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Analog Devices Inc. LT3689EMSE#PBF
- Part No.:
- LT3689EMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3689EMSE#PBF.pdf
- Description:
- IC REG BUCK ADJ 700MA 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,364
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Product details
Overview
LT3689EMSE#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 requiring robust supervision and compact 36V-input power conversion.
For engineers reviewing the LT3689EMSE#PBF datasheet, LT3689EMSE#PBF pinout, LT3689EMSE#PBF application, or LT3689EMSE#PBF equivalent, key selection considerations include its 16-pin MSOP package with exposed pad, programmable POR and watchdog timing via external capacitors (CPOR/CWDT), 350kHz–2.2MHz adjustable switching frequency, 85µA quiescent current at 12VIN, and fault protections including overvoltage lockout, thermal shutdown, and DA-pin current limiting.
Technical Context
The LT3689EMSE#PBF implements constant-frequency current-mode control with slope compensation and frequency foldback during overload. Its internal bipolar NPN switch supports up to 700mA continuous output, with BST-driven gate drive enabling efficient saturation. The regulator integrates two independent supervisory functions: a POR comparator monitoring VOUT against 90% of regulation threshold and a glitch-immune watchdog with user-configurable window or timeout behavior.
Supervision timing is capacitor-programmed: CPOR sets reset timeout (2.3ms/nF), CWDT sets watchdog upper (tWDU = 18.2 × CWDT ms) and lower (tWDL = 0.588 × CWDT ms) boundaries. EN/UVLO provides programmable undervoltage lockout with hysteresis, while SYNC allows external clock synchronization with ≥20% margin below selected fSW.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.6V to 36V continuous; withstands nonrepetitive 60V transients - enables direct connection to 24V/36V industrial or automotive rails without pre-regulation. |
| Output Current | 700mA continuous - sufficient for powering microcontrollers, sensors, and interface ICs in embedded systems. |
| Feedback Reference | 0.800V ±12mV - allows precise output setting with standard resistor dividers; supports both adjustable and fixed 5V (LT3689-5) variants. |
| Quiescent Current | 85µA at 12VIN → 3.3VOUT in Burst Mode® - extends battery life in always-on applications such as telematics or remote sensors. |
| Switching Frequency | 350kHz to 2.2MHz, resistor-programmable via RT pin - permits optimization of inductor size (e.g., 12µH at 700kHz) versus efficiency and EMI. |
| Reset Threshold Accuracy | 90% of VFB (±2%) - ensures reliable µP reset assertion when output drops below regulation, with immunity to noise-induced false triggers. |
| Watchdog Modes | Pin-selectable window or timeout mode via W/T pin - supports safety-critical firmware validation where either periodic activity or bounded timing windows are required. |
Pinout & Package
LT3689EMSE#PBF is housed in a 16-lead plastic MSOP package with exposed thermal pad (pin 17, GND). The exposed pad must be soldered to PCB ground for thermal and electrical integrity (θJA = 43°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (WDO) | Watchdog output | Open-collector active-low signal indicating watchdog timeout or window violation; weak pull-up to VOUT. |
| 2 (CWDT) | Watchdog timing capacitor | Connects to GND to set tWDU and tWDL; timing accuracy depends on capacitor tolerance and temperature stability. |
| 3 (CPOR) | Reset delay capacitor | Connects to GND to set RST assertion duration (2.3ms/nF); determines minimum system boot stabilization time. |
| 4 (RT) | Oscillator frequency set | Resistor-to-GND sets fSW from 350kHz to 2.2MHz; higher values yield lower frequencies and better high-VIN operation. |
| 5 (SYNC) | External clock input | Accepts logic-level sync signal; requires ≥80ns pulse width; fSW must be set ≥20% below lowest sync frequency. |
| 6 (OUT) | Bias supply path | Provides bias current path to internal boost diode; reduces VIN quiescent current when VOUT > 3V. |
| 7 (BST) | Bootstrap drive | Drives internal NPN switch gate above SW; requires external 0.1µF ceramic capacitor to SW. |
| 8 (VIN) | Main power input | Supplies internal circuitry and switch; rated to 60V transient; UVLO and OVLO protection active here. |
| 9 (RST) | Power-on reset output | Open-collector active-low POR signal; asserts until VOUT exceeds 90% of target and CPOR timeout expires. |
| 10 (WDI) | Watchdog input | Receives µP-generated pulses; falling edges monitored for timing compliance in window or timeout mode. |
| 11 (W/T) | Watchdog mode select | Low = window mode (detects too-close/too-far WDI edges); High = timeout mode (detects missing transitions). |
| 12 (WDE) | Watchdog enable | High (>1V) disables watchdog; WDO remains high; allows runtime deactivation for debug or safe modes. |
