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Analog Devices Inc. LT3688EUF#TRPBF
- Part No.:
- LT3688EUF#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LT3688EUF#TRPBF.pdf
- Description:
- IC REG BUCK ADJ 800MA DL 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,500
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Product details
Overview
LT3688EUF#TRPBF from Analog Devices (formerly Linear Technology) is a dual monolithic step-down switching regulator IC with integrated 800mA power switches, programmable power-on reset timers, and a window watchdog timer. It operates from 3.8V to 36V input, delivers adjustable 5V/3.3V outputs, and maintains <25mVP-P output ripple in Burst Mode at 115μA quiescent current - ideal for automotive ECU and industrial μProcessor power supervision.
For engineers reviewing the LT3688EUF#TRPBF datasheet, LT3688EUF#TRPBF pinout, LT3688EUF#TRPBF application, or LT3688EUF#TRPBF equivalent, key selection criteria include its dual-channel 800mA regulation, 350kHz–2.2MHz synchronizable frequency, ±2% FB voltage accuracy, 24-pin 4mm × 4mm QFN package with exposed thermal pad, and independent CPOR/CWDT capacitor-programmable timing.
Technical Context
The LT3688EUF#TRPBF implements constant-frequency current-mode control per channel with internal slope compensation and VC-clamped current limiting. Its dual independent regulators share no power stage coupling but coordinate startup sequencing via the CONFIG pin, supporting three modes: staggered (CONFIG = VIN), simultaneous (CONFIG = open), or synchronized enable (CONFIG = GND).
Reset and watchdog functions are hardware-based: RST1/RST2 assert low when respective FB voltage falls below 90% of 0.800V reference; timeout periods scale linearly with CPOR1/CPOR2 capacitance (e.g., 4700pF → 23.5ms typical); the watchdog monitors WDI edge spacing against user-defined tWDL/tWDU boundaries set by CWDT capacitance (e.g., 1000pF → 1.25ms/20ms).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3.8V to 36V - supports wide automotive battery transients and industrial DC rails without external pre-regulation. |
| Output Current per Channel | 800mA - sufficient to power dual-core microcontrollers, FPGAs, or sensor interfaces without external pass devices. |
| Feedback Reference Voltage | 0.790V to 0.814V (±2%) - enables precise output regulation with standard resistor dividers; line regulation 0.002%/V minimizes drift over input range. |
| Quiescent Current (Burst Mode) | 115μA at 12VIN → 3.3V/5V - extends battery life in always-on systems while maintaining <25mVP-P ripple. |
| Switching Frequency Range | 350kHz to 2.2MHz - adjustable via RT resistor; higher frequencies allow smaller magnetics (e.g., 1MHz → 4.7μH inductor), lower frequencies improve efficiency at high VIN/VOUT ratios. |
| Power-On Reset Accuracy | ±2% threshold (90% of FB), ±10% timeout - ensures reliable μP initialization across temperature (-40°C to 125°C junction). |
| Watchdog Window Timing | tWDL = 0.8–1.6ms, tWDU = 18–22ms (CWDT = 1000pF) - provides robust fault detection for safety-critical firmware execution monitoring. |
Pinout & Package
LT3688EUF#TRPBF uses a thermally enhanced 24-lead (4mm × 4mm) plastic QFN package with exposed GND pad (Pin 25). The package has θJA = 37°C/W and requires soldering the exposed pad directly 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); 110kΩ → 500kHz typical. |
| SYNC (Pin 2) | External clock synchronization input | Accepts logic-level signal ≥150ns pulse width; ties to GND if unused to prevent floating. |
| EN/UVLO (Pin 3) | Enable and undervoltage lockout | 1.25V threshold enables operation; <0.3V forces shutdown (<1μA IQ); hysteresis prevents chatter near trip point. |
| FB1/FB2 (Pins 4, 12) | Output voltage feedback inputs | Regulated to 0.800V ±2%; connects to resistor divider taps for precise VOUT setting (e.g., 5V or 3.3V). |
| RUN/SS1/RUN/SS2 (Pins 5, 11) | Soft-start timing control | Capacitor to GND programs soft-start ramp time; internal discharge ensures controlled startup after fault recovery. |
| BST1/BST2 (Pins 3, 10) | Bootstrap drive voltage supply | Charges external 0.22μF capacitor to drive internal NPN switch; requires ≥2.15V above SW for full saturation. |
| SW1/SW2 (Pins 4, 9) | Internal power switch outputs | Connect to inductor, catch diode, and BST capacitor; rated for 1.7A peak switch current limit (DC = 15%). |
| DA1/DA2 (Pins 5, 8) | Catch diode anode current monitor | Detects >1.2A diode current during overload; disables switching until valley current falls below limit - protects during short-circuit. |
| VIN (Pin 6) | Main input power supply | Supplies internal circuitry and power switches; must be locally bypassed with ≥22μF ceramic + bulk capacitance. |
| CONFIG (Pin 7) | Startup and timing configuration selector | Three states: VIN = staggered start, GND = simultaneous POR, open = concurrent enable - determines RST1/RST2 dependency and WDO activation timing. |
| CPOR1/CPOR2 (Pins 20, 18) | Power-on reset timeout capacitors | Capacitor to GND sets reset delay (e.g., 4700pF → 23.5ms); linear scaling allows precise μP reset hold time. |
