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Analog Devices Inc. LT3905IUD#PBF
- Part No.:
- LT3905IUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3905IUD#PBF.pdf
- Description:
- IC REG BOOST ADJ 350MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:132
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Product details
Overview
LT3905IUD#PBF from Analog Devices (formerly Linear Technology) is a fixed-frequency current-mode boost DC/DC converter with integrated APD current monitoring and regulation, designed specifically for biasing avalanche photodiodes in optical receivers. It delivers up to 54V output from 2.7V–12V input, features 65V/350mA internal DMOS switch, integrated Schottky rectifier, and monitors APD current from 3µA to 3mA with ±2% relative accuracy.
For engineers reviewing the LT3905IUD#PBF datasheet, LT3905IUD#PBF pinout, LT3905IUD#PBF application, or LT3905IUD#PBF equivalent, key selection considerations include its 1MHz/2MHz selectable switching frequency, four-decade APD current monitoring range, programmable loss-of-signal and fast overload protection, and compact 3mm × 3mm QFN-16 package with exposed thermal pad.
Technical Context
The LT3905IUD#PBF implements a current-mode boost topology with internal compensation, 400mA switch current limit, and 0.75Ω on-resistance DMOS FET. Its control loop supports dual regulation paths: FB pin for fixed-output voltage and ILIM_MON pin for adaptive APD current regulation.
Three dedicated current mirror outputs-MON (1:5), LOS_MON (1:10), and ILIM_MON (1:20)-feed independent comparators and clamped buffers, enabling simultaneous APD current monitoring, loss-of-signal detection (with 20mV hysteresis), and fast overload limiting (1.348V threshold with 50mV release hysteresis).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.7V to 12V - supports common low-voltage rails including 3.3V and 5V systems without external LDO pre-regulation. |
| Output Voltage Range | Up to 54V - sufficient for high-bias APDs used in fiber optic receivers and LiDAR front-ends. |
| APD Current Monitoring Accuracy | ±2% over 3µA–3mA - enables precise optical power calibration and closed-loop gain control in transimpedance amplifier stages. |
| Switching Frequency | Selectable 1MHz or 2MHz via fSEL pin - allows trade-off between EMI filtering complexity and inductor size in space-constrained modules. |
| Internal Power Switch | 65V, 350mA DMOS with 0.75Ω RDS(on) - eliminates need for external high-voltage switch and reduces BOM count and layout area. |
| Quiescent Current (Shutdown) | <1µA - critical for battery-powered optical sensors and always-on receiver modules requiring ultra-low standby power. |
| Operating Temperature Range | –40°C to +125°C - qualified for industrial and telecom-grade optical equipment deployed in uncontrolled environments. |
Pinout & Package
LT3905IUD#PBF is housed in a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (Pin 17), which must be soldered to PCB ground plane for thermal management and electrical stability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ILIM (Pin 1) | Open-drain overload indicator | Pulls low when ILIM_MON ≥ 1.348V; signals active APD current limiting; requires external pull-up for logic-level interfacing. |
| LOS_MON (Pin 2) | Loss-of-signal monitor output | Sources 10% of APD current; feeds comparator for optical signal dropout detection; clamped to 2.25V internally. |
| ILIM_MON (Pin 3) | APD overload monitor input | Sources 5% of APD current; primary feedback for adaptive APD current regulation and fast limiter trigger at 1.348V. |
| MON (Pin 4) | Primary APD current monitor | Sources 20% of APD current; enables high-accuracy system-level monitoring and calibration; clamped to 2.25V. |
| APD (Pin 5) | APD cathode connection | High-voltage node rated to 65V; carries full APD bias current (up to 7mA typ); must be decoupled locally for noise immunity. |
| MONIN (Pin 6) | APD supply and monitor reference | Connects to VOUT via low-pass filter; supplies all current mirrors and sets common-mode reference for MON/LOS_MON/ILIM_MON. |
| SW (Pin 7) | Switch node | Drain of internal DMOS and anode of integrated Schottky; high di/dt node requiring minimal trace length and tight loop layout. |
| VOUT (Pin 8) | Boost output | Cathode of internal Schottky; connects to output capacitor and APD supply rail; maximum 65V rating. |
| GND (Pins 9 & 17) | Power and thermal ground | Exposes thermal pad (Pin 17) - mandatory solder connection to large copper pour for junction temperature control below 125°C. |
| VIN (Pin 10) | Input supply | 2.7V–12V input; requires local 1µF ceramic bypass capacitor placed adjacent to pin for EMI suppression. |
| EN/UVLO (Pin 11) | Enable and undervoltage lockout | 1.2V threshold with 25mV hysteresis; supports resistor-divider programming for custom UVLO or direct digital enable. |
| CTRL (Pin 12) | External reference input | Overrides internal 1.248V FB reference when <1.248V; enables dynamic APD bias adjustment during operation. |
