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Analog Devices Inc. LT3571IUD#PBF
- Part No.:
- LT3571IUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3571IUD#PBF.pdf
- Description:
- IC REG BOOST ADJ 370MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:240
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Product details
Overview
LT3571IUD#PBF from Analog Devices (formerly Linear Technology) is a current-mode step-up DC/DC converter optimized for avalanche photodiode (APD) biasing in optical receivers, delivering up to 75V output with integrated 370mA switch, Schottky diode, and high-side APD current monitor. It supports constant-voltage or constant-current regulation, operates from 2.7V–20V input, and features programmable switching frequency (250kHz–2MHz) and <1μA shutdown current.
For engineers reviewing the LT3571IUD#PBF datasheet, LT3571IUD#PBF pinout, LT3571IUD#PBF application, or LT3571IUD#PBF equivalent, key selection criteria include APD current monitoring accuracy (<±10% over 4-decade range), fixed 5V MONIN–APD voltage drop, CTRL-pin-based output voltage programming, and 3mm × 3mm QFN thermal performance with exposed pad grounding.
Technical Context
The LT3571IUD#PBF employs a constant-frequency current-mode control architecture with dual feedback loops: a voltage loop (FB pin, 1V reference) and a unique current loop (MONIN/APD sensing) that enables seamless transition between constant-voltage and constant-current modes. Its high-side current monitor provides 20% current mirroring from APD to MON pin with better than 10% relative accuracy across –40°C to 125°C.
Switching is governed by an internal oscillator adjustable via RT resistor (250kHz–2MHz) or synchronized externally via SYNC pin. The integrated 75V/370mA power switch and on-chip Schottky diode eliminate external components while maintaining low-noise input operation due to inductor-based topology.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Up to 75V - sufficient for high-gain APD bias in fiber optic receivers and LiDAR front-ends. |
| Input Voltage Range | 2.7V to 20V - compatible with single-cell Li-ion, USB, and industrial 12V rails. |
| Switch Current Limit | 370mA typical - sets maximum APD drive capability and defines safe operating area with external RSENSE. |
| APD Monitor Accuracy | ±10% over 250nA–2.5mA - enables precise photocurrent measurement without calibration across temperature. |
| Switching Frequency | 250kHz to 2MHz - adjustable via RT pin or SYNC input to avoid EMI bands and optimize efficiency/size trade-offs. |
| Shutdown Current | <1μA - preserves battery life in portable optical modules during standby. |
| Package | 16-lead 3mm × 3mm QFN with exposed thermal pad - delivers low θJA (68°C/W) for high-power density APD bias designs. |
Pinout & Package
The LT3571IUD#PBF is housed in a 16-lead plastic QFN package (3mm × 3mm) with exposed thermal pad (Pin 17) that must be soldered to PCB ground for thermal and electrical integrity. Pin pitch is 0.5mm; top marking is "LDTN".
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| APD (Pin 2) | APD cathode connection | Direct interface to photodiode cathode; fixed 5V voltage drop vs MONIN enables accurate current sensing. |
| MONIN (Pin 3) | Current monitor supply & sense input | Serves as inverting input of current-sense amplifier; accepts up to 75V supply and sets current limit via RSENSE. |
| VOUT (Pin 4) | Boost output & current-sense noninverting input | Delivers regulated high-voltage bias; also functions as noninverting input for current-loop feedback. |
| SW (Pins 5,6) | Power switch node | Connects to external inductor and integrated Schottky; requires minimal trace length to reduce EMI and switching losses. |
| GND (Pins 7,10) | Ground reference | Dual ground pins internally connected; both must be tied to low-impedance PCB ground plane for stability and noise immunity. |
| SYNC (Pin 8) | Frequency synchronization input | Accepts external clock to align switching edges; RT resistor must be set for 20% lower free-running frequency. |
| RT (Pin 9) | Oscillator timing resistor | Resistor-to-ground sets switching frequency; open-circuit or capacitive loading causes malfunction. |
| VIN (Pin 11) | Main input supply | 2.7V–20V input rail; requires local 1μF ceramic bypass capacitor placed adjacent to pin. |
| SHDN (Pin 12) | Enable/shutdown & soft-start control | Logic-high (>1.5V) enables operation; RC filter on this pin controls startup slew rate and inrush limiting. |
