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Analog Devices Inc. LT3905IUD#TRPBF
- Part No.:
- LT3905IUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3905IUD#TRPBF.pdf
- Description:
- IC REG BOOST ADJ 350MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,400
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Product details
Overview
LT3905IUD#TRPBF 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 a 65V/350mA DMOS switch, integrated Schottky rectifier, and monitors APD current from 3µA to 3mA with ±2% relative accuracy.
For engineers reviewing the LT3905IUD#TRPBF datasheet, LT3905IUD#TRPBF pinout, LT3905IUD#TRPBF application, or LT3905IUD#TRPBF equivalent, this page provides verified functional identity, validated 16-pin QFN package mapping, confirmed APD bias control architecture, real-world loss-of-signal and overload protection behavior, and two rigorously cross-checked alternative parts for optical receiver designs requiring high-accuracy photodiode current regulation.
Technical Context
The LT3905IUD#TRPBF implements a current-mode boost topology with internal compensation, selectable 1MHz/2MHz switching frequency via fSEL pin, and dual regulation paths: FB pin for fixed-output voltage control and ILIM_MON pin for adaptive APD current regulation. Its error amplifier accepts either internal 1.248V reference or external reference via CTRL pin.
Three dedicated monitor outputs-MON (20% IAPD), LOS_MON (10% IAPD), and ILIM_MON (5% IAPD)-feed independent comparators and clamped buffers, enabling simultaneous loss-of-signal detection, fast overload limiting (1.348V threshold with 50mV hysteresis), and precise current feedback without external op-amps.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 2.7V to 12V - supports single-cell Li-ion, USB, and industrial 3.3V/5V rails without pre-regulation. |
| Output Voltage Range | Up to 54V - programmable via FB resistor divider or dynamic control via CTRL pin for APD bias tuning. |
| APD Current Monitoring Range | 3µA to 3mA with ±2% relative accuracy - enables linear optical power measurement across four decades. |
| Switching Frequency | Selectable 1MHz or 2MHz - higher frequency allows smaller magnetics; lower frequency improves efficiency at light loads. |
| Internal Power Switch | 65V, 350mA DMOS FET with 0.75Ω RDS(on) - eliminates external high-voltage switch and reduces BOM count. |
| Integrated Schottky Diode | 780mV forward drop at 150mA - removes need for external diode, minimizes conduction loss and layout area. |
| Shutdown Current | <1µA - enables ultra-low-power standby in battery-operated optical modules. |
| Operating Temperature | –40°C to +125°C - qualified for industrial and telecom infrastructure environments. |
Pinout & Package
LT3905IUD#TRPBF is housed in a 3mm × 3mm, 16-lead plastic QFN package with exposed thermal pad (Pin 17 = GND). The compact footprint supports high-density optical module layouts while enabling efficient heat dissipation when the exposed pad is soldered to PCB ground plane.
| 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 interface. |
| LOS_MON (Pin 2) | Loss-of-signal monitor output | Sources 10% of APD current; feeds comparator for LOS detection; clamped to 2.25V to prevent overvoltage. |
| ILIM_MON (Pin 3) | APD current limit monitor | Sources 5% of APD current; sets regulation threshold (1.248V) and fast-limit threshold (1.348V); must not float. |
| MON (Pin 4) | Primary APD current monitor | Sources 20% of APD current; used for precision system-level monitoring or closed-loop bias control; clamped to 2.25V. |
| APD (Pin 5) | APD cathode connection | High-voltage node rated to 65V; sinks up to 7mA APD current; directly interfaces photodiode cathode. |
| MONIN (Pin 6) | APD supply and monitor power rail | Connects to VOUT via low-pass filter; supplies all current monitors and defines APD bias path; noise-sensitive node. |
| SW (Pin 7) | Switch node | Drain of internal DMOS FET and anode of internal Schottky; high di/dt node requiring minimized trace length. |
| VOUT (Pin 8) | Boost output | Cathode of internal Schottky; connects to output capacitor; delivers regulated high-voltage bias to MONIN/APD. |
| GND (Pins 9 & 17) | Power and thermal ground | Pin 17 is exposed pad - mandatory solder connection to large PCB copper area for thermal management and noise control. |
| VIN (Pin 10) | Input supply | 2.7V–12V input; requires local 1µF ceramic bypass capacitor placed adjacent to pin for stability. |
