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Analog Devices Inc. LT8685SRV#PBF
- Part No.:
- LT8685SRV#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 36-TFQFN Exposed Pad
- Datasheet:
-
LT8685SRV#PBF.pdf
- Description:
- IC REG BUCK ADJ QUAD 36LQFN
- Quantity:
- Payment:
- Shipping:
Inventory:703
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Product details
Overview
LT8685SRV#PBF from Analog Devices is a 42V-input, quad-channel synchronous step-down regulator with two 42V/2.5A high-voltage channels and two 8V/4A low-voltage channels, featuring Silent Switcher 2 architecture, spread-spectrum modulation, and AEC-Q100 qualification for automotive power systems.
For engineers reviewing the LT8685SRV#PBF datasheet, LT8685SRV#PBF pinout, LT8685SRV#PBF application, or LT8685SRV#PBF equivalent, key selection considerations include channel gangability (up to 5A HV / 8A LV), 12µA quiescent current with all channels active, 350kHz–3MHz adjustable switching frequency, and integrated thermal shutdown with per-channel cycle-by-cycle current limiting.
Technical Context
The LT8685SRV#PBF implements four independent current-mode buck regulators in a single monolithic IC: CH1/CH2 support 3V–42V input and deliver up to 2.5A each with 0.8V feedback reference; CH3/CH4 support 3V–8V input and deliver up to 4A each with 0.7V feedback reference. All channels feature programmable soft-start via TRK/SS pins and open-drain PG outputs with ±7.5% trip thresholds.
Its Silent Switcher 2 architecture uses integrated input capacitors and symmetrical layout to minimize magnetic field emissions, while selectable spread-spectrum mode further reduces peak EMI by dithering switching frequency - validated to meet CISPR 25 Class 5 radiated and conducted emission limits without external filters.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | CH1/CH2: 3V–42V; CH3/CH4: 3V–8V - enables direct battery-fed HV rails and post-regulated LV rails from intermediate supplies. |
| Output Current Capability | CH1/CH2: 2.5A each; CH3/CH4: 4A each - supports multi-rail SoC/FPGA core & I/O supply with scalable parallel operation. |
| Quiescent Current | 12µA (all channels active, no load) - sustains ultra-low-power always-on subsystems in automotive infotainment and ADAS modules. |
| Switching Frequency Range | 350kHz–3MHz (RT-programmable) - allows optimization of size (high-f) vs. efficiency (mid-f) and avoids AM band interference. |
| Feedback Reference Voltage | CH1/CH2: 0.800V ±1.5%; CH3/CH4: 0.700V ±1.5% - enables precise output regulation with standard resistor dividers and tight load/line regulation. |
| EMI Performance | CISPR 25 Class 5 compliant (radiated & conducted) with internal Silent Switcher 2 + optional spread spectrum - eliminates need for external EMI filters in space-constrained automotive PCBs. |
| Operating Junction Temp | –40°C to +150°C - qualified per AEC-Q100 Grade 1, enabling under-hood deployment without derating in harsh thermal environments. |
Pinout & Package
LT8685SRV#PBF is housed in a 36-lead LQFN package (5mm × 6mm × 0.95mm) with exposed thermal pad (pins 37–40) requiring solder connection to PCB ground for thermal and electrical integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN1, VIN2 | CH1/CH2 input supply | Supports 3V–42V input; VIN2 must short to VIN1 when gangable HV channels are combined for 5A output. |
| VIN3, VIN4 | CH3/CH4 input supply | Supports 3V–8V input; VIN4 must short to VIN3 when gangable LV channels are combined for 8A output. |
| FB1–FB4 | Output voltage feedback | CH1/CH2 reference = 0.8V; CH3/CH4 reference = 0.7V - sets regulated output via external resistor divider. |
| EN/UVLO, EN2–EN4 | Channel enable & UVLO | EN/UVLO threshold = 0.8V (falling); EN2–EN4 = 0.81V - enables programmable input undervoltage lockout per rail. |
| PG1–PG4 | Power good status | Open-drain outputs pulled low when FBx deviates >±7.5% from reference - provides sequencing-ready fault signaling. |
| TRK/SS1–TRK/SS4 | Soft-start & tracking control | 2µA internal pull-up enables capacitor-programmed slew rate; supports output voltage tracking during startup. |
| BST1–BST4 | Bootstrap gate drive | Provides gate drive voltage >VIN for top FETs - requires external ceramic bootstrap capacitors (typically 0.1µF). |
| SW1–SW4 | Power switch node | Connects to inductor and boost capacitor; SW pins tied together when channels are paralleled. |
| SYNC/MODE | Mode selection & sync input | GND = Burst Mode; floating = Pulse-Skipping; INTVCC = Pulse-Skipping + spread spectrum; external clock = synchronization. |
| RT | Frequency programming | Resistor-to-ground sets fSW from 350kHz to 3MHz - enables precise frequency tuning and EMI band avoidance. |