| LOS (Pin 13) | Open-drain loss-of-signal flag | Asserts high when LOS_MON falls below LOS_ADJ threshold; requires external pull-up; sink capability ≤2mA. |
| LOS_ADJ (Pin 14) | LOS comparator reference | Sets negative input of LOS comparator; tied to VIN for fixed 1.248V threshold or driven externally for programmable trip point. |
| FB (Pin 15) | Feedback input | Regulated to 1.248V (or CTRL voltage); used with resistor divider to set max output voltage; pulled >1.8V disables switching. |
| fSEL (Pin 16) | Frequency select | Tied to GND = 1MHz; tied to VIN = 2MHz; threshold 0.9V with 50mV hysteresis; no external bias required. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated Schottky rectifier | Eliminates external diode, reduces solution size by ~30%, and improves efficiency by removing forward voltage drop and reverse recovery losses. |
| Four-decade APD current monitoring | Accurate 3µA–3mA sensing enables single-device support across diverse optical link budgets-from low-light sensing to high-power burst-mode receivers. |
| Programmable loss-of-signal indicator | Configurable trip point via LOS_ADJ and LOS_MON resistor allows system-specific optical signal dropout thresholds without firmware changes. |
| Fast APD current limiter with indicator | Responds within nanoseconds to optical flooding events; actively limits APD current while asserting ILIM flag-prevents device damage and maintains signal integrity. |
| Internally compensated current-mode control | Removes need for external compensation components; ensures stable operation across wide input/output and load ranges with minimal design iteration. |
| Adjustable output voltage via CTRL pin | Enables real-time APD bias tuning during system calibration or adaptive gain control loops-critical for temperature-compensated optical receivers. |
Applications
| Fiber Optic Receiver Modules | Optical Time-Domain Reflectometers (OTDR) |
|---|---|
|
Use Scenario: High-sensitivity 1310nm/1550nm SFP+ and XFP transceivers requiring stable APD bias under varying optical input power. IC Role / Device Role / Timing Role: Primary APD bias supply and real-time current monitor; regulates APD voltage to maintain constant multiplication factor despite temperature drift. Use Value: ±2% APD current accuracy enables <1dB gain error across temperature, supporting 10Gbps+ data rates with BER <10⁻¹². |
Use Scenario: Pulse-based OTDR front-end where APD must handle high peak currents during short optical pulses and recover rapidly. IC Role / Device Role / Timing Role: Fast-response APD bias controller with overload limiting; synchronizes APD bias with laser pulse timing via CTRL pin modulation. Use Value: Nanosecond-scale ILIM response prevents APD saturation during 10ns–100ns pulses, preserving dynamic range and measurement linearity. |
| LiDAR Signal Conditioning | Industrial Optical Sensors |
|
Use Scenario: Automotive and robotics LiDAR receivers detecting weak return signals from distant or low-reflectivity targets. IC Role / Device Role / Timing Role: Low-noise, high-PSRR APD bias generator; MON output feeds TIA feedback loop for automatic gain control. Use Value: Integrated low-ESR filtering on MONIN and 2.25V clamping on MON reduce broadband noise to <100nV/√Hz, improving SNR by 6dB. |
Use Scenario: Factory-floor smoke detectors, gas analyzers, or position sensors operating in harsh industrial environments with wide ambient temperature swings. IC Role / Device Role / Timing Role: Robust APD bias IC with –40°C to +125°C operation; LOS flag triggers maintenance alerts before optical path degradation causes failure. Use Value: Guaranteed performance over full temp range eliminates derating, reducing qualification time and enabling single-BOM deployment across global sites. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar APD bias supply applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX3865ESE+ | Fixed 3.3V input only; no adjustable switching frequency; lacks ILIM_MON fast limiter; ±5% APD current accuracy. | Targeted at lower-cost, lower-performance optical modules where 100ns overload response is not required. | Choose MAX3865ESE+ only if input is strictly 3.3V and ±5% APD current tolerance is acceptable. |
| LM3489MMX/NOPB | General-purpose boost controller (no integrated APD monitor); requires external current sense, op-amps, and comparators for APD functions. | Used in custom APD bias designs where flexibility outweighs BOM count and layout area constraints. | Choose LM3489MMX/NOPB only when full analog signal chain customization is needed and board space is not constrained. |
Compared with MAX3865ESE+ and LM3489MMX/NOPB, LT3905IUD#PBF provides superior integration (monitors, regulators, protectors in one QFN), tighter APD current accuracy (±2% vs ±5%), and faster overload response-reducing total solution size by >40% and eliminating 12+ external components.