| CWDT (Pin 21) | Watchdog window timing capacitor | Single capacitor sets both tWDL and tWDU; 1000pF yields 1.25ms lower / 20ms upper boundary for robust firmware supervision. |
| WDI/WDO/WDE (Pins 17, 15, 16) | Watchdog interface signals | WDI accepts μP pulses; WDO asserts low on timing violation; WDE disables watchdog when >1V applied - all support 300ns min pulse width. |
| RST1/RST2 (Pins 14, 13) | Open-drain reset outputs | Active-low, weak-pull-up to BIAS (2.5μA); require external 100kΩ pull-up for faster rise and VOH > VBIAS. |
| BIAS (Pin 19) | Internal bias supply input | Accepts ≥3V external rail (e.g., 3.3V output) to reduce VIN quiescent current and charge BST capacitors via internal Schottky path. |
| GND (Pin 25) | Power and signal ground | Exposed thermal pad - must be electrically and thermally connected to PCB ground plane for θJA = 37°C/W performance. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 800mA buck regulators | Enables compact dual-rail power for SoCs requiring separate 5V I/O and 3.3V core supplies - no cross-regulation or shared thermal stress. |
| Programmable window watchdog timer | Monitors WDI edge spacing against user-defined fast/slow boundaries (tWDL/tWDU) - detects both stuck and runaway firmware without software intervention. |
| Two independently adjustable power-on reset timers | CPOR1/CPOR2 capacitors set distinct reset hold times per channel - supports asymmetric startup sequences (e.g., memory initialize before CPU boot). |
| Low-ripple Burst Mode operation | Maintains <25mVP-P output ripple at light loads while drawing only 115μA from VIN - critical for noise-sensitive analog or RF subsystems. |
| Configurable startup sequencing | CONFIG pin selects among three modes: staggered (channel 2 waits for channel 1), simultaneous (both channels enabled together), or concurrent (independent enable) - simplifies system-level power management. |
| Thermally optimized 4mm × 4mm QFN | Exposed GND pad and θJA = 37°C/W enable >1.5W dissipation at 125°C ambient - suitable for convection-cooled industrial enclosures without heatsinks. |
Applications
| Automotive Electronic Control Units | Industrial Programmable Logic Controllers |
|---|---|
Use Scenario: Powering microcontroller, CAN transceiver, and sensor interface in engine control module under 12V/24V battery with load dump transients up to 36V. IC Role / Device Role / Timing Role: Dual-buck regulator provides isolated 5V (I/O) and 3.3V (core) rails; RST1/RST2 ensure deterministic μP reset after cold crank; watchdog monitors firmware execution. Use Value: Eliminates need for discrete reset IC and external watchdog; 36V absolute max rating withstands ISO 7637-2 pulse 5a; -40°C to 125°C operation meets AEC-Q100 Grade 1. | Use Scenario: Supplying FPGA, ADC, and communication interface in DIN-rail mounted PLC operating continuously in 60°C ambient industrial cabinets. IC Role / Device Role / Timing Role: Regulates 3.3V FPGA core and 5V I/O banks; CPOR1/CPOR2 capacitors set 25ms reset hold for FPGA configuration; CONFIG = GND ensures both rails enable only after stable VOUT. Use Value: Reduces BOM count by integrating power, reset, and watchdog; 4mm × 4mm QFN fits dense PCB layouts; thermal pad sustains >1.2W dissipation without forced air. |
| High-Reliability Microprocessor Systems | Medical Diagnostic Equipment |
Use Scenario: Powering ARM Cortex-M7 processor with real-time OS in avionics data concentrator requiring fail-safe boot sequence and runtime supervision. IC Role / Device Role / Timing Role: LT3688EUF#TRPBF delivers 3.3V/5V; WDI receives periodic heartbeat from OS scheduler; WDO triggers system-level fault response if missed. Use Value: Hardware-enforced watchdog eliminates software-only failure modes; ±2% reset threshold ensures reliable boot across voltage/temp; 115μA Burst Mode extends backup battery life. | Use Scenario: Providing regulated power and supervision for imaging sensor array and digital signal processor in portable ultrasound device with Li-ion battery input. IC Role / Device Role / Timing Role: Dual buck supplies 1.8V DSP core and 3.3V sensor interface; BIAS pin connected to 3.3V rail reduces total IQ to extend battery runtime; RST pins hold processor in reset until both rails stabilize. Use Value: Single-chip solution replaces discrete DC/DC + supervisor + watchdog; low-noise Burst Mode prevents interference with sensitive analog front-end; RoHS-compliant QFN meets medical EMC requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-output buck regulator with supervisory functions applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3689EUF#TRPBF | Same pinout and feature set, but supports 1.2A per channel and wider 3.4V–42V input range; includes additional PG (power good) outputs. | Better suited for higher-current applications (e.g., multi-core processors) or systems with >36V transients (e.g., 48V industrial buses). | Select LT3689EUF#TRPBF when load exceeds 800mA per rail or input may exceed 36V; otherwise, LT3688EUF#TRPBF offers optimal cost/performance for ≤800mA designs. |
