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Analog Devices Inc. LT3694EUFD#TRPBF
- Part No.:
- LT3694EUFD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Voltage Regulators - Linear + Switching
- Package:
- 28-WFQFN Exposed Pad
- Datasheet:
-
LT3694EUFD#TRPBF.pdf
- Description:
- IC REG TRIPLE BUCK/LINEAR 28QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,535
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Product details
Overview
LT3694EUFD#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic 36V, 2.6A step-down DC/DC converter with dual LDO regulator controllers. It delivers up to 2.6A from its buck output and supports two independent linear regulators via external NPN pass transistors. Its 4V–36V input range, 0.75V feedback reference, and 250kHz–2.5MHz adjustable switching frequency enable compact triple-output power solutions in industrial and telecom applications.
For engineers reviewing the LT3694EUFD#TRPBF datasheet, LT3694EUFD#TRPBF pinout, LT3694EUFD#TRPBF application, or LT3694EUFD#TRPBF equivalent, key selection considerations include its triple-regulator architecture (1 buck + 2 LDO controllers), thermal shutdown and overvoltage protection (70V transient tolerance), 28-lead 4mm × 5mm QFN package with exposed ground pad, and support for power supply sequencing via three TRK/SS pins.
Technical Context
The LT3694EUFD#TRPBF integrates a constant-frequency current-mode buck regulator with internal bipolar NPN switch and two independent LDO controller channels using external NPN pass transistors. Its VC1 error amplifier output controls peak switch current, while DA pin sensing enables catch-diode current limiting during overload.
It features independent track/soft-start inputs (TRK/SS1–3) for coordinated power-up sequencing, PGOOD monitoring across all three outputs, and BIAS pin operation to reduce quiescent dissipation. The device uses slope compensation for stable current-mode control and includes frequency foldback under short-circuit conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V continuous; survives 70V non-repetitive transients - supports wide-source applications including wall adapters and lead-acid batteries. |
| Buck Output Current | Up to 2.6A - sufficient for primary system rail in DSL modems or industrial I/O modules. |
| Switching Frequency Range | 250kHz to 2.5MHz (set by RT resistor or SYNC clock) - enables small 4.7µH inductors and ceramic output capacitors. |
| Feedback Reference Voltage | 750mV ±15mV - allows precise low-voltage outputs (e.g., 1.8V, 2.5V, 3.3V) with standard resistor dividers. |
| Overvoltage Shutdown Threshold | 38V typical - disables switching before internal components are stressed by high-line surges. |
| Thermal Shutdown | Activates above 165°C junction temperature - protects against sustained overload or poor PCB heatsinking. |
| PGOOD Accuracy | Monitors all three FB pins; asserts low when any falls below 90% of nominal - ensures reliable system power-good signaling. |
Pinout & Package
LT3694EUFD#TRPBF is housed in a thermally enhanced 28-lead 4mm × 5mm plastic QFN package with exposed ground pad (Pin 29), requiring soldering to PCB for thermal and electrical integrity. θJA = 34°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pins 1, 27, 28) | Main input power supply | Supplies internal switch, bias circuits, and startup logic; must be locally bypassed with ≥4.7µF ceramic capacitor. |
| EN/UVLO (Pin 2) | Enable and undervoltage lockout input | Shuts down device below 380mV; initiates switching above 1.20V; supports resistor-divider UVLO configuration. |
| SYNC (Pin 3) | Frequency synchronization input | Accepts external clock (0.25–2.5MHz, TTL/CMOS); disables internal oscillator when driven - used only on LT3694 (not -1 variant). |
| PGOOD (Pin 4) | Open-collector power-good output | Pulled low if any FB voltage drops below 90% of target - provides system-level rail monitoring with single-wire interface. |
| RT (Pin 5) | Frequency-setting resistor terminal | Connects to ground to set fSW = 49.8/(RT + 8.8) MHz; RT = 40.2kΩ yields 1MHz typical. |
| TRK/SS1–3 (Pins 6, 7, 14) | Tracking/soft-start inputs | Override 0.75V reference when <0.75V; enable ratiometric start-up or soft-start via capacitor-to-ground connection. |
| FB1–3 (Pins 15, 8, 13) | Negative error amplifier inputs | Each regulates to min(0.75V, corresponding TRK/SS voltage); connect to resistor divider taps for output voltage setting. |
| DRV2/DRV3 (Pins 9, 12) | LDO base drive outputs | Supply up to 6V/15mA base current to external NPN pass transistors - enable high-current LDO rails without integrated pass devices. |
| LIM2/LIM3 (Pins 10, 11) | LDO current limit sense inputs | Monitor voltage across external sense resistors connected to BIAS; provide foldback current limiting for external pass transistors. |
| VC1 (Pin 16) | Error amplifier output | Controls peak switch current; clamped at 2V; used for loop compensation and can shut down regulator when pulled to GND. |
