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Analog Devices Inc. LT3689EUD#TRPBF
- Part No.:
- LT3689EUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3689EUD#TRPBF.pdf
- Description:
- IC REG BUCK ADJ 700MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,999
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Product details
Overview
LT3689EUD#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 via 0.800V feedback reference, and maintains <15mVP-P output ripple in Burst Mode® at light load. It is used in automotive ECU power rails requiring fault-tolerant supervision.
For engineers reviewing the LT3689EUD#TRPBF datasheet, LT3689EUD#TRPBF pinout, LT3689EUD#TRPBF application, or LT3689EUD#TRPBF equivalent, key selection criteria include its 350kHz–2.2MHz programmable switching frequency, 85µA quiescent current at 12VIN/3.3VOUT, independent capacitor-programmable POR (tRST) and watchdog (tWDU/tWDL) timing, EN/UVLO hysteresis control, and robust 60V transient tolerance.
Technical Context
The LT3689EUD#TRPBF implements constant-frequency current-mode PWM control with slope compensation and frequency foldback during overload. Its internal bipolar NPN switch (1.55A typical current limit, 450mV VCE(SAT) at 0.8A) is driven by a bootstrap circuit (BST pin), enabling efficient operation up to 36V input. The regulator integrates dedicated analog comparators for POR (90% VFB threshold), watchdog window/timer logic, and DA-pin-based catch diode current monitoring (1.2A limit).
Supervisory functions are hardware-configured: CPOR sets reset timeout (2.3ms/nF), CWDT sets watchdog boundaries (tWDU = 18.2·CWDT, tWDL = 0.588·CWDT), W/T selects window vs. timeout mode, and WDE enables/disables the watchdog. RST and WDO are open-collector outputs with weak 1µA pull-up to VOUT, supporting direct interfacing to µP reset and interrupt inputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; survives 60V/1s nonrepetitive transients - enables use in 24V automotive and industrial systems without external TVS. |
| Output Current | 700mA maximum DC load - sufficient for powering microcontrollers, sensors, and interface ICs in compact embedded systems. |
| Quiescent Current | 85µA at 12VIN/3.3VOUT in Burst Mode - extends battery life in always-on monitoring applications. |
| Feedback Reference | 0.800V ±12mV (0.780V–0.812V) - allows precise output regulation with standard 1% resistors; supports 3.3V, 5V, or custom outputs. |
| Switching Frequency | 350kHz to 2.2MHz, resistor-programmable via RT pin - balances inductor size (e.g., 12µH @ 700kHz) against efficiency and EMI. |
| Reset Threshold Accuracy | 90% of VFB (±2%) - ensures reliable µP reset assertion when output drops below regulation, with glitch immunity. |
| Watchdog Timing | Capacitor-programmable: tWDU = 18.2·CWDT (ms), tWDL = 0.588·CWDT (ms); e.g., 10nF yields 182ms/5.9ms - enables flexible firmware watchdog window tuning. |
Pinout & Package
LT3689EUD#TRPBF is housed in a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (GND). The package provides θJA = 68°C/W and θJC = 4.2°C/W, requiring soldered GND pad for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BST | Bootstrap supply | Drives internal NPN switch gate above VIN; requires external 2.2µF ceramic capacitor to SW. |
| VIN | Main input supply | Supplies internal circuitry and power switch; rated to 60V transient, 36V continuous. |
| SW | Switch node | Connects to inductor, catch diode anode, and BST capacitor; carries high di/dt switching current. |
| DA | Catch diode anode monitor | Detects overcurrent in external Schottky diode; disables switching if current exceeds ~1.2A. |
| EN/UVLO | Enable & undervoltage lockout | 1.26V threshold with hysteresis; resistor divider enables programmable UVLO turn-on/turn-off points. |
| FB | Feedback input | Regulated to 0.800V; connects to resistor divider tap for output voltage setting. |
| RT | Frequency programming | Resistor to GND sets switching frequency from 350kHz to 2.2MHz (e.g., 20.5kΩ = 700kHz). |
| SYNC | External clock sync input | Accepts logic-level signal ≥80ns pulse width; enables deterministic EMI reduction via master clock alignment. |
| OUT | Bias supply output | Provides bias current path to internal boost diode; reduces VIN quiescent current when VOUT > 3V. |
| RST | Open-collector reset output | Asserts low when VOUT < 90% VFB; timing set by CPOR capacitor; weak 1µA pull-up to VOUT. |
| WDI | Watchdog input | Receives µP watchdog pulses; falling edges monitored for window/timer compliance. |
| W/T | Watchdog mode select | Low = window mode (detects too-close/too-far WDI edges); High = timeout mode (no edge within tWDU). |
