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Analog Devices Inc. LT3689IUD#TRPBF
- Part No.:
- LT3689IUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3689IUD#TRPBF.pdf
- Description:
- IC REG BUCK ADJ 700MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,827
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Product details
Overview
LT3689IUD#TRPBF from Analog Devices (formerly Linear Technology) is a 700mA monolithic step-down switching regulator with integrated power-on reset (POR) and pin-selectable watchdog timer (window or timeout mode). It operates from 3.6V to 36V input, withstands 60V transients, delivers adjustable output voltage with 0.800V feedback reference, and achieves <15mVP-P output ripple in Burst Mode® at 85µA quiescent current. It is used in automotive ECU power rails requiring reliable microprocessor supervision.
For engineers reviewing the LT3689IUD#TRPBF datasheet, LT3689IUD#TRPBF pinout, LT3689IUD#TRPBF application, or LT3689IUD#TRPBF equivalent, key selection criteria include its programmable POR delay (via CPOR), independently adjustable watchdog boundaries (via CWDT), 350kHz–2.2MHz frequency setting (RT resistor), EN/UVLO hysteresis programming, and QFN-16 (3mm × 3mm) thermal performance with exposed pad grounding.
Technical Context
The LT3689IUD#TRPBF implements constant-frequency current-mode PWM control with slope compensation and frequency foldback during overload. Its internal bipolar NPN switch supports up to 700mA load with 450mV VCE(SAT) at 0.8A, while the BST boost circuit enables full saturation via external capacitor. The regulator integrates dedicated analog comparators for POR (90% VFB threshold), RST timing (CPOR-programmed), and dual-mode watchdog (W/T pin selectable).
Supervisory functions are hardware-decoupled: RST asserts low when VOUT drops below 90% of regulation and remains asserted for tRST; WDO pulls low on watchdog fault (timeout or window violation), with independent tWDU/tWDL set by CWDT capacitance. EN/UVLO provides programmable undervoltage lockout with 1.26V threshold and 2.8–4.8µA hysteresis current, enabling precise input rail sequencing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; withstands 60V nonrepetitive transients - enables direct connection to automotive battery rails with transient immunity. |
| Output Current | 700mA maximum - sufficient for powering microcontrollers, sensors, and interface ICs in embedded systems. |
| Feedback Reference | 0.800V ±12mV - allows precise output programming (e.g., 3.3V with 316k/20.5k divider) and stable regulation across temperature. |
| Quiescent Current | 85µA typical at 12VIN→3.3VOUT in Burst Mode® - extends battery life in always-on monitoring applications. |
| Switching Frequency | 350kHz to 2.2MHz (RT-programmable) - balances inductor size, efficiency, and EMI in space-constrained designs. |
| Reset Threshold Accuracy | ±2% of VFB (88–92%) - ensures deterministic POR assertion without false triggering during brownout recovery. |
| Watchdog Timing | tWDU = 18.2·CWDT, tWDL = 0.588·CWDT (ms, CWDT in nF) - enables flexible firmware watchdog windowing with external capacitor tuning. |
Pinout & Package
LT3689IUD#TRPBF uses a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (GND). The package supports θJA = 68°C/W and requires soldering the exposed pad to PCB ground for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BST | Boost supply for internal NPN switch driver | Connects to external bootstrap capacitor; must be ≥1.8V above SW to ensure full switch saturation and low conduction loss. |
| VIN | Main power input (3.6–36V) | Supplies internal bias and switch; withstands 60V transients; local ceramic bypassing required. |
| SW | Switch node | Drives external inductor and catch diode; high dV/dt node requiring careful layout and ground plane isolation. |
| DA | Catch diode anode monitor | Current-sense input disabling switching if >1.2A - protects against short-circuit overcurrent without external sensing. |
| EN/UVLO | Enable and programmable undervoltage lockout | Pull below 0.3V for shutdown; 1.26V threshold with hysteresis enables precise input rail sequencing. |
| FB | Feedback input | Regulated to 0.800V; connects to resistor divider tap - determines output voltage and enables remote sensing. |
| RT | Oscillator frequency set | Resistor-to-GND sets fSW from 350kHz to 2.2MHz - trade-off between efficiency, component size, and minimum on-time limits. |
| SYNC | External clock synchronization input | Accepts logic-level signal ≥80ns pulse width; RT must be set ≥20% below sync frequency to avoid instability. |
| WDI | Watchdog input | Receives microcontroller pulses; falling edges monitored for timing compliance in window or timeout mode. |
| RST | Open-collector reset output | Active-low; weak pull-up to VOUT; asserts when VOUT < 90% VREF, then releases after CPOR-programmed delay. |
