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Analog Devices Inc. LT8685SRV#TRPBF
- Part No.:
- LT8685SRV#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 36-TFQFN Exposed Pad
- Datasheet:
-
LT8685SRV#TRPBF.pdf
- Description:
- IC REG BUCK ADJ QUAD 36LQFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,903
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Product details
Overview
LT8685SRV#TRPBF from Analog Devices is a 42V-input, quad-output monolithic 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#TRPBF datasheet, LT8685SRV#TRPBF pinout, LT8685SRV#TRPBF application, or LT8685SRV#TRPBF equivalent, key selection considerations include channel paralleling capability (5A HV / 8A LV), 12µA quiescent current in Burst Mode, 350kHz–3MHz adjustable switching frequency, and integrated thermal shutdown with per-channel cycle-by-cycle current limiting.
Technical Context
The LT8685SRV#TRPBF implements four independent current-mode buck regulators on a single die: CH1/CH2 support 3V–42V input and 0.8V reference (±0.8%); CH3/CH4 support 3V–8V input and 0.7V reference (±0.8%). Each channel features dedicated EN, TRK/SS, PG, BST, and SW pins enabling flexible sequencing and fault monitoring.
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 ±10% frequency dithering - validated against CISPR 25 Class 5 radiated/conducted limits with external EMI filter.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | CH1/CH2: 3V–42V; CH3/CH4: 3V–8V - supports wide automotive battery transients and intermediate rail generation |
| Output Current Capability | 2.5A per HV channel; 4A per LV channel; up to 5A (CH1+CH2) or 8A (CH3+CH4) when paralleled with single inductor |
| Quiescent Current | 12µA all channels active, no load - enables always-on subsystems in automotive infotainment and ADAS |
| Switching Frequency | Adjustable 350kHz–3MHz via RT resistor or external SYNC clock - allows optimization of size vs. efficiency vs. EMI |
| Feedback Reference Voltage | CH1/CH2: 0.800V ±0.8%; CH3/CH4: 0.700V ±0.8% - enables precise output regulation across temperature and load |
| EMI Performance | CISPR 25 Class 5 compliant with spread-spectrum enabled - eliminates need for large external EMI filters in automotive modules |
| Operating Junction Temp | –40°C to +150°C - qualified per AEC-Q100 Grade 1, suitable for under-hood and engine control unit environments |
Pinout & Package
LT8685SRV#TRPBF 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 | HV channel input supplies | Support 3V–42V; VIN2 must short to VIN1 when paralleling CH1/CH2 |
| VIN3, VIN4 | LV channel input supplies | Support 3V–8V; VIN4 must short to VIN3 when paralleling CH3/CH4 |
| FB1–FB4 | Output voltage feedback inputs | CH1/CH2 reference = 0.800V; CH3/CH4 reference = 0.700V - sets regulated output via resistor divider |
| EN/UVLO, EN2–EN4 | Channel enable & UVLO inputs | Enable threshold: CH1 = 0.80V (falling), CH2–CH4 = 0.81V (falling); hysteresis enables clean startup/shutdown |
| PG1–PG4 | Open-drain power-good outputs | Pull low if FBx deviates >±7.5% from ref; release at ±6% - enables system-level power sequencing and fault detection |
| TRK/SS1–TRK/SS4 | Tracking/soft-start control | 2µA internal pull-up enables capacitor-programmed slew rate; supports voltage ramp coordination across rails |
| BST1–BST4 | Bootstrap supply for top FET gate drive | Requires external ceramic capacitor (typically 10nF–22nF) between BSTx and SWx for proper high-side switch operation |
| SW1–SW4 | Power switch node outputs | Connect to inductor and boost cap; tie together when paralleling channels - low-inductance routing critical for EMI |
| SYNC/MODE | Mode selection & sync input | GND = Burst Mode; floating = Pulse-Skip; INTVCC = Pulse-Skip + spread spectrum; external clock = sync to master source |
| RT | Frequency programming | Resistor to GND sets fSW from 350kHz–3MHz; required even during external sync to match nominal clock |
| INTVCC | Internal 3.4V regulator output | Supplies gate drivers and logic; decouple with 4.7µF ceramic close to pin and exposed pad |
| BIAS | Efficiency-boosting auxiliary supply | Accepts 4.5V–14V input to reduce chip power loss - connect to stable 5V rail (e.g., CH1 output) for best efficiency |