| 13 (FB) | Feedback input | Regulated to 0.800V; connects to resistor divider tap; 800mV reference enables accurate output programming. |
| 14 (EN/UVLO) | Enable & undervoltage lockout | 1.26V threshold with hysteresis; pulling below 0.3V shuts down regulator; resistor divider enables custom UVLO point. |
| 15 (DA) | Catch diode anode sense | Monitors external Schottky diode current; disables switching if >1.2A (typical), protecting against short-circuit overcurrent. |
| 16 (SW) | Switch node | Connects to inductor, catch diode cathode, and BST capacitor; carries high dI/dt switching current; requires tight layout. |
Key Features
| Feature | Design Value |
|---|---|
| Burst Mode® operation | Maintains <15mVP-P output ripple and 85µA IQ at light load - eliminates audible noise and extends battery runtime without sacrificing regulation. |
| Capacitor-programmable supervision | Independent CPOR and CWDT pins allow precise, board-level tuning of reset delay and watchdog boundaries - no firmware or external logic needed. |
| Robust input protection | Withstands 60V transients and includes overvoltage lockout (38V typ.) - eliminates need for external TVS or pre-regulator in harsh environments. |
| Thermal and fault protection | Includes thermal shutdown, current limit foldback, and DA-pin valley-current limiting - prevents damage during overload, short-circuit, or high-temp operation. |
| Flexible frequency control | RT-resistor programming and SYNC input support both standalone operation and synchronized multi-rail systems - reduces beat-frequency EMI in dense layouts. |
Applications
| Automotive Engine Control Unit (ECU) | Industrial PLC Power Supply |
|---|---|
Use Scenario: Powers MCU, CAN transceiver, and analog front-end from 12V/24V battery rail with cold-crank and load-dump resilience. IC Role / Device Role / Timing Role: Primary 3.3V/5V buck converter with POR ensuring clean µP boot after ignition, and watchdog validating firmware execution. Use Value: Eliminates discrete reset IC and external supervision logic; 60V transient tolerance avoids external TVS; MSOP package fits space-constrained ECU modules. |
Use Scenario: Generates stable 5V for logic and 3.3V for I/O in DIN-rail mounted programmable logic controllers. IC Role / Device Role / Timing Role: Regulator + supervisor combo providing regulated power and fail-safe watchdog reset for deterministic control loop execution. Use Value: Reduces BOM count by integrating reset/watchdog; programmable UVLO adapts to varying input conditions; wide temp range (–40°C to 125°C) supports uncooled enclosures. |
| Telematics Control Unit (TCU) | Railway Onboard Monitoring System |
Use Scenario: Powers GPS module, cellular modem, and microcontroller in vehicle tracking units operating across 9V–36V input range. IC Role / Device Role / Timing Role: High-efficiency buck regulator with low-IQ for battery backup mode and watchdog-enforced firmware health checks. Use Value: 85µA quiescent current extends GPS holdover during engine-off; capacitor-programmable watchdog matches modem polling intervals. |
Use Scenario: Supplies critical sensors and communication interfaces in train-mounted condition monitoring systems exposed to wide ambient temperatures. IC Role / Device Role / Timing Role: Input-tolerant power source with POR ensuring deterministic startup after power interruption and watchdog preventing runaway code in safety-relevant subsystems. Use Value: –40°C to 125°C guaranteed operation meets EN 5012X standards; 36V max input accommodates 32V nominal railway supply with margin. |
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 |
|---|---|---|---|
| LT3689IMSE#PBF | Same silicon, rated for full –40°C to 125°C junction temperature with production testing - tighter parametric guarantees over full range. | Suitable for extended-temperature industrial or automotive applications where data-sheet min/max specs must be guaranteed across temperature. | Select LT3689IMSE#PBF when full-temperature-range performance validation is required; LT3689EMSE#PBF is qualified for 0°C to 125°C with design assurance over –40°C to 125°C. |
| LT3689EMSE-5#PBF | Fixed 5V output variant (not adjustable); identical supervision features, package, and temperature grade - eliminates FB resistor divider. | Used where 5V rail is mandatory (e.g., legacy peripherals, USB PHYs) and output adjustability is unnecessary. | Choose LT3689EMSE-5#PBF to simplify design and reduce component count when 5V output suffices; retains same POR, watchdog, and protection features. |
Compared with LT3689IMSE#PBF, the LT3689EMSE#PBF offers cost-optimized qualification for commercial-extended temperature use, while LT3689EMSE-5#PBF trades adjustability for BOM reduction in fixed-voltage systems - both preserve identical supervision architecture and fault protections.