| WDE | Watchdog enable | High (>1V) disables watchdog; WDO remains high - allows runtime watchdog deactivation. |
| WDO | Open-collector watchdog output | Asserts low on watchdog fault; timing controlled by CWDT; weak 1µA pull-up to VOUT. |
| CPOR | Reset timeout capacitor | Capacitor to GND sets reset delay: tRST = 2.3ms/nF (e.g., 68nF → 157ms). |
| CWDT | Watchdog timing capacitor | Capacitor to GND sets watchdog boundaries: tWDU = 18.2·CWDT, tWDL = 0.588·CWDT. |
Key Features
| Feature | Design Value |
|---|---|
| Low-Ripple Burst Mode® | Maintains <15mVP-P output ripple and 85µA IQ at light load - eliminates audible noise and extends battery runtime without sacrificing regulation accuracy. |
| Capacitor-Programmable Supervision | Independent CPOR and CWDT pins allow precise, layout-tolerant tuning of reset delay (2.3ms/nF) and watchdog windows (18.2/0.588 ms/nF) - no trimming resistors or firmware overhead required. |
| Robust Input Transient Protection | Withstands 60V/1s transients while maintaining latch-free operation - eliminates need for upstream TVS in 24V automotive power designs. |
| Integrated Catch Diode Current Monitoring | DA pin detects >1.2A diode current and halts switching during short-circuit - prevents thermal runaway and enables safe valley-current limiting. |
| Programmable Undervoltage Lockout | EN/UVLO pin supports resistor-divider UVLO with hysteresis - ensures clean power-up sequencing across wide input ranges (e.g., cold-crank 6V to run 16V). |
Applications
| Automotive Engine Control Unit (ECU) | Industrial PLC I/O Module |
|---|---|
|
Use Scenario: Powering 3.3V microcontroller, CAN transceiver, and sensor interface in under-hood ECU exposed to load dump (60V) and cold-crank (6V) conditions. IC Role / Device Role / Timing Role: Primary 3.3V buck regulator with POR ensuring µP reset on valid VOUT, and watchdog monitoring firmware liveness during engine runtime. Use Value: Eliminates discrete reset IC and external UVLO circuit; 60V transient tolerance avoids TVS diode; capacitor-programmed tRST (157ms) matches µP boot time. |
Use Scenario: Generating stable 5V rail for isolated digital I/O drivers and ADC references in DIN-rail mounted PLC modules operating from 24V DC bus. IC Role / Device Role / Timing Role: Adjustable-output buck converter with fixed 5V option (LT3689-5 variant), using SYNC to align switching with system clock and reduce conducted EMI. Use Value: 350kHz–2.2MHz frequency range allows optimization for 10µH inductor size vs. efficiency; EN/UVLO hysteresis prevents oscillation during brownout. |
| Medical Patient Monitor Sensor Hub | Ruggedized IoT Gateway |
|
Use Scenario: Powering low-noise analog front-end (AFE) and BLE SoC in portable patient monitor where battery life and EMI must be tightly controlled. IC Role / Device Role / Timing Role: Low-IQ buck regulator in Burst Mode® delivering 3.3V with <15mV ripple; RST tied to AFE reset; WDI fed by BLE SoC watchdog timer. Use Value: 85µA IQ extends coin-cell or LiPo battery life; open-collector RST/WDO simplify level-shifting to mixed-voltage subsystems. |
Use Scenario: Power management for outdoor cellular/IoT gateway with wide-temp operation (–40°C to +125°C) and requirement for firmware crash recovery. IC Role / Device Role / Timing Role: Supervisory buck regulator providing 3.3V to host processor; watchdog configured in window mode to detect both stuck and runaway firmware loops. Use Value: –40°C to +125°C guaranteed operation meets industrial temp grade; W/T pin allows field-upgradeable watchdog behavior without BOM change. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator with supervisory functions applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3689IMSE#TRPBF | Same silicon, MSOP-16 package (4.0mm × 3.0mm); θJA = 43°C/W vs. QFN's 68°C/W; exposed pad is Pin 17 (GND). | Preferred for lower thermal resistance in space-constrained but thermally managed layouts; larger footprint than QFN. | Select when board layout allows MSOP and thermal performance is prioritized over size. |
| LT3689EUD-5#TRPBF | Fixed 5V output version; identical supervision features, package, and temperature range; FB pin repurposed for phase-lead compensation. | Eliminates feedback resistors for 5V designs; not adjustable - unsuitable for 3.3V or custom outputs. | Choose for cost-sensitive 5V-only applications where design simplicity outweighs output flexibility. |
Compared with LT3689IMSE#TRPBF, the LT3689EUD#TRPBF offers smaller PCB area and higher power density but requires more careful thermal pad soldering; compared with LT3689EUD-5#TRPBF, it provides full output adjustability at the cost of two external resistors, making it suitable for multi-voltage systems.