| WDO | Open-collector watchdog output | Active-low; weak pull-up to VOUT; pulls low on watchdog fault and remains low for tRST duration. |
| CWDT | Watchdog timing capacitor | Grounded capacitor sets tWDU and tWDL; 1nF → 18.2ms / 0.588ms; enables firmware-independent safety timing. |
| CPOR | Reset delay capacitor | Grounded capacitor sets tRST = 2.3ms/nF; 68nF → 157ms - ensures stable power-up before processor release. |
| WDE | Watchdog enable | Logic-high (>1V) disables watchdog; allows safe bootloader or debug modes without spurious resets. |
| W/T | Watchdog mode select | Low = window mode (detects too-close or too-far WDI edges); high = timeout mode (detects missing edge). |
Key Features
| Feature | Design Value |
|---|---|
| Low-ripple Burst Mode® operation | Maintains <15mVP-P output ripple at light loads while drawing only 85µA IQ, eliminating need for external LDO post-regulation in battery-powered systems. |
| Independent POR and watchdog timing | CPOR and CWDT pins allow separate, capacitor-programmed delays - enables system-specific reset hold times and watchdog windows without firmware dependency. |
| Pin-selectable watchdog modes | W/T pin configures window or timeout behavior - supports both legacy polling-based and modern event-driven microcontroller supervision strategies. |
| Robust input transient protection | Withstands 60V transients and disables switching above 38V (typical) - eliminates need for external TVS or overvoltage clamping in 24V/36V industrial and automotive supplies. |
| Programmable EN/UVLO with hysteresis | Resistor divider on EN/UVLO sets turn-on threshold and hysteresis - enables clean power sequencing across multiple rails with controlled startup order. |
Applications
| Automotive Engine Control Unit (ECU) | Industrial PLC I/O Module |
|---|---|
Use Scenario: Powers 3.3V microcontroller and CAN transceiver in under-hood ECU exposed to 12V battery with load-dump transients. IC Role / Device Role / Timing Role: Primary 3.3V buck regulator with integrated POR and watchdog - replaces discrete supervisor + regulator combo. Use Value: Eliminates external reset IC and reduces BOM count; 60V transient tolerance avoids external TVS; CPOR-set 157ms reset hold ensures MCU boot stability after cold crank. | Use Scenario: Supplies 5V logic and isolated sensor interface in DIN-rail mounted PLC with wide input range (18–32V DC). IC Role / Device Role / Timing Role: Adjustable-output buck regulator with programmable UVLO - sequences power to FPGA and ADC subsystems. Use Value: RT-programmable 700kHz switching enables compact 4.7µH inductor; EN/UVLO hysteresis prevents oscillation during brownout; DA pin current limiting protects against field-wiring shorts. |
| Medical Patient Monitor Power Rail | Railway Signaling Controller |
Use Scenario: Generates 1.8V core voltage for ARM Cortex-M7 processor in portable diagnostic device with Li-ion backup. IC Role / Device Role / Timing Role: High-efficiency buck converter with Burst Mode® - manages standby current and supervises processor health. Use Value: 85µA IQ extends battery runtime; WDO ties to processor's watchdog feed pin; window-mode W/T detects stuck firmware loops without false triggers from noise. | Use Scenario: Powers safety-critical microcontroller in track-side signaling unit operating from 72V DC traction supply with high dv/dt transients. IC Role / Device Role / Timing Role: Input-transient-hardened buck regulator with fail-safe reset - meets EN 50121-3-2 EMC and safety requirements. Use Value: 36V max continuous input + 60V transient rating meets railway surge standards; open-collector RST/WDO enable external pull-ups to higher-voltage logic rails; GND-exposed QFN aids thermal management in sealed enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator with integrated supervision applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3637EMSE#TRPBF | 40V input, 500mA output, no integrated watchdog; includes precision enable threshold and soft-start. | Lacks watchdog timer and POR delay programming - requires external supervisor IC for full microprocessor supervision. | Choose when lower output current suffices and external watchdog integration is acceptable to reduce cost. |
| MAX20404ATPA/VY+ | 36V input, 800mA output, integrated watchdog and POR, but fixed 3.3V/5V outputs only; no adjustable FB reference. | Fixed-output variants only - cannot support custom voltages like 1.8V or 2.5V without external feedback scaling. | Choose when standard 3.3V/5V rails are sufficient and footprint compatibility with MSOP-16 is preferred over QFN. |
Compared with LTC3637EMSE#TRPBF and MAX20404ATPA/VY+, the LT3689IUD#TRPBF uniquely combines adjustable output voltage (via 0.800V FB), capacitor-programmable POR/watchdog timing, and 60V transient tolerance in a thermally optimized QFN package - making it optimal for custom-voltage, safety-critical embedded power rails.
