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Analog Devices Inc. LT1725IGN#PBF
- Part No.:
- LT1725IGN#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
LT1725IGN#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,414
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Product details
Overview
LT1725IGN#PBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed to drive an external N-channel MOSFET in primary-side regulated offline and telecom power supplies. It features 