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Analog Devices Inc. LT3689IUD#PBF
- Part No.:
- LT3689IUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3689IUD#PBF.pdf
- Description:
- IC REG BUCK ADJ 700MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,590
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Product details
Overview
LT3689IUD#PBF 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 features programmable 350kHz–2.2MHz switching frequency. Used in automotive ECUs and industrial power supplies requiring reliable microprocessor supervision.
For engineers reviewing the LT3689IUD#PBF datasheet, LT3689IUD#PBF pinout, LT3689IUD#PBF application, or LT3689IUD#PBF equivalent, key selection criteria include its 85µA quiescent current in Burst Mode®, ±2% FB voltage accuracy, independent CPOR/CWDT capacitor-programmable reset and watchdog timing, and QFN-16 (3mm × 3mm) package with exposed thermal pad.
Technical Context
The LT3689IUD#PBF implements constant-frequency current-mode PWM control with slope compensation, frequency foldback during overload, and internal bipolar NPN power switch rated for 1.55A typical current limit. Its oscillator is resistor-programmable (RT pin) or synchronizable (SYNC pin), supporting precise frequency setting from 350kHz to 2.2MHz.
Supervisory functions are hardware-based and independent of regulation: POR asserts RST low when VOUT drops below 90% of programmed value and holds it for tRST (set by CPOR capacitor); watchdog monitors WDI transitions and drives WDO low on timeout or window violation, with timing set by CWDT capacitor and W/T pin logic level.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; survives 60V/1s nonrepetitive transients - enables robust operation in automotive and industrial 24V systems. |
| Output Current | 700mA DC load capability - supports mid-power microcontrollers, sensors, and interface ICs without external boost. |
| Quiescent Current | 85µA at 12VIN→3.3VOUT in Burst Mode® - extends battery life in always-on systems with light-load standby. |
| Feedback Reference | 0.800V ±1% (min/max) - allows precise output setting from 0.8V to >30V using standard resistor dividers. |
| Switching Frequency | Adjustable 350kHz–2.2MHz via RT resistor or SYNC input - balances inductor size, efficiency, and EMI in space-constrained designs. |
| Reset Threshold Accuracy | RST triggers when VOUT falls ≤90% of regulated value - ensures deterministic microprocessor reset before brownout. |
| Watchdog Timing | tWDU = 18.2·CWDT (ms), tWDL = 0.588·CWDT (ms) - enables flexible fault-detection windows from sub-ms to seconds using standard ceramic capacitors. |
Pinout & Package
LT3689IUD#PBF uses a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (GND), optimized for thermal performance in high-density layouts. Pin numbering follows top-view orientation with pin 1 at bottom-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (BST) | Bootstrap supply | Drives internal NPN switch gate above VIN; requires external 10nF ceramic capacitor to SW. |
| 2 (VIN) | Main power input | Supplies internal circuitry and switch; accepts 3.6V–36V; clamped at 60V transient rating. |
| 3 (SW) | Switch node | Connects to inductor, catch diode anode, and BST capacitor; carries high di/dt switching current. |
| 4 (DA) | Diode anode monitor | Detects catch diode current; disables switching if >1.2A to protect during short-circuit faults. |
| 5 (CWDT) | Watchdog timing | Capacitor-to-GND sets watchdog upper/lower boundaries (tWDU/tWDL) with 18.2×/0.588× scaling. |
| 6 (WDO) | Watchdog output | Open-collector active-low signal; pulled weakly to VOUT; asserts on watchdog timeout or window violation. |
| 7 (RST) | Reset output | Open-collector active-low signal; held low until VOUT ≥90% and tRST delay (set by CPOR) expires. |
| 8 (WDI) | Watchdog input | Accepts microprocessor pulse train; monitored for edge timing compliance in window or timeout mode. |
| 9 (OUT) | Bias supply output | Provides bias current path to internal boost diode; reduces VIN quiescent current when VOUT >3V. |
| 10 (SYNC) | Frequency sync input | Accepts external clock ≥80ns pulse width; forces LT3689IUD#PBF to slave frequency, reducing EMI. |
| 11 (RT) | Oscillator programming | Resistor-to-GND sets switching frequency from 350kHz–2.2MHz per Linear Table 1 (e.g., 20.5kΩ = 700kHz). |
| 12 (CPOR) | Reset timing | Capacitor-to-GND sets reset timeout tRST = 2.3ms/nF (e.g., 68nF → 157ms typical). |
| 13 (EN/UVLO) | Enable & UVLO input | 1.26V threshold enables operation; resistor divider enables programmable undervoltage lockout with hysteresis. |
