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Analog Devices Inc. LT3641IUFD#PBF
- Part No.:
- LT3641IUFD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 28-WFQFN Exposed Pad
- Datasheet:
-
LT3641IUFD#PBF.pdf
- Description:
- IC REG BCK ADJ 1.3A/1.DL 28QFN
- Quantity:
- Payment:
- Shipping:
Inventory:122
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Product details
Overview
LT3641IUFD#PBF from Analog Devices (formerly Linear Technology) is a dual-channel monolithic buck switching regulator IC with integrated power-on reset and window-mode watchdog timer. It delivers 5V/0.8A from 4–42V input (HV channel) and 3.3V/0.5A from 2.5–5.5V input (LV channel), operating synchronously at 350kHz–2.5MHz. Used in automotive ECU power rails requiring transient robustness and microprocessor supervision.
For engineers reviewing the LT3641IUFD#PBF datasheet, LT3641IUFD#PBF pinout, LT3641IUFD#PBF application, or LT3641IUFD#PBF equivalent, key selection criteria include its dual-buck architecture with independent soft-start, programmable POR/watchdog timing via external capacitors, 55V transient tolerance on VIN, and thermally enhanced 28-pin 4mm × 5mm QFN package with exposed GND pad.
Technical Context
The LT3641IUFD#PBF integrates two independent current-mode PWM controllers sharing one adjustable oscillator. The high-voltage channel uses a nonsynchronous NPN switch with internal 2.4A top switch and DA-pin-based valley current sensing; the low-voltage channel employs fully synchronous MOSFETs with PMOS/NMOS current limits of 1.9A/1.6A respectively. Both channels feature cycle-by-cycle current limiting and enter Burst Mode® at light loads to maintain efficiency >85% down to 10mA output.
Power-on reset is triggered when FB1 exceeds 1.165V and FB2 exceeds 550mV, with timeout set by CPOR capacitor (typ. 9.5ms). The window-mode watchdog monitors WDI pulse edges using CWDT capacitor (upper bound 32ms, lower bound 2ms at 820pF); failure asserts WDO and restarts RST timer. All timing functions are fully decoupled from switching operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range (HV) | 4V to 42V continuous, 55V nonrepetitive 1s transient - enables direct battery-input operation in 12V/24V automotive systems |
| VIN2 Range (LV) | 2.5V to 5.5V - supports post-regulation from HV output or independent low-voltage rail |
| Switching Frequency | 350kHz to 2.5MHz, RT-programmable - allows optimization of inductor size vs. efficiency (e.g., 2MHz → 2.2μH for 5V/0.8A) |
| FB1 Reference | 1.265V ±1.2% over –40°C to 125°C - sets precise 5V output with 100k/226k resistor divider (R1/R2) |
| FB2 Reference | 600mV ±2.5% over –40°C to 125°C - enables accurate 3.3V output with 49.9k/301k divider (R3/R4) |
| Quiescent Current | 290μA typical at VIN = 12V - ensures low standby power in always-on ECU modules |
| Thermal Package | 28-pin 4mm × 5mm QFN with exposed GND pad (θJC = 3.4°C/W) - supports 3W+ continuous dissipation without forced airflow |
Pinout & Package
LT3641IUFD#PBF is housed in a thermally enhanced 28-lead plastic QFN package (4mm × 5mm) with exposed GND pad (Pin 29), requiring soldering to PCB ground for thermal and electrical integrity. θJA = 43°C/W, θJC = 3.4°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Pin 1 (SYNC) | External clock input | Synchronizes both regulators to external 350kHz–2.5MHz signal; ignores SYNC until FB1 > 1.165V |
| Pin 2 (SS1) | HV soft-start control | Charges to 1.265V reference; capacitor to GND sets ramp time for 5V output startup |
| Pin 3 (FB1) | HV feedback node | Regulated to 1.265V; connects to resistor divider tap for precise 5V output setting |
| Pin 4 (RT) | Oscillator frequency set | Resistor to GND programs switching frequency (e.g., 32.4kΩ → 2MHz) |
| Pin 5 (RST2) | LV power-on reset output | Open-drain; asserts low until FB2 > 550mV + CPOR timeout (~9.5ms) |
