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Analog Devices Inc. LT3685EDD#PBF
- Part No.:
- LT3685EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LT3685EDD#PBF.pdf
- Description:
- IC REG BUCK ADJ 2A 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,748
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Product details
Overview
LT3685EDD#PBF from Analog Devices is a 36V, 2A, 2.4MHz monolithic step-down switching regulator with integrated 0.25Ω bipolar NPN switch, boost Schottky diode, and overvoltage lockout (36V min, 38V typ) enabling safe 60V transient tolerance. It delivers regulated 0.79V–20V output in automotive battery regulation and industrial supply applications.
For engineers reviewing the LT3685EDD#PBF datasheet, LT3685EDD#PBF pinout, LT3685EDD#PBF application, or LT3685EDD#PBF equivalent, key selection factors include adjustable 200kHz–2.4MHz switching frequency, power good flag, soft-start via RUN/SS, 1µA shutdown current, and thermal performance in the 3mm × 3mm DFN package with exposed pad.
Technical Context
The LT3685EDD#PBF implements constant-frequency current-mode control using an internal error amplifier (gm = 500 µmho), slope compensation, and RS flip-flop timing. Switching frequency is set by an external RT resistor (200kHz–2.4MHz range) and supports synchronization (250kHz–2MHz).
Its architecture integrates a boost capacitor drive path (BD/BOOST pins), active VC clamp for current limiting, and frequency foldback during startup or overload. The 0.790V feedback reference enables precise output regulation, while the PG open-collector flag asserts when FB reaches 89% of target voltage.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous operation; withstands 60V nonrepetitive transients via OVP shutdown |
| Max Output Current | 2A DC load capability with peak switch current limit ≥3.2A at low duty cycle |
| Switching Frequency | Adjustable 200kHz–2.4MHz via RT resistor; synchronizable 250kHz–2MHz |
| Feedback Reference | 0.790V ±10mV over temperature; sets output via resistor divider on FB pin |
| Shutdown Current | <1µA at VIN when RUN/SS ≤ 0.2V; enables ultra-low-power system standby |
| Power Good Threshold | Asserts when VOUT reaches 89% of programmed value; open-drain PG pin with 100µA sink capability |
| On-Resistance | 0.25Ω typical for internal bipolar NPN switch; minimizes conduction loss at 2A |
| Package Thermal Resistance | JC = 10°C/W, JA = 45°C/W in 10-pin 3mm × 3mm DFN with soldered exposed pad |
Pinout & Package
The LT3685EDD#PBF is housed in a thermally enhanced 10-pin (3mm × 3mm) plastic DFN package with exposed pad (Pin 11), which must be soldered to PCB ground for optimal thermal performance (JC = 10°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BD (1) | Boost Diode Anode Supply | Connects to external Schottky anode; supplies bias current to internal regulator when >3V |
| BOOST (2) | Switch Drive Voltage Boost | Provides >VIN voltage to fully saturate internal bipolar NPN switch; requires external boost cap/diode |
| SW (3) | Switch Node Output | Drives inductor, catch diode, and boost capacitor; high dv/dt node requiring careful layout |
| VIN (4) | Main Input Power Supply | Supplies internal regulator and switch; bypass locally with ≥4.7µF ceramic capacitor |
| RUN/SS (5) | Enable & Soft-Start Control | Logic-level enable (≥2.5V = on); RC network here controls output voltage ramp rate |
| SYNC (6) | External Clock Input | Accepts TTL/CMOS clock edges (rise/fall <1µs) to synchronize switching frequency |
| PG (7) | Power Good Flag | Open-collector output asserting when FB ≥ 89% of regulation; requires external pull-up |
| FB (8) | Feedback Input | Regulated to 0.790V; connects to resistor divider tap for output voltage programming |
| VC (9) | Error Amplifier Output | Controls peak switch current; RC network here provides loop compensation |
| RT (10) | Oscillator Frequency Set | Resistor-to-ground sets switching frequency (e.g., 8.66kΩ = 2.4MHz) |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Boost Schottky Diode Driver | Eliminates external boost diode; BD pin supplies bias current when output voltage >3V, improving efficiency |
| Overvoltage Lockout Protection | Disables switching at VIN ≥36V (min), allowing safe 60V transient survival without external clamping |
| Current-Mode Control Architecture | Enables fast transient response and inherent loop stability without requiring ESR in output capacitor |
| Thermally Optimized DFN Package | 3mm × 3mm footprint with exposed GND pad achieves JC = 10°C/W for high-power density designs |
| Programmable Soft-Start | RUN/SS pin accepts RC network to control output voltage ramp time, preventing inrush current and overshoot |
| Power Good Monitoring | PG pin signals valid regulation (FB ≥ 89% of target) with hysteresis; supports system sequencing and fault detection |
Applications
| Automotive Battery Regulation | Industrial Power Supplies |
|---|---|
Use Scenario: Regulating 12V/24V vehicle battery rails to 3.3V or 5V for infotainment ECUs and ADAS sensors under cold-crank (4.5V) and load-dump (60V) conditions. IC Role / Device Role / Timing Role: Primary step-down regulator providing stable, transient-tolerant DC output with PG signaling for microcontroller reset coordination. Use Value: 60V transient tolerance eliminates need for external TVS; 2.4MHz operation enables compact 4.7µH inductor and ceramic output caps. | Use Scenario: Distributed 2A point-of-load conversion in programmable logic controllers and industrial I/O modules powered from 24V or 36V DC bus. IC Role / Device Role / Timing Role: High-efficiency buck converter delivering regulated voltage to FPGA cores, ADCs, and isolated communication interfaces. Use Value: Adjustable frequency allows optimization for EMI compliance; soft-start prevents brownout during hot-swap insertion. |
| Set-Top Box Power | Wall Transformer Replacement |
