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Analog Devices Inc. LT3689EUD#PBF
- Part No.:
- LT3689EUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3689EUD#PBF.pdf
- Description:
- IC REG BUCK ADJ 700MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,719
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Product details
Overview
LT3689EUD#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 maintains <15mVP-P output ripple in Burst Mode® at light load. It is used in automotive ECUs and industrial power supplies requiring robust supervision and high-voltage tolerance.
For engineers reviewing the LT3689EUD#PBF datasheet, LT3689EUD#PBF pinout, LT3689EUD#PBF application, or LT3689EUD#PBF 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 QFN-16 (3mm × 3mm) thermal performance (θJA = 68°C/W).
Technical Context
The LT3689EUD#PBF 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 trip).
Supervisory functions are hardware-configurable: RST asserts low when VOUT drops below 90% of regulation and remains asserted for tRST (set by CPOR capacitor); WDO asserts low on watchdog fault and stays low for tRST; W/T pin selects between timeout-only or dual-boundary window mode; WDE enables/disables the watchdog independently. All timing parameters are capacitor-programmable with guaranteed accuracy over –40°C to 125°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; survives 60V/1s nonrepetitive transients - enables direct battery-input designs in 24V automotive and industrial systems. |
| Output Current | 700mA DC load capability - supports mid-power microcontrollers, sensors, and interface ICs without external pass devices. |
| Feedback Reference | 0.790V to 0.812V (±1.25% max) - ensures tight output regulation across temperature and line, critical for precision analog subsystems. |
| 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) - allows optimization of inductor size (e.g., 12µH @ 700kHz) vs. efficiency (peak >90% at 500mA). |
| Reset Threshold Accuracy | ±2% (88%–92% of VFB) - prevents false resets during output voltage droop caused by transient load steps. |
| Watchdog Timing Range | tWDU = 17–21ms, tWDL = 610–785µs (CWDT = 1nF) - provides configurable fault-detection windows for diverse MCU firmware cycles. |
Pinout & Package
LT3689EUD#PBF is housed in a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (GND). The package offers 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 10nF ceramic capacitor to SW for full saturation and low VCE(SAT). |
| VIN | Main power input | Supplies internal bias and switch; rated 60V absolute max; includes OVLO (38V typ.) to disable switching during transients. |
| SW | Switch node | Connects to inductor, catch diode cathode, and BST capacitor; carries high di/dt; requires tight layout to minimize EMI. |
| DA | Catch diode anode monitor | Detects reverse recovery current; disables switching if diode current exceeds 1.2A - protects against short-circuit induced valley-current runaway. |
| EN/UVLO | Enable & undervoltage lockout | 1.26V threshold with 3.8µA hysteresis; resistor divider enables programmable UVLO with precise turn-on/off points. |
| FB | Feedback input | Regulated to 0.800V ±1.25%; connects to resistor divider; supports phase-lead compensation for transient response tuning. |
| RT | Frequency set | Resistor-to-GND sets fSW from 350kHz to 2.2MHz; enables synchronization via SYNC pin with ≥20% margin. |
| SYNC | External clock input | Accepts logic-level signal (≥80ns pulse width); forces LT3689EUD#PBF to slave to external clock, reducing EMI in multi-rail systems. |
| OUT | Bias supply output | Provides bias current path when VOUT > 3V; reduces VIN quiescent current and enables boost diode charging. |
| CPOR | POR delay capacitor | 2.3ms/nF time constant sets reset assertion duration (e.g., 68nF → 157ms); guarantees clean MCU boot after power stabilization. |
| CWDT | Watchdog timing capacitor | 18.2ms/nF (tWDU) and 0.588ms/nF (tWDL) scaling - enables precise match to MCU watchdog service intervals. |
| RST | Open-drain reset output | Active-low, weak pull-up to VOUT; asserts when VOUT < 90% VREF and holds for tRST; compatible with standard µP reset inputs. |
| WDO | Open-drain watchdog output | Active-low, weak pull-up to VOUT; asserts on watchdog fault (timeout or window violation) and holds for tRST. |
| WDI | Watchdog input | Accepts falling-edge-triggered pulses from MCU; glitch-immune design prevents spurious timeouts during noise events. |
| W/T | Watchdog mode select | Logic-high = timeout mode (single-period check); logic-low = window mode (dual-boundary edge timing) - selectable per system safety requirements. |
