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Analog Devices Inc. LTC3785IUF#PBF
- Part No.:
- LTC3785IUF#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 24-WFQFN Exposed Pad
- Datasheet:
-
LTC3785IUF#PBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 24QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,280
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Product details
Overview
LTC3785IUF#PBF from Analog Devices (formerly Linear Technology) is a high-efficiency, synchronous, No RSENSE™ buck-boost DC/DC controller driving all-N-channel MOSFETs in single-inductor four-switch topology. It operates with input and output voltages from 2.7V to 10V, supports up to 10A output current, delivers up to 96% efficiency, and enables true output disconnect during shutdown - ideal for Li-ion-powered handheld instruments and wireless modems.
For engineers reviewing the LTC3785IUF#PBF datasheet, LTC3785IUF#PBF pinout, LTC3785IUF#PBF application, or LTC3785IUF#PBF equivalent, key selection criteria include programmable 100kHz–1MHz switching frequency, ±6.5% undervoltage/±10% overvoltage protection thresholds, soft-start/fault timer integration via RUN/SS capacitor, CCM-controlled reverse current limiting, and thermal shutdown at 125°C junction temperature.
Technical Context
The LTC3785IUF#PBF implements voltage-mode control with a 1.225V internal reference and error amplifier output (VC) directly setting duty cycle across buck, buck-boost, and boost regions. Its proprietary drain-to-source sensing eliminates external current-sense resistors while supporting forward and reverse current limit detection using ISVIN/ISSW1 and ISVOUT/ISSW2 pairs.
Operation spans three continuous modes: buck (VIN > VOUT, DMAX_BUCK ≈ 90%), four-switch buck-boost (VIN ≈ VOUT, governed by 300ns × f dead-time), and boost (VIN < VOUT, DMAX ≈ 90%). Burst Mode® is user-enabled via MODE pin and reduces quiescent current to 86µA at light loads without compromising regulation accuracy.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input/Output Range | 2.7V to 10V - supports single/dual-cell Li-ion, alkaline/NiMH inputs while regulating stable output across VIN above, below, or equal to VOUT. |
| Max Output Current | 10A - determined by external MOSFET selection and thermal design; IC provides gate drive and current-limit control only. |
| Switching Frequency | 100kHz to 1MHz - set by RT resistor; higher frequencies enable smaller magnetics but increase switching losses. |
| Efficiency | Up to 96% - achieved with synchronous N-MOSFET operation and No RSENSE™ architecture minimizing conduction loss. |
| Protection Features | Foldback current limit, short-circuit shutdown timer, OV/UV thresholds (±10%/±6.5% of FB), thermal shutdown at 125°C - ensures robust operation under fault conditions. |
| Junction Temp Range | –40°C to +125°C - specified and guaranteed for LTC3785I grade; enables industrial and extended-temperature embedded applications. |
| Quiescent Current | 86µA in Burst Mode - critical for battery life extension in always-on portable devices with intermittent load demand. |
Pinout & Package
Package: 24-lead (4mm × 4mm) plastic QFN with exposed pad (Pin 25 = GND), θJA = 30°C/W on 4-layer board. Exposed pad must be soldered to PCB ground for thermal and electrical performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RUN/SS (1) | Enable & soft-start control | Internal 1µA charge source sets soft-start time; also serves as fault timer discharge node - determines latch-off or recycle behavior after current limit. |
| VC (2) | Error amplifier output | Directly controls PWM duty cycle; clamped during soft-start and fault recovery; requires external compensation network to FB. |
| FB (3) | Feedback reference input | Connects to resistor divider from VOUT; 1.225V nominal reference enables adjustable output from 2.7V to 10V. |
| VSENSE (4) | OV/UV sense input | Monitors VOUT via dedicated divider; triggers shutdown if VOUT exceeds +10% or drops below –6.5% of FB voltage. |
| ILSET (5) | Forward current limit programming | Resistor to GND sets ISVIN–ISSW1 threshold (e.g., 59kΩ → ~105mV → ~10A with typical RDS(ON)). |
| CCM (6) | Continuous conduction mode select | Low = –15mV reverse limit (ideal diode); high = symmetric ±current limit - selects between low-loss or bidirectional power flow. |
| RT (7) | Oscillator frequency set | Resistor to GND programs fOSC ≈ 25 MHz / RT(kΩ); e.g., 49.9kΩ → ~500kHz. |
| MODE (8) | Burst Mode enable | High = variable-frequency light-load operation (86µA IQ); low = fixed-frequency, low-noise mode. |
| NC (9) | No connect | Internally unconnected; no routing required. |
| ISVOUT (10) | Reverse current sense non-inverting | Connected to drain of top boost MOSFET (D); used with ISSW2 to detect reverse conduction. |
| VBST2 (11) | Boost supply for TG2 | Charged via external diode/CAP from VCC; swings to ~VOUT + VCC to drive high-side N-MOSFET D. |
| TG2 (12) | Top gate driver for switch D | Drives gate of N-MOSFET D referenced to SW2; requires bootstrap supply (VBST2) for full enhancement. |
| SW2 (13) | Switch node for boost path | Common connection point of switches C and D; serves as return for TG2/BG2 drivers and inductor connection. |
| ISSW2 (14) | Reverse current sense inverting | Connected to source of MOSFET D; differential pair with ISVOUT detects reverse current magnitude. |
| BG2 (15) | Bottom gate driver for switch C | Drives N-MOSFET C referenced to SW2; complements TG2 in synchronous boost operation. |