Availability
LT3689EMSE#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLCs, and telematics systems requiring stable component supply, long-term lifecycle support, and guaranteed performance under harsh electrical conditions.
Supply support for LT3689EMSE#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 high-reliability analog and power management portfolio. Linear's legacy designs emphasize precision, ruggedness, and integration for demanding industrial and automotive applications.
The LT3689 product line was designed to integrate step-down regulation with microprocessor supervision in a single monolithic IC - targeting space-constrained, high-reliability systems where discrete power + reset + watchdog solutions increase cost and failure risk.
FAQ
What is the maximum input voltage the LT3689EMSE#PBF can withstand?
The LT3689EMSE#PBF operates continuously from 3.6V to 36V input and withstands nonrepetitive 60V transients for up to 1 second. Its overvoltage lockout activates at ~38V (typical), disabling switching to protect downstream circuitry while maintaining safe biasing. This makes LT3689EMSE#PBF suitable for automotive and industrial applications with load-dump or surge events.
How is the watchdog timer configured on the LT3689EMSE#PBF?
The LT3689EMSE#PBF watchdog timer is configured using three pins: W/T selects window (low) or timeout (high) mode; WDE enables (≤1V) or disables (>1V) the function; and CWDT sets timing via an external capacitor. For example, a 10nF CWDT yields tWDU ≈ 182ms and tWDL ≈ 5.9ms. The LT3689EMSE#PBF does not require firmware configuration - all timing is hardware-defined.
Does the LT3689EMSE#PBF require an external catch diode?
Yes, the LT3689EMSE#PBF requires an external Schottky catch diode connected between SW and OUT. The DA pin monitors diode anode current and disables switching if it exceeds ~1.2A, providing valley-current limiting during overload. Diode selection must consider forward voltage, reverse leakage (critical at high temperature), and thermal rating - typical choices include Diodes Inc. B140HB.
What is the purpose of the OUT pin on the LT3689EMSE#PBF?
The OUT pin on the LT3689EMSE#PBF serves two roles: it provides a current path to charge the internal BST capacitor via an integrated Schottky diode, and it supplies bias current to internal circuitry when VOUT > 3V - reducing VIN quiescent current. In LT3689-5 variants, OUT also connects to the internal 5V feedback divider. This dual functionality improves light-load efficiency and simplifies bootstrap design.
Can the LT3689EMSE#PBF be synchronized to an external clock?
Yes, the LT3689EMSE#PBF supports external synchronization via the SYNC pin. A logic-level clock signal with ≥80ns high/low pulse widths can be applied, provided the LT3689EMSE#PBF's RT-set switching frequency is at least 20% lower than the lowest expected sync frequency. This feature enables EMI reduction in multi-rail systems and deterministic switching alignment across power domains.
LT3689EMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TFSOP (0.118", 3.00mm Width) 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-MSOP-EP
LT3689EMSE#PBF FAQ
1.How can I place an order for LT3689EMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3689EMSE#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 LT3689EMSE#PBF reliable?
The price and inventory of LT3689EMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3689EMSE#PBF is usually 5 days.
3.What payment methods are accepted for LT3689EMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3689EMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3689EMSE#PBF?
LT3689EMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3689EMSE#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 LT3689EMSE#PBF?
For technical support, including LT3689EMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3689EMSE#PBF requirements.
6.How does Aetrix verify that LT3689EMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3689EMSE#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 LT3689EMSE#PBF meets industry standards.
7.What is the process for return or replacement of LT3689EMSE#PBF?
All LT3689EMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3689EMSE#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 LT3689EMSE#PBF part is unused and in its original packaging.
Return procedure for LT3689EMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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