| EN/UVLO (Pin 11) | Enable and undervoltage lockout | 1.2V threshold with 25mV hysteresis; supports resistor-divider programming 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; requires external pull-up; sink-limited to 2mA. |
| LOS_ADJ (Pin 14) | LOS comparator reference input | Sets negative input of LOS comparator; tied to VIN for 1.248V threshold or driven externally for adjustable trip point. |
| FB (Pin 15) | Feedback input | Regulated to 1.248V (or CTRL voltage); connects to resistor divider from MONIN to set max output voltage. |
| fSEL (Pin 16) | Frequency select | Tie to GND for 1MHz, to VIN for 2MHz; determines switching frequency and impacts inductor size/noise trade-off. |
Key Features
| Feature | Design Value |
|---|---|
| Four-decade APD current monitoring | 3µA–3mA range with ±2% relative accuracy enables calibrated optical power measurement across fiber link budgets. |
| Programmable loss-of-signal detection | Configurable threshold via LOS_ADJ and LOS_MON resistor; 20mV internal hysteresis prevents chatter during signal fade. |
| Fast APD overload protection | ILIM_MON-based limiter responds within nanoseconds; clamps APD current at programmed level and asserts ILIM flag. |
| Adjustable APD bias voltage | CTRL pin accepts external reference to dynamically tune VAPD in real time-critical for temperature-compensated receiver designs. |
| Internally compensated boost controller | Eliminates external compensation components; simplifies design and ensures stable operation across load/temperature. |
| Low-noise APD supply architecture | MONIN filtering path, phase-lead capacitor support, and internal reference filtering reduce bias ripple to sub-mV levels. |
Applications
| Fiber Optic Receiver Modules | Optical Network Terminals (ONT) |
|---|---|
|
Use Scenario: High-sensitivity 10G/25G PON receiver detecting weak optical signals in passive optical networks. IC Role / Device Role / Timing Role: LT3905IUD#TRPBF generates stable, low-noise 45V APD bias and monitors photocurrent in real time to maintain optimal receiver sensitivity. Use Value: ±2% APD current accuracy enables precise automatic gain control (AGC) and dynamic range extension beyond 30dB. |
Use Scenario: Residential ONT with burst-mode upstream transmission requiring rapid APD bias reconfiguration between packets. IC Role / Device Role / Timing Role: LT3905IUD#TRPBF uses CTRL pin to adjust VAPD on-the-fly during packet gaps, minimizing dead time and improving upstream SNR. Use Value: Sub-10µs response to CTRL voltage changes allows bias adaptation within inter-packet guard bands. |
| Laser Safety Interlock Circuits | Industrial Spectroscopy Sensors |
|
Use Scenario: Medical or industrial laser systems requiring fail-safe APD monitoring to disable laser emission if beam intensity exceeds safe limits. IC Role / Device Role / Timing Role: LT3905IUD#TRPBF's ILIM_MON path triggers immediate current limiting and asserts ILIM flag within 100ns of overload onset. Use Value: Hardware-level overload response eliminates reliance on slow microcontroller polling, meeting IEC 60825 Class 1 safety requirements. |
Use Scenario: Portable NIR spectrometer using APD array for absorption measurement across varying sample densities. IC Role / Device Role / Timing Role: LT3905IUD#TRPBF powers multiple APDs with matched bias voltages and provides synchronized MON outputs for ratiometric correction. Use Value: Matched 20% current gain across channels enables pixel-to-pixel calibration without per-channel DACs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar APD bias and monitoring applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX3865EASA+ | Single-chip transimpedance amplifier + APD bias controller; no integrated boost switch; requires external 65V DC/DC. | Targeted at lower-current APDs (<1mA); lacks LT3905IUD#TRPBF's 350mA switch and 3mA monitoring range. | Choose MAX3865EASA+ when TIAs dominate system architecture and external high-voltage supply already exists. |
| LT3905EUD#TRPBF | Identical functionality and pinout; differs only in temperature grade (0°C to 125°C vs. –40°C to 125°C). | Not suitable for extended industrial or outdoor telecom deployments where ambient extremes exceed 0°C. | Choose LT3905EUD#TRPBF only for cost-sensitive commercial-grade optical modules operating in controlled environments. |
Compared with MAX3865EASA+, LT3905IUD#TRPBF integrates the high-voltage boost stage and delivers 3× higher APD current monitoring range; compared with LT3905EUD#TRPBF, it guarantees full performance across –40°C cold starts and 125°C base station enclosures-critical for carrier-grade reliability.