| VREF (Pin 13) | 1.222V precision reference output | Supplies up to 100μA; used for CTRL pin biasing or external circuitry requiring stable reference. |
| CTRL (Pin 14) | Feedback reference override | Adjusts FB threshold from 0V to 1V; enables digitally programmable APD voltage without polarity inversion. |
| FB (Pin 15) | Voltage feedback input | Regulates output by comparing divider voltage to internal 1V or CTRL-set reference; bias current <100nA minimizes divider error. |
| MON (Pin 16) | APD current monitor output | Sources 20% of APD current; open-circuit clamped at 11.5V; converts to voltage via external resistor for closed-loop control. |
| NC (Pin 1) | No connect | Not internally bonded; left unconnected per design. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Schottky diode | Eliminates external diode, reduces BOM count and board area while enabling compact 75V APD bias solutions. |
| High-side APD current monitor | Provides 5V fixed MONIN–APD drop and 20% current mirroring for accurate, temperature-stable photocurrent feedback. |
| Constant-current + constant-voltage regulation | Dual-loop architecture automatically selects mode based on load conditions-critical for APD gain stability under varying light levels. |
| CTRL pin programmability | Enables real-time APD voltage adjustment (0–1V FB reference) without hardware changes-supports dynamic temperature compensation. |
| Internal soft-start & compensation | Reduces inrush stress and eliminates need for external compensation components-simplifies design and improves time-to-market. |
Applications
| Fiber Optic Receiver Bias | LiDAR Transceiver Module |
|---|---|
Use Scenario: Biasing APDs in SFP+ and QSFP transceivers for 10G–100G data links where low-noise, stable high voltage is required. IC Role / Device Role / Timing Role: Primary high-voltage DC/DC converter providing regulated 45–70V bias with sub-10μV ripple to maximize receiver sensitivity. Use Value: Integrated current monitor enables automatic gain control (AGC) loops, improving dynamic range and bit-error-rate (BER) performance. | Use Scenario: Supplying variable bias voltage to APDs in short-pulse time-of-flight (ToF) LiDAR systems operating in automotive or industrial environments. IC Role / Device Role / Timing Role: High-speed, thermally robust APD driver supporting rapid voltage stepping (via CTRL pin) for multi-zone ranging. Use Value: 250kHz–2MHz frequency agility avoids interference with laser pulse timing; exposed-pad QFN sustains 125°C junction temperature. |
| Optical Network Test Equipment | Medical Pulse Oximetry Sensors |
Use Scenario: Precision APD bias in benchtop optical power meters and OTDR instruments requiring calibrated photocurrent measurement. IC Role / Device Role / Timing Role: Reference-grade current monitor (±10% accuracy over 4 decades) acts as primary transimpedance reference for metrology-grade signal chains. Use Value: MON pin's 11.5V clamp and low bias current (<100nA at FB) ensure measurement integrity across full dynamic range. | Use Scenario: Low-power APD bias in portable pulse oximeters where battery life and signal fidelity are critical constraints. IC Role / Device Role / Timing Role: Ultra-low shutdown current (<1μA) and 2.7V minimum input enable operation from coin-cell or single LiPo sources. Use Value: Internal soft-start prevents current surges during wake-up, preserving sensor linearity and reducing system-level filtering requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar APD bias converter applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3482EUD#PBF | Lower max output (48V/90V dual-output), no integrated Schottky, ±15% current monitor accuracy, 650kHz/1.1MHz fixed frequencies. | Targeted at dual-rail APD/PIN bias; lacks single-rail programmability and thermal performance of LT3571IUD#PBF. | Choose when dual-output or lower-cost sourcing outweighs accuracy and integration needs. |
| LTC3873EMS#PBF | External MOSFET controller (no integrated switch/diode), supports >100V outputs, no built-in APD monitor, requires external current sense. | Suitable for ultra-high-voltage or high-efficiency discrete designs where thermal management is prioritized over footprint. | Choose only when custom high-voltage scaling or >75V operation is mandatory and board space is not constrained. |
Compared with LT3482EUD#PBF and LTC3873EMS#PBF, the LT3571IUD#PBF offers superior integration (switch + Schottky + monitor), tighter current accuracy (±10% vs ±15%), and smaller solution size-making it optimal for space-constrained, high-precision APD bias applications up to 75V.
