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Analog Devices Inc. LT3694EUFD-1#TRPBF
- Part No.:
- LT3694EUFD-1#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Voltage Regulators - Linear + Switching
- Package:
- 28-WFQFN Exposed Pad
- Datasheet:
-
LT3694EUFD-1#TRPBF.pdf
- Description:
- IC REG TRIPLE BUCK/LINEAR 28QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,486
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Product details
Overview
LT3694EUFD-1#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic 36V, 2.6A step-down DC/DC converter with dual independent LDO regulator controllers. It delivers three regulated outputs (buck + two LDOs), supports 4V–36V input, features adjustable 250kHz–2.5MHz switching frequency via RT resistor, and includes PGOOD, TRK/SS, and CLKOUT for power sequencing and synchronization in multi-rail systems - used in industrial power supplies and DSL modems.
For engineers reviewing the LT3694EUFD-1#TRPBF datasheet, LT3694EUFD-1#TRPBF pinout, LT3694EUFD-1#TRPBF application, or LT3694EUFD-1#TRPBF equivalent, key selection criteria include its triple-output architecture, 28-lead 4mm × 5mm QFN package with exposed thermal pad, integrated overvoltage shutdown (38V trip), and precise 0.75V feedback reference across all three regulators.
Technical Context
The LT3694EUFD-1#TRPBF implements constant-frequency current-mode control for the buck stage, with peak-current sensing and slope compensation to maintain stability across duty cycles. Its internal bipolar NPN switch is driven by a bootstrap circuit (BST/BIAS), enabling high-efficiency operation up to 36V input while maintaining <140ns minimum off-time.
All three regulation loops - buck (FB1), LDO1 (FB2), and LDO2 (FB3) - share a common 0.75V reference but operate independently, each with dedicated TRK/SS pins for soft-start or supply tracking, and separate current-limiting (LIM2/LIM3) and base-drive (DRV2/DRV3) interfaces for external NPN pass transistors.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V continuous; survives 70V transients via overvoltage shutdown - enables direct use with lead-acid batteries and unregulated wall adapters. |
| Buck Output Current | Up to 2.6A with internal switch - eliminates need for external MOSFET in mid-power applications. |
| Switching Frequency | Adjustable 250kHz–2.5MHz via RT resistor (e.g., 40.2kΩ sets 1MHz) - allows optimization of size (high-freq) vs. efficiency (low-freq). |
| Feedback Reference | 0.75V ±15mV over temperature - ensures tight output voltage accuracy for all three regulators (buck + two LDOs). |
| CLKOUT Function | Digital clock output (1.6V–2.6V VOH, 0.3V VOL at 50µA) - enables synchronization of other switching regulators without external oscillator. |
| Thermal Package | 28-lead 4mm × 5mm QFN with exposed GND pad (θJA = 34°C/W) - supports >2.5A continuous operation with standard PCB copper area. |
| Protection Features | Overvoltage shutdown (38V), thermal shutdown, frequency foldback, and DA-pin-based diode-current sensing - prevents damage during short-circuit or overload. |
Pinout & Package
LT3694EUFD-1#TRPBF is housed in a thermally enhanced 28-lead (4mm × 5mm) plastic QFN package with exposed GND pad (Pin 29), requiring soldering to PCB for thermal and electrical integrity. Pin numbering follows top-view layout with Pin 1 at top-left corner.
