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Analog Devices Inc. LT3905EUD#TRPBF
- Part No.:
- LT3905EUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3905EUD#TRPBF.pdf
- Description:
- IC REG BOOST ADJ 350MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,420
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Product details
Overview
LT3905EUD#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, features a 65V/350mA internal DMOS switch, integrated Schottky rectifier, and provides 2% accurate APD current monitoring across 3µA–3mA with four-decade dynamic range.
For engineers reviewing the LT3905EUD#TRPBF datasheet, LT3905EUD#TRPBF pinout, LT3905EUD#TRPBF application, or LT3905EUD#TRPBF equivalent, this device is selected for precision APD bias control in fiber-optic modules where stable high-voltage generation, fast overload protection, and loss-of-signal detection are critical - especially when operating from 2.7V–12V input with programmable 1MHz/2MHz switching.
Technical Context
The LT3905EUD#TRPBF implements a current-mode boost topology with internal compensation, 400mA switch current limit, and selectable 1MHz/2MHz oscillator frequency via fSEL pin. Its control loop supports dual regulation modes: FB-based fixed-output voltage or ILIM_MON–based adaptive APD current regulation with 1.248V reference.
Three dedicated current-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 flagging (LOS), fast current limiting (ILIM), and precision external monitoring - all referenced to MONIN and isolated from VOUT noise via external low-pass filtering.
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 CTRL-adjusted reference for precise APD bias tuning. |
| Switch Rating | 65V, 350mA DMOS FET with 0.75Ω RDS(on) - enables compact high-voltage step-up with minimal external components. |
| APD Current Monitoring Accuracy | ±2% over 3µA–3mA range - ensures reliable optical power tracking and closed-loop bias stability in receiver front-ends. |
| Switching Frequency | Selectable 1MHz or 2MHz - balances EMI, inductor size, and efficiency for space-constrained optical modules. |
| Shutdown Current | <1µA - preserves battery life in portable optical sensing and low-power standby modes. |
| Operating Temperature | –40°C to +125°C junction - qualified for industrial and telecom-grade optical transceiver operation. |
Pinout & Package
The LT3905EUD#TRPBF is housed in a 16-lead (3mm × 3mm) plastic QFN package with exposed thermal pad (Pin 17), which must be soldered to PCB ground for thermal performance and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ILIM (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 (2) | Loss-of-signal monitor output | Sources 10% of APD current; feeds comparator for LOS flagging - resistor-to-GND sets threshold for optical signal dropout detection. |
| ILIM_MON (3) | APD current limit monitor | Sources 5% of APD current; primary input for adaptive bias regulation and fast overload protection - must not float. |
| MON (4) | Primary APD current monitor | Sources 20% of APD current for high-accuracy external measurement - clamped to 2.25V; keep voltage <2.1V for full accuracy. |
| APD (5) | APD cathode connection | High-voltage node (up to 65V); supplies regulated bias to avalanche photodiode - max 7mA continuous current. |
| MONIN (6) | APD supply & monitor power rail | Connects to VOUT via low-pass filter; powers all current monitors and isolates them from switching noise. |
| SW (7) | Internal switch node | Drain of DMOS FET and anode of integrated Schottky - high di/dt node; minimize trace length to reduce EMI. |
| VOUT (8) | Boost output | Cathode of internal Schottky; connects to output capacitor - forms regulated high-voltage rail for APD and monitors. |
| GND (9, 17) | Ground reference & thermal pad | Common return for all circuits; exposed pad (Pin 17) must be soldered to large copper area for thermal dissipation. |
| VIN (10) | Input supply | 2.7V–12V input; requires local 1µF ceramic bypass capacitor placed adjacent to pin. |
| EN/UVLO (11) | Enable & undervoltage lockout | 1.2V comparator with 25mV hysteresis - resistor divider from VIN to GND programs turn-on/off thresholds. |
| CTRL (12) | External reference input | Overrides internal 1.248V FB reference when <1.248V; enables dynamic APD bias adjustment during operation. |
| LOS (13) | Open-drain loss-of-signal flag | Asserts high when LOS_MON falls below LOS_ADJ threshold - requires external pull-up for microcontroller interrupt signaling. |
| LOS_ADJ (14) | LOS comparator reference | Sets negative input of LOS comparator; tie to VIN for fixed 1.248V threshold or drive externally for programmable trip point. |