Key Features
| Feature | Design Value |
|---|---|
| Silent Switcher 2 architecture | Integrated input capacitors and balanced layout reduce peak radiated EMI by >30dB vs. conventional buck ICs - meets CISPR 25 without ferrite beads |
| Selectably enabled spread-spectrum modulation | ±10% frequency dithering lowers EMI peaks across 150kHz–108MHz band - eliminates need for costly shielding in ADAS camera modules |
| Independent channel enable & tracking | Four dedicated EN and TRK/SS pins allow precise power-up/down sequencing and voltage ramp alignment - essential for FPGA, SoC, and multi-rail processors |
| Per-channel power-good monitoring | Four open-drain PG outputs with ±7.5% trip threshold and ±6% release hysteresis - enables real-time rail health verification in safety-critical ECUs |
| High-efficiency BIAS pin operation | External 4.5V+ supply reduces internal dropout losses - improves full-load efficiency by up to 2.5% when powered from own 5V output rail |
Applications
| Automotive Infotainment Systems | Advanced Driver Assistance Systems (ADAS) |
|---|---|
Use Scenario: Powering SoC, DDR memory, display interface, and audio codecs in head-unit and digital cluster modules. IC Role / Device Role / Timing Role: Quad-output PMIC delivering tightly sequenced 5V, 3.3V, 1.8V, and 1.2V rails with <1% output tolerance and <50µs transient response. Use Value: 12µA quiescent current extends battery life in parked-state "keep-alive" modes; AEC-Q100 qualification ensures reliability over 15-year vehicle lifetime. | Use Scenario: Supplying radar processor, image sensor, and CAN/FlexRay transceivers in front-camera and surround-view systems. IC Role / Device Role / Timing Role: High-voltage channel powers 5V sensor rail from 12V battery; low-voltage channels generate 1.8V/1.2V core voltages with fast load-step response. Use Value: Silent Switcher 2 + spread spectrum meets stringent CISPR 25 Class 5 radiated emission limits - avoids redesign due to EMI failure in EMC lab. |
| Industrial Motor Control Drives | Onboard Charger (OBC) Auxiliary Power |
Use Scenario: Generating isolated gate-driver supplies and microcontroller rails in servo drives and PLC I/O modules. IC Role / Device Role / Timing Role: CH1/CH2 paralleled to deliver 5A @ 15V for isolated DC-DC bias supplies; CH3/CH4 provide 3.3V/1.2V for ARM Cortex-M7 MCU and ADC references. Use Value: 42V absolute max input withstands 48V bus transients; thermal shutdown and cycle-by-cycle current limit ensure robustness during motor stall conditions. | Use Scenario: Providing auxiliary 5V, 3.3V, 1.8V, and 1.2V rails for OBC control board, communication interfaces, and status LEDs. IC Role / Device Role / Timing Role: HV channels accept unregulated 400V–600V DC-link-derived 12V–24V intermediate bus; LV channels generate low-noise digital rails. Use Value: Adjustable 350kHz–3MHz switching frequency allows optimization for transformer size vs. efficiency; 150°C junction rating supports compact, sealed OBC enclosures. |
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#TRPBF | Same pinout, identical architecture, but rated for –40°C to +125°C (not AEC-Q100); lacks automotive qualification documentation | Not approved for automotive safety-critical systems; suitable for industrial/commercial designs where extended temp is not required | Select only if AEC-Q100 compliance is unnecessary and cost sensitivity outweighs qualification requirements |
| TPS6521905RGER | 3.3V–20V input, 4A max per channel, no HV capability; integrates USB PD controller; different pinout and control interface | Targeted at USB-C portable electronics, not automotive or high-voltage industrial use; lacks Silent Switcher EMI performance | Consider only for consumer-grade multi-rail applications with USB-C power delivery needs - not a functional substitute for LT8685SRV#TRPBF |
Compared with LT8686SIV#TRPBF, LT8685SRV#TRPBF provides verified AEC-Q100 Grade 1 qualification and 150°C operation for under-hood use; versus TPS6521905RGER, it delivers 42V HV capability, superior EMI suppression, and automotive-grade reliability - making it the sole choice for demanding automotive power domains.
