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Analog Devices Inc. LT3688IUF#PBF
- Part No.:
- LT3688IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LT3688IUF#PBF.pdf
- Description:
- IC REG BUCK ADJ 800MA DL 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,592
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Product details
Overview
LT3688IUF#PBF from Analog Devices (formerly Linear Technology) is a dual monolithic step-down switching regulator IC with integrated power-on reset (POR) and watchdog timer functions, operating from 3.8V to 36V input, delivering two 800mA outputs at adjustable frequencies (350kHz–2.2MHz), and featuring low-ripple Burst Mode operation (115μA IQ, <25mVP-P ripple) for automotive ECU and industrial μProcessor power systems.
For engineers reviewing the LT3688IUF#PBF datasheet, LT3688IUF#PBF pinout, LT3688IUF#PBF application, or LT3688IUF#PBF equivalent, key selection criteria include programmable POR timeout (via CPOR1/CPOR2), windowed watchdog timing (CWDT), independent RUN/SS soft-start control, and thermal performance in the 4mm × 4mm QFN-24 package with exposed pad.
Technical Context
The LT3688IUF#PBF implements constant-frequency current-mode PWM control with dual independent oscillator channels synchronized via RT/SYNC pins, supporting frequency programming from 350kHz to 2.2MHz using an external resistor. Each channel integrates an internal NPN power switch, BST-driven gate drive, and DA-pin-based catch diode current monitoring for short-circuit protection.
Its supervisory subsystem includes two precision voltage-monitoring comparators (90% FB threshold, ±2% accuracy), independently programmable POR timers (CPOR1/CPOR2), and a windowed watchdog timer (CWDT) with configurable upper/lower boundaries (e.g., 0.8–22ms range), all implemented with glitch-immune logic and open-drain RST/WDO outputs referenced to BIAS.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.8V to 36V - supports wide-range industrial and automotive battery-fed rails without pre-regulation. |
| Output Current per Channel | 800mA - sufficient to power dual-core microcontrollers, FPGAs, or sensor interfaces directly. |
| Switching Frequency Range | 350kHz to 2.2MHz - enables compact magnetics (e.g., 4.7μH at 1MHz) while avoiding AM radio band. |
| Quiescent Current (Burst Mode) | 115μA at 12VIN → 3.3V/5V - ensures ultra-low standby power in always-on systems. |
| FB Regulation Voltage | 0.790V to 0.814V (±1.4%) - high-accuracy reference enables tight output tolerance with standard 1% resistors. |
| POR Timeout Accuracy | ±10% over temperature (tRST = 23.5ms typ. @ CPOR = 4700pF) - reliable sequencing for multi-rail μProcessor systems. |
| Watchdog Window Range | tWDL = 0.8–1.6ms / tWDU = 18–22ms @ CWDT = 1000pF - configurable fault-detection timing for diverse firmware loop durations. |
Pinout & Package
The LT3688IUF#PBF is housed in a thermally enhanced 24-lead (4mm × 4mm) plastic QFN package with exposed pad (Pin 25), rated θJA = 37°C/W, requiring direct solder connection to PCB ground plane for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RT (Pin 1) | Oscillator frequency programming | Resistor-to-GND sets switching frequency (350kHz–2.2MHz); critical for EMI control and inductor sizing. |
| SYNC (Pin 2) | External clock synchronization input | Accepts logic-level signal ≥150ns pulse width; enables deterministic phase alignment across multiple regulators. |
| EN/UVLO (Pin 3) | Enable and undervoltage lockout input | 1.25V threshold enables startup only when VIN ≥3.5V; prevents brownout operation and false resets. |
| FB1/FB2 (Pins 4, 12) | Output voltage feedback inputs | Regulated to 0.800V ±1.4%; defines VOUT via resistor divider; monitors output health for RST assertion. |
| RUN/SS1/RUN/SS2 (Pins 5, 11) | Soft-start timing control | Capacitor-to-GND programs startup ramp time; internal discharge ensures repeatable cold-start behavior. |
| BST1/BST2 (Pins 3, 10) | Bootstrap supply for internal NPN switches | Drives gate above VIN via external 0.22μF capacitor; enables full saturation and low RCE(sat) (~280mV). |
| RST1/RST2 (Pins 14, 13) | Open-drain power-on reset outputs | Pull low if respective VOUT drops >10% below regulation; timing set by CPOR1/CPOR2 capacitors. |
| WDO (Pin 15) | Watchdog timeout output | Open-drain active-low signal pulses low on watchdog violation; duration = 1/8 × tWDU for system recovery. |
| WDI (Pin 17) | Watchdog input trigger | Accepts negative edges from μP; requires ≥300ns pulse width; monitors firmware liveness within windowed timing. |