| BIAS | Efficiency-boosting auxiliary supply | Accepts ≥4.5V external supply (e.g., CH1 5V output) to reduce on-chip power loss and improve overall system efficiency. |
| INTVCC | Internal regulator output | 3.4V output powers internal logic and gate drivers - requires 4.7µF ceramic decoupling; not for external loads. |
Key Features
| Feature | Design Value |
|---|---|
| Gangable dual-channel architecture | CH1+CH2 deliver up to 5A with single inductor; CH3+CH4 deliver up to 8A - reduces BOM count and board area vs. discrete solutions. |
| Silent Switcher 2 + spread spectrum | Meets CISPR 25 Class 5 without external filters - critical for automotive EMC compliance in compact ECU layouts. |
| Per-channel precision enable & PG | Independent EN/UVLO thresholds (0.8V/0.81V) and ±7.5% PG windows enable robust, sequenced multi-rail power-up in complex SoC systems. |
| Ultra-low IQ with full functionality | 12µA total input current with all four channels enabled and no load - extends battery life in always-on vehicle subsystems. |
| AEC-Q100 Grade 1 qualification | Rated for –40°C to +150°C junction temperature - certified for under-hood automotive applications including engine control and ADAS. |
Applications
| Automotive Infotainment Head Unit | ADAS Camera Module Power |
|---|---|
Use Scenario: Powering SoC (core, GPU, memory), display interface, audio codec, and USB peripherals from 12V battery rail. IC Role / Device Role / Timing Role: Quad-output PMIC delivering 5V/2.5A (SoC I/O), 3.3V/2.5A (interface), 1.8V/4A (memory), 1.2V/4A (core) with synchronized soft-start. Use Value: Eliminates four discrete buck converters; Silent Switcher 2 ensures clean power without compromising EMC test margins. |
Use Scenario: Supplying image sensor (1.2V), ISP (1.8V), MIPI PHY (3.3V), and lens actuator driver (5V) in compact rear-view camera housing. IC Role / Device Role / Timing Role: Single-chip solution providing tightly regulated, low-noise, sequenced rails with thermal robustness for sealed enclosures. Use Value: 150°C rating enables operation without heatsink; gangable channels allow future resolution upgrades (e.g., 8MP → 12MP) without layout change. |
| Industrial PLC I/O Module | Electric Vehicle Battery Management System |
Use Scenario: Generating isolated DC-DC bias rails (5V, 3.3V) and analog front-end supplies (1.8V, 1.2V) from 24V industrial bus. IC Role / Device Role / Timing Role: Centralized multi-rail regulator with independent enable/PG for modular hot-swap I/O card detection and fault isolation. Use Value: Per-channel UVLO prevents brownout-induced resets; 42V input withstands 48V transients per IEC 61000-4-5. |
Use Scenario: Powering MCU, CAN transceiver, cell monitor ICs, and isolated gate drivers in BMS master controller board. IC Role / Device Role / Timing Role: High-reliability quad-buck supplying 5V (MCU), 3.3V (CAN), 1.8V (monitor IC), 1.2V (digital logic) with AEC-Q100 traceability. Use Value: 12µA IQ extends sleep-mode battery life; exposed pad thermal path ensures stable operation during high-current cell balancing cycles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar quad-output buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8686SIV#PBF | Same pinout, identical architecture, but rated for –40°C to +125°C (non-automotive grade); lacks AEC-Q100 certification. | Suitable for industrial/commercial use only; not qualified for automotive safety-critical systems. | Select when AEC-Q100 is unnecessary and cost sensitivity favors non-automotive variant. |
| TPS6521905RGER | 3.3V–20V input, 4A max per channel, 1.2V–5.5V output range; no gangability; lower EMI performance (no Silent Switcher). | Limited to mid-voltage applications; requires external EMI filtering for automotive compliance. | Consider for cost-sensitive, non-automotive designs where 42V input capability and CISPR 25 Class 5 are not required. |
Compared with LT8685SRV#PBF, LT8686SIV#PBF offers identical functionality at lower temperature grade and cost, while TPS6521905RGER trades input voltage range, gangability, and EMI performance for integration density and lower unit price in non-automotive contexts.
Availability
LT8685SRV#PBF is available at Aetrix Electronics and suitable for automotive infotainment, ADAS camera modules, industrial PLCs, and EV battery management systems requiring stable component supply across extended temperature and high-reliability requirements.
Supply support for LT8685SRV#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. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving automotive, industrial, communications, and healthcare markets.