| 14 (FB) | Feedback input | Regulated to 0.800V; connects to resistor divider tap; determines output voltage as VOUT = 0.8V·(1+R1/R2). |
| 15 (WDE) | Watchdog enable | Logic-high (>1V) disables watchdog; WDO remains high regardless of WDI activity. |
| 16 (W/T) | Watchdog mode select | Low = window mode (detects too-close/too-far WDI edges); high = timeout mode (detects missing edges). |
Key Features
| Feature | Design Value |
|---|---|
| Low-Ripple Burst Mode® Operation | Maintains <15mVP-P output ripple at light loads while achieving 85µA IQ - eliminates audible noise and preserves efficiency in standby. |
| Independent POR and Watchdog Timing | CPOR and CWDT pins use separate external capacitors - enables simultaneous optimization of system boot reliability and runtime fault detection. |
| Robust Input Transient Protection | Withstands 60V/1s transients and includes overvoltage lockout at 38V (typ) - meets ISO 7637-2 pulse 1/2/5a requirements for automotive 12V/24V systems. |
| Programmable Undervoltage Lockout | EN/UVLO pin supports resistor-divider UVLO with user-defined threshold and hysteresis - prevents erratic startup during slow-rising battery inputs. |
| Thermally Enhanced QFN Package | 3mm × 3mm QFN with exposed GND pad (θJC = 4.2°C/W) - enables >1W power dissipation in compact PCB footprints without heatsinks. |
Applications
| Automotive Engine Control Unit (ECU) | Industrial PLC I/O Module |
|---|---|
Use Scenario: Powering 3.3V microcontroller, CAN transceiver, and analog front-end in under-hood ECU exposed to 12V battery transients and wide temperature swings. IC Role / Device Role / Timing Role: Primary 3.3V/700mA buck regulator with POR ensuring clean MCU boot after ignition, and watchdog monitoring firmware execution integrity. Use Value: Eliminates need for discrete reset supervisor and external watchdog IC; 60V transient tolerance avoids TVS diodes on VIN. |
Use Scenario: Generating stable 5V rail for digital logic and isolated communication interfaces in DIN-rail mounted programmable logic controller. IC Role / Device Role / Timing Role: Adjustable-output buck converter with fixed 5V option (LT3689-5 variant), delivering regulated power while supervising host processor health. Use Value: Reduces BOM count by integrating power conversion and dual-supervision functions in single 3mm × 3mm footprint. |
| Medical Patient Monitor | Ruggedized Handheld Terminal |
Use Scenario: Supplying 1.8V/3.3V rails to ADCs, displays, and wireless modules in battery-powered portable diagnostic equipment. IC Role / Device Role / Timing Role: High-efficiency step-down regulator operating from Li-ion (3.0–4.2V) or 24V adapter, with POR preventing corrupted sensor data during power-up. Use Value: 85µA Burst Mode® IQ extends battery runtime; programmable tRST ensures sufficient time for FPGA configuration before system release. |
Use Scenario: Power management in barcode scanner or RFID reader subjected to frequent drop-induced power interruptions. IC Role / Device Role / Timing Role: Regulator with fast POR response (<30µs tUV) and window-mode watchdog detecting firmware hangs caused by mechanical shock. Use Value: Prevents silent failure during field use; tWDL/tWDU tuning allows rejection of false triggers from brief power glitches. |
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 |
|---|---|---|---|
| LT3689EUD#PBF | Same silicon, –40°C to 125°C grade (vs. LT3689IUD#PBF's industrial temp range); identical electrical specs and pinout. | Valid for commercial/industrial environments where extended temperature qualification is not required. | Select LT3689EUD#PBF for cost-sensitive designs meeting 125°C max junction temperature; LT3689IUD#PBF adds guaranteed performance at full –40°C to 125°C range. |
| LT3689IMSE#PBF | Same functionality in 16-lead MSOP package (4.9mm × 3mm vs. QFN's 3mm × 3mm); θJA = 43°C/W (vs. 68°C/W for QFN). | Better thermal performance in low-airflow enclosures; larger footprint may conflict with ultra-compact layouts. | Choose LT3689IMSE#PBF when board-level thermal resistance dominates and MSOP soldering is preferred; LT3689IUD#PBF prioritizes miniaturization and thermal pad soldering. |
Compared with LT3689EUD#PBF, LT3689IUD#PBF provides guaranteed operation across the full industrial temperature range without derating, while versus LT3689IMSE#PBF it offers 33% smaller footprint and direct thermal pad attachment - critical for handheld and automotive modules where space and thermal mass are constrained.
