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Analog Devices Inc. LTC3805EDD#PBF
- Part No.:
- LTC3805EDD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 10-WFDFN Exposed Pad
- Datasheet:
-
LTC3805EDD#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 10DFN
- Quantity:
- Payment:
- Shipping:
Inventory:416
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Product details
Overview
LTC3805EDD#PBF from Analog Devices (formerly Linear Technology) is a current-mode DC/DC controller IC designed specifically for flyback, boost, and SEPIC converters, driving an external N-channel MOSFET. It delivers ±1.5% output voltage accuracy, programmable 70–700 kHz switching frequency via a single resistor, and operates from a 9.5 V internal shunt-regulated supply-enabling high-input-voltage applications such as 36–72 V telecom supplies delivering 5 V/2 A.
For engineers reviewing the LTC3805EDD#PBF datasheet, LTC3805EDD#PBF pinout, LTC3805EDD#PBF application, or LTC3805EDD#PBF equivalent, key selection considerations include its adjustable slope compensation, micropower startup (40 µA), RUN pin with precision hysteresis, soft-start/fault timeout programmability, and dual-package availability in 3 mm × 3 mm DFN.
Technical Context
The LTC3805EDD#PBF implements peak current-mode control using an error amplifier output at ITH to set the current comparator threshold, with built-in 10 µA linear ramp injection on ISENSE for slope compensation. Its oscillator supports both resistor-programmed operation (70–700 kHz) and external synchronization via SYNC pin.
Protection architecture includes dual-level overcurrent detection: primary current limiting via ISENSE (100 mV typical trip) and secondary fault shutdown triggered by OC pin exceeding 100 mV, with programmable automatic restart via SSFLT capacitor. The RUN pin provides precision undervoltage lockout (1.207 V turn-on, 1.170 V turn-off) with 5 µA hysteresis current.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Topology Support | Flyback, boost, SEPIC - no internal power switch; requires external N-MOSFET. |
| Switching Frequency | 70 kHz to 700 kHz, set by single resistor on FS pin; synchronizable to external clock. |
| Output Voltage Accuracy | ±1.5% over temperature - achieved via 0.8 V reference with <±10 mV drift from –40°C to 85°C. |
| Quiescent Current | 360 µA normal operation; 40 µA micropower startup - enables low-noise biasing from high VIN via resistor. |
| VCC Supply Range | Internally clamped to 9.5 V (±0.25 V) with 25 mA sink capability - allows direct high-voltage powering (e.g., 72 V input). |
| Overcurrent Protection | Dual-stage: ISENSE limits peak current (100 mV typical); OC pin triggers fault shutdown and auto-restart. |
| Soft-Start / Fault Timeout | Programmable via SSFLT capacitor - controls ramp rate during startup and sets retry delay after OC fault. |
Pinout & Package
Package: 10-lead (3 mm × 3 mm) plastic DFN with exposed pad (Pin 11 = GND). Thermal resistance θJA = 45°C/W; exposed pad must be soldered to PCB ground for electrical and thermal performance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SSFLT (1) | Soft-Start & Fault Timeout Control | Capacitor to GND sets startup ramp time and post-fault retry delay; internal 6 µA charge / 2 µA discharge currents. |
| ITH (2) | Error Amplifier Output / Compensation Node | Voltage-controlled PWM threshold (0.7–1.9 V range); connects to RC network for loop stability and transient response tuning. |
| FB (3) | Feedback Input | Monitors output via resistor divider; regulates to 0.8 V reference - sets output voltage independently of transformer turns ratio. |
| RUN (4) | Enable/Shutdown Control | Precision UVLO input (1.207 V ON / 1.170 V OFF) with 5 µA hysteresis current - enables input-voltage sequencing and brownout protection. |
| FS (5) | Frequency Set | Resistor to GND programs oscillator frequency per fOSC = 24×10⁹/(RFS − 1500); supports 70–700 kHz range. |
| SYNC (6) | External Clock Input | Accepts TTL/CMOS clock; rising edge triggers GATE high - enables EMI reduction and multi-phase synchronization. |
| ISENSE (7) | Current Sense & Slope Compensation Source | Senses MOSFET current via external resistor; injects 10 µA linear ramp for duty-cycle-dependent slope compensation. |
| OC (8) | Overcurrent Fault Detection | Secondary fault sense input; trips shutdown if voltage exceeds 100 mV - configurable with external resistor for higher/lower thresholds. |
