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Analog Devices Inc. LT3681EDE#PBF
- Part No.:
- LT3681EDE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 14-WFDFN Exposed Pad
- Datasheet:
-
LT3681EDE#PBF.pdf
- Description:
- IC REG BUCK ADJ 2A 14DFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,806
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Product details
Overview
LT3681EDE#PBF from Analog Devices (formerly Linear Technology) is a monolithic 36V, 2A, 2.8MHz current-mode step-down switching regulator with integrated power Schottky diode and boost Schottky diode. It features 0.18Ω internal switch, 1.265V feedback reference, adjustable frequency (300kHz–2.8MHz), and Power Good flag. Used in automotive battery regulation and industrial supplies where wide input range (3.6V–34V) and compact solution size are critical.
For engineers reviewing the LT3681EDE#PBF datasheet, LT3681EDE#PBF pinout, LT3681EDE#PBF application, or LT3681EDE#PBF equivalent, key selection considerations include its integrated Schottky diode reducing external component count, low-ripple Burst Mode operation (<15mVP-P), soft-start via RUN/SS pin, and thermal performance enabled by 4mm × 3mm DFN package with exposed GND pad.
Technical Context
The LT3681EDE#PBF employs constant-frequency current-mode control with an internal oscillator set by RT pin resistor, enabling precise loop stability and fast transient response. Its bipolar NPN power switch is driven via BOOST pin voltage higher than VIN, ensuring full saturation and low conduction loss (360mV VCE(SAT) at 2A).
It integrates two Schottky diodes: a 2A power Schottky (DA/DC pins) for catch function and a dedicated boost Schottky (BD/BOOST) to generate gate drive voltage. Bias current is drawn from VOUT when above 3V, improving light-load efficiency (50µA IQ at 12VIN/3.3VOUT), while PG flag asserts when VFB reaches 90% of regulation threshold.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 34V operating; 36V absolute max - supports 12V/24V automotive and industrial rails with transient tolerance. |
| Output Current | 2A continuous - sufficient for powering FPGA cores, microcontrollers, and sensor subsystems without external current boosting. |
| Switching Frequency | 300kHz to 2.8MHz (RT-programmable) - enables trade-off between small magnetics (high fSW) and high VIN/VOUT ratio support (low fSW). |
| Feedback Reference | 1.265V ±15mV - sets output voltage accuracy; allows 1.265V–20V adjustable VOUT using standard resistor divider. |
| Quiescent Current | 50µA typical at 12VIN/3.3VOUT in Burst Mode - extends battery life in portable applications with light-load duty cycles. |
| Power Good Threshold | VFB ≥ 90% of 1.265V (i.e., ≥1.1385V) - provides reliable system enable signaling with 122mV hysteresis for noise immunity. |
| Thermal Package | 14-pin 4mm × 3mm DFN with exposed GND pad (θJA = 43°C/W) - enables >1.5W dissipation at 85°C ambient without heatsink. |
Pinout & Package
LT3681EDE#PBF is housed in a thermally enhanced 14-pin plastic DFN package (4mm × 3mm), with Exposed Pad 15 connected internally to GND and Exposed Pad 16 connected to DC (cathode of integrated power Schottky diode). The package supports low thermal resistance and high-current PCB routing.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PG (Pin 1) | Open-collector power good output | Signals regulation status; requires external pull-up; valid only when VIN > 3.5V and RUN/SS high. |
| BIAS (Pin 2) | Bias supply input | Accepts ≥3V external source (e.g., VOUT) to reduce VIN current draw and improve efficiency at high VIN/VOUT ratios. |
| FB (Pin 3) | Feedback input | Regulated to 1.265V; connects to resistor divider tap to set output voltage; bias current <100nA ensures minimal divider error. |
| GND (Pins 4, 7, Pad 15) | Signal and thermal ground | All three connect to internal signal GND; Pad 15 must be soldered to large copper pour for thermal management. |
| VC (Pin 5) | Error amplifier output | Controls peak switch current; RC network to ground sets loop compensation; clamped to RUN/SS during soft-start. |
| RT (Pin 6) | Oscillator frequency setting | Resistor to GND sets switching frequency from 300kHz (187kΩ) to 2.8MHz (8.66kΩ); enables EMI optimization. |
| DA (Pin 8) | Power Schottky anode | Connects to GND; carries high-frequency, high-amplitude catch current; requires low-impedance PCB trace. |
| DC (Pin 9, Pad 16) | Power Schottky cathode | Connects to SW node; shares high di/dt current path with switch; Pad 16 must be routed to SW with minimal inductance. |
| BD (Pin 10) | Boost Schottky anode | Connects to BOOST capacitor's low-side; forms charge pump for NPN switch drive voltage. |
| BOOST (Pin 11) | Boost capacitor connection | Capacitor between BOOST and SW generates >VIN voltage to saturate internal bipolar switch; reverse leakage <2µA. |