| 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 ceramic capacitor. |
| EN/UVLO (Pin 2) | Enable and undervoltage lockout input | Shuts down device below 0.35V; initiates switching above 1.20V; supports resistor-divider UVLO configuration. |
| CLKOUT (Pin 3) | Digital clock output | Provides synchronized clock signal (1.6–2.6V) to coordinate timing with other DC/DC converters - unique to LT3694-1 variant. |
| PGOOD (Pin 4) | Open-collector power-good indicator | Pulls low if any FB pin drops below 90% of nominal (i.e., VFB < 0.675V) - signals fault across all three outputs. |
| RT (Pin 5) | Frequency-setting resistor node | Connects to ground to set switching frequency (fSW = 49.8/(RT + 8.8) MHz); unused when SYNC is active. |
| TRK/SS1–3 (Pins 6, 7, 14) | Tracking/soft-start inputs | Override 0.75V reference when <0.75V - enables ratiometric start-up or controlled ramp-up of each output. |
| FB1–3 (Pins 15, 8, 13) | Negative error amplifier inputs | Regulated to 0.75V (or lower, per TRK/SS); connect resistor dividers to set VOUT1/VOUT2/VOUT3. |
| DRV2/DRV3 (Pins 9, 12) | LDO base drive outputs | Supply up to 6V base drive to external NPN transistors - supports high-current linear regulation with low dropout. |
| LIM2/LIM3 (Pins 10, 11) | LDO current limit sense inputs | Monitor voltage across external sense resistors tied to BIAS - enable foldback current limiting for LDO pass devices. |
| VC1 (Pin 16) | Buck error amplifier output | Controls peak switch current; clamped at 2V max; used for loop compensation and shutdown via NMOS/NPN pull-down. |
| BIAS (Pin 17) | Bias supply input | Must be ≥3V (typically connected to VOUT1); powers internal regulators and reduces VIN current draw. |
| BST (Pin 18) | Bootstrap drive node | Generates >VIN voltage for NPN switch saturation; requires external BST capacitor between BST and SW. |
| DA (Pin 19) | Diode current sense input | Detects catch diode conduction to prevent excessive inductor current during overload or short-circuit. |
| SW (Pins 20, 23, 24) | Switch node output | Connects to inductor and Schottky catch diode; carries high di/dt switching waveform - requires tight layout. |
| GND (Pins 10, 11, 12, 13, 25, 26) | Power and signal ground | Multiple GND pins minimize impedance; exposed pad (Pin 29) must be soldered to PCB ground plane for thermal performance. |
Key Features
| Feature | Design Value |
|---|---|
| Triple-output architecture | Single IC delivers one 2.6A buck + two programmable LDO controllers - reduces board space and BOM count in multi-rail systems. |
| Independent TRK/SS control per regulator | Enables flexible power sequencing (e.g., VOUT2 tracks VOUT1, VOUT3 delayed) without external timers or supervisors. |
| CLKOUT synchronization capability | Eliminates need for external clock generator when coordinating multiple switching regulators - improves EMI predictability. |
| Robust 70V transient survival | Overvoltage shutdown activates at 38V, protecting internal circuitry during load-dump or hot-swap events in automotive/industrial environments. |
| Low-impedance 0.75V reference | Ensures ±1% output accuracy across temperature and line/load variations - critical for FPGA, DSP, and ASIC core rails. |
| Thermally optimized QFN package | Exposed pad and low θJA (34°C/W) allow full 2.6A buck output without forced air - simplifies thermal design in enclosed enclosures. |
Applications
| Industrial Power Supply | DSL/Cable Modem |
|---|---|
|
Use Scenario: Centralized 24V-to-multiple-rail conversion in programmable logic controllers and sensor hubs. IC Role / Device Role / Timing Role: Primary triple-output PMIC managing 3.3V CPU core, 2.5V I/O, and 1.8V memory rails with coordinated soft-start. Use Value: Reduces component count by replacing three discrete regulators; TRK/SS pins ensure safe power-up sequence preventing latch-up. |
Use Scenario: Compact AC/DC adapter replacement powering PHY, MAC, and analog front-end in broadband gateways. IC Role / Device Role / Timing Role: Buck regulator supplies 3.3V system rail; LDO controllers generate clean 1.2V and 1.8V analog/RF supplies. Use Value: CLKOUT synchronizes auxiliary DC/DC converters, minimizing beat frequencies and conducted EMI in FCC-compliant designs. |
| Distributed Power Regulation | Wall Transformer Regulation |
|
Use Scenario: Point-of-load regulation in distributed bus architectures (e.g., 12V or 24V backplane feeding remote modules). IC Role / Device Role / Timing Role: Step-down converter generates local 5V rail; LDOs provide isolated low-noise 3.3V and 2.5V for communication interfaces. Use Value: Wide 4V–36V input range accepts variable bus voltages; overvoltage shutdown protects against bus faults up to 70V. |
Use Scenario: Regulated output stage in universal-input wall adapters powering consumer electronics and IoT edge devices. IC Role / Device Role / Timing Role: Primary buck regulator converts rectified AC to stable 5V/9V/12V; LDOs trim for USB-C PD or legacy USB compliance. Use Value: Adjustable switching frequency avoids AM radio band interference; small ceramic capacitors meet compact form factor requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar triple-output buck+LDO regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3631EFE#PBF | Single 3A buck + single LDO controller; no CLKOUT; TSSOP-20 package; max 36V input. | Lacks second LDO channel and clock output - suitable only for dual-rail systems without synchronization needs. | Choose when board space permits TSSOP and third rail is generated externally or omitted. |
| LT8614EUD#PBF | 42V, 4A synchronous buck only (no LDO controllers); 16-lead QFN; includes spread-spectrum modulation. | No integrated LDO control - requires external linear regulators for auxiliary rails; higher peak current capability. | Prefer when highest efficiency and lowest EMI are critical, and LDO functionality is implemented separately. |
Compared with LTC3631EFE#PBF and LT8614EUD#PBF, the LT3694EUFD-1#TRPBF uniquely integrates dual LDO controllers with CLKOUT in a single 28-lead QFN, enabling compact, synchronized triple-rail designs without external timing components or discrete LDO drivers.
