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Analog Devices Inc. LT3905EUD#PBF
- Part No.:
- LT3905EUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LT3905EUD#PBF.pdf
- Description:
- IC REG BOOST ADJ 350MA 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,491
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Product details
Overview
LT3905EUD#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 a 65V/350mA DMOS switch, integrated Schottky rectifier, and monitors APD current from 3µA to 3mA with ±2% relative accuracy.
For engineers reviewing the LT3905EUD#PBF datasheet, LT3905EUD#PBF pinout, LT3905EUD#PBF application, or LT3905EUD#PBF equivalent, key selection criteria include APD current monitoring accuracy over four decades, programmable loss-of-signal and fast overload protection, adjustable 1MHz/2MHz switching frequency, and compact 3mm × 3mm QFN-16 package with exposed thermal pad.
Technical Context
The LT3905EUD#PBF implements a current-mode boost topology with internal compensation, 400mA switch current limit, and dual regulation paths: FB pin for fixed-output voltage control and ILIM_MON pin for adaptive APD current regulation. Its block diagram integrates three precision current mirrors (1:5 MON, 1:10 LOS_MON, 1:20 ILIM_MON), each clamped to 2.25V, feeding dedicated comparators and error amplifiers.
It supports two operating modes: full converter operation with dynamic bias control via CTRL/FB, and low-power standby (250µA) with only LOS_MON active when FB > 1.8V. The fSEL pin selects 1MHz or 2MHz switching frequency, and EN/UVLO provides programmable undervoltage lockout with 25mV hysteresis.
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 external LDO. |
| Output Voltage Range | Up to 54V - sufficient for high-gain APD bias in fiber optic receivers and long-haul transceivers. |
| APD Current Monitoring Accuracy | ±2% over 3µA–3mA range - enables precise optical power calibration and closed-loop gain control. |
| Switching Frequency | Selectable 1MHz or 2MHz - allows trade-off between EMI filtering complexity and inductor size. |
| Internal Power Switch | 65V, 350mA DMOS with 0.75Ω RDS(on) - eliminates need for external high-voltage MOSFET and reduces BOM count. |
| Integrated Schottky Diode | 780mV forward drop at 150mA - improves efficiency and removes discrete diode placement and routing challenges. |
| Shutdown Current | <1µA - critical for battery-powered optical modules requiring ultra-low quiescent power. |
Pinout & Package
LT3905EUD#PBF is housed in a thermally enhanced 16-lead (3mm × 3mm) plastic QFN package with exposed GND pad (Pin 17), requiring soldering to PCB copper for thermal and electrical integrity. θJA = 68°C/W, θJC = 7.5°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| ILIM (1) | Open-drain overload indicator | Pulls low when ILIM_MON ≥ 1.348V; signals APD current limit activation with 50mV hysteresis. |
| LOS_MON (2) | Loss-of-signal monitor output | Sources 10% of APD current; feeds comparator that drives LOS pin when signal drops below threshold. |
| ILIM_MON (3) | APD current limit monitor | Sources 5% of APD current; primary feedback for adaptive APD current regulation and fast limiter trigger. |
| MON (4) | Primary APD current monitor | Sources 20% of APD current; used for precision system-level monitoring and closed-loop bias control. |
| APD (5) | APD cathode connection | High-voltage node rated to 65V; carries up to 7mA APD current with integrated current limiting. |
| MONIN (6) | APD supply and monitor power rail | Connects to VOUT via low-pass filter; powers all current mirrors and sets common-mode reference. |
| SW (7) | Switch node | Drain of internal DMOS and anode of internal Schottky; requires minimal trace length to reduce EMI. |
| VOUT (8) | Boost output | Cathode of internal Schottky; connects to output capacitor and APD supply path. |
| GND (9, 17) | Power and signal ground | Exposed pad (Pin 17) must be soldered to large PCB copper area for thermal dissipation and noise immunity. |
| VIN (10) | Input supply | 2.7V–12V input; requires local 1µF ceramic bypass capacitor placed adjacent to pin. |
| EN/UVLO (11) | Enable and undervoltage lockout | 1.2V comparator with 25mV hysteresis; supports resistor-divider programming or direct logic-level enable. |