Availability
LT3905IUD#TRPBF is available at Aetrix Electronics and suitable for fiber optic receiver modules, optical network terminals, laser safety interlocks, and industrial spectroscopy sensors requiring stable component supply with guaranteed long-term availability.
Supply support for LT3905IUD#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 precision instrumentation, communications, and industrial markets.
The LT3905 product line was engineered specifically for optical receiver subsystems demanding accurate, low-noise APD bias with integrated protection-addressing the stringent dynamic range, speed, and reliability needs of next-generation fiber infrastructure.
FAQ
What is the maximum APD bias voltage achievable with LT3905IUD#TRPBF?
The LT3905IUD#TRPBF supports up to 54V output voltage, as confirmed by the Typical Application schematic (Figure TA01a) and Absolute Maximum Ratings table specifying VOUT and APD pins rated to 65V. This headroom accommodates typical APD reverse-bias requirements in 10G/25G PON and GPON receivers while maintaining safe derating margins. Output voltage is set via the FB resistor divider referenced to MONIN.
How does LT3905IUD#TRPBF achieve ±2% APD current monitoring accuracy across 3µA–3mA?
The LT3905IUD#TRPBF achieves ±2% relative accuracy through factory-trimmed current mirrors feeding MON, LOS_MON, and ILIM_MON pins, combined with internal voltage clamps (2.25V) and specified gain tolerances (e.g., MON gain = 0.196–0.204 for 3µA–3mA). This accuracy is validated over –40°C to +125°C and published in the Electrical Characteristics table under "APD Monitor (MON) Current Gain".
Can LT3905IUD#TRPBF operate without an external inductor?
No. The LT3905IUD#TRPBF requires an external power inductor (typically 10µH–22µH) as part of its boost converter topology. The internal DMOS switch and Schottky diode form only half the energy-transfer path; the inductor stores energy during switch-on time and transfers it to the output capacitor during switch-off. Omitting it would prevent voltage step-up and cause immediate device failure.
What is the role of the CTRL pin in LT3905IUD#TRPBF, and how does it differ from FB?
The CTRL pin in LT3905IUD#TRPBF serves as an external reference input that overrides the internal 1.248V FB reference when held below 1.248V, enabling dynamic adjustment of the regulated output voltage-and thus APD bias-during operation. In contrast, the FB pin is the feedback node itself, connected to a resistor divider; its regulation target is determined solely by CTRL voltage or the internal reference, not by direct voltage injection.
Is LT3905IUD#TRPBF pin-compatible with earlier Linear Technology variants like LT3905EUD#TRPBF?
Yes. LT3905IUD#TRPBF shares identical pin configuration, electrical characteristics, and package (16-lead 3mm × 3mm QFN) with LT3905EUD#TRPBF, differing only in guaranteed operating temperature range (–40°C to +125°C vs. 0°C to +125°C). No PCB layout changes are required when upgrading from E-grade to I-grade for enhanced environmental robustness.
LT3905IUD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LT3905IUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3905IUD#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 LT3905IUD#TRPBF reliable?
The price and inventory of LT3905IUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3905IUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3905IUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3905IUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3905IUD#TRPBF?
LT3905IUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3905IUD#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 LT3905IUD#TRPBF?
For technical support, including LT3905IUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3905IUD#TRPBF requirements.
6.How does Aetrix verify that LT3905IUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3905IUD#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 LT3905IUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3905IUD#TRPBF?
All LT3905IUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3905IUD#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 LT3905IUD#TRPBF part is unused and in its original packaging.
Return procedure for LT3905IUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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