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Analog Devices Inc. LT3685IDD#PBF
- Part No.:
- LT3685IDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3685IDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,515
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Product details
Overview
LT3685IDD#PBF from Analog Devices is a 36V, 2A, 2.4MHz monolithic step-down switching regulator with integrated 0.25Ω bipolar NPN switch and boost Schottky diode. It operates from 3.6V to 36V input, withstands 60V transients via overvoltage lockout (36V min), delivers 0.790V feedback reference, and supports adjustable frequency (200kHz–2.4MHz) for compact power supply design in automotive battery regulation and industrial supplies.
For engineers reviewing the LT3685IDD#PBF datasheet, LT3685IDD#PBF pinout, LT3685IDD#PBF application, or LT3685IDD#PBF equivalent, this page provides verified technical context, package-validated pin functions, real-world efficiency curves at 12V/24V/34V input, confirmed soft-start implementation via RUN/SS RC network, and two validated alternative regulators with documented functional trade-offs.
Technical Context
The LT3685IDD#PBF implements constant-frequency current-mode control using an internal oscillator set by RT resistor, enabling fast transient response and stable loop behavior across 3.6V–36V input range. Its bipolar NPN switch is driven via BOOST pin with external capacitor-diode network to ensure saturation, while VC pin serves as error amplifier output controlling peak switch current.
Overvoltage protection disables switching when VIN exceeds 36V (min), allowing safe 60V transient tolerance without external clamping. Power Good (PG) asserts when FB reaches 89% of 0.790V reference, and RUN/SS enables shutdown (<1µA IQ) and soft-start via external RC ramp - both functions validated in typical application schematics and electrical characteristics tables.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous operation; withstands 60V non-repetitive transients via OVP circuit |
| Output Current | Up to 2A DC load; switch current limit ≥3.2A at low duty cycle ensures margin under peak conditions |
| Switching Frequency | Adjustable 200kHz–2.4MHz via RT resistor; enables use of ≤4.7µH inductors and ceramic capacitors |
| Feedback Reference | 0.790V ±10mV over temperature; sets output voltage via resistor divider (e.g., 3.3V = 0.79V × (1 + R1/R2)) |
| Shutdown Current | <1µA at RUN/SS = 0V; enables ultra-low-power system standby without external disconnect |
| Power Good Threshold | 89% of regulated VOUT (i.e., 0.703V at FB for 3.3V output); open-collector PG signal valid above 3.6V VIN |
| Thermal Package | 10-pin (3mm × 3mm) DFN with exposed pad; θJA = 45°C/W, θJC = 10°C/W for high-power density layout |
Pinout & Package
LT3685IDD#PBF uses a thermally enhanced 10-pin (3mm × 3mm) plastic DFN package with exposed pad (Pin 11) soldered to PCB ground for low thermal resistance. Pin functions are validated per Analog Devices Rev. C datasheet Figure 1 (DD Package Top View) and Pin Functions section.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Supply | Connects to Schottky diode anode; supplies bias current to internal regulator - improves efficiency when tied to VOUT |
| BOOST (2) | Switch Drive Voltage Source | Provides >VIN voltage to fully saturate internal bipolar NPN switch; requires external capacitor-diode network |
| SW (3) | Switch Node Output | Drives inductor and catch diode; high dv/dt node requiring tight layout and Kelvin connection to BOOST capacitor |
| VIN (4) | Main Input Supply | Supplies internal regulator and switch; must be locally bypassed with ≥4.7µF X7R ceramic capacitor |
| RUN/SS (5) | Enable & Soft-Start Control | Logic-level enable (≥2.5V = on, ≤0.2V = off); RC network here generates controlled VOUT ramp during startup |
| SYNC (6) | External Clock Input | Accepts 250kHz–2MHz square wave for EMI reduction or multi-rail synchronization; 0.5V/0.7V logic thresholds |
| PG (7) | Power Good Flag | Open-collector output active low until FB reaches 89% of 0.790V; requires external pull-up resistor |
| FB (8) | Feedback Input | Regulated to 0.790V; connects to resistor divider tap - determines output voltage accuracy and line/load regulation |
| VC (9) | Error Amplifier Output | Controls peak switch current; compensation network (RC + CC) connected here stabilizes current-mode loop |
| RT (10) | Oscillator Frequency Set | Resistor to ground sets switching frequency (e.g., 8.66kΩ = 2.4MHz); tolerance directly impacts fSW accuracy |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Boost Schottky Diode | Eliminates external diode; reduces BOM count and board area while maintaining <2µA reverse leakage at 10V |
| Saturating Bipolar NPN Switch | 0.25Ω typical RCE(SAT) at 2A ensures low conduction loss and thermal stability up to 125°C junction |
| Programmable Frequency Foldback | Automatically reduces fSW during startup/overload to limit peak inductor current and improve reliability |
| Exposed Pad Thermal Management | Pin 11 (GND) exposed pad lowers θJA to 45°C/W - enables 2A operation without heatsink in 1-in² layout |
| Robust Overvoltage Protection | Locks out switching at VIN ≥36V (min); allows safe 60V transient survival without derating or external TVS |
Applications
| Automotive Battery Regulation | Set Top Box Power |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery to 3.3V/5V for infotainment MCU and interface ICs under cold-crank (4.5V) and load-dump (60V) conditions. IC Role / Device Role / Timing Role: Primary buck converter providing isolated, transient-hardened DC-DC conversion with PG signaling for system boot sequencing. Use Value: Withstands 60V transients without external protection; maintains regulation down to 3.6V input; PG flag enables safe processor reset and I/O initialization. |
Use Scenario: Generating 3.3V/5V rails from 12V wall adapter in cable/satellite STB with strict EMI limits and space constraints. IC Role / Device Role / Timing Role: High-frequency synchronous buck controller delivering low-noise, low-ripple power to video decoders and Ethernet PHYs. Use Value: 2.4MHz operation enables 4.7µH inductor and 22µF ceramic output cap; SYNC pin allows clock alignment to avoid beat frequencies with video clocks. |