| VCC (9) | Supply Input | Internally regulated to ~9.5 V; accepts up to 25 mA sink - powers gate driver and logic; bypass with ≥1 µF ceramic capacitor. |
| GATE (10) | MOSFET Gate Driver Output | Push-pull driver (GND to VCC swing); 30 ns rise/fall times into 3000 pF - directly drives N-channel MOSFET gates. |
Key Features
| Feature | Design Value |
|---|---|
| Adjustable Frequency | 70–700 kHz via single resistor on FS pin - enables optimization of size, efficiency, and EMI across wide input/output ranges. |
| Programmable Slope Compensation | 10 µA linear ramp injected at ISENSE - eliminates subharmonic oscillation in continuous conduction mode flyback designs. |
| Two-Stage Overcurrent Protection | Primary current limit (ISENSE) + secondary fault shutdown (OC) - prevents MOSFET destruction under short-circuit while enabling auto-recovery. |
| Low-IQ Micropower Startup | 40 µA quiescent current during startup - allows reliable initiation from high-VIN resistor-fed bias without auxiliary winding. |
| Flexible VCC Bias Architecture | Internal 9.5 V shunt regulator - supports direct connection to input, output, or auxiliary winding, decoupling controller operation from converter topology constraints. |
Applications
| Telecom Power Supplies | Automotive 42V Systems |
|---|---|
|
Use Scenario: 36–72 V input telecom rectifier supplying isolated 5 V/2 A for line card electronics. IC Role / Device Role / Timing Role: Flyback controller regulating output via FB feedback; GATE drives primary-side N-MOSFET; SYNC aligns switching to system clock. Use Value: ±1.5% regulation accuracy maintains downstream ASIC voltage tolerance; programmable frequency avoids noise bands in sensitive analog circuits. |
Use Scenario: 42 V battery-powered infotainment module requiring 5 V/1.5 A with cold-crank immunity down to 6 V. IC Role / Device Role / Timing Role: Boost controller operating from battery rail; RUN pin enables start-up only above 9 V and disables below 7 V to prevent brownout resets. Use Value: Micropower startup (40 µA) ensures reliable boot from weak battery; VCC shunt regulator tolerates 72 V transients without external LDO. |
| Isolated Industrial Sensors | Nonisolated Flyback Converters |
|
Use Scenario: Isolated 24 V to 5 V/0.5 A supply for fieldbus interface with reinforced insulation requirements. IC Role / Device Role / Timing Role: Flyback controller implementing primary-side regulation; ITH compensation network optimized for wide load step response. Use Value: Current-mode control delivers <50 µs load transient recovery; adjustable slope compensation ensures stability across full CCM/DCM boundary. |
Use Scenario: Compact 36–72 V to 5 V/2 A nonisolated flyback for PoE-powered edge devices. IC Role / Device Role / Timing Role: Controller managing single-switch flyback with integrated VCC bias from output winding. Use Value: SSFLT capacitor configures 10 ms soft-start to limit inrush into large output capacitors; OC pin enables safe retry after output overload. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar DC/DC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3873EDD#PBF | Fixed 300 kHz frequency; no SYNC or FS pin; lower quiescent current (25 µA startup). | Lacks programmable frequency and synchronization - suitable only for fixed-frequency, low-EMI designs where flexibility is not required. | Select when board space is constrained and frequency agility is unnecessary; not drop-in due to missing FS/SYNC pins. |
| UCC28C43DR | Voltage-mode control; no internal slope compensation; 1.5% reference accuracy; 2.5–30 V VCC range. | Requires external slope compensation circuitry; lacks RUN pin hysteresis and programmable soft-start - increases BOM count and design complexity. | Choose for cost-sensitive, non-critical applications where current-mode benefits (line/load regulation, inherent cycle-by-cycle limiting) are secondary. |
Compared with LTC3873EDD#PBF and UCC28C43DR, the LTC3805EDD#PBF uniquely combines programmable frequency, dual-stage overcurrent protection, and micropower startup in a compact DFN - making it optimal for high-reliability, variable-input telecom and industrial flyback designs where robust fault management and flexible timing are essential.
Availability
LTC3805EDD#PBF is available at Aetrix Electronics and suitable for telecom power supplies, automotive 42V systems, isolated industrial sensors, and nonisolated flyback converters requiring stable component supply, long-term lifecycle support, and guaranteed lead-free compliance.