Key Features
| Feature | Design Value |
|---|---|
| Low-Ripple Burst Mode® | Maintains <15mVP-P output ripple at light load while drawing only 85µA from VIN - eliminates need for post-regulation LDOs in noise-sensitive analog chains. |
| Capacitor-Programmable Supervision | Independent CPOR and CWDT pins enable precise, drift-free POR delay (157ms typical) and watchdog boundaries (182ms/5.9ms typical) - replaces discrete RC timers and improves long-term reliability. |
| Robust Input Protection | Integrated 60V transient tolerance + 38V OVLO + programmable EN/UVLO with hysteresis - eliminates need for external TVS or pre-regulator in harsh environments. |
| Thermal-Enhanced QFN Package | 3mm × 3mm exposed-pad QFN delivers θJC = 4.2°C/W - supports 700mA continuous output in compact layouts without heatsinks. |
| Current-Limit Foldback & DA Monitoring | Reduces switch frequency under overload and disables switching if DA pin current exceeds 1.2A - prevents thermal runaway during sustained short-circuit conditions. |
Applications
| Automotive Engine Control Unit (ECU) | Industrial Programmable Logic Controller (PLC) |
|---|---|
Use Scenario: Powering 3.3V microcontroller, CAN transceiver, and sensor interface in engine bay with 12V/24V battery input and load-dump transients. IC Role / Device Role / Timing Role: Primary 700mA step-down regulator with integrated POR and watchdog; CPOR ensures MCU reset until stable 3.3V rail; WDO monitors firmware execution. Use Value: Eliminates discrete reset IC and external watchdog, reduces BOM count by 2 components, and sustains operation through 60V/100ms load-dump events. |
Use Scenario: Generating 5V supply for I/O modules and communication processors in factory-floor PLC backplanes exposed to 24VDC brownouts and EFT noise. IC Role / Device Role / Timing Role: Adjustable-output buck converter with programmable UVLO (via EN/UVLO divider) and window-mode watchdog (W/T = LOW) for deterministic fault detection. Use Value: UVLO hysteresis prevents chattering during brownouts; window-mode watchdog catches both stuck and runaway firmware - meets IEC 61000-4-4 immunity requirements. |
| Medical Patient Monitor Power Rail | Ruggedized IoT Edge Gateway |
Use Scenario: Providing isolated 3.3V supply to ADC front-end and wireless SoC in portable diagnostic equipment powered by Li-ion battery packs. IC Role / Device Role / Timing Role: High-efficiency buck regulator operating in Burst Mode® at standby; RST ensures clean boot after battery insertion; tRST calibrated to MCU wake-up latency. Use Value: 85µA quiescent current extends battery runtime; low-noise regulation avoids ADC quantization errors; POR accuracy prevents false alarms during low-battery transitions. |
Use Scenario: Powering LTE modem, GPS receiver, and environmental sensors in outdoor cellular gateway subjected to wide temperature (-40°C to +85°C) and voltage (9–36V) ranges. IC Role / Device Role / Timing Role: Wide-input buck regulator with -40°C to 125°C qualified operation; SYNC pin enables EMI reduction by locking to system clock; CWDT tuned to modem heartbeat interval. Use Value: Guaranteed functionality across full industrial temp range; synchronized switching minimizes conducted emissions in RF-sensitive bands; watchdog integration simplifies firmware validation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar step-down regulator with supervision applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3631EMSE#PBF | 40V input, 500mA output, no integrated watchdog; uses external RC for POR; 12-lead MSOP package. | Lacks hardware watchdog - requires MCU firmware or external timer IC for supervision; lower current rating limits use in higher-power nodes. | Select when watchdog is unnecessary and board space permits larger MSOP; verify external POR timing matches system requirements. |
| MAX20004AATP+T | 42V input, 600mA output, integrated watchdog and POR, but fixed 3.3V/5V outputs only; 20-pin TQFN. | Fixed-output variants only - no adjustable VOUT via FB divider; higher pin count increases layout complexity. | Select for drop-in replacement where fixed 5V is acceptable; confirm tRST/tWDU programmability via external caps is retained. |
Compared with LTC3631EMSE#PBF and MAX20004AATP+T, the LT3689EUD#PBF uniquely combines adjustable output voltage, capacitor-programmable POR/watchdog timing, and 700mA capability in a thermally optimized 3mm × 3mm QFN - making it optimal for space-constrained, safety-critical embedded systems requiring flexible supervision.