| SW (Pin 12) | Switch node | Drives external inductor; connects to DC/Pad 16 and BOOST capacitor; handles full switching current and voltage transitions. |
| VIN (Pin 13) | Main input supply | Supplies internal regulator and switch; requires local 4.7µF ceramic bypass close to pin and DA/DC pads. |
| RUN/SS (Pin 14) | Enable and soft-start control | Logic-high (>2.5V) enables operation; RC ramp on this pin controls output voltage slew rate during startup. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Power Schottky Diode | 2A rated, 0.56V VF at 2A - eliminates external catch diode, reduces BOM count and board area in 4mm × 3mm footprint. |
| Low-Ripple Burst Mode Operation | <15mVP-P output ripple at light load - maintains clean power for noise-sensitive analog circuits without sacrificing efficiency (50µA IQ). |
| Adjustable Switching Frequency | 300kHz–2.8MHz via single RT resistor - enables EMI compliance tuning and optimization of inductor size vs. efficiency trade-off. |
| Power Good Flag with Hysteresis | 122mV hysteresis on 90% VFB threshold - prevents false toggling during line/load transients; open-drain output simplifies interfacing. |
| Thermally Enhanced DFN Package | θJA = 43°C/W with exposed GND pad - sustains 2A load at 85°C ambient without forced air or heatsink in typical 2-layer PCB layout. |
| Soft-Start via RUN/SS Pin | Externally programmable voltage ramp - prevents inrush current and output overshoot; no additional IC or timing capacitor required. |
Applications
| Automotive Battery Regulation | Industrial Distributed Supply |
|---|---|
|
Use Scenario: Regulating 12V/24V vehicle battery rail to 3.3V/5V for infotainment MCU and CAN transceivers under cold-crank (4.5V) and load-dump (36V) conditions. IC Role / Device Role / Timing Role: Primary buck converter providing stable, low-noise power with integrated Schottky diode to withstand high ambient temperature and vibration. Use Value: Eliminates need for external catch diode and reduces solution size by >30% versus discrete solutions; PG flag synchronizes system boot sequence. |
Use Scenario: Point-of-load conversion in PLC backplane modules converting 24V field supply to 12V/5V for I/O drivers and communication interfaces. IC Role / Device Role / Timing Role: High-reliability DC/DC regulator supporting wide input range and operating up to 85°C ambient in enclosed enclosures. Use Value: 36V absolute max rating and robust thermal design ensure uninterrupted operation during 24V rail surges; adjustable fSW avoids EMI coupling into analog signal paths. |
| Portable Product Power | Wall Transformer Regulation |
|
Use Scenario: Powering ARM Cortex-M7-based handheld test equipment from single-cell Li-ion (3.0–4.2V) or dual-cell (6–8.4V) battery packs. IC Role / Device Role / Timing Role: Efficient step-down regulator leveraging BIAS pin to draw bias from VOUT, achieving 50µA quiescent current in Burst Mode. Use Value: Extends battery runtime by >20% versus non-BIAS-optimized regulators; soft-start prevents brownout during wake-from-sleep transitions. |
Use Scenario: Replacing linear regulators in AC/DC wall adapters to improve efficiency and reduce heat in compact enclosures (e.g., [email protected] adapter). IC Role / Device Role / Timing Role: High-efficiency switching regulator accepting unregulated rectified DC input (up to 34V) with integrated diode reducing component count. Use Value: Achieves >88% efficiency at full load (vs. ~40% for linear), eliminating heatsink requirement and enabling smaller, cooler adapter designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3630AEDD#PBF | Same manufacturer, 36V/1.5A, 3mm × 4mm DFN, but uses MOSFET switch (no integrated Schottky) and lacks BIAS pin for VOUT-sourced bias. | Requires external catch diode; lower max current limits use in 2A systems; better suited for space-constrained 1.5A loads where MOSFET RDS(on) matters more than diode integration. | Select LTC3630AEDD#PBF only if external diode is acceptable and 1.5A output suffices; not drop-in due to different pinout and missing BIAS/PG functionality. |
| TPS54227DDAR | Texas Instruments part: 28V/2A, 2.2MHz, integrated MOSFET (no Schottky), no BIAS pin, different compensation scheme (Type II vs. LT3681's Type III). | Lacks integrated Schottky and VOUT-bias capability; requires external diode and larger input capacitance; PG signal absent - needs external monitoring circuit. | Choose TPS54227DDAR for cost-sensitive industrial supplies where TI ecosystem support is preferred and external diode layout is feasible. |
Compared with LTC3630AEDD#PBF and TPS54227DDAR, LT3681EDE#PBF uniquely combines integrated 2A Schottky diode, BIAS pin for efficiency optimization, and PG flag in a 4mm × 3mm DFN - making it the only option among the three that eliminates the catch diode while maintaining full 2A capability and system monitoring.