Availability
LT3694EUFD-1#TRPBF is available at Aetrix Electronics and suitable for industrial power supplies, DSL/cable modem designs, and distributed power regulation requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.
Supply support for LT3694EUFD-1#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 industrial, automotive, communications, and healthcare markets.
The LT3694-1 product line delivers highly integrated triple-output DC/DC solutions targeting space-constrained, multi-rail applications where sequencing, synchronization, and robustness to input transients are critical - such as network infrastructure and factory automation equipment.
FAQ
What is the key functional difference between LT3694EUFD-1#TRPBF and LT3694EUFD#TRPBF?
The LT3694EUFD-1#TRPBF includes a CLKOUT pin (Pin 3) that provides a digital clock signal for synchronizing other switching regulators, whereas the LT3694EUFD#TRPBF has a SYNC pin for accepting an external clock input. This makes LT3694EUFD-1#TRPBF ideal as a master timing source in multi-converter systems, while the non-"-1" version serves as a slave. Both share identical buck and LDO specifications, pinout, and package.
Does LT3694EUFD-1#TRPBF require an external catch diode, and what type is recommended?
Yes, LT3694EUFD-1#TRPBF requires an external Schottky catch diode connected between SW and GND. The datasheet specifies use of the B340A (40V, 3A) or equivalent low-forward-voltage, fast-recovery Schottky diode. This diode conducts inductor current during the switch-off phase and must handle peak currents up to 2.6A with minimal VF to preserve efficiency and thermal performance.
How is output voltage programmed for the buck regulator in LT3694EUFD-1#TRPBF?
The buck output voltage (VOUT1) is set using a resistor divider from VOUT1 to FB1, with R1 connected to VOUT1 and R2 to GND. The formula is R1 = R2 × ((VOUT1 / 0.75V) − 1). The parallel resistance of R1 and R2 must be ≤10kΩ to minimize error from FB1 bias current (±500nA). Typical values for 3.3V output are R1 = 41.2kΩ and R2 = 11kΩ.
Can LT3694EUFD-1#TRPBF operate with input voltage below 4V?
No - LT3694EUFD-1#TRPBF has a guaranteed minimum operating input voltage of 4V due to internal undervoltage lockout (UVLO) activation at 3.8V typical. Below this threshold, the device remains in shutdown mode drawing <2µA. It cannot regulate outputs or initiate soft-start even if external bias (e.g., on BIAS pin) is present, as VIN powers critical internal circuitry including the oscillator and reference.
What thermal design considerations apply to the exposed pad of LT3694EUFD-1#TRPBF?
The exposed pad (Pin 29) of LT3694EUFD-1#TRPBF is electrically and thermally connected to GND and must be soldered to a minimum 100mm² copper area on the PCB's inner or outer layer. Thermal vias (≥6×0.3mm diameter) should connect it to internal ground planes. Failure to properly attach the pad increases junction-to-ambient thermal resistance beyond the specified 34°C/W, risking thermal shutdown under 2.6A load conditions.
LT3694EUFD-1#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-1#TRPBF FAQ
1.How can I place an order for LT3694EUFD-1#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3694EUFD-1#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-1#TRPBF reliable?
The price and inventory of LT3694EUFD-1#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-1#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3694EUFD-1#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3694EUFD-1#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3694EUFD-1#TRPBF?
LT3694EUFD-1#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3694EUFD-1#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-1#TRPBF?
For technical support, including LT3694EUFD-1#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3694EUFD-1#TRPBF requirements.
6.How does Aetrix verify that LT3694EUFD-1#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3694EUFD-1#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-1#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3694EUFD-1#TRPBF?
All LT3694EUFD-1#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3694EUFD-1#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-1#TRPBF part is unused and in its original packaging.
Return procedure for LT3694EUFD-1#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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