Availability
LT3689EUD#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial programmable logic controllers, and medical patient monitor power rails requiring stable component supply across extended temperature and voltage ranges.
Supply support for LT3689EUD#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. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors.
The LT3689 product line was designed specifically for automotive and industrial power management applications demanding integrated supervision, high input voltage tolerance, and robust fault protection - targeting systems where reliability and functional safety are paramount.
FAQ
What is the maximum input voltage the LT3689EUD#PBF can withstand without damage?
The LT3689EUD#PBF has an absolute maximum VIN rating of 60V for nonrepetitive 1-second transients. It operates continuously from 3.6V to 36V, and incorporates overvoltage lockout that disables switching when VIN exceeds ~38V (typical), allowing safe clamping during load-dump events. This makes the LT3689EUD#PBF suitable for 24V automotive systems with ISO 7637-2 compliance requirements.
How is the power-on reset timeout period set for the LT3689EUD#PBF?
The LT3689EUD#PBF uses an external capacitor on the CPOR pin to set the reset timeout period, with a scaling factor of 2.3ms per nanofarad. For example, a 68nF capacitor yields a tRST of approximately 157ms. This capacitor must be placed close to the CPOR pin and GND, and the timing is guaranteed over the full –40°C to 125°C junction temperature range specified for the LT3689EUD#PBF.
Can the LT3689EUD#PBF be synchronized to an external clock, and what are the requirements?
Yes, the LT3689EUD#PBF supports external synchronization via the SYNC pin. The external clock must have positive and negative pulse widths of at least 80ns, and the LT3689EUD#PBF's RT-resistor must be selected so its free-running frequency is at least 20% lower than the lowest expected synchronization frequency to ensure reliable locking and avoid subharmonic behavior.
What is the function of the DA pin on the LT3689EUD#PBF, and how does it improve system reliability?
The DA pin on the LT3689EUD#PBF monitors the anode of the external catch Schottky diode. If diode current exceeds 1.2A (typical), the LT3689EUD#PBF disables switching until current falls below threshold. This prevents inductor valley-current runaway during output short-circuits, avoiding thermal failure and enabling safe auto-recovery - a critical feature for unattended industrial equipment powered by the LT3689EUD#PBF.
Does the LT3689EUD#PBF support both timeout and window modes for its watchdog timer?
Yes, the LT3689EUD#PBF supports both modes via the W/T pin: logic high configures timeout mode (WDO asserts if no WDI transition occurs within tWDU), while logic low enables window mode (WDO asserts if successive WDI falling edges occur either too close together or too far apart). This dual-mode capability allows the LT3689EUD#PBF to meet diverse functional safety requirements across automotive ASIL and industrial SIL applications.
LT3689EUD#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)
LT3689EUD#PBF FAQ
1.How can I place an order for LT3689EUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3689EUD#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 LT3689EUD#PBF reliable?
The price and inventory of LT3689EUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3689EUD#PBF is usually 5 days.
3.What payment methods are accepted for LT3689EUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3689EUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3689EUD#PBF?
LT3689EUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3689EUD#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 LT3689EUD#PBF?
For technical support, including LT3689EUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3689EUD#PBF requirements.
6.How does Aetrix verify that LT3689EUD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3689EUD#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 LT3689EUD#PBF meets industry standards.
7.What is the process for return or replacement of LT3689EUD#PBF?
All LT3689EUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3689EUD#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 LT3689EUD#PBF part is unused and in its original packaging.
Return procedure for LT3689EUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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