBF?
For technical support, including LT3505IMS8E#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3505IMS8E#PBF requirements.
6.How does Aetrix verify that LT3505IMS8E#PBF is sourced from the original manufacturer or authorized distributors?
All LT3505IMS8E#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 LT3505IMS8E#PBF meets industry standards.
7.What is the process for return or replacement of LT3505IMS8E#PBF?
All LT3505IMS8E#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3505IMS8E#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 LT3505IMS8E#PBF part is unused and in its original packaging.
Return procedure for LT3505IMS8E#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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