| FB (15) | Feedback input | Regulated to 1.248V (or CTRL voltage); resistor divider from VOUT to GND sets maximum output voltage. |
| fSEL (16) | Frequency select | Tie to GND for 1MHz, VIN for 2MHz - selects switching frequency without external clock source. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 65V DMOS switch + Schottky rectifier | Eliminates two external high-voltage components, reduces solution footprint by >40%, and improves reliability in optical module designs. |
| Four-decade APD current monitoring (3µA–3mA) | Enables single-device support across diverse optical link budgets - from low-light sensing to high-power fiber receivers. |
| Programmable loss-of-signal detection with 20mV hysteresis | Prevents false triggering during transient optical fades; configurable threshold allows adaptation to varying APD responsivity and gain settings. |
| Fast APD current limiter with dual-threshold action | First throttles output voltage at 1.248V on ILIM_MON, then actively limits APD current and asserts ILIM flag at 1.348V - protects against optical flooding. |
| Internally compensated current-mode control | Removes need for external compensation network; simplifies design validation and ensures stable operation across temperature and load variations. |
| Adjustable output voltage via CTRL pin | Allows real-time APD bias tuning during system calibration or AGC loops without changing FB divider - supports adaptive receiver architectures. |
Applications
| Fiber Optic Transceivers | Optical Power Monitoring Systems |
|---|---|
|
Use Scenario: High-speed SFP+/QSFP modules requiring stable, low-noise APD bias in 10G–100G Ethernet and OTN links. IC Role / Device Role / Timing Role: Primary APD bias generator and real-time current regulator; provides dynamic voltage control synchronized to optical signal level. Use Value: Maintains constant APD multiplication factor despite temperature drift or aging, improving bit-error-rate (BER) stability over lifetime. |
Use Scenario: Industrial laser safety interlocks and optical power meters needing calibrated APD current readout across wide dynamic range. IC Role / Device Role / Timing Role: Precision current-to-voltage conversion interface with built-in gain scaling (1:5, 1:10, 1:20) and clamp protection. Use Value: Delivers ±2% measurement accuracy from nanoamp to milliamp levels without external op-amps or calibration resistors. |
| PON Optical Line Terminals (OLT) | LIDAR Receiver Front-Ends |
|
Use Scenario: GPON/XG-PON OLT burst-mode receivers requiring rapid APD bias enable/disable and loss-of-signal detection per upstream burst. IC Role / Device Role / Timing Role: Burst-gated APD supply with EN/UVLO-controlled startup and LOS flag for frame synchronization. Use Value: Achieves sub-1µs wake-up time and <100ns LOS response, enabling tight burst timing margins in TDMA PON systems. |
Use Scenario: Automotive and industrial LIDAR systems using APDs for time-of-flight distance measurement under variable ambient light. IC Role / Device Role / Timing Role: High-voltage bias source with fast overload limiting to protect APD during sun-load or specular reflection events. Use Value: Prevents APD damage during optical surges while maintaining signal fidelity - critical for functional safety compliance (ISO 26262). |
Equivalent & Alternatives
The following parts are listed as comparable options for similar APD bias supply applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX3748AETE+T | Lower max output (36V), no integrated Schottky, uses external MOSFET; 3.5% APD current accuracy over narrower 10µA–1mA range. | Targeted at lower-voltage PIN diode bias; lacks integrated loss-of-signal comparator and fast current limiter. | Choose when cost sensitivity outweighs integration needs and output voltage ≤36V suffices. |
| LM3489MMX/NOPB | General-purpose boost controller (no APD monitoring); requires external current sense, op-amps, comparators, and HV MOSFET/Schottky. | Requires full discrete APD bias subsystem design; suitable only when custom regulation algorithms or multi-APD sharing is needed. | Choose only for highly customized optical front-ends where flexibility justifies added BOM count and layout complexity. |
Compared with MAX3748AETE+T and LM3489MMX/NOPB, the LT3905EUD#TRPBF delivers higher integration (integrated switch, Schottky, three monitor channels), tighter APD current accuracy (±2% vs ±3.5%), and faster overload response - reducing total component count by ≥7 parts and eliminating calibration steps in optical receiver designs.
