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Analog Devices Inc. LT3686IDD#PBF
- Part No.:
- LT3686IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3686IDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 1.2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:929
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Product details
Overview
LT3686IDD#PBF from Analog Devices (formerly Linear Technology) is a current-mode PWM step-down DC/DC converter with integrated 1.2A bipolar NPN power switch, designed for industrial and automotive power regulation. It operates from 3.6V to 37V input, delivers up to 1.2A at adjustable output voltages (e.g., 3.3V or 5V), and supports switching frequencies from 300kHz to 2.5MHz - enabling compact 3mm × 3mm DFN designs suitable for 24V industrial rails and 12V/24V automotive battery systems.
For engineers reviewing the LT3686IDD#PBF datasheet, LT3686IDD#PBF pinout, LT3686IDD#PBF application, or LT3686IDD#PBF equivalent, key selection considerations include its 100ns minimum on-time for high VIN-to-VOUT ratios, BD-pin active load for fixed-frequency light-load operation, cycle-by-cycle current limiting, internal boost diode, and guaranteed –40°C to 125°C junction temperature performance.
Technical Context
The LT3686IDD#PBF implements peak-current-mode control with slope compensation, using an external RT resistor to set oscillator frequency and an internal 0.8V reference for feedback regulation. Its bipolar NPN switch requires BOOST voltage ≥2.2V above SW for saturation, supplied via internal Schottky diode and external capacitor.
Protection includes overvoltage lockout (37V–39V trip), undervoltage lockout (3.4V–3.6V), thermal shutdown, and dual current sensing: DA-pin valley current limit (1.2A–1.7A) for fault detection and switch peak current limit (1.85A–2.65A) with duty-cycle-dependent slope compensation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 37V - supports direct regulation from 24V industrial supplies and automotive batteries with transient tolerance up to 55V. |
| Output Current | 1.2A continuous - sufficient for powering microcontrollers, sensors, and interface ICs in embedded systems. |
| Switching Frequency | 300kHz to 2.5MHz - programmable via RT pin; enables use of sub-10µH inductors and avoids AM-band interference. |
| Feedback Reference | 0.785V to 0.815V - precise 0.8V nominal reference with ±1.9% tolerance over temperature, enabling accurate output voltage setting. |
| Minimum On-Time | 100ns - allows stable 3.3V output from 16V input at 2MHz, critical for high-step-down automotive applications. |
| Quiescent Current (Shutdown) | <1µA - ensures ultra-low standby power in battery-backed or always-on systems. |
| Junction Temperature Range | –40°C to 125°C - rated for extended industrial and under-hood automotive environments. |
Pinout & Package
LT3686IDD#PBF is housed in a 10-lead 3mm × 3mm plastic DFN package with exposed thermal pad (Pin 11 = GND). The exposed pad must be soldered to PCB copper for thermal management (θJA = 43°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 1) | Power Input | Supplies internal regulator and power switch; requires local 2.2µF ceramic bypass. |
| BD (Pin 2) | Boost Diode Anode | Connects to VOUT to enable internal active load; regulates ~30–40mA when MODE > 0.8V for fixed-frequency light-load operation. |
| FB (Pin 3) | Feedback Sense | Regulated to 0.8V; sets output via resistor divider (e.g., R1=32.4kΩ, R2=10kΩ for 3.3V). |
| SS (Pin 4) | Soft-Start/Tracking | Internal 2µA current source ramps external capacitor; controls both FB reference and oscillator frequency during startup. |
| RT (Pin 5) | Frequency Set | Resistor to GND programs switching frequency (e.g., 15.4kΩ → 2.1MHz); determines minimum practical inductor value. |
| EN/UVLO (Pin 6) | Enable / UVLO Input | 1.27V threshold enables operation; can be programmed with resistor divider for custom UVLO; <0.4V forces shutdown. |
| MODE (Pin 7) | Active Load Control | Tie >0.8V to enable BD-pin active load; tie <0.4V to disable pulse-skipping suppression. |
| BOOST (Pin 8) | Switch Driver Supply | Provides boosted gate drive (>VIN) to saturate internal bipolar NPN switch; requires 0.22µF capacitor to SW. |
| DA (Pin 9) | Catch Diode Anode Sense | Monitors catch diode current; triggers frequency foldback if valley current exceeds 1.2A–1.7A to limit fault current. |
| SW (Pin 10) | Switch Node | Connects to inductor, catch diode cathode, and BOOST capacitor; carries high di/dt switching waveform. |
Key Features
| Feature | Design Value |
|---|---|
| Internally Compensated Control Loop | Eliminates need for external compensation components, reducing BOM count and layout sensitivity. |
| Constant Switching Frequency at Light Loads | BD-pin active load maintains full frequency (e.g., 2MHz) down to mA-level loads, ensuring predictable EMI and low audio-band ripple. |
| Cycle-by-Cycle Current Limit + DA Valley Sensing | Dual protection: peak switch current limit prevents MOSFET overstress; DA-pin valley limit throttles frequency during short-circuit or overload. |
| Adjustable UVLO with Hysteresis | EN/UVLO pin supports programmable start-up threshold (e.g., 12V) and 2.4µA hysteresis current for stable brown-out recovery. |
| Overvoltage Lockout (OVLO) | Shuts down at 37V–39V input transients - protects against load-dump events in 24V automotive systems. |
Applications
| Automotive Power Regulation | Industrial 24V DC-DC Conversion |
|---|---|
Use Scenario: Regulating 24V battery rail to 3.3V/5V for infotainment MCU, CAN transceivers, and sensor interfaces in passenger vehicles. IC Role / Device Role / Timing Role: Primary buck regulator with 37V OVLO, 100ns min-on-time, and AM-band-avoiding 2.1MHz operation. Use Value: Enables compact, EMI-compliant power supply meeting ISO 7637-2 pulse 5a load-dump immunity without external TVS. |
Use Scenario: Converting unregulated 24V factory-floor supply to 5V for PLC I/O modules and fieldbus gateways. IC Role / Device Role / Timing Role: High-input-voltage buck controller with internal 1.2A switch and –40°C to 125°C operation. Use Value: Eliminates need for external high-voltage MOSFET and driver, reducing solution size and qualification effort for industrial certifications. |