Use Scenario: Replacing linear regulators in cable/satellite STBs where 12V input must generate 3.3V/1.8V rails for SoCs and memory with low acoustic noise. IC Role / Device Role / Timing Role: Main DC-DC converter operating in CCM with synchronized frequency to avoid beat frequencies with video clocks. Use Value: Synchronizable 250kHz–2MHz range enables EMI spread-spectrum alignment; low 1µA shutdown current meets Energy Star standby requirements. | Use Scenario: Integrated AC-DC adapter replacement in medical monitors and portable test equipment requiring 5V/2A output from 9–36V DC input. IC Role / Device Role / Timing Role: Isolated secondary-side buck regulator accepting wide-input unregulated DC, delivering tightly regulated output with PG confirmation. Use Value: 3.6V minimum input enables operation down to depleted battery levels; exposed-pad DFN ensures thermal reliability in sealed enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3630EMSE#PBF | 40V max input, 1.5A output, fixed 2MHz frequency, no SYNC pin, no integrated boost diode | Lower current, no external boost diode needed, but requires external bootstrap circuit | Preferred for space-constrained 1.5A designs where fixed 2MHz simplifies filtering |
| TPS54240DGQR | 40V max input, 2.5A output, 100kHz–2.5MHz adjustable frequency, no integrated boost diode, different pinout | Higher current rating, requires external bootstrap diode/cap, no PG flag | Selected when higher output current or wider frequency range is required, accepting added BOM count |
Compared with LTC3630EMSE#PBF and TPS54240DGQR, the LT3685EDD#PBF uniquely combines 2A capability, integrated boost diode driver, PG flag, and 60V transient tolerance in a 3mm × 3mm DFN-making it optimal for automotive and industrial systems demanding robustness and minimal external components.
Availability
LT3685EDD#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial power supplies, set-top box power, and wall transformer replacement requiring stable component supply across extended temperature and transient-voltage environments.
Supply support for LT3685EDD#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, communications, and automotive markets.
The LT3685EDD#PBF belongs to the LT® monolithic switching regulator product line, designed specifically for high-input-voltage, high-transient-immunity DC-DC conversion in harsh environments such as automotive and industrial systems.
FAQ
What is the absolute maximum input voltage rating for the LT3685EDD#PBF?
The LT3685EDD#PBF has an absolute maximum VIN rating of 60V for nonrepetitive 1-second transients and 40V for continuous operation. Its overvoltage lockout activates at 36V (min), disabling switching to protect the device while sustaining up to 60V input safely. This makes the LT3685EDD#PBF suitable for automotive load-dump scenarios without external clamping.
Does the LT3685EDD#PBF require an external boost diode?
No-the LT3685EDD#PBF integrates the boost Schottky diode driver function internally. The BD pin connects directly to the anode of an external Schottky diode, while the BOOST pin provides the elevated gate drive voltage. The datasheet confirms no external diode is needed on-chip; only one external Schottky diode is required per application circuit, and the LT3685EDD#PBF's BD pin supplies bias current when voltage exceeds 3V.
How is the switching frequency set on the LT3685EDD#PBF?
The switching frequency of the LT3685EDD#PBF is set by connecting a resistor from the RT pin to ground. Values range from 8.66kΩ (2.4MHz) to 187kΩ (200kHz), with intermediate values specified in the datasheet's Figure 1. The LT3685EDD#PBF also supports external synchronization between 250kHz and 2MHz via the SYNC pin, enabling EMI reduction through clock alignment.
What is the purpose of the exposed pad on the LT3685EDD#PBF DFN package?
The exposed pad (Pin 11) on the LT3685EDD#PBF is electrically connected to GND and must be soldered to a PCB thermal pad for effective heat dissipation. It reduces junction-to-case thermal resistance to 10°C/W, critical for maintaining safe operating temperatures at 2A continuous load. Failure to solder the exposed pad degrades thermal performance and may cause premature thermal shutdown.
Can the LT3685EDD#PBF operate with an input voltage below 3.6V?
No-the LT3685EDD#PBF has a minimum operating input voltage of 3.6V (typical), below which regulation cannot be maintained. This is specified in the Absolute Maximum Ratings and Electrical Characteristics tables. Attempting operation below 3.6V results in dropout or shutdown; the device will not regulate output voltage, and PG will remain inactive. For sub-3.6V inputs, a different regulator such as the LT3643 is required.
What does the Power Good (PG) flag indicate on the LT3685EDD#PBF?
The PG flag on the LT3685EDD#PBF is an open-collector output that goes high (via external pull-up) when the FB pin voltage reaches 89% of its final regulated value (i.e., 0.790V × 0.89 ≈ 0.703V). It remains valid only when VIN > 3.6V and RUN/SS is enabled. This signal enables system-level power sequencing, reset assertion, or fault monitoring-ensuring downstream circuits activate only after stable output is confirmed.
LT3685EDD#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)
LT3685EDD#PBF FAQ
1.How can I place an order for LT3685EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3685EDD#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 LT3685EDD#PBF reliable?
The price and inventory of LT3685EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3685EDD#PBF is usually 5 days.
3.What payment methods are accepted for LT3685EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3685EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3685EDD#PBF?
LT3685EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3685EDD#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 LT3685EDD#PBF?
For technical support, including LT3685EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3685EDD#PBF requirements.
6.How does Aetrix verify that LT3685EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3685EDD#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 LT3685EDD#PBF meets industry standards.
7.What is the process for return or replacement of LT3685EDD#PBF?
All LT3685EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3685EDD#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 LT3685EDD#PBF part is unused and in its original packaging.
Return procedure for LT3685EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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