| VDRV (16) | Driver supply reference | Connected to VCC; supplies logic-level bias for BG1/BG2 drivers and internal circuitry. |
| BG1 (17) | Bottom gate driver for switch B | Drives N-MOSFET B referenced to SW1; complements TG1 in synchronous buck operation. |
| ISSW1 (18) | Forward current sense inverting | Connected to source of MOSFET A; differential pair with ISVIN detects input-side current during TG1 on-time. |
| SW1 (19) | Switch node for buck path | Common connection point of switches A and B; serves as return for TG1/BG1 drivers and inductor connection. |
| TG1 (20) | Top gate driver for switch A | Drives gate of N-MOSFET A referenced to SW1; requires bootstrap supply (VBST1) for full enhancement. |
| VBST1 (21) | Boost supply for TG1 | Charged via external diode/CAP from VCC; swings to ~VIN + VCC to drive high-side N-MOSFET A. |
| ISVIN (22) | Forward current sense non-inverting | Connected to drain of MOSFET A; used with ISSW1 to detect input current during buck operation. |
| VCC (23) | Internal LDO output | 4.35V regulated supply (100mA peak) powering drivers and control logic; requires ≥4.7µF ceramic bypass to GND. |
| VIN (24) | Main input supply | Input to VCC LDO; accepts 2.7V–10V; requires ≥10µF ceramic decoupling near pin. |
| GND (25) | Power/ground reference | Exposed pad tied to PCB ground plane - mandatory for thermal dissipation (θJA = 30°C/W) and noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| No RSENSE™ current sensing | Eliminates power loss and board space of external sense resistors by using MOSFET RDS(ON) as current sensor for both forward and reverse paths. |
| True output disconnect | Disables all four switches during shutdown, blocking reverse current flow and isolating VOUT from VIN - essential for battery backup systems. |
| Programmable burst mode | User-selectable via MODE pin; reduces light-load IQ to 86µA while maintaining tight output regulation - extends battery runtime in portable devices. |
| Integrated fault timer & latch | RUN/SS capacitor doubles as soft-start and fault timer; configurable for auto-recycle (32× SS time) or latch-off based on external pull-up current. |
| Wide temperature grade | LTC3785IUF#PBF rated for –40°C to +125°C junction operation - qualified for industrial, automotive-infotainment, and harsh-environment embedded designs. |
Applications
| Handheld Instruments | Wireless Modems |
|---|---|
Use Scenario: Portable multimeters and oscilloscopes powered by dual-cell Li-ion (6V–8.4V) requiring stable 3.3V/5V rails with minimal standby power draw. IC Role / Device Role / Timing Role: Buck-boost controller managing wide-input conversion while enabling true output disconnect during sleep mode. Use Value: 96% peak efficiency and 86µA Burst Mode IQ extend battery life; programmable soft-start prevents inrush into sensitive analog front-ends. | Use Scenario: LTE/5G cellular modems operating from single-cell Li-ion (3.0V–4.2V) needing regulated 3.3V for RF transceivers and 5V for USB interfaces. IC Role / Device Role / Timing Role: Four-switch synchronous controller delivering seamless transition between buck, buck-boost, and boost modes as battery discharges. Use Value: Single-inductor architecture reduces BOM cost and PCB area; ±6.5% UV/±10% OV protection safeguards RF ICs against transient overvoltage events. |
| Palmtop Computers | Cellular Telephones |
Use Scenario: Legacy palmtop PDAs with alkaline/NiMH battery packs (4.5V–9V) powering 3.3V SoC and 5V peripheral buses. IC Role / Device Role / Timing Role: High-power buck-boost controller supporting up to 10A load with all-N-MOSFET drive and No RSENSE™ sensing. Use Value: 2.7V–10V I/O range accommodates aging battery profiles; CCM pin allows selectable reverse-current blocking for USB OTG host mode. | Use Scenario: Feature phones with single-cell Li-ion (2.7V–4.2V) supplying 3.3V to baseband processors and 5V to camera modules. IC Role / Device Role / Timing Role: Synchronous buck-boost regulator providing stable output despite deep battery discharge and dynamic load steps. Use Value: Fast transient response (<100µs settling per 2A step) maintains processor stability; thermal shutdown at 125°C prevents overheating in compact enclosures. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck-boost controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3786IUF#PBF | Pin-compatible upgrade with improved current limit accuracy (±3% vs ±10%), integrated VCC bootstrap diode, and enhanced light-load efficiency. | Preferred for new designs requiring tighter current regulation and reduced external component count. | Select LTC3786IUF#PBF when upgrading legacy LTC3785-based designs for improved precision and simplified layout. |
| MPQ4333GL-AEC1 | Automotive-grade (AEC-Q100 Grade 1), integrated MOSFETs (40V max), fixed 500kHz frequency, lower max output current (5A). | Suitable for automotive infotainment and ADAS subsystems where qualification and integration outweigh flexibility needs. | Choose MPQ4333GL-AEC1 only for automotive applications requiring AEC-Q100 compliance and integrated power stages. |
Compared with LTC3785IUF#PBF, LTC3786IUF#PBF offers superior current-sense accuracy and built-in bootstrap diode for reduced BOM, while MPQ4333GL-AEC1 trades programmability and current capability for automotive qualification and monolithic integration - making LTC3785IUF#PBF optimal for high-flexibility, high-current industrial portable designs.
