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Analog Devices Inc. LTC1735CF
- Part No.:
- LTC1735CF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 20-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
LTC1735CF.pdf
- Description:
- IC REG CTRLR BUCK 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,385
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Product details
Overview
LTC1735CF from Analog Devices (formerly Linear Technology) is a synchronous step-down switching regulator controller driving external N-channel MOSFETs in fixed-frequency current-mode architecture. It delivers 0.8V to 6V output at up to 9A, supports 4V–30V input, features ±1% output voltage accuracy, OPTI-LOOP™ compensation, and Burst Mode™ operation for high efficiency at light loads. It is used in notebook computers and DC power distribution systems requiring precise, low-noise regulation.
For engineers reviewing the LTC1735CF datasheet, LTC1735CF pinout, LTC1735CF application, or LTC1735CF equivalent, key selection factors include its 20-pin TSSOP package with PGOOD output, forced continuous mode control via FCB pin, programmable soft-start via RUN/SS capacitor, remote sense capability, and thermal design based on θJA = 110°C/W.
Technical Context
The LTC1735CF implements a constant-frequency, current-mode control architecture with dual N-channel MOSFET gate drivers (TG and BG), internal 5.2V INTVCC regulator, and precision 0.8V reference. Its error amplifier output (ITH) controls peak inductor current, while VOSENSE provides feedback from an external resistive divider.
Burst Mode™ operation activates when ITH falls below 0.86V (FCB tied to INTVCC), clamping peak current to ~20mV/RSENSE; forced continuous mode engages when FCB ≤ 0.76V, disabling Burst Mode and enabling cycle-skipping synchronization. The device includes foldback current limiting, overvoltage crowbar protection, latched short-circuit shutdown with defeat option, and dropout detection with bootstrap recharge.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 30V operating; 36V absolute max - supports wide industrial and computing supply rails. |
| Output Voltage Range | 0.8V to 6V - compatible with core voltages of microprocessors and ASICs. |
| Output Voltage Accuracy | ±1% over temperature - ensures stable regulation for sensitive digital loads. |
| Switching Frequency | 265–335 kHz (COSC = 47 pF); synchronizable up to 500 kHz - balances efficiency vs. size and EMI control. |
| Max Duty Cycle | 98–99.4% - enables ultra-low dropout operation down to VIN – VOUT ≈ 100 mV at full load. |
| Quiescent Current | <25 µA in shutdown - minimizes standby power in battery-backed systems. |
| Thermal Resistance | θJA = 110°C/W (20-lead TSSOP) - defines junction-to-ambient rise under PCB layout constraints. |
Pinout & Package
The LTC1735CF is housed in a 20-lead plastic TSSOP package (JEDEC MO-153), with exposed pad for thermal enhancement. Pin 1 is marked by a dot; pins 11 and 19 are NC (no connect).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (NC) | No Connect | Unused terminal; must remain floating or grounded per layout guidelines. |
| 2 (COSC) | Oscillator Timing Input | Connects external capacitor to set switching frequency; determines fOSC and sync range. |
| 3 (RUN/SS) | Run Control / Soft-Start | Capacitor-based ramp initiates startup; <1.5V forces shutdown; discharge triggers latchoff on overcurrent. |
| 4 (ITH) | Error Amplifier Output | Controls peak inductor current; voltage range 0–2.4V sets current limit and transient response. |
| 5 (FCB) | Forced Continuous / Sync Input | Ground = forced continuous; INTVCC = Burst Mode; external clock = synchronized discontinuous operation. |
| 6 (SGND) | Small-Signal Ground | Reference point for COSC, CSS, feedback divider; must single-point tie to PGND. |
| 7 (VOSENSE) | Feedback Voltage Input | Receives divided output voltage; servo loop maintains 0.8V reference with ±1% accuracy. |
| 8 (PGOOD) | Power-Good Output | Open-drain signal asserted low when VOSENSE deviates >±7.5% from setpoint - unique to F variant. |
| 9 (SENSE–) | Current Sense (–) | Inverting input to current comparator; used with SENSE+ and RSENSE to set current limit threshold. |
| 10 (SENSE+) | Current Sense (+) | Non-inverting input to current comparator; built-in offset with SENSE– sets trip point at 60–85 mV. |
| 12 (TG) | Top Gate Driver Output | Drives gate of high-side N-MOSFET; floating driver referenced to SW node; 3A peak current capability. |
| 13 (BOOST) | Bootstrap Supply | Return for external bootstrap capacitor; voltage swing = INTVCC superimposed on SW node. |
| 14 (SW) | Switch Node | Connection to inductor and bootstrap diode; swings from ground to VIN; critical for EMI and layout. |