| Distributed Supply Regulation | Industrial Supplies |
Use Scenario: Point-of-load conversion in programmable logic controllers where multiple 3.3V/5V rails are derived from 24V/48V backplane. IC Role / Device Role / Timing Role: Compact, thermally efficient buck regulator supporting remote sensing and daisy-chained PG signaling for system health monitoring. Use Value: Exposed-pad DFN package achieves 45°C/W θJA; RUN/SS pin enables coordinated power-up sequencing across multiple LT3685IDD#PBF units. |
Use Scenario: Powering sensors, analog front-ends, and microcontrollers in factory automation equipment exposed to wide ambient temperatures (–40°C to 125°C). IC Role / Device Role / Timing Role: Industrial-grade DC-DC converter with guaranteed –40°C to 125°C operation and 0.790V precision reference for accurate ADC biasing. Use Value: Guaranteed specs over full temp range; 0.790V reference enables ±1% output accuracy; BD pin biasing from VOUT improves light-load efficiency. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8609S | 42V input, 2.5A, 2MHz sync buck; integrated MOSFETs, lower IQ (2.5µA), no BOOST pin required | Better suited for ultra-low-IQ battery-powered systems; lacks BD pin for bias optimization from VOUT | Select LT8609S when minimizing quiescent current is critical and external boost diode is acceptable |
| MP2451DT-LF-Z | 36V input, 0.6A, 2MHz; smaller 8-pin SOIC, no PG or SYNC, higher RDS(on) (0.45Ω) | Limited to sub-1A loads; no power-good signaling or frequency synchronization capability | Select MP2451DT-LF-Z only for cost-sensitive, low-current applications where PG and SYNC are unnecessary |
Compared with LT3685IDD#PBF, LT8609S offers lower IQ and integrated MOSFETs but sacrifices BD pin flexibility and OVP robustness at 60V; MP2451DT-LF-Z provides footprint savings but lacks PG, SYNC, and current capability - making LT3685IDD#PBF optimal for industrial 2A designs requiring transient hardening and system-level control signals.
Availability
LT3685IDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, set top box power, and industrial supplies requiring stable component supply, long-term lifecycle support, and guaranteed −40°C to +125°C operation.
Supply support for LT3685IDD#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 is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving precision instrumentation, industrial automation, and automotive markets since 1965.
The LT3685IDD#PBF belongs to Analog Devices' monolithic step-down regulator product line, designed specifically for high-input-voltage industrial and automotive applications demanding transient robustness, thermal efficiency, and system-level control features like PG and SYNC.
FAQ
What is the maximum input voltage the LT3685IDD#PBF can safely withstand?
The LT3685IDD#PBF has overvoltage lockout that disables switching when VIN exceeds 36V (minimum), allowing it to safely withstand non-repetitive 60V transients without damage. Continuous operation is rated up to 36V, and the device remains functional - though not regulating - during 60V events. This is confirmed in Absolute Maximum Ratings and Electrical Characteristics tables of the Rev. C datasheet.
Does the LT3685IDD#PBF require an external boost diode?
No, the LT3685IDD#PBF integrates a boost Schottky diode on-die - the BD pin connects directly to its anode. This eliminates the need for an external diode, reducing component count and PCB area. The datasheet specifies BD pin reverse leakage as ≤2µA at 10V, confirming internal integration and performance validation.
How is soft-start implemented on the LT3685IDD#PBF?
Soft-start on the LT3685IDD#PBF is implemented via an RC network connected to the RUN/SS pin. When enabled, the internal circuitry ramps the RUN/SS voltage, which in turn controls the VC pin and limits inrush current. This is explicitly described in the Applications Information section and validated in Typical Application schematic TA01.
What package type does the LT3685IDD#PBF use, and is thermal pad connection mandatory?
The LT3685IDD#PBF uses a 10-pin (3mm × 3mm) plastic DFN package with exposed thermal pad (Pin 11). Per the Pin Configuration diagram and Absolute Maximum Ratings notes, the exposed pad must be soldered to PCB ground to achieve specified θJA = 45°C/W and ensure reliable 2A operation at 125°C junction temperature.
Can the LT3685IDD#PBF synchronize to an external clock, and what is the supported frequency range?
Yes, the LT3685IDD#PBF supports external clock synchronization via the SYNC pin, accepting square-wave inputs from 250kHz to 2MHz. The datasheet specifies logic thresholds of 0.5V (low) and 0.7V (high), with rise/fall times <1µs required - enabling EMI reduction and multi-rail timing coordination in noise-sensitive systems.
LT3685IDD#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):
- 36V
- Voltage - Output (Min/Fixed):
- 0.79V
- Voltage - Output (Max):
- 20V
- Current - Output:
- 2A
- Frequency - Switching:
- 200kHz ~ 2.4MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LT3685IDD#PBF FAQ
1.How can I place an order for LT3685IDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3685IDD#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 LT3685IDD#PBF reliable?
The price and inventory of LT3685IDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3685IDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3685IDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3685IDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3685IDD#PBF?
LT3685IDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3685IDD#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 LT3685IDD#PBF?
For technical support, including LT3685IDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3685IDD#PBF requirements.
6.How does Aetrix verify that LT3685IDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3685IDD#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 LT3685IDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3685IDD#PBF?
All LT3685IDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3685IDD#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 LT3685IDD#PBF part is unused and in its original packaging.
Return procedure for LT3685IDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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