Availability
LTC3785IUF#PBF is available at Aetrix Electronics and suitable for handheld instruments, wireless modems, and cellular telephones requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LTC3785IUF#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 and maintains its high-performance power management portfolio with rigorous testing and long-term product commitments.
The LTC3785 belongs to Linear's No RSENSE™ synchronous controller family, designed specifically for high-efficiency, wide-input-range DC/DC conversion in space-constrained portable electronics where thermal performance and battery longevity are critical.
FAQ
What is the guaranteed operating junction temperature range for the LTC3785IUF#PBF?
The LTC3785IUF#PBF is fully specified and guaranteed to operate from –40°C to +125°C junction temperature. This industrial-grade rating distinguishes it from the commercial-grade LTC3785EUF#PBF (–40°C to +85°C) and enables use in demanding environments such as automotive infotainment housings and industrial handheld test equipment where ambient temperatures exceed 85°C.
How does the LTC3785IUF#PBF achieve current sensing without an external RSENSE resistor?
The LTC3785IUF#PBF uses drain-to-source voltage sensing across the external N-channel MOSFETs (e.g., ISVIN to ISSW1 for forward current, ISVOUT to ISSW2 for reverse current) to infer current based on their known RDS(ON). The ILSET pin programs the comparator threshold voltage, allowing precise current limiting without power loss or footprint penalty of discrete sense resistors - a core feature of Linear's No RSENSE™ architecture.
Can the LTC3785IUF#PBF support true output disconnect during shutdown?
Yes, the LTC3785IUF#PBF supports true output disconnect: when disabled via RUN/SS pin, all four power switches (A–D) turn off completely, breaking the conductive path between VIN and VOUT. This prevents reverse current flow and isolates downstream circuitry - critical for battery-powered systems where leakage must be minimized during standby or sleep states.
What is the purpose of the CCM pin on the LTC3785IUF#PBF, and how does it affect operation?
The CCM (Continuous Conduction Mode) pin on the LTC3785IUF#PBF selects reverse current limiting behavior: when pulled low, it enables a fixed –15mV threshold for reverse conduction (ideal diode mode); when driven high, it sets symmetric ±current limits matching the forward limit programmed by ILSET. This allows designers to choose between ultra-low reverse leakage or bidirectional power handling - essential for USB OTG or battery backup applications.
How is switching frequency programmed on the LTC3785IUF#PBF, and what is the accuracy over temperature?
Switching frequency on the LTC3785IUF#PBF is set by a resistor (RT) from Pin 7 to GND, following fOSC ≈ 25 MHz / RT(kΩ). Over the –40°C to +125°C junction range, frequency accuracy is specified as ±20% (min 370kHz, max 650kHz at 500kHz nominal), ensuring predictable timing for loop compensation and EMI filtering across full operating conditions.
LTC3785IUF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 24-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck-Boost
- Number of Outputs:
- 2
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 2.7V ~ 10V
- Frequency - Switching:
- 100kHz ~ 1MHz
- Duty Cycle (Max):
- 99%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Current Limit, Enable, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-QFN (4x4)
LTC3785IUF#PBF FAQ
1.How can I place an order for LTC3785IUF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3785IUF#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 LTC3785IUF#PBF reliable?
The price and inventory of LTC3785IUF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3785IUF#PBF is usually 5 days.
3.What payment methods are accepted for LTC3785IUF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3785IUF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3785IUF#PBF?
LTC3785IUF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3785IUF#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 LTC3785IUF#PBF?
For technical support, including LTC3785IUF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3785IUF#PBF requirements.
6.How does Aetrix verify that LTC3785IUF#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3785IUF#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 LTC3785IUF#PBF meets industry standards.
7.What is the process for return or replacement of LTC3785IUF#PBF?
All LTC3785IUF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3785IUF#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 LTC3785IUF#PBF part is unused and in its original packaging.
Return procedure for LTC3785IUF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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