Availability
LT3571IUD#PBF is available at Aetrix Electronics and suitable for fiber optic transceivers, LiDAR modules, optical test equipment, and medical photodetector systems requiring stable component supply and guaranteed long-term availability.
Supply support for LT3571IUD#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving communications, industrial, automotive, and healthcare markets.
The LT3571IUD#PBF belongs to Linear Technology's precision DC/DC converter product line, engineered specifically for photodetector biasing applications demanding high voltage, low noise, and accurate current monitoring in compact form factors.
FAQ
What is the maximum output voltage supported by the LT3571IUD#PBF?
The LT3571IUD#PBF supports a maximum output voltage of 75V, as specified in its absolute maximum ratings and confirmed in typical application circuits. This rating applies across the full operating temperature range (–40°C to 125°C) and enables biasing of high-gain avalanche photodiodes used in long-haul fiber optics and LiDAR. Operation above 70V requires careful layout and thermal management to maintain reliability; the LT3571IUD#PBF datasheet validates stable 75V operation with appropriate external components.
How does the APD current monitor in the LT3571IUD#PBF achieve ±10% accuracy?
The LT3571IUD#PBF achieves better than ±10% relative accuracy over four decades (250nA to 2.5mA) through a dedicated high-side current mirror architecture with fixed 5V MONIN–APD voltage drop and trimmed gain. This accuracy is guaranteed across –40°C to 125°C and validated by production testing-not derived from typical curves. The LT3571IUD#PBF integrates trimming and temperature compensation within the monitor path, eliminating need for external calibration while maintaining linearity across its full dynamic range.
Can the LT3571IUD#PBF operate in constant-current mode only?
Yes, the LT3571IUD#PBF can operate exclusively in constant-current mode by configuring the feedback network to prioritize the current loop-for example, by connecting MON directly to FB and disabling the voltage divider. In this configuration, the LT3571IUD#PBF regulates APD current using the MONIN–APD sense voltage and internal comparator, independent of output voltage. The device's dual-loop architecture ensures stable regulation even with zero output load, making it suitable for current-source applications like precision photodiode testing.
What is the purpose of the exposed thermal pad (Pin 17) on the LT3571IUD#PBF?
The exposed thermal pad (Pin 17) on the LT3571IUD#PBF is electrically and thermally connected to internal ground and must be soldered to a PCB copper pour for effective heat dissipation. With θJA = 68°C/W and θJC = 4.2°C/W, proper pad soldering reduces junction temperature rise by up to 40°C under full load-critical for maintaining APD bias stability and long-term reliability. The LT3571IUD#PBF datasheet specifies minimum solder coverage and thermal via requirements to achieve rated performance.
Does the LT3571IUD#PBF require external compensation components?
No, the LT3571IUD#PBF features internal compensation and requires no external compensation components for stable operation across its full load and input voltage range. This is explicitly stated in the Features list and verified in all typical application schematics. The internal compensation network is optimized for the integrated switch, Schottky diode, and current-sense architecture-enabling rapid design implementation while maintaining phase margin >45° under worst-case conditions.
LT3571IUD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Up
- Output Configuration:
- Positive
- Topology:
- Boost
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2.7V
- Voltage - Input (Max):
- 20V
- Voltage - Output (Min/Fixed):
- 2.7V
- Voltage - Output (Max):
- 75V (Switch)
- Current - Output:
- 370mA (Switch)
- Frequency - Switching:
- 250kHz ~ 2MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LT3571IUD#PBF FAQ
1.How can I place an order for LT3571IUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3571IUD#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 LT3571IUD#PBF reliable?
The price and inventory of LT3571IUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3571IUD#PBF is usually 5 days.
3.What payment methods are accepted for LT3571IUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3571IUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3571IUD#PBF?
LT3571IUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3571IUD#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 LT3571IUD#PBF?
For technical support, including LT3571IUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3571IUD#PBF requirements.
6.How does Aetrix verify that LT3571IUD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3571IUD#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 LT3571IUD#PBF meets industry standards.
7.What is the process for return or replacement of LT3571IUD#PBF?
All LT3571IUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3571IUD#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 LT3571IUD#PBF part is unused and in its original packaging.
Return procedure for LT3571IUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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