| Wall Adapter Post-Regulation | Distributed Point-of-Load Supply |
Use Scenario: Tight-regulation post-converter after wide-range AC/DC adapter (e.g., 9–36V input) powering medical instrumentation analog front-ends. IC Role / Device Role / Timing Role: Low-noise, fixed-frequency buck with 0.8V reference accuracy and soft-start tracking. Use Value: Delivers <10mVpp output ripple at 2MHz, avoiding audible noise and minimizing filtering requirements in sensitive signal chains. |
Use Scenario: Local 3.3V supply for FPGA I/O banks or high-speed SerDes in telecom line cards with distributed 12V intermediate bus. IC Role / Device Role / Timing Role: Fast-transient-response buck with BD-pin active load and internal compensation. Use Value: Maintains stable 2MHz switching during dynamic load steps (0.25A ↔ 1A), simplifying loop stability across board variants. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8609SIS8#TRPBF | Silicon-based synchronous buck; 42V max input; 2.5A output; requires external compensation. | Better efficiency at light loads (Burst Mode™); higher current capability but larger solution size. | Select for higher output current or lower IQ (<2.5µA) where synchronous rectification improves thermal performance. |
| TPS54240DGQR | CMOS-based buck; 40V max input; 2.5A output; adjustable soft-start; no BD-pin active load. | Lacks fixed-frequency light-load mode; uses external high-side FET; wider VIN range but no internal boost diode. | Select when cost-sensitive design tolerates pulse-skipping ripple or requires adjustable soft-start timing independent of frequency. |
Compared with LT3686IDD#PBF, LT8609S offers higher current and lower quiescent current but requires external compensation and lacks the BD-pin active load for predictable light-load EMI; TPS54240 provides higher current and CMOS efficiency but introduces layout complexity with external FET and no built-in boost diode or valley-current fault protection.
Availability
LT3686IDD#PBF is available at Aetrix Electronics and suitable for automotive power systems, industrial 24V DC-DC conversion, and wall-adapter post-regulation requiring stable component supply across extended temperature ranges.
Supply support for LT3686IDD#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 full technical and manufacturing continuity for the LT® product family, known for high-reliability analog and power management ICs.
The LT3686IDD#PBF belongs to Linear's high-voltage monolithic buck regulator product line, engineered specifically for robust operation in harsh environments including automotive under-hood and industrial control cabinets.
FAQ
What is the maximum input voltage the LT3686IDD#PBF can withstand continuously?
The LT3686IDD#PBF has an absolute maximum VIN rating of 55V, but its guaranteed continuous operating input range is 3.6V to 37V. Operation above 37V triggers overvoltage lockout (OVLO), shutting down the device until input drops below 36V–38V hysteresis band. This protects against 24V automotive load-dump transients while maintaining reliable 24V system operation.
Does the LT3686IDD#PBF require an external catch diode?
Yes, the LT3686IDD#PBF requires an external Schottky catch diode (e.g., MBRM140) connected between SW and GND. The device integrates a boost diode for the internal NPN switch driver but does not include synchronous rectification or an integrated catch diode - this external component is mandatory for proper flyback energy recirculation and efficiency.
How does the BD pin function in the LT3686IDD#PBF?
The BD pin on the LT3686IDD#PBF connects to the output and enables an internal active load (~30–40mA) when the MODE pin exceeds 0.8V. This load maintains full switching frequency during light-load conditions, eliminating pulse-skipping and associated low-frequency output ripple - critical for EMI-sensitive and audio-band-avoidance applications.
Can the LT3686IDD#PBF operate at 2MHz with a 3.3V output from 12V input?
Yes, the LT3686IDD#PBF supports 2MHz operation with 3.3V output from 12V input. With a typical minimum on-time of 100ns, the required duty cycle (~29%) is well within continuous conduction mode limits. Application Note DC2222 and Figure 3686 G16 confirm stable 2MHz operation at this condition with 6.8µH inductor and 22µF output capacitance.
What is the purpose of the DA pin on the LT3686IDD#PBF?
The DA pin on the LT3686IDD#PBF senses current through the external catch diode. When valley current exceeds 1.2A–1.7A (temperature-dependent), the DA comparator triggers frequency foldback to reduce average output current - providing robust short-circuit protection without relying solely on peak switch current limiting.
LT3686IDD#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:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 3.6V
- Voltage - Input (Max):
- 37V
- Voltage - Output (Min/Fixed):
- 0.8V
- Voltage - Output (Max):
- 37V
- Current - Output:
- 1.2A
- Frequency - Switching:
- 300kHz ~ 2.5MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT3686IDD#PBF FAQ
1.How can I place an order for LT3686IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3686IDD#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 LT3686IDD#PBF reliable?
The price and inventory of LT3686IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3686IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3686IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3686IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3686IDD#PBF?
LT3686IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3686IDD#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 LT3686IDD#PBF?
For technical support, including LT3686IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3686IDD#PBF requirements.
6.How does Aetrix verify that LT3686IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3686IDD#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 LT3686IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3686IDD#PBF?
All LT3686IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3686IDD#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 LT3686IDD#PBF part is unused and in its original packaging.
Return procedure for LT3686IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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