| 15 (VIN) | Main Input Supply | Primary power input (4–30V); requires local ceramic + bulk decoupling near PGND. |
| 16 (INTVCC) | Internal Regulator Output | 5.2V supply for logic and drivers; can be overridden by EXTVCC ≥4.7V for higher efficiency. |
| 17 (BG) | Bottom Gate Driver Output | Drives gate of low-side N-MOSFET; rail-to-rail swing from PGND to INTVCC; 3A peak current. |
| 18 (PGND) | Power Ground | Return for bottom MOSFET source, CIN (–), Schottky cathode; high-current path requiring low-inductance routing. |
| 19 (NC) | No Connect | Unused terminal; must remain floating or grounded per layout guidelines. |
| 20 (EXTVCC) | External VCC Input | Optional 4.5–7V supply to bypass INTVCC LDO; improves gate drive strength and efficiency. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP™ Compensation | Allows stable loop response across wide range of output capacitance and ESR values without redesigning compensation network. |
| Burst Mode™ Operation | Enables >85% efficiency at 10mA load by disabling switching until output capacitor discharges to hysteresis threshold. |
| Forced Continuous Control (FCB) | Eliminates low-frequency ripple and audible noise by disabling Burst Mode; enables secondary winding regulation in multi-output designs. |
| Remote Output Voltage Sensing | Compensates for IR drop in PCB traces or connectors, maintaining ±1% regulation at load point instead of IC pins. |
| Power-Good Output (PGOOD) | Provides system-level sequencing and fault monitoring by asserting open-drain low when output deviates >±7.5% from target. |
| Programmable Soft-Start | Capacitor on RUN/SS pin sets controlled ramp time (~1.25 s/µF), preventing inrush current and ensuring proper supply sequencing. |
Applications
| Notebook Computers | DC Power Distribution Systems |
|---|---|
Use Scenario: Regulating CPU core voltage (1.2V/6A) from 12V or 19V adapter input in space-constrained clamshell design. IC Role / Device Role / Timing Role: Primary synchronous buck controller managing dynamic load transients and thermal throttling events. Use Value: Burst Mode™ sustains >90% efficiency at idle; PGOOD enables BIOS-controlled reset sequencing; remote sense ensures voltage accuracy at processor socket. | Use Scenario: Generating 3.3V/5A intermediate bus from 24V industrial supply for downstream POL converters and FPGA I/O banks. IC Role / Device Role / Timing Role: High-efficiency intermediate converter with tight line/load regulation and robust overvoltage protection. Use Value: ±1% output accuracy maintains downstream converter headroom; 99% duty cycle supports brownout operation; EXTVCC input allows self-powered gate drive from 3.3V rail. |
| Cellular Baseband Power | Wireless Modems |
Use Scenario: Supplying 1.8V/3A to LTE baseband processor in compact mobile gateway, subject to 4–28V automotive input variation. IC Role / Device Role / Timing Role: Input-flexible buck controller with UVLO (3.5V) and thermal foldback for unregulated battery-fed operation. Use Value: Wide 4–30V input range accommodates cold-crank transients; foldback current limiting prevents thermal runaway during short-circuit faults. | Use Scenario: Providing 5V/2A USB-powered modem module with low-noise operation and fast transient response to RF burst loading. IC Role / Device Role / Timing Role: Low-EMI synchronous buck controller with forced continuous mode for clean spectral profile during data transmission. Use Value: FCB pin enables noise-free continuous conduction; OPTI-LOOP™ ensures stable response to 10A/µs load steps without output overshoot. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC1735IF | Same functionality and pinout; rated for –40°C to 85°C industrial temperature range vs. LTC1735CF's 0°C to 85°C. | Required for extended-temperature deployments (e.g., outdoor telecom, industrial automation). | Select LTC1735IF when ambient operating temperature may fall below 0°C; otherwise LTC1735CF suffices for commercial environments. |
| MP2451DT-LF-Z | Integrated power stage (no external MOSFETs); fixed 500kHz frequency; no PGOOD or remote sense; lower IQ (250µA active). | Suitable for cost-sensitive, lower-current (<3A) applications where board space and BOM count are prioritized over flexibility. | Choose MP2451DT-LF-Z only for simple, low-power designs lacking need for programmable frequency, remote sensing, or multi-rail sequencing. |
Compared with LTC1735IF, the LTC1735CF offers identical performance in commercial temperature range but lower cost and qualification burden; versus MP2451DT-LF-Z, it trades integration for design flexibility, higher current capability, and advanced features like PGOOD and OPTI-LOOP™.
