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Analog Devices Inc. LT3694IUFD#TRPBF
- Part No.:
- LT3694IUFD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- Voltage Regulators - Linear + Switching
- Package:
- 28-WFQFN Exposed Pad
- Datasheet:
-
LT3694IUFD#TRPBF.pdf
- Description:
- IC REG TRIPLE BUCK/LINEAR 28QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,876
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Product details
Overview
LT3694IUFD#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 three regulated outputs (buck + two LDOs), supports 4V–36V input, features adjustable 250kHz–2.5MHz switching frequency, and integrates independent track/soft-start for power sequencing in industrial power supplies.
For engineers reviewing the LT3694IUFD#TRPBF datasheet, LT3694IUFD#TRPBF pinout, LT3694IUFD#TRPBF application, or LT3694IUFD#TRPBF equivalent, key selection considerations include its triple-output architecture, 28-lead 4mm × 5mm QFN package with exposed thermal pad, overvoltage shutdown up to 70V transients, and support for external clock synchronization (SYNC pin) - critical for noise-sensitive distributed power systems.
Technical Context
The LT3694IUFD#TRPBF implements constant-frequency current-mode control for its main buck regulator, using VC1 voltage to modulate peak switch current per cycle. Its internal bipolar NPN power switch is driven via BST bootstrap circuitry requiring ≥1.8V boost headroom above SW.
Each of the two LDO controllers operates independently with programmable current limit via external sense resistors on LIM2/LIM3, base drive output on DRV2/DRV3 (up to 6V, 15mA), and foldback protection triggered at 47–70mV FB voltage drop. PGOOD asserts low when any FB pin falls below 90% of nominal regulation (735–765mV).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 36V continuous; survives 70V non-repetitive transients - enables use with lead-acid batteries, wall adapters, and unregulated 24V/36V rails. |
| Buck Output Current | 2.6A maximum - sufficient for core logic rails (e.g., 3.3V @ 1.7A, 2.5V @ 450mA, 1.8V @ 450mA in typical application). |
| Switching Frequency | Adjustable 250kHz–2.5MHz via RT resistor - allows optimization of size (high fSW → small inductors/ceramics) vs. efficiency (low fSW → reduced switching loss). |
| Feedback Reference Voltage | 750mV ±15mV (buck & LDOs) - sets output voltage accuracy; enables precise 0.75V minimum VOUT with resistor divider scaling. |
| Overvoltage Shutdown | 38V threshold (typical) - disables switching under overvoltage to protect internal circuitry and external components. |
| Thermal Package | 28-lead 4mm × 5mm QFN with exposed GND pad (θJA = 34°C/W) - requires PCB thermal pad soldering for reliable 125°C junction operation. |
| Enable Threshold | 1.20V (typ) for switching enable; 500mV (typ) for bias-on - supports precise undervoltage lockout via resistor divider from VIN. |
Pinout & Package
LT3694IUFD#TRPBF is housed in a thermally enhanced 28-lead plastic QFN (4mm × 5mm) with exposed GND pad (Pin 29), requiring soldering to PCB for thermal and electrical integrity. Pin numbering follows standard top-view layout with GND on multiple pins (10, 11, 12, 13, 25, 26) and VIN on Pins 1, 27, 28.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pins 1, 27, 28) | Main input power supply | Supplies internal switch, reference, and startup circuits; must be locally bypassed with ceramic capacitor. |
| EN/UVLO (Pin 2) | Enable and undervoltage lockout input | Shuts down device below 0.35V; initiates bias circuits at >0.5V; enables switching above 1.20V - configurable as logic enable or analog UVLO. |
| SYNC (Pin 3) | External clock synchronization input | Accepts 250kHz–2.5MHz CMOS/TTL clock (1.8V–5V); forces LT3694IUFD#TRPBF to slave mode - eliminates beat frequencies in multi-regulator systems. |
| PGOOD (Pin 4) | Open-collector power-good indicator | Pulls low if any FB pin drops below 90% of target (e.g., due to overload or dropout) - used for system power sequencing and fault monitoring. |
| RT (Pin 5) | Frequency setting resistor connection | Sets switching frequency via resistor to GND (e.g., 40.2kΩ → 1MHz); internal 0.75V bias enables accurate fSW calculation: fSW = 49.8/(RT + 8.8) MHz. |
| TRK/SS1–3 (Pins 6, 7, 14) | Tracking/soft-start inputs | Override 0.75V FB reference when <0.75V - enables ratiometric start-up or soft-start via external capacitor; open if unused. |
| FB1–3 (Pins 15, 8, 13) | Negative error amplifier inputs | Regulated to 0.75V (or TRK/SS voltage if lower); connect resistor dividers from each output to set VOUT precisely. |
| DRV2/DRV3 (Pins 9, 12) | LDO base drive outputs | Provide up to 6V/15mA to drive external NPN pass transistors - enables high-current, low-noise linear regulation alongside buck output. |
| LIM2/LIM3 (Pins 10, 11) | LDO current limit sense inputs | Monitor voltage across external sense resistor connected to BIAS - trigger foldback current limit at 47–70mV (adjustable via resistor value). |
| VC1 (Pin 16) | Internal error amplifier output | Controls peak switch current; used for loop compensation; pulling to GND disables buck regulator - enables precise enable/disable control. |