Availability
LT3681EDE#PBF is available at Aetrix Electronics and suitable for automotive battery regulation, industrial distributed supply, and portable product power applications requiring stable component supply, long-term lifecycle support, and guaranteed lead-free compliance.
Supply support for LT3681EDE#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, Inc. (including legacy Linear Technology products) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial automation, and automotive markets.
The LT3681EDE#PBF belongs to Linear Technology's high-voltage monolithic buck regulator family, designed specifically for rugged, compact DC/DC conversion in automotive, industrial, and portable systems where input transients, thermal constraints, and solution size are critical.
FAQ
What is the maximum input voltage rating for LT3681EDE#PBF, and how does switching frequency affect it?
The LT3681EDE#PBF has an absolute maximum input voltage of 36V, but safe continuous operation is limited to 34V unless the output is in regulation with no start-up or short-circuit events. At higher switching frequencies, minimum on-time constraints reduce the allowable VIN/VOUT ratio; for example, at 2.8MHz, VIN must stay below ~28V for a 5V output to avoid violating tON(MIN) ≈150ns. The LT3681EDE#PBF datasheet provides the exact equation to calculate fSW(MAX) based on your VIN, VOUT, and diode/switch drops.
Does LT3681EDE#PBF require an external catch diode?
No, LT3681EDE#PBF integrates a 36V, 2A power Schottky diode connected between DA (anode) and DC/Pad 16 (cathode), eliminating the need for an external catch diode. This reduces bill-of-materials count, PCB area, and layout complexity. The diode's forward voltage is 0.56V at 2A, and leakage is ≤100µA at 40V reverse bias - verified in the LT3681EDE#PBF electrical characteristics table.
How does the BIAS pin improve efficiency in LT3681EDE#PBF?
The BIAS pin on LT3681EDE#PBF allows the IC to draw bias current from VOUT (when ≥3V) instead of VIN, reducing total input current and improving light-load efficiency. In a 12VIN/3.3VOUT application, this lowers quiescent current to 50µA in Burst Mode - a >3× improvement over drawing bias solely from VIN. This feature is confirmed in the LT3681EDE#PBF Electrical Characteristics table under "Quiescent Current from BIAS".
What is the purpose of the BOOST and BD pins on LT3681EDE#PBF?
The BOOST and BD pins on LT3681EDE#PBF form a charge-pump circuit to generate a voltage higher than VIN, which drives the base of the internal bipolar NPN power switch. BOOST connects to the capacitor's high side, BD to its low side. This ensures full saturation of the switch, minimizing VCE(SAT) to 360mV at 2A. Reverse leakage of the integrated boost Schottky is specified at ≤2µA - critical for maintaining drive voltage under light loads.
Can LT3681EDE#PBF operate in discontinuous conduction mode (DCM), and is it supported?
Yes, LT3681EDE#PBF supports discontinuous conduction mode (DCM) at light loads, especially when inductor value is reduced or input voltage is low. Its current-mode architecture remains stable in DCM, and Burst Mode operation inherently engages during DCM-like conditions. However, maximum output current decreases in DCM; the LT3681EDE#PBF datasheet specifies IOUT(MAX) = ILIM – ΔIL/2, where ILIM drops from 3.5A (low duty cycle) to 2.5A (duty cycle = 0.8), confirming DCM-aware design.
LT3681EDE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 14-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):
- 34V
- Voltage - Output (Min/Fixed):
- 1.265V
- Voltage - Output (Max):
- 20V
- Current - Output:
- 2A
- Frequency - Switching:
- 300kHz ~ 2.8MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-DFN (4x3)
LT3681EDE#PBF FAQ
1.How can I place an order for LT3681EDE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3681EDE#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 LT3681EDE#PBF reliable?
The price and inventory of LT3681EDE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3681EDE#PBF is usually 5 days.
3.What payment methods are accepted for LT3681EDE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3681EDE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3681EDE#PBF?
LT3681EDE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3681EDE#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 LT3681EDE#PBF?
For technical support, including LT3681EDE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3681EDE#PBF requirements.
6.How does Aetrix verify that LT3681EDE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3681EDE#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 LT3681EDE#PBF meets industry standards.
7.What is the process for return or replacement of LT3681EDE#PBF?
All LT3681EDE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3681EDE#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 LT3681EDE#PBF part is unused and in its original packaging.
Return procedure for LT3681EDE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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