Availability
LTC1735CF is available at Aetrix Electronics and suitable for notebook computers, DC power distribution systems, and wireless modems requiring stable component supply with guaranteed long-term availability and traceable sourcing.
Supply support for LTC1735CF 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. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and power management ICs for precision, reliability, and efficiency-critical applications.
The LTC1735 product line was developed by Linear Technology (acquired by ADI in 2017) to address high-efficiency, high-current DC/DC conversion needs in portable computing and communications infrastructure, emphasizing thermal robustness, low-noise operation, and flexible control architecture.
FAQ
What is the maximum output current supported by the LTC1735CF?
The LTC1735CF itself does not deliver current directly-it controls external N-channel MOSFETs. Its current sense circuitry supports peak inductor currents up to ~9A average output, determined by RSENSE, inductor value, thermal design, and PCB layout. The datasheet confirms operation at 9A in typical application circuits using appropriate MOSFETs and heatsinking.
Does the LTC1735CF include an integrated power MOSFET?
No, the LTC1735CF is a controller-only IC and requires two external N-channel MOSFETs-one for the high-side switch (driven by TG) and one for the low-side synchronous rectifier (driven by BG). This architecture enables optimization for specific voltage, current, and thermal requirements beyond what integrated solutions offer.
What is the purpose of the PGOOD pin on the LTC1735CF?
The PGOOD pin on the LTC1735CF is an open-drain output that asserts low when the VOSENSE voltage deviates more than ±7.5% from the 0.8V reference-indicating out-of-regulation condition. It enables system-level power sequencing, fault detection, and safe startup/shutdown coordination in multi-rail systems.
How does the FCB pin affect operating mode in the LTC1735CF?
The FCB pin selects among three modes: tied to INTVCC → Burst Mode™ for highest light-load efficiency; tied to ground → forced continuous conduction for lowest noise and EMI; driven by external clock → synchronized discontinuous operation with constant frequency and no 25% current clamp. Mode selection directly impacts efficiency, ripple, and acoustic noise.
Can the LTC1735CF operate with input voltage below 4V?
No-the LTC1735CF has a guaranteed minimum operating input voltage of 4V, with undervoltage lockout (UVLO) releasing at 3.9V (typical) and latching off below 3.5V. Operation below 4V violates the Absolute Maximum Ratings and risks improper gate drive, loss of regulation, or undefined behavior.
LTC1735CF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 4V ~ 30V
- Frequency - Switching:
- 300kHz
- Duty Cycle (Max):
- 99.4%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Enable, Power Good, Soft Start
- Operating Temperature:
- 0°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP
LTC1735CF FAQ
1.How can I place an order for LTC1735CF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC1735CF 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 LTC1735CF reliable?
The price and inventory of LTC1735CF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC1735CF is usually 5 days.
3.What payment methods are accepted for LTC1735CF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC1735CF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC1735CF?
LTC1735CF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC1735CF 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 LTC1735CF?
For technical support, including LTC1735CF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC1735CF requirements.
6.How does Aetrix verify that LTC1735CF is sourced from the original manufacturer or authorized distributors?
All LTC1735CF 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 LTC1735CF meets industry standards.
7.What is the process for return or replacement of LTC1735CF?
All LTC1735CF units undergo pre-shipment inspection (PSI). If there is an issue with LTC1735CF, 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 LTC1735CF part is unused and in its original packaging.
Return procedure for LTC1735CF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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