| BIAS (Pin 17) | Bias supply input | Provides current to internal regulators and boost circuit; must be ≥3V (typically tied to VOUT1) to minimize VIN current draw. |
| BST (Pin 18) | Bootstrap supply terminal | Drives internal NPN switch with voltage >VIN; requires external 0.1µF ceramic capacitor between BST and SW. |
| DA (Pin 19) | Catch diode current sense | Detects reverse diode conduction at cycle start; delays switch-on to prevent inductor current runaway during overload. |
| SW (Pins 20, 23, 24) | Internal switch output | Connects to inductor and Schottky catch diode; carries full buck switching current and high dv/dt edges. |
| GND (Pins 10, 11, 12, 13, 25, 26) | Power and signal ground | Multiple dedicated ground pins minimize impedance; exposed pad (Pin 29) must be soldered to PCB ground plane. |
Key Features
| Feature | Design Value |
|---|---|
| Triple-output architecture | One 2.6A buck regulator + two programmable LDO controllers - eliminates need for separate LDO ICs in multi-rail systems. |
| Independent TRK/SS inputs | Three dedicated tracking/soft-start pins enable precise power sequencing for microcontrollers and FPGAs without external timers. |
| 70V transient survival | Overvoltage shutdown activates at 38V, protecting internal circuitry during automotive load-dump or industrial surge events. |
| Adjustable high-frequency switching | 250kHz–2.5MHz range allows optimization of size (high fSW) vs. efficiency (low fSW) for specific board area and thermal constraints. |
| Integrated current-mode control | Peak-current regulation with slope compensation ensures stability across wide duty-cycle ranges and fast transient response. |
| Thermally enhanced QFN | 28-lead 4mm × 5mm package with exposed pad achieves θJA = 34°C/W - supports 2.6A continuous operation without forced air. |
Applications
| DSL/Cable Modem Power | Industrial I/O Module |
|---|---|
Use Scenario: Powering triple-rail subsystems (3.3V CPU core, 2.5V PHY, 1.8V memory) in broadband access equipment with limited board space. IC Role / Device Role / Timing Role: Primary buck regulator generates 3.3V main rail; dual LDO controllers regulate 2.5V and 1.8V auxiliary rails using discrete NPN transistors. Use Value: Single-chip solution reduces component count by 3–4 discrete regulators and simplifies layout while maintaining independent sequencing via TRK/SS pins. |
Use Scenario: Providing isolated, sequenced 5V, 3.3V, and 2.4V supplies for analog front-end, digital logic, and sensor interfaces in factory automation modules. IC Role / Device Role / Timing Role: Buck stage powers 5V analog section; LDO controllers deliver low-noise 3.3V and 2.4V rails with foldback current limiting for field-side protection. Use Value: Overvoltage shutdown (38V threshold) withstands 24VDC field bus transients; PGOOD monitors all three rails for centralized fault reporting. |
| Wall Transformer Regulation | Automotive Infotainment |
Use Scenario: Regulating unregulated 9–36V AC/DC wall adapter outputs into stable 3.3V, 2.5V, and 1.8V system rails for embedded networking gear. IC Role / Device Role / Timing Role: Buck converter handles bulk conversion; LDO controllers condition noise-sensitive rails with external pass transistors for PSRR enhancement. Use Value: 4V minimum input enables operation down to brownout conditions; adjustable fSW permits use of low-cost 2.2µH inductors at 500kHz. |
Use Scenario: Generating sequenced 5V, 3.3V, and 1.2V supplies for head-unit MCU, display driver, and audio codec in 12V vehicle systems. IC Role / Device Role / Timing Role: Buck regulator powers 5V domain; LDO controllers manage lower-voltage rails with soft-start to avoid inrush current during cold-cranking. Use Value: 70V transient tolerance survives ISO 7637-2 pulse 5a load dump; EN/UVLO threshold programmability supports custom battery undervoltage cutoff. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar triple-output regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3631EFE#TRPBF | Single 3A buck regulator only; no LDO controllers - requires external LDOs for auxiliary rails. | Suitable where only one high-current rail is needed; lacks integrated sequencing capability for multi-rail systems. | Select when board space allows discrete LDOs and sequencing is handled externally; not a functional substitute for LT3694EUFD#TRPBF's dual-LDO-controller architecture. |
| TPS546B24RVFT | 6V–18V input, 12A buck with PMBus; no LDO controllers - targets high-current single-rail servers, not triple-output embedded systems. | Designed for digital power management in datacom; lacks TRK/SS pins, PGOOD aggregation, or LDO control logic. | Choose only for high-efficiency, digitally controlled 12V→0.8V conversion; incompatible with LT3694EUFD#TRPBF's 4–36V range and LDO controller functionality. |
Compared with LTC3631EFE#TRPBF and TPS546B24RVFT, the LT3694EUFD#TRPBF uniquely integrates buck + dual LDO controllers in one package, enabling compact triple-rail designs with hardware-based sequencing - neither alternative replicates this combined function or 4–36V input capability.