| CONFIG (Pin 7) | Startup sequencing mode selector | Tied to VIN/GND/floating to configure POR dependency, channel enable order, and watchdog activation conditions. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 800mA buck regulators | Enables single-chip dual-rail power for SoCs or split-voltage logic (e.g., 5V + 3.3V), eliminating discrete solutions and layout complexity. |
| Programmable windowed watchdog timer | Prevents runaway code by detecting both too-frequent and too-infrequent WDI edges-critical for safety-critical automotive ECUs. |
| Two independently adjustable power-on reset timers | Allows staggered or coincident rail sequencing (via CPOR1/CPOR2 caps), ensuring proper initialization order in multi-voltage systems. |
| Low-ripple Burst Mode operation | Maintains <25mVP-P output ripple at light loads while drawing only 115μA from VIN-ideal for battery-backed sensors and sleep-mode IoT nodes. |
| Thermally optimized 4mm × 4mm QFN-24 | Exposed pad and 37°C/W θJA enable 1.6W dissipation at 125°C ambient-supports high-current operation without heatsinks in space-constrained designs. |
Applications
| Automotive Electronic Control Units | Industrial Programmable Logic Controllers |
|---|---|
Use Scenario: Powering dual-rail microcontrollers (e.g., ARM Cortex-M7 + CAN transceiver) in engine control modules under 12V/24V battery input with load dump transients. IC Role / Device Role / Timing Role: Primary DC/DC converter and system supervisor-regulates 5V core and 3.3V I/O rails while asserting POR after battery reconnection and triggering WDO on firmware hang. Use Value: Eliminates need for separate reset IC and dual buck controllers; withstands 36V transients and operates down to –40°C with guaranteed 125°C junction rating. | Use Scenario: Supplying FPGA configuration voltage (1.2V/3.3V) and I/O banks in factory automation controllers with watchdog-enforced firmware integrity. IC Role / Device Role / Timing Role: Dual-output power manager and real-time fault monitor-delivers stable 800mA per rail and pulses WDO within 22ms of missed WDI edge to initiate safe shutdown. Use Value: Reduces BOM count by integrating POR, watchdog, and dual bucks; CPOR1/CPOR2 capacitors allow precise sequencing to meet FPGA power-up timing requirements. |
| High-Reliability Microprocessor Systems | Medical Diagnostic Imaging Subsystems |
Use Scenario: Providing clean, sequenced power to radiation-hardened processors in satellite telemetry units where latch-up immunity and long-term reliability are mandatory. IC Role / Device Role / Timing Role: Radiation-tolerant power supervisor-uses internal BIAS regulation to minimize VIN current draw and leverages open-drain RST outputs for OR-ing with other system resets. Use Value: 115μA quiescent current extends battery life in orbital missions; ±2% FB accuracy ensures consistent processor voltage across temperature extremes. | Use Scenario: Powering analog front-end ASICs and ADCs in portable ultrasound machines requiring ultra-low noise and fail-safe supervision during battery operation. IC Role / Device Role / Timing Role: Low-noise dual buck + safety monitor-employs Burst Mode to suppress switching noise near sensitive analog circuits while asserting RST1/RST2 on any rail droop >10%. Use Value: <25mVP-P ripple meets medical-grade analog noise specs; watchdog windowing prevents false triggers from transient EMI during probe movement. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-buck-with-supervision applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3649EMSE#PBF | Single 4A buck with programmable POR/watchdog; no dual-output capability; higher current, larger package (16-MSOP). | Suitable for single-rail high-current apps (e.g., GPU core), but cannot replace dual-rail sequencing in LT3688IUF#PBF designs. | Select when only one regulated rail is needed and >800mA per channel is required; not a functional substitute for dual-output use cases. |
| TPS65217CRSLR | Quad-buck PMIC with integrated LDOs and fuel gauge; fixed 3.3V/1.8V/1.2V/1.0V outputs; no programmable POR/watchdog; 48-QFN. | Targets handheld/tablet SoC power; lacks external frequency adjustment, CPOR/CWDT capacitor programming, and wide 3.8–36V input. | Choose for consumer mobile SoCs with fixed voltages; unsuitable for industrial/automotive designs needing adjustable rails and robust supervision. |
Compared with LTC3649EMSE#PBF and TPS65217CRSLR, the LT3688IUF#PBF uniquely delivers dual independently programmable 800mA bucks with user-configurable POR and windowed watchdog timing in a compact 4mm × 4mm QFN-making it irreplaceable for space-constrained, safety-critical dual-rail systems requiring field-adjustable supervision windows.