The LT8685S product line delivers highly integrated, AEC-Q100-qualified quad buck regulators targeting space-constrained, EMI-sensitive automotive power systems requiring multi-rail sequencing, ultra-low IQ, and robust transient response.
FAQ
What is the maximum output current achievable with LT8685SRV#PBF when combining channels?
The LT8685SRV#PBF supports channel combination: CH1 and CH2 can be paralleled using a single inductor to deliver up to 5A at 5V; CH3 and CH4 can be paralleled for up to 8A at 1.8V. This configuration maintains regulation accuracy and thermal sharing, as confirmed in the Applications Information section of the official datasheet. The LT8685SRV#PBF's dedicated gang-control pins (e.g., FB2 tied to INTVCC for CH1+CH2) ensure safe, coordinated operation.
Does LT8685SRV#PBF require external components for EMI compliance in automotive applications?
No - the LT8685SRV#PBF meets CISPR 25 Class 5 radiated and conducted emission limits with its integrated Silent Switcher 2 architecture and optional spread-spectrum mode, as verified on the EVAL-LT8685S demo board with EMI filter installed. External filters are optional for margin enhancement but not required for baseline compliance, reducing bill-of-materials and PCB area. This behavior is explicitly documented in Figures G33–G35 of the LT8685S datasheet Rev. A.
How does the BIAS pin improve efficiency in LT8685SRV#PBF designs?
The BIAS pin on the LT8685SRV#PBF allows routing an external 4.5V–14V supply (e.g., from CH1's 5V output) to power the internal INTVCC regulator, bypassing the higher-loss VIN1-to-INTVCC LDO path. This reduces on-chip power dissipation and improves overall system efficiency - especially beneficial in multi-stage architectures where one channel powers others. The datasheet specifies BIAS must exceed 4.5V and VIN1 must be > BIAS + 1V for this mode to activate.
Can LT8685SRV#PBF operate with different input voltages on each channel simultaneously?
Yes - the LT8685SRV#PBF features fully independent VIN pins: VIN1/VIN2 accept 3V–42V, while VIN3/VIN4 accept 3V–8V. This enables flexible power tree architectures, such as using a 12V battery for CH1/CH2 and a 5V intermediate rail (e.g., from another LT8685SRV#PBF channel) for CH3/CH4. The datasheet confirms this in the "OPERATION" section and PIN FUNCTIONS table, noting that VIN3/VIN4 decoupling depends on source type (external vs. internal).
What is the purpose of the SYNC/MODE pin on LT8685SRV#PBF, and what modes does it support?
The SYNC/MODE pin on the LT8685SRV#PBF controls operating mode and synchronization: grounding enables Burst Mode®; floating enables Pulse-Skipping Mode; connecting to INTVCC enables Pulse-Skipping + spread spectrum; applying an external clock synchronizes all channels to that frequency. Each mode affects light-load efficiency and EMI profile - Burst Mode achieves 12µA IQ, while spread spectrum reduces peak EMI by frequency dithering. These behaviors are defined in the PIN FUNCTIONS section (Page 10) and confirmed in Figure G26/G27.
LT8685SRV#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- Silent Switcher®2
- Package/Case:
- 36-TFQFN Exposed Pad
- Packaging:
- Tray
- Product Status:
- Active
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 4
- Voltage - Input (Min):
- 2.8V, 3V
- Voltage - Input (Max):
- 8V, 42V
- Voltage - Output (Min/Fixed):
- 0.7V, 0.8V
- Voltage - Output (Max):
- 8V, 42V
- Current - Output:
- 2.5A, 2.5A, 4A, 4A
- Frequency - Switching:
- 350kHz ~ 3MHz
- Synchronous Rectifier:
- Yes
- Operating Temperature:
- -40°C ~ 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- AEC-Q100
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 36-LQFN (5x6)
LT8685SRV#PBF FAQ
1.How can I place an order for LT8685SRV#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8685SRV#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 LT8685SRV#PBF reliable?
The price and inventory of LT8685SRV#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8685SRV#PBF is usually 5 days.
3.What payment methods are accepted for LT8685SRV#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8685SRV#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8685SRV#PBF?
LT8685SRV#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8685SRV#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 LT8685SRV#PBF?
For technical support, including LT8685SRV#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8685SRV#PBF requirements.
6.How does Aetrix verify that LT8685SRV#PBF is sourced from the original manufacturer or authorized distributors?
All LT8685SRV#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 LT8685SRV#PBF meets industry standards.
7.What is the process for return or replacement of LT8685SRV#PBF?
All LT8685SRV#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8685SRV#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 LT8685SRV#PBF part is unused and in its original packaging.
Return procedure for LT8685SRV#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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