| TPS65270RGET | TI dual 1.2A buck with integrated LDOs and sequencer; lacks dedicated watchdog timer; fixed 500kHz/1MHz frequencies; no programmable CPOR/CWDT timing. | Requires external watchdog IC for safety-critical supervision; simpler timing setup but less flexible for custom reset/watchdog windows. | Choose TPS65270RGET for cost-sensitive, non-safety applications where fixed timing and integrated LDOs outweigh need for programmable watchdog; LT3688EUF#TRPBF remains preferred for certified functional safety designs. |
Compared with LT3689EUF#TRPBF and TPS65270RGET, the LT3688EUF#TRPBF uniquely balances 800mA dual regulation, fully programmable reset/watchdog timing via external capacitors, and 36V input capability in a compact 4mm × 4mm QFN - making it optimal for space-constrained automotive and industrial systems requiring hardware-enforced supervision without over-specifying current or voltage headroom.
Availability
LT3688EUF#TRPBF 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, long-term lifecycle support, and guaranteed -40°C to 125°C operation.
Supply support for LT3688EUF#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 acquired Linear Technology in 2017 and maintains full product support, datasheets, and application notes for the LT3688 series.
The LT3688 belongs to Linear's high-voltage monolithic buck regulator family designed for automotive, industrial, and medical systems requiring integrated power conversion with hardware-based system supervision - eliminating discrete supervisors and reducing design complexity.
FAQ
What is the maximum input voltage rating for the LT3688EUF#TRPBF?
The LT3688EUF#TRPBF has an absolute maximum input voltage rating of 36V on the VIN pin, as specified in the Absolute Maximum Ratings table. It operates continuously over 3.8V to 36V input range, making it suitable for 12V and 24V automotive and industrial systems with transient overvoltage tolerance. Exceeding 36V risks permanent damage.
How does the CONFIG pin affect startup behavior of the LT3688EUF#TRPBF?
The CONFIG pin on the LT3688EUF#TRPBF selects among three startup modes: tied to VIN enables staggered startup (Channel 2 starts only after FB1 rises above 0.72V); tied to GND enables simultaneous enable after both FB pins exceed 0.72V and CPOR1 expires; left floating enables concurrent startup with independent RST timing. This flexibility simplifies power sequencing in complex systems.
Can the LT3688EUF#TRPBF operate in Burst Mode with both channels active?
Yes, the LT3688EUF#TRPBF automatically enters Burst Mode independently on each channel when its respective output load drops below ~10mA. This reduces total input quiescent current to 115μA while maintaining <25mVP-P output ripple - confirmed in Typical Performance Characteristics Figure G04. Both channels can burst simultaneously or individually based on their load conditions.
What is the purpose of the DA1 and DA2 pins on the LT3688EUF#TRPBF?
The DA1 and DA2 pins on the LT3688EUF#TRPBF monitor catch diode anode current. If diode current exceeds 1.2A (typical), the part disables switching until current falls below the threshold - protecting against short-circuit faults by regulating inductor valley current. This function is independent per channel and does not require external components.
Is the LT3688EUF#TRPBF pin-compatible with other packages in the LT3688 family?
Yes, the LT3688EUF#TRPBF (4mm × 4mm QFN) shares identical pinout and functionality with the LT3688EFE#TRPBF (24-lead TSSOP), as confirmed in the Pin Configuration diagrams. Both packages use the same 24-pin numbering scheme and electrical connections, enabling direct PCB footprint interchangeability where thermal or space constraints permit.
LT3688EUF#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 24-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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)
LT3688EUF#TRPBF FAQ
1.How can I place an order for LT3688EUF#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3688EUF#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 LT3688EUF#TRPBF reliable?
The price and inventory of LT3688EUF#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3688EUF#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3688EUF#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3688EUF#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3688EUF#TRPBF?
LT3688EUF#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3688EUF#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 LT3688EUF#TRPBF?
For technical support, including LT3688EUF#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3688EUF#TRPBF requirements.
6.How does Aetrix verify that LT3688EUF#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3688EUF#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 LT3688EUF#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3688EUF#TRPBF?
All LT3688EUF#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3688EUF#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 LT3688EUF#TRPBF part is unused and in its original packaging.
Return procedure for LT3688EUF#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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