Availability
LT3694EUFD#TRPBF is available at Aetrix Electronics and suitable for industrial I/O modules, DSL/cable modem power supplies, and automotive infotainment systems requiring stable component supply across extended temperature ranges (–40°C to 125°C).
Supply support for LT3694EUFD#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial, automotive, and communications markets.
The LT3694 product line was designed for compact, high-reliability multi-rail power conversion in space-constrained industrial and telecom equipment - emphasizing wide-input operation, robust protection, and hardware-controlled sequencing without microcontroller dependency.
FAQ
What is the maximum continuous output current of the buck regulator in LT3694EUFD#TRPBF?
The LT3694EUFD#TRPBF buck regulator delivers up to 2.6A continuously under typical thermal conditions (θJA = 34°C/W, 25°C ambient, proper PCB copper). Its internal bipolar NPN switch current limit is 3.5A minimum at low duty cycles, derating to ~2.8A at 80% duty cycle per datasheet Figure G05. Actual achievable output depends on input voltage, output voltage, switching frequency, and PCB thermal design.
Does LT3694EUFD#TRPBF support synchronization with external clock sources?
Yes, the LT3694EUFD#TRPBF supports external clock synchronization via its SYNC pin (Pin 3), accepting TTL/CMOS signals from 0.25MHz to 2.5MHz with ≥100ns minimum high/low times. Note that this part number corresponds to the LT3694 (not LT3694-1), which has SYNC functionality - the LT3694-1 variant replaces SYNC with CLKOUT for driving other converters.
How does the PGOOD function monitor all three outputs in LT3694EUFD#TRPBF?
The LT3694EUFD#TRPBF's PGOOD pin (Pin 4) is an open-collector output that pulls low whenever the voltage on any of the three FB pins (FB1, FB2, or FB3) falls below 90% of its nominal regulated value. This aggregated monitoring ensures system-level power integrity detection across the buck and both LDO-controlled outputs without requiring separate fault signals.
What is the role of the BIAS pin in LT3694EUFD#TRPBF, and what voltage must it receive?
The BIAS pin (Pin 17) supplies current to the LT3694EUFD#TRPBF's internal regulators and boost circuitry. It must be connected to a stable voltage ≥3V - typically tied to the buck output (VOUT1) - to minimize power dissipation. If BIAS drops below 2.7V, quiescent current draws from VIN instead, reducing efficiency. Minimum BIAS-to-DRV voltage is 0.3V at 10mA DRV load.
Can LT3694EUFD#TRPBF operate with input voltages below 4V?
No, the LT3694EUFD#TRPBF has a guaranteed minimum operating input voltage of 4V due to its internal undervoltage lockout (UVLO) threshold of 3.8V typical. Below this, the EN/UVLO circuit prevents startup. While absolute maximum ratings allow –0.3V, operation below 4V is not characterized or supported - the device will remain in shutdown state.
LT3694EUFD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 28-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Topology:
- Step-Down (Buck) (1), Linear (LDO) (2)
- Number of Outputs:
- 3
- Frequency - Switching:
- 250kHz ~ 2.5MHz
- Voltage/Current - Output 1:
- 0.75V ~ 16V, 2.6A
- Voltage/Current - Output 2:
- Controller
- Voltage/Current - Output 3:
- Controller
- w/LED Driver:
- No
- w/Supervisor:
- No
- w/Sequencer:
- Yes
- Voltage - Supply:
- 4V ~ 36V
- Operating Temperature:
- -40°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 28-QFN (4x5)
LT3694EUFD#TRPBF FAQ
1.How can I place an order for LT3694EUFD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3694EUFD#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 LT3694EUFD#TRPBF reliable?
The price and inventory of LT3694EUFD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3694EUFD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3694EUFD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3694EUFD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3694EUFD#TRPBF?
LT3694EUFD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3694EUFD#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 LT3694EUFD#TRPBF?
For technical support, including LT3694EUFD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3694EUFD#TRPBF requirements.
6.How does Aetrix verify that LT3694EUFD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3694EUFD#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 LT3694EUFD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3694EUFD#TRPBF?
All LT3694EUFD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3694EUFD#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 LT3694EUFD#TRPBF part is unused and in its original packaging.
Return procedure for LT3694EUFD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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