| CTRL (12) | External reference input | Overrides internal 1.248V FB reference; enables real-time APD bias voltage adjustment during operation. |
| LOS (13) | Open-drain loss-of-signal flag | Asserts high when LOS_MON falls below LOS_ADJ; requires external pull-up for logic interface. |
| LOS_ADJ (14) | LOS comparator reference | Sets loss-of-signal threshold; tied to VIN for fixed 1.248V or driven externally for programmable trip point. |
| FB (15) | Feedback input | Regulated to 1.248V (or CTRL voltage); used to set maximum output voltage or enter standby mode (>1.8V). |
| fSEL (16) | Frequency select | Tied to GND for 1MHz, VIN for 2MHz; determines switching frequency and impacts inductor sizing. |
Key Features
| Feature | Design Value |
|---|---|
| Four-decade APD current monitoring | Accurate 3µA–3mA sensing with 20×, 10×, and 5× current mirror outputs for simultaneous monitoring, LOS detection, and regulation. |
| Adaptive APD bias control | ILIM_MON-based regulation maintains constant APD current across temperature and aging, eliminating manual recalibration. |
| Dual-threshold overload protection | Soft regulation at 1.248V followed by hard current limiting and ILIM flag assertion at 1.348V - prevents APD damage during optical flooding. |
| Programmable loss-of-signal detection | Configurable LOS threshold via LOS_ADJ and external resistor on LOS_MON - enables application-specific optical power fault thresholds. |
| Internally compensated current-mode control | Stable operation with minimal external components; no loop compensation network required for standard configurations. |
Applications
| Fiber Optic Transceiver Modules | Optical Line Terminal (OLT) Equipment |
|---|---|
|
Use Scenario: Biasing APDs in SFP+/QSFP+ pluggable transceivers for 10G/25G PON and Ethernet links. IC Role / Device Role / Timing Role: Provides regulated, noise-filtered 40–54V APD bias while continuously monitoring photocurrent for automatic gain control (AGC). Use Value: Enables stable receiver sensitivity over temperature and lifetime with <±2% APD current accuracy, reducing bit-error-rate drift. |
Use Scenario: High-reliability APD bias in GPON/XG-PON OLT line cards handling multiple downstream wavelengths. IC Role / Device Role / Timing Role: Delivers synchronized APD bias and real-time loss-of-signal indication across parallel optical channels. Use Value: Programmable LOS threshold per channel allows differentiated fault reporting without external comparators or ADCs. |
| Industrial Laser Distance Sensors | Medical Optical Coherence Tomography (OCT) |
|
Use Scenario: Compact APD bias in handheld laser rangefinders where size, efficiency, and EMI are critical. IC Role / Device Role / Timing Role: Integrates boost conversion, current monitoring, and overload protection in a 3mm × 3mm footprint. Use Value: Eliminates 4–5 discrete components (MOSFET, diode, op-amps, references), reducing PCB area by >40% vs. discrete solutions. |
Use Scenario: Low-noise APD bias in portable OCT systems requiring sub-nA current resolution and ultra-low shutdown current. IC Role / Device Role / Timing Role: Supplies clean, ripple-free APD voltage with internal phase-lead filtering and <1µA shutdown draw. Use Value: Internal 0.1µF phase-lead capacitor option suppresses switching noise near crossover frequency, preserving OCT signal fidelity. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar APD bias supply applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MAX3272ETA+ | Lower max output (40V), no integrated Schottky, requires external current sense amplifier for APD monitoring. | Limited to lower-voltage APDs; lacks native 4-decade monitoring and fast overload flag. | Choose when cost sensitivity outweighs integration and monitoring precision requirements. |
| TPS613222ADBVR | General-purpose boost IC (no APD-specific monitoring), 28V max output, no current mirror outputs or LOS/ILIM flags. | Requires full external analog front-end for APD current measurement and protection logic. | Choose only if APD bias is secondary to main power rail generation and monitoring is handled elsewhere. |
Compared with MAX3272ETA+ and TPS613222ADBVR, LT3905EUD#PBF uniquely integrates APD current mirroring, dual-threshold regulation, and optical fault signaling in one QFN package-reducing design time, component count, and board space while guaranteeing ±2% monitoring accuracy across temperature.