Supply support for LTC3805EDD#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. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LTC3805EDD#PBF belongs to Linear's high-voltage DC/DC controller product line, engineered for rugged flyback, boost, and SEPIC topologies in telecom infrastructure, automotive electronics, and industrial power systems demanding precision regulation and fault resilience.
FAQ
What is the maximum input voltage the LTC3805EDD#PBF can control in a flyback application?
The LTC3805EDD#PBF itself imposes no intrinsic VIN limit - its absolute maximum VCC rating is 8.8 V, but it can control converters with input voltages up to 72 V or higher via external components. In the documented 36–72 V to 5 V/2 A flyback reference design, the LTC3805EDD#PBF uses its internal 9.5 V shunt regulator to derive VCC from VIN through a series resistor, enabling safe operation without auxiliary windings or LDOs.
How does the LTC3805EDD#PBF implement slope compensation, and is an external component required?
The LTC3805EDD#PBF injects a 10 µA linear current ramp from the ISENSE pin, beginning at 6% duty cycle and peaking at 80%. This ramp develops slope compensation voltage across an optional external resistor connected between ISENSE and the current sense resistor. While slope compensation is optional for discontinuous conduction mode (DCM), it is required for stable continuous conduction mode (CCM) operation - and the LTC3805EDD#PBF provides the necessary current source on-chip.
Can the LTC3805EDD#PBF be synchronized to an external clock, and what are the timing requirements?
Yes, the LTC3805EDD#PBF supports external synchronization via the SYNC pin (Pin 6). A rising edge on SYNC forces the GATE pin high, initiating a new switching cycle. The external clock frequency must fall within 70–700 kHz - matching the internally programmed fOSC range - and the SYNC signal must meet TTL/CMOS logic levels (≥2.9 V amplitude, <10 ns rise time). Pulse width is flexible and does not affect operation.
What is the function of the OC pin on the LTC3805EDD#PBF, and how does it differ from ISENSE-based current limiting?
The OC pin (Pin 8) provides secondary overcurrent protection independent of the primary ISENSE current limit. While ISENSE regulates peak MOSFET current during normal operation (e.g., 100 mV threshold), the OC pin monitors the same current sense resistor but triggers a full shutdown and automatic restart sequence if its voltage exceeds 100 mV - indicating sustained overload or short-circuit. This two-tier protection prevents MOSFET destruction while allowing controlled recovery, unlike ISENSE-only limiting which reduces duty cycle but continues switching.
Does the LTC3805EDD#PBF require an external bootstrap capacitor for gate drive?
No, the LTC3805EDD#PBF does not use bootstrap gate drive. Its GATE pin (Pin 10) is a push-pull driver that swings from GND to VCC (typically ~9.5 V), directly driving the gate of an N-channel MOSFET referenced to source. No high-side driver or bootstrap capacitor is needed - simplifying layout and eliminating reliability concerns associated with floating supply generation. This architecture is standard for controllers targeting low-side N-MOSFET configurations in flyback, boost, and SEPIC topologies.
LTC3805EDD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 10-WFDFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Flyback
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 3.95V ~ 9.5V
- Frequency - Switching:
- 70kHz ~ 700kHz
- Duty Cycle (Max):
- 80%
- Synchronous Rectifier:
- No
- Clock Sync:
- Yes
- Serial Interfaces:
- -
- Control Features:
- Enable, Soft Start
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 10-DFN (3x3)
LTC3805EDD#PBF FAQ
1.How can I place an order for LTC3805EDD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3805EDD#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 LTC3805EDD#PBF reliable?
The price and inventory of LTC3805EDD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3805EDD#PBF is usually 5 days.
3.What payment methods are accepted for LTC3805EDD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3805EDD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3805EDD#PBF?
LTC3805EDD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3805EDD#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 LTC3805EDD#PBF?
For technical support, including LTC3805EDD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3805EDD#PBF requirements.
6.How does Aetrix verify that LTC3805EDD#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3805EDD#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 LTC3805EDD#PBF meets industry standards.
7.What is the process for return or replacement of LTC3805EDD#PBF?
All LTC3805EDD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3805EDD#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 LTC3805EDD#PBF part is unused and in its original packaging.
Return procedure for LTC3805EDD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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