| BIAS (Pin 17) | Internal regulator and boost supply | Must be connected to ≥3V source (typically VOUT1); supplies internal circuits and LDO base current - reduces dissipation vs. VIN sourcing. |
| BST (Pin 18) | Bootstrap drive voltage | Provides >VIN drive to internal NPN switch via external capacitor; requires ≥1.8V headroom above SW for full saturation and low VCESAT. |
| DA (Pin 19) | Diode current sense | Detects catch diode conduction at cycle start - delays switch-on during overload/short-circuit to limit inductor current and prevent runaway. |
| SW (Pins 20, 23, 24) | Switch node output | Connects to inductor and Schottky catch diode; carries high di/dt pulses - requires tight layout and low-inductance routing. |
| GND (Pins 10, 11, 12, 13, 25, 26) | Power and signal ground | Multiple dedicated GND pins minimize impedance; exposed pad (Pin 29) must be soldered to PCB ground plane for thermal and EMI performance. |
Key Features
| Feature | Design Value |
|---|---|
| Triple-output power management | Single IC delivers one high-current buck (2.6A) plus two independently programmable LDO controllers - reduces component count and board space in multi-rail systems. |
| Independent track/soft-start | Three TRK/SS pins allow coordinated startup sequencing (e.g., core before I/O) or individual soft-start via RC networks - prevents inrush current and bus droop. |
| Robust input transient protection | 70V absolute max rating with 38V overvoltage shutdown - ensures survivability in automotive, industrial, and telecom environments with load-dump or surge events. |
| Flexible clock interface | SYNC pin accepts external clock (LT3694 variant) - enables deterministic switching alignment across multiple regulators to suppress EMI peaks and beat frequencies. |
| Thermally optimized QFN | 28-lead 4mm × 5mm package with exposed GND pad (θJA = 34°C/W) - supports full 2.6A output at 125°C ambient when properly heatsinked to PCB. |
Applications
| Industrial PLC Power Supply | DSL/Cable Modem Power |
|---|---|
|
Use Scenario: Distributed 3.3V, 2.5V, and 1.8V rails powering FPGA, PHY, and memory in DIN-rail mounted controllers. IC Role / Device Role / Timing Role: Primary triple-output PMIC managing isolated rail generation, sequencing, and fault reporting via PGOOD. Use Value: Eliminates need for separate buck + dual LDO ICs; 4V–36V input accommodates wide-range 24V DC industrial supplies and brownout resilience. |
Use Scenario: Compact power solution for broadband access equipment requiring low-noise analog (2.5V) and digital (3.3V/1.8V) supplies. IC Role / Device Role / Timing Role: Central regulator with synchronized switching (via SYNC) to avoid interference with ADSL line signals and RF sections. Use Value: Adjustable 250kHz–2.5MHz fSW enables EMI tuning; LDO controllers provide ultra-low-noise 10Hz–100kHz output (<10µV RMS) for sensitive analog circuits. |
| Distributed Telecom Power | Automotive Infotainment Core Supply |
|
Use Scenario: Point-of-load regulation from 48V intermediate bus to 3.3V microcontroller, 2.5V SerDes, and 1.8V DDR in remote radio units. IC Role / Device Role / Timing Role: High-input-voltage buck-LDO hybrid delivering stable, sequenced outputs with overvoltage protection against 48V bus transients. Use Value: 36V max input + 70V transient survival meets Telcordia GR-1089 requirements; PGOOD enables system-level fault isolation and reset coordination. |
Use Scenario: Central power block for head unit MCU, display interface, and audio codec requiring clean, sequenced 3.3V, 2.5V, and 1.8V rails. IC Role / Device Role / Timing Role: Automotive-grade (I-temp) triple-output regulator with robust UVLO/overvoltage protection and thermal shutdown. Use Value: –40°C to 125°C operation certified for under-hood environments; EN/UVLO threshold (1.20V) enables precise battery undervoltage detection down to ~9V. |
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 |
|---|---|---|---|
| LT3694-1IUFD#TRPBF | Replaces SYNC pin with CLKOUT pin; provides clock output for synchronizing other regulators - no external sync source needed. | Preferred where master clock distribution is required (e.g., multi-IC power trees), not where external clock injection is available. | Select LT3694-1IUFD#TRPBF when acting as clock master; LT3694IUFD#TRPBF when slaving to existing system clock. |
| LT3573EFE#TRPBF | Single 3A buck with dual LDO controllers in 20-lead TSSOP; lacks TRACK/SS pins, PGOOD, and overvoltage shutdown - simpler feature set. | Suitable for cost-sensitive, space-constrained designs without sequencing or transient protection requirements. | Choose LT3573EFE#TRPBF only if TRK/SS, PGOOD, and 70V transient survival are unnecessary - otherwise LT3694IUFD#TRPBF offers superior integration. |
Compared with LT3694-1IUFD#TRPBF, the LT3694IUFD#TRPBF provides external clock synchronization instead of clock output, making it ideal for systems with a centralized timing source. Versus LT3573EFE#TRPBF, the LT3694IUFD#TRPBF adds critical features including power-good signaling, independent soft-start, and 70V transient protection - essential for industrial and telecom reliability.