| Pin 6 (RST1) | HV power-on reset output | Open-drain; asserts low until FB1 > 1.165V + CPOR timeout (~9.5ms) |
| Pin 7 (WDO) | Watchdog fault output | Open-drain; pulled low if WDI pulses violate window bounds (tWDL/tWDU) |
| Pin 8 (CWDT) | Watchdog timing capacitor | Capacitor to GND sets watchdog window (e.g., 820pF → tWDU = 32ms, tWDL = 2ms) |
| Pin 9 (CPOR) | POR/watchdog timer capacitor | Capacitor to GND sets both RST timeout and WDO assertion period (~9.5ms) |
| Pin 10 (WDE) | Watchdog enable input | Active-high; must be >0.7V to activate watchdog monitoring of WDI |
| Pin 11 (WDI) | Watchdog input | Accepts μP pulse train; falling edges monitored for window violation detection |
| Pins 12,13,20,23,29 | GND | Ground terminals including exposed pad - all must be soldered to PCB GND plane |
| Pin 15 (DA) | Catch diode current sense | Connects to anode of external catch diode; enables valley current limit protection |
| Pin 16 (SW1) | HV switch node | Connects to HV inductor and cathode of catch diode; handles up to 2.4A peak |
| Pin 17 (SW) | Bootstrap switch node | Drives BST capacitor; internal 5mA charge current starts switching when BST–SW > 2V |
| Pin 18 (BST) | Bootstrap supply | Connects to external boost diode/capacitor; supplies gate drive >VIN for HV NPN switch |
| Pin 19 (VIN) | HV input supply | Primary power input for HV channel and internal circuitry; bypass locally with ≥10μF ceramic |
| Pin 21 (VIN2) | LV input supply | Input for LV channel; can be tied to VOUT1 (5V) for two-stage regulation |
| Pin 22 (SW2) | LV switch node | Connects to LV inductor; synchronous NMOS/PMOS switching up to 1.6A/1.9A |
| Pin 24 (EN2) | LV enable input | Threshold = VFB2 − 100mV (≈500mV); 50mV hysteresis prevents chatter during UVLO |
| Pin 25 (SS2) | LV soft-start control | Charges to 0.6V reference; capacitor to GND sets ramp time for 3.3V output startup |
| Pin 26 (FB2) | LV feedback node | Regulated to 600mV; connects to resistor divider tap for precise 3.3V output setting |
| Pin 27 (PGOOD2) | LV power-good indicator | Open-drain; pulls low when FB2 < 560mV or > 640mV (40mV hysteresis) |
| Pin 28 (EN/UVLO) | HV enable/UVLO input | 1.26V threshold; 2μA hysteresis current enables accurate undervoltage lockout (e.g., 4V min) |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent soft-start | SS1 and SS2 pins allow separate capacitor-controlled ramp times for HV and LV outputs, preventing cross-regulation during startup |
| Window-mode watchdog | Monitors WDI pulse timing against programmable upper/lower bounds (tWDU/tWDL), detecting both stuck and runaway μP behavior |
| Nonsynchronous HV + synchronous LV | HV channel uses cost-effective external Schottky diode; LV channel eliminates diode loss with integrated MOSFETs, achieving >95% efficiency at 3.3V/0.5A |
| 55V transient protection | VIN withstands 55V for 1 second - eliminates need for external TVS in 24V automotive load-dump scenarios |
| Burst Mode® operation | Maintains <15mVpp output ripple and >80% efficiency at 10mA load, critical for low-power sleep modes |
| Thermally optimized QFN | Exposed GND pad and low θJC (3.4°C/W) enable full 3W dissipation in compact 4mm × 5mm footprint without heatsink |
Applications
| Automotive Engine Control Unit (ECU) | Industrial PLC I/O Module |
|---|---|
Use Scenario: Powering MCU core (3.3V) and CAN transceiver (5V) from 12V battery with load dump immunity. IC Role / Device Role / Timing Role: Dual-buck regulator providing isolated, sequenced 5V and 3.3V rails; POR ensures deterministic MCU boot after ignition; watchdog supervises firmware execution. Use Value: Eliminates need for discrete POR IC and external TVS; 55V transient rating survives ISO 7637-2 Pulse 5a; single-package solution reduces BOM count by 4 components. | Use Scenario: Generating 5V logic and 3.3V FPGA I/O supplies in DIN-rail mounted controller with wide input range. IC Role / Device Role / Timing Role: Primary DC-DC converter with programmable UVLO (via EN/UVLO divider) and fault signaling (PGOOD2, RST1/RST2) for system-level health monitoring. Use Value: 4–42V input range accommodates 24V nominal industrial supply with brownout margin; PGOOD2 enables safe I/O initialization before FPGA configuration. |