Availability
LT3689IUD#TRPBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLC modules, medical patient monitors, and railway signaling controllers requiring stable component supply with guaranteed long-term availability and traceable sourcing.
Supply support for LT3689IUD#TRPBF 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 product support, documentation, and manufacturing continuity for the LT® series.
The LT3689IUD#TRPBF belongs to Linear's high-voltage monolithic regulator family designed for harsh-environment embedded systems requiring integrated power conversion and microprocessor supervision in a single IC.
FAQ
What is the maximum input voltage the LT3689IUD#TRPBF can safely withstand?
The LT3689IUD#TRPBF withstands nonrepetitive 60V transients on the VIN pin for up to 1 second, while continuous operation is rated from 3.6V to 36V. When VIN exceeds 38V (typical), the part disables switching to protect downstream circuitry, allowing the output to fall out of regulation while maintaining device integrity. This makes the LT3689IUD#TRPBF suitable for automotive and industrial applications with unregulated input sources.
How is the output voltage programmed on the LT3689IUD#TRPBF?
The LT3689IUD#TRPBF uses an adjustable feedback architecture with a precise 0.800V reference at the FB pin. Output voltage is set using a resistor divider between OUT and GND, with the tap connected to FB. For example, to achieve 3.3V output, use R1 = 316kΩ and R2 = 20.5kΩ (3.3V = 0.800V × (1 + R1/R2)). The LT3689IUD#TRPBF does not have a fixed-output variant - all configurations require external resistors, ensuring design flexibility across voltage rails.
Can the LT3689IUD#TRPBF's watchdog timer operate in both window and timeout modes?
Yes, the LT3689IUD#TRPBF's watchdog timer supports both modes via the W/T pin: pulling W/T low selects window mode (detects WDI falling edges too close together or too far apart), while pulling W/T high selects timeout mode (detects missing WDI transitions). Both modes use the same CWDT capacitor to set tWDU and tWDL, and WDE can disable the watchdog entirely. This dual-mode capability makes the LT3689IUD#TRPBF adaptable to diverse firmware architectures without changing hardware.
What is the purpose of the DA pin on the LT3689IUD#TRPBF?
The DA pin on the LT3689IUD#TRPBF monitors current through the external catch Schottky diode. If DA pin current exceeds 1.2A (typical), the regulator disables switching until current falls below the threshold - providing automatic valley-current limiting during output short-circuits or overloads. This eliminates the need for external current-sense resistors or protection ICs, simplifying design and improving reliability in fault-prone environments where the LT3689IUD#TRPBF is deployed.
How does the LT3689IUD#TRPBF reduce power consumption in standby mode?
The LT3689IUD#TRPBF reduces standby power via three mechanisms: (1) Burst Mode® operation cuts input quiescent current to 85µA at light loads while maintaining <15mVP-P ripple; (2) shutdown via EN/UVLO lowers VIN current to <1µA; and (3) bias current shifts from VIN to OUT when VOUT > 3V, improving light-load efficiency. These features make the LT3689IUD#TRPBF ideal for always-on systems such as telematics gateways and smart sensors where ultra-low IQ is critical.
LT3689IUD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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):
- 0.8V
- Voltage - Output (Max):
- 36V
- Current - Output:
- 700mA
- Frequency - Switching:
- 500kHz ~ 2MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LT3689IUD#TRPBF FAQ
1.How can I place an order for LT3689IUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3689IUD#TRPBF 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 LT3689IUD#TRPBF reliable?
The price and inventory of LT3689IUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3689IUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3689IUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3689IUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3689IUD#TRPBF?
LT3689IUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3689IUD#TRPBF 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 LT3689IUD#TRPBF?
For technical support, including LT3689IUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3689IUD#TRPBF requirements.
6.How does Aetrix verify that LT3689IUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3689IUD#TRPBF 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 LT3689IUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3689IUD#TRPBF?
All LT3689IUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3689IUD#TRPBF, 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 LT3689IUD#TRPBF part is unused and in its original packaging.
Return procedure for LT3689IUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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