Availability
LT3688IUF#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial programmable logic controllers, and high-reliability microprocessor systems requiring stable component supply, extended temperature support (–40°C to 125°C), and long-term lifecycle continuity.
Supply support for LT3688IUF#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. (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, formed through the acquisition of Linear Technology in 2017.
The LT3688 product line was designed by Linear Technology specifically for demanding automotive and industrial power management applications requiring integrated supervision, high input voltage tolerance, and thermal robustness in compact packages.
FAQ
What is the maximum input voltage supported by the LT3688IUF#PBF?
The LT3688IUF#PBF supports a maximum continuous input voltage of 36V, as specified in its Absolute Maximum Ratings. This allows direct operation from 24V industrial buses or 12V automotive systems with load dump transients. Operation above 36V risks permanent damage, and the device incorporates internal UVLO (3.5V threshold) to prevent startup below minimum operating voltage.
How does the LT3688IUF#PBF implement Burst Mode operation, and what is its impact on output ripple?
The LT3688IUF#PBF enters Burst Mode at light loads to reduce quiescent current to 115μA, disabling switching circuitry between energy bursts. This maintains high efficiency but introduces low-frequency envelope modulation. In typical applications, output ripple remains below 25mVP-P due to careful control of burst depth and output capacitor selection-verified in the datasheet's TA01a schematic and G01–G03 efficiency plots.
Can the LT3688IUF#PBF's watchdog timer be disabled, and how is this accomplished?
Yes, the LT3688IUF#PBF's watchdog timer can be disabled by driving the WDE (Watchdog Enable) pin above 1V. Per the datasheet, tying WDE to VIN or applying a logic-high signal disables watchdog functionality, allowing the WDO pin to remain high regardless of WDI activity. Floating or grounding WDE enables normal watchdog operation-this configurability supports development/debug modes and production safety requirements.
What thermal considerations apply to the LT3688IUF#PBF's exposed pad in the QFN-24 package?
Pin 25 of the LT3688IUF#PBF is an exposed pad that must be electrically and thermally connected to the PCB ground plane via multiple vias. With θJA = 37°C/W, inadequate pad soldering or insufficient copper area increases junction temperature, potentially triggering thermal shutdown or degrading long-term reliability. The datasheet mandates direct solder connection-not optional-to ensure specified thermal performance and electrical grounding of internal circuitry.
How are the power-on reset timeout periods programmed on the LT3688IUF#PBF?
The LT3688IUF#PBF uses external capacitors on CPOR1 (Pin 20) and CPOR2 (Pin 18) to set independent power-on reset timeout periods. For example, a 4700pF capacitor yields a typical tRST of 23.5ms (±10%). The relationship is linear: doubling capacitance doubles timeout. These capacitors interface directly with internal 2.5μA current sources, enabling precise, temperature-stable sequencing without external resistors or complex timing ICs.
LT3688IUF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 24-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 2
- Voltage - Input (Min):
- 3.8V
- Voltage - Input (Max):
- 36V
- Voltage - Output (Min/Fixed):
- 0.8V
- Voltage - Output (Max):
- 36V
- Current - Output:
- 800mA
- Frequency - Switching:
- 500kHz ~ 2.1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-QFN (4x4)
LT3688IUF#PBF FAQ
1.How can I place an order for LT3688IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3688IUF#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 LT3688IUF#PBF reliable?
The price and inventory of LT3688IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3688IUF#PBF is usually 5 days.
3.What payment methods are accepted for LT3688IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3688IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3688IUF#PBF?
LT3688IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3688IUF#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 LT3688IUF#PBF?
For technical support, including LT3688IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3688IUF#PBF requirements.
6.How does Aetrix verify that LT3688IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LT3688IUF#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 LT3688IUF#PBF meets industry standards.
7.What is the process for return or replacement of LT3688IUF#PBF?
All LT3688IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3688IUF#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 LT3688IUF#PBF part is unused and in its original packaging.
Return procedure for LT3688IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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