Availability
LT3689EUD#TRPBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLCs, medical sensor hubs, and ruggedized IoT gateways requiring stable component supply, extended temperature operation, and integrated power supervision.
Supply support for LT3689EUD#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, Inc. (ADI) acquired Linear Technology in 2017 and continues its legacy of high-performance analog, power management, and precision signal conditioning ICs.
The LT3689 product line was designed for automotive and industrial applications demanding robust DC/DC conversion with integrated microprocessor supervision - combining high-voltage capability, low quiescent current, and hardware-configurable reset/watchdog timing.
FAQ
What is the maximum input voltage the LT3689EUD#TRPBF can withstand?
The LT3689EUD#TRPBF operates continuously from 3.6V to 36V input and is rated to withstand nonrepetitive 60V transients for up to 1 second without damage or latch-up. During transients above 38V (typical), switching is disabled to protect downstream circuitry while maintaining safe bias operation - a key feature for automotive load-dump immunity.
How is the output voltage set on the LT3689EUD#TRPBF?
The LT3689EUD#TRPBF uses an adjustable feedback architecture with a precise 0.800V reference at the FB pin. Output voltage is set by a resistor divider: VOUT = 0.800V × (1 + R1/R2). For example, R1 = 316kΩ and R2 = 20.5kΩ yields 3.3V. The LT3689EUD#TRPBF does not have a fixed-output variant; the -5 suffix (e.g., LT3689EUD-5#TRPBF) denotes a separate part with internal 5V feedback divider.
Can the LT3689EUD#TRPBF's watchdog timer be disabled in-system?
Yes. The LT3689EUD#TRPBF watchdog timer is disabled when the WDE pin voltage exceeds 1V, causing WDO to remain high regardless of WDI activity. This allows runtime deactivation via a GPIO or logic signal - useful during firmware updates or debug modes. The LT3689EUD#TRPBF retains all other functions (regulation, POR) during watchdog disable.
What thermal considerations apply to the LT3689EUD#TRPBF's QFN package?
The LT3689EUD#TRPBF uses a 3mm × 3mm QFN with exposed thermal pad (Pin 17, GND). To achieve θJA = 68°C/W, the pad must be soldered to a minimum 1cm² copper pour connected to internal/external GND planes via ≥4 thermal vias. Inadequate pad soldering causes junction temperature rise and potential thermal shutdown - verified in the LT3689EUD#TRPBF's absolute max rating table (TJ ≤ 125°C for E-grade).
Does the LT3689EUD#TRPBF support synchronization to an external clock?
Yes. The LT3689EUD#TRPBF's SYNC pin accepts logic-level input signals (≥80ns pulse width) to synchronize switching frequency. When enabled, the internal oscillator locks to the external clock, reducing EMI peak amplitude and enabling deterministic noise placement - critical for EMC-compliant designs in automotive and industrial systems using the LT3689EUD#TRPBF.
LT3689EUD#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)
LT3689EUD#TRPBF FAQ
1.How can I place an order for LT3689EUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3689EUD#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 LT3689EUD#TRPBF reliable?
The price and inventory of LT3689EUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3689EUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3689EUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3689EUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3689EUD#TRPBF?
LT3689EUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3689EUD#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 LT3689EUD#TRPBF?
For technical support, including LT3689EUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3689EUD#TRPBF requirements.
6.How does Aetrix verify that LT3689EUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3689EUD#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 LT3689EUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3689EUD#TRPBF?
All LT3689EUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3689EUD#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 LT3689EUD#TRPBF part is unused and in its original packaging.
Return procedure for LT3689EUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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