| Medical Diagnostic Imaging Subsystem | Telecom Remote Radio Head (RRH) |
Use Scenario: Powering ADC front-end (3.3V) and analog signal chain (5V) in portable ultrasound device with battery backup. IC Role / Device Role / Timing Role: Low-noise dual-output regulator with Burst Mode® for battery life extension; soft-start prevents inrush into sensitive analog circuits. Use Value: 290μA quiescent current extends battery runtime; independent SS1/SS2 pins enable staggered startup to avoid supply droop during sensor initialization. | Use Scenario: Providing bias rails for GaN PA drivers (5V) and digital control logic (3.3V) in outdoor base station RF unit. IC Role / Device Role / Timing Role: High-reliability power manager with watchdog supervision of FPGA-based control processor and thermal shutdown for PA thermal management. Use Value: Window watchdog detects both firmware hangs and excessive loop execution in real-time control; thermal shutdown (150°C) protects GaN devices during overload. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3642EFE#PBF | Single-channel 40V buck with integrated MOSFETs; no LV channel or watchdog; 3mm × 4mm TSSOP | Lacks dual-rail capability and system supervision features; suitable only for single-output designs | Select when only one regulated rail is needed and space is constrained; not a functional substitute for LT3641IUFD#PBF's dual-channel + watchdog architecture |
| TPS65270PWP | TI dual-buck (3A/2A), 4.5–18V input, no POR/watchdog, 24-pin HTSSOP | Lower input voltage ceiling (18V vs 42V); no transient protection or microprocessor supervision functions | Consider for cost-sensitive industrial applications with stable 12V input where 55V transient immunity and watchdog are unnecessary |
Compared with LTC3642EFE#PBF and TPS65270PWP, LT3641IUFD#PBF uniquely combines 42V input capability, 55V transient tolerance, dual independent buck regulation, and integrated window-mode watchdog - making it the only option for automotive ECU power management requiring simultaneous rail generation and μP supervision in a single 4mm × 5mm package.
Availability
LT3641IUFD#PBF is available at Aetrix Electronics and suitable for automotive electronic control units, industrial PLC I/O modules, and medical diagnostic imaging subsystems requiring stable component supply across extended temperature ranges (–40°C to 125°C).
Supply support for LT3641IUFD#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 acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for the LT3641 family.
The LT3641 product line was designed specifically for high-reliability dual-rail power management in automotive and industrial environments where input transients, microprocessor supervision, and thermal constraints demand integrated solutions beyond basic DC-DC conversion.
FAQ
What is the maximum input voltage rating for LT3641IUFD#PBF, and how does it handle transients?
The LT3641IUFD#PBF has a continuous input voltage rating of 4V to 42V on the VIN pin, with absolute maximum rating of 55V for nonrepetitive 1-second transients. This 55V tolerance enables direct connection to automotive batteries without external TVS diodes during load-dump events per ISO 7637-2 Pulse 5a. The device remains functional during the transient and resumes normal regulation once voltage returns within spec. LT3641IUFD#PBF incorporates internal clamping and robust layout design to sustain this rating without derating.