Availability
LT3905IUD#PBF is available at Aetrix Electronics and suitable for fiber optic transceivers, LiDAR receivers, OTDR test equipment, and industrial optical sensors requiring stable component supply with guaranteed long-term availability.
Supply support for LT3905IUD#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.
The LT3905IUD#PBF belongs to Linear's precision optical power management product line, engineered specifically for high-reliability, low-noise APD biasing in telecom, test & measurement, and sensing applications.
FAQ
What is the maximum APD bias voltage achievable with LT3905IUD#PBF?
The LT3905IUD#PBF supports output voltages up to 54V, as confirmed in the Typical Application schematic and Absolute Maximum Ratings table. This is achieved using external feedback resistors on the FB pin, with the internal 1.248V reference or an external voltage applied to the CTRL pin. The APD pin is rated to 65V, providing 11V margin for transient suppression and layout parasitics.
How does LT3905IUD#PBF achieve ±2% APD current monitoring accuracy over four decades?
The LT3905IUD#PBF achieves ±2% accuracy through matched current mirror architecture with on-chip trimming, internal 2.25V clamping to prevent saturation, and temperature-compensated gain stages validated across –40°C to +125°C. Electrical Characteristics tables specify 0.196–0.204 gain (1:5) for 3µA–3mA range, and MON accuracy vs temperature plots confirm <±1.5% error across full range.
Can LT3905IUD#PBF operate with a 2.5V input supply?
No. The LT3905IUD#PBF has a minimum input voltage of 2.7V per Absolute Maximum Ratings and Electrical Characteristics tables. Operation below 2.7V is not characterized or guaranteed; attempting to use 2.5V may result in unstable regulation, failure to start, or undefined behavior in the EN/UVLO and internal bias circuits.
What is the role of the exposed thermal pad (Pin 17) on LT3905IUD#PBF?
The exposed thermal pad (Pin 17) is electrically and thermally connected to GND. Per the Pin Configuration diagram and thermal specs (θJA = 68°C/W), it must be soldered to a large PCB copper area to maintain junction temperature ≤125°C under full load. Omitting this connection risks thermal shutdown, parameter drift, or premature failure-especially at high output voltages and ambient temperatures.
How is the loss-of-signal threshold programmed on LT3905IUD#PBF?
The loss-of-signal threshold is programmed by connecting a resistor from LOS_MON (Pin 2) to GND. For internal 1.248V threshold (LOS_ADJ tied to VIN), use RLOS_MON = 10 × 1.248V / IAPD_LOS. For external threshold, replace 1.248V with the applied LOS_ADJ voltage. The comparator includes 20mV built-in hysteresis to prevent chatter near trip point.
LT3905IUD#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):
- 12V
- Voltage - Output (Min/Fixed):
- 1.248V
- Voltage - Output (Max):
- 65V (Switch)
- Current - Output:
- 350mA (Switch)
- Frequency - Switching:
- 1MHz ~ 2MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LT3905IUD#PBF FAQ
1.How can I place an order for LT3905IUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3905IUD#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 LT3905IUD#PBF reliable?
The price and inventory of LT3905IUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3905IUD#PBF is usually 5 days.
3.What payment methods are accepted for LT3905IUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3905IUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3905IUD#PBF?
LT3905IUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3905IUD#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 LT3905IUD#PBF?
For technical support, including LT3905IUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3905IUD#PBF requirements.
6.How does Aetrix verify that LT3905IUD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3905IUD#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 LT3905IUD#PBF meets industry standards.
7.What is the process for return or replacement of LT3905IUD#PBF?
All LT3905IUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3905IUD#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 LT3905IUD#PBF part is unused and in its original packaging.
Return procedure for LT3905IUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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