Availability
LT3689IUD#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial programmable logic controllers, and medical patient monitors requiring stable component supply, long-term lifecycle support, and AEC-Q200-aligned reliability.
Supply support for LT3689IUD#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 acquired Linear Technology in 2017 and maintains its legacy of high-performance analog and power management ICs with rigorous characterization and automotive-grade validation.
The LT3689 product line was designed for demanding embedded systems requiring integrated power conversion and microprocessor supervision - targeting automotive, industrial, and medical applications where reliability, transient immunity, and small form factor are essential.
FAQ
What is the maximum input voltage the LT3689IUD#PBF can withstand?
The LT3689IUD#PBF operates continuously from 3.6V to 36V input and safely withstands nonrepetitive 60V transients for up to 1 second. Its overvoltage lockout activates at ~38V (typical), halting switching to protect internal circuitry while maintaining safe bias conditions. This makes LT3689IUD#PBF suitable for 24V automotive and industrial systems subject to load-dump events.
How do I configure the LT3689IUD#PBF for fixed 5V output?
The LT3689IUD#PBF is adjustable only; for fixed 5V output, use the pin-compatible LT3689-5 variant (e.g., LT3689IUD-5#PBF). That part integrates an internal resistor divider to set VOUT = 5.00V ±1%, eliminating external FB resistors. The LT3689IUD#PBF requires external R1/R2 to achieve 5V: R2 = 100kΩ, R1 = 525kΩ yields VOUT = 0.8V × (1 + 525k/100k) = 5.00V.
What is the minimum recommended capacitor value for CPOR on the LT3689IUD#PBF?
The LT3689IUD#PBF specifies a minimum CPOR capacitance of 1nF, yielding tRST ≈ 2.3ms. However, for robust POR timing across temperature and voltage, Linear recommends ≥10nF (e.g., 68nF for 157ms typical). Values below 1nF risk insufficient reset hold time during slow-rising VOUT or cold-temperature operation, potentially causing premature MCU release.
Can the LT3689IUD#PBF be synchronized to an external clock?
Yes, the LT3689IUD#PBF supports external synchronization via the SYNC pin. Drive it with a logic-level square wave having ≥80ns high/low pulse widths. The internal oscillator will lock to the external frequency if it exceeds the RT-set frequency by ≥20%; otherwise, the LT3689IUD#PBF operates at its programmed fSW. This feature reduces EMI in noise-sensitive systems like medical imaging or precision instrumentation.
Does the LT3689IUD#PBF require a catch diode, and what are the key selection criteria?
Yes, the LT3689IUD#PBF requires an external Schottky catch diode connected between SW and GND. Key criteria: 40V+ PIV rating (to handle 60V transients), ≤0.5V forward drop at peak inductor current, and low reverse leakage (<5µA at 125°C) to prevent efficiency loss. Diodes Inc. B140HB is validated in Linear's typical applications and matches these specs.
LT3689IUD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN 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):
- 0.8V
- 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#PBF FAQ
1.How can I place an order for LT3689IUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3689IUD#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 LT3689IUD#PBF reliable?
The price and inventory of LT3689IUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3689IUD#PBF is usually 5 days.
3.What payment methods are accepted for LT3689IUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3689IUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3689IUD#PBF?
LT3689IUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3689IUD#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 LT3689IUD#PBF?
For technical support, including LT3689IUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3689IUD#PBF requirements.
6.How does Aetrix verify that LT3689IUD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3689IUD#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 LT3689IUD#PBF meets industry standards.
7.What is the process for return or replacement of LT3689IUD#PBF?
All LT3689IUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3689IUD#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 LT3689IUD#PBF part is unused and in its original packaging.
Return procedure for LT3689IUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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