Availability
LT3905EUD#PBF is available at Aetrix Electronics and suitable for fiber optic transceivers, optical line terminal equipment, industrial laser sensors, and medical OCT systems requiring stable component supply with guaranteed long-term availability.
Supply support for LT3905EUD#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, communications, and industrial markets.
The LT3905EUD#PBF belongs to Linear's specialized optical power management product line, engineered explicitly for avalanche photodiode biasing in high-speed, low-noise optical receivers where accuracy, reliability, and integration are non-negotiable.
FAQ
What is the maximum APD bias voltage achievable with the LT3905EUD#PBF?
The LT3905EUD#PBF supports up to 54V output voltage, verified under typical conditions with VIN = 5V and VAPD = 45V in the datasheet's Figure TA01a. This headroom accommodates APD reverse-bias requirements in 10G/25G fiber optic receivers and ensures margin for voltage drop across external filtering components. Operation beyond 54V is not specified and may compromise reliability.
How does the LT3905EUD#PBF achieve ±2% APD current monitoring accuracy over four decades?
The LT3905EUD#PBF achieves ±2% accuracy from 3µA to 3mA using matched on-chip current mirrors (1:5 MON, 1:10 LOS_MON, 1:20 ILIM_MON) with built-in voltage clamps (2.25V) and temperature-compensated reference circuitry. Electrical Characteristics tables confirm this performance applies over –40°C to 125°C junction temperature, with MON accuracy vs. temperature plots (Figure G10) showing ≤±1.5% error across the full range.
Can the LT3905EUD#PBF operate in both fixed-output and adaptive APD current regulation modes?
Yes. The LT3905EUD#PBF supports dual regulation: FB pin sets a fixed maximum output voltage (e.g., for open-circuit protection), while ILIM_MON pin enables adaptive regulation to maintain constant APD current. When ILIM_MON reaches 1.248V, the auxiliary error amplifier throttles VOUT; if overload occurs, it triggers hard limiting at 1.348V and asserts the ILIM flag - all within the same LT3905EUD#PBF device.
What is the role of the exposed thermal pad (Pin 17) on the LT3905EUD#PBF QFN package?
The exposed pad (Pin 17) is electrically and thermally connected to GND and must be soldered to a large PCB copper area. With θJC = 7.5°C/W, it provides the primary thermal conduction path from the die to the board. Failure to solder this pad results in excessive junction temperature rise, potential thermal shutdown, and degraded long-term reliability - as explicitly stated in the Absolute Maximum Ratings table and Pin Configuration diagram.
Does the LT3905EUD#PBF require external compensation components for stable operation?
No. The LT3905EUD#PBF features internal compensation for its current-mode boost controller, eliminating the need for external RC networks on the FB or COMP pins. Stability is ensured across the full input/output range and load conditions, as confirmed by the "Internally Compensated" feature listing and typical application circuits showing zero external compensation components in the feedback loop.
LT3905EUD#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)
LT3905EUD#PBF FAQ
1.How can I place an order for LT3905EUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3905EUD#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 LT3905EUD#PBF reliable?
The price and inventory of LT3905EUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3905EUD#PBF is usually 5 days.
3.What payment methods are accepted for LT3905EUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3905EUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3905EUD#PBF?
LT3905EUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3905EUD#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 LT3905EUD#PBF?
For technical support, including LT3905EUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3905EUD#PBF requirements.
6.How does Aetrix verify that LT3905EUD#PBF is sourced from the original manufacturer or authorized distributors?
All LT3905EUD#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 LT3905EUD#PBF meets industry standards.
7.What is the process for return or replacement of LT3905EUD#PBF?
All LT3905EUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3905EUD#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 LT3905EUD#PBF part is unused and in its original packaging.
Return procedure for LT3905EUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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