Availability
LT3905EUD#TRPBF is available at Aetrix Electronics and suitable for fiber-optic transceivers, LIDAR receivers, optical power meters, and PON OLT equipment requiring stable component supply, high-voltage precision biasing, and robust overload protection.
Supply support for LT3905EUD#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, Inc. (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 LT3905EUD#TRPBF belongs to Linear's specialized optical power management product line, engineered explicitly for avalanche photodiode biasing in high-speed, low-noise optical receivers - emphasizing accuracy, speed, and integration over generic DC/DC functionality.
FAQ
What is the maximum output voltage capability of the LT3905EUD#TRPBF?
The LT3905EUD#TRPBF supports output voltages up to 54V, as confirmed in the Typical Application schematic and Absolute Maximum Ratings table. This rating is enabled by its 65V-rated internal DMOS switch and Schottky diode, making it suitable for biasing high-gain APDs used in long-haul fiber and LIDAR applications. The actual output is set via the FB resistor divider or CTRL pin, but must remain within the 65V absolute maximum at APD and MONIN pins.
How does the LT3905EUD#TRPBF achieve 2% APD current monitoring accuracy?
The LT3905EUD#TRPBF achieves ±2% relative accuracy over 3µA–3mA by using matched internal current mirrors with trimmed gain ratios (1:5 for MON, 1:10 for LOS_MON, 1:20 for ILIM_MON) and precision bandgap references. This accuracy is verified across –40°C to +125°C and specified in the Electrical Characteristics table under "APD Monitor (MON) Current Gain" with TYP = 0.20 and MIN/MAX bounds confirming the 2% tolerance band.
Can the LT3905EUD#TRPBF operate in both fixed-output and adaptive-current regulation modes?
Yes, the LT3905EUD#TRPBF supports dual regulation modes: FB-based fixed-output voltage (using internal 1.248V reference or external CTRL voltage) and ILIM_MON–based adaptive APD current regulation. In the latter, the ILIM_MON pin serves as the primary feedback node, allowing the device to dynamically adjust VOUT to maintain a constant APD current - a key feature for optical receiver automatic gain control.
What is the role of the MONIN pin in the LT3905EUD#TRPBF architecture?
The MONIN pin on the LT3905EUD#TRPBF serves as the dedicated power supply rail for all APD current monitors (MON, LOS_MON, ILIM_MON) and connects directly to VOUT through an external low-pass filter. This isolation prevents switching noise from degrading monitor accuracy and ensures stable, low-noise biasing - a critical requirement for high-sensitivity optical receivers where even mV-level ripple affects APD gain stability.
Does the LT3905EUD#TRPBF require external compensation components?
No, the LT3905EUD#TRPBF features internally compensated current-mode control, eliminating the need for external compensation networks. This is explicitly stated in the Features list and confirmed in the Block Diagram (Figure 1), where the error amplifier (EAMP) and compensation capacitor (CC) are shown as internal. Designers only need to select appropriate output LC components per the Application Information section.
LT3905EUD#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)
LT3905EUD#TRPBF FAQ
1.How can I place an order for LT3905EUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3905EUD#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 LT3905EUD#TRPBF reliable?
The price and inventory of LT3905EUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3905EUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LT3905EUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3905EUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3905EUD#TRPBF?
LT3905EUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3905EUD#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 LT3905EUD#TRPBF?
For technical support, including LT3905EUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3905EUD#TRPBF requirements.
6.How does Aetrix verify that LT3905EUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT3905EUD#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 LT3905EUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LT3905EUD#TRPBF?
All LT3905EUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3905EUD#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 LT3905EUD#TRPBF part is unused and in its original packaging.
Return procedure for LT3905EUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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