Availability
LT3694IUFD#TRPBF is available at Aetrix Electronics and suitable for industrial PLC power supplies, DSL/cable modem power systems, and distributed telecom power applications requiring stable component supply, long-term lifecycle support, and AEC-Q200-aligned reliability.
Supply support for LT3694IUFD#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 product line was designed for compact, high-reliability multi-rail power conversion in harsh environments - integrating buck regulation, LDO control, sequencing, and protection in a single QFN package for space- and noise-constrained systems.
FAQ
What is the maximum input voltage the LT3694IUFD#TRPBF can withstand without damage?
The LT3694IUFD#TRPBF has an absolute maximum input voltage rating of 70V for non-repetitive 1-second transients. Its overvoltage shutdown activates at 38V (typical), disabling the internal switch to protect downstream circuitry. For continuous operation, the rated input range remains 4V to 36V - ensuring safe, reliable function in industrial and telecom power environments where load-dump events occur.
How does the LT3694IUFD#TRPBF support power supply sequencing across its three outputs?
The LT3694IUFD#TRPBF supports sequencing via three independent TRK/SS pins (TRK/SS1–3), each tied to a corresponding FB pin. When a TRK/SS pin voltage ramps up slower than 0.75V (e.g., via RC network), the associated regulator tracks that ramp - enabling coincident or staggered startup. This eliminates external sequencers and ensures controlled turn-on of core, I/O, and memory rails in FPGAs or processors.
Can the LT3694IUFD#TRPBF synchronize its switching frequency to an external clock source?
Yes - the LT3694IUFD#TRPBF includes a dedicated SYNC pin (Pin 3) that accepts external CMOS/TTL clock signals from 250kHz to 2.5MHz. When enabled, the internal oscillator locks to the external frequency, eliminating switching frequency beat notes and reducing EMI peaks. The RT resistor must be set to program a free-running frequency at least 20% below the sync frequency for stable locking.
What thermal design considerations apply to the LT3694IUFD#TRPBF's 28-lead QFN package?
The LT3694IUFD#TRPBF uses a 4mm × 5mm QFN with exposed thermal pad (Pin 29). This pad must be soldered to a PCB copper area connected to GND for effective heat dissipation. With θJA = 34°C/W, achieving full 2.6A output at 125°C ambient requires ≥250mm² of 2-oz copper thermal pad and 4+ thermal vias. Failure to solder the exposed pad risks thermal shutdown and premature failure under sustained load.
Does the LT3694IUFD#TRPBF integrate protection features beyond overcurrent and thermal shutdown?
Yes - the LT3694IUFD#TRPBF includes comprehensive protection: overvoltage shutdown (38V trip), undervoltage lockout (3.8V enable threshold), diode-current sensing (DA pin) for short-circuit limiting, frequency foldback during overload, and PGOOD monitoring of all three outputs. These features collectively ensure robust operation in unregulated or noisy input environments such as automotive or industrial power buses.
LT3694IUFD#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)
LT3694IUFD#TRPBF FAQ
1.How can I place an order for LT3694IUFD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3694IUFD#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 LT3694IUFD#TRPBF reliable?
The price and inventory of LT3694IUFD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3694IUFD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3694IUFD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3694IUFD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3694IUFD#TRPBF?
LT3694IUFD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3694IUFD#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 LT3694IUFD#TRPBF?
For technical support, including LT3694IUFD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3694IUFD#TRPBF requirements.
6.How does Aetrix verify that LT3694IUFD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3694IUFD#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 LT3694IUFD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3694IUFD#TRPBF?
All LT3694IUFD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3694IUFD#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 LT3694IUFD#TRPBF part is unused and in its original packaging.
Return procedure for LT3694IUFD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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