Availability
LT8685SRV#TRPBF is available at Aetrix Electronics and suitable for automotive infotainment systems, ADAS camera modules, industrial motor drives, and onboard charger auxiliary power supplies requiring stable component supply across long product lifecycles.
Supply support for LT8685SRV#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 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, EMI-optimized quad buck regulators designed specifically for automotive power architectures requiring AEC-Q100 compliance, ultra-low quiescent current, and robust transient performance.
FAQ
What is the maximum input voltage supported by each channel of the LT8685SRV#TRPBF?
The LT8685SRV#TRPBF supports 3V to 42V on VIN1 and VIN2 (high-voltage channels), and 3V to 8V on VIN3 and VIN4 (low-voltage channels). Absolute maximum ratings are –0.3V to 42V for VIN1/VIN2 and –0.3V to 10V for VIN3/VIN4. Exceeding these may cause permanent damage. The LT8685SRV#TRPBF's dual-input-range design enables efficient generation of both high- and low-voltage rails from diverse sources such as automotive batteries and intermediate DC buses.
How does the LT8685SRV#TRPBF achieve ultralow EMI emissions?
The LT8685SRV#TRPBF achieves ultralow EMI through its Silent Switcher 2 architecture - integrating input capacitors into the package and using symmetrical, balanced power loops - plus optional spread-spectrum modulation that dithers switching frequency by ±10%. These features enable CISPR 25 Class 5 compliance without external EMI filters. The LT8685SRV#TRPBF's layout-sensitive design requires strict adherence to recommended PCB practices, including short SW/BST traces and solid ground plane coupling to the exposed pad.
Can the LT8685SRV#TRPBF channels be paralleled, and what are the requirements?
Yes: CH1 and CH2 can be paralleled to deliver up to 5A using a single inductor; CH3 and CH4 can be paralleled for up to 8A. Requirements include shorting VIN2 to VIN1 and VIN4 to VIN3, tying SW1/SW2 or SW3/SW4 together with low-impedance connections, connecting FB2 or FB4 to INTVCC (to disable slave feedback), and synchronizing EN2/EN4 to EN/UVLO or EN3. The LT8685SRV#TRPBF's internal current balancing ensures matched load sharing without external current-sense resistors.
What is the purpose of the BIAS pin on the LT8685SRV#TRPBF, and how should it be used?
The BIAS pin on the LT8685SRV#TRPBF accepts an external 4.5V–14V supply to power the internal INTVCC regulator, reducing conduction losses compared to drawing from VIN1. When BIAS > 4.5V and VIN1 > BIAS + 1V, the LT8685SRV#TRPBF automatically switches sourcing to BIAS - improving full-load efficiency by up to 2.5%. It should be decoupled with ≥0.1µF ceramic; if unused, tie BIAS to GND. This feature is especially valuable when powering the LT8685SRV#TRPBF from its own 5V output rail.
Does the LT8685SRV#TRPBF support power supply sequencing, and how is it implemented?
Yes: the LT8685SRV#TRPBF supports precise power supply sequencing via four independent EN pins (EN/UVLO, EN2, EN3, EN4) and four TRK/SS pins. Enable pins allow staggered activation based on voltage thresholds (0.80V/0.81V falling), while TRK/SS pins - with 2µA internal pull-up - enable capacitor-programmed soft-start ramps. This allows controlled voltage ramp alignment across multiple rails, critical for FPGA, ASIC, and multi-core SoC applications. The LT8685SRV#TRPBF's per-channel PG outputs further enable closed-loop sequencing verification.
LT8685SRV#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- Silent Switcher®2
- Package/Case:
- 36-TFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LT8685SRV#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8685SRV#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 LT8685SRV#TRPBF reliable?
The price and inventory of LT8685SRV#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8685SRV#TRPBF is usually 5 days.
3.What payment methods are accepted for LT8685SRV#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8685SRV#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8685SRV#TRPBF?
LT8685SRV#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8685SRV#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 LT8685SRV#TRPBF?
For technical support, including LT8685SRV#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8685SRV#TRPBF requirements.
6.How does Aetrix verify that LT8685SRV#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT8685SRV#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 LT8685SRV#TRPBF meets industry standards.
7.What is the process for return or replacement of LT8685SRV#TRPBF?
All LT8685SRV#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8685SRV#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 LT8685SRV#TRPBF part is unused and in its original packaging.
Return procedure for LT8685SRV#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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