How do the power-on reset and watchdog timer functions interact in LT3641IUFD#PBF?
In LT3641IUFD#PBF, the power-on reset (POR) and watchdog timer operate independently but share the CPOR capacitor for timing. RST1 and RST2 assert low until their respective feedback nodes (FB1 > 1.165V, FB2 > 550mV) are reached, then time out after CPOR delay (~9.5ms). The watchdog starts only after RST2 releases, using the same CPOR capacitor for its assertion period but separate CWDT capacitor for window boundaries. WDO assertion triggers a new RST timeout, enabling chained reset recovery. LT3641IUFD#PBF thus provides layered supervision: POR ensures clean boot, watchdog ensures runtime integrity.
Can LT3641IUFD#PBF generate 5V and 3.3V outputs simultaneously, and what external components are required?
Yes, LT3641IUFD#PBF is configured by default to deliver 5V/0.8A (HV channel) and 3.3V/0.5A (LV channel) simultaneously. Required external components include: two inductors (2.2μH for HV, 4.7μH for LV), input/output capacitors (10–22μF ceramic), feedback dividers (100k/226k for 5V, 49.9k/301k for 3.3V), BST diode/capacitor, catch diode for HV channel, and timing capacitors (220pF CPOR, 820pF CWDT). No additional ICs are needed - LT3641IUFD#PBF integrates all control, drivers, and supervision logic.
What thermal performance can be expected from LT3641IUFD#PBF in its QFN package?
LT3641IUFD#PBF in the 4mm × 5mm QFN package achieves θJC = 3.4°C/W and θJA = 43°C/W with standard 2-layer PCB and 1-in² copper pour under the exposed pad. At 3W total dissipation (e.g., 5V/0.8A + 3.3V/0.5A at 85% efficiency), junction temperature rise above ambient is ~10°C above case and ~130°C above ambient - well within the –40°C to 125°C operating range when ambient is ≤25°C. For higher ambient, thermal vias to inner ground layers reduce θJA to <30°C/W. LT3641IUFD#PBF includes thermal shutdown at ~160°C for safety.
Is LT3641IUFD#PBF pin-compatible with other variants in the LT3641 family?
Yes, LT3641IUFD#PBF is pin-compatible with all LT3641 variants in the same UFD (QFN) package, including LT3641EUFD#PBF and LT3641HUFD#PBF. Differences are limited to temperature grade (I-grade = –40°C to 125°C), AC/DC performance specifications, and screening - all share identical pinout, electrical behavior, and PCB footprint. Migration between grades requires no layout change; only qualification testing differs. LT3641IUFD#PBF is not pin-compatible with FE (TSSOP) variants due to different pin numbering and package dimensions.
LT3641IUFD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 28-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):
- 2.5V
- Voltage - Input (Max):
- 42V
- Voltage - Output (Min/Fixed):
- 0.6V, 1.265V
- Voltage - Output (Max):
- 39.48V
- Current - Output:
- 1.3A, 1.1A
- Frequency - Switching:
- 500kHz ~ 2MHz
- Synchronous Rectifier:
- Both
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 28-QFN (4x5)
LT3641IUFD#PBF FAQ
1.How can I place an order for LT3641IUFD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3641IUFD#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 LT3641IUFD#PBF reliable?
The price and inventory of LT3641IUFD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3641IUFD#PBF is usually 5 days.
3.What payment methods are accepted for LT3641IUFD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3641IUFD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3641IUFD#PBF?
LT3641IUFD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3641IUFD#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 LT3641IUFD#PBF?
For technical support, including LT3641IUFD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3641IUFD#PBF requirements.
6.How does Aetrix verify that LT3641IUFD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3641IUFD#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 LT3641IUFD#PBF meets industry standards.
7.What is the process for return or replacement of LT3641IUFD#PBF?
All LT3641IUFD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3641IUFD#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 LT3641IUFD#PBF part is unused and in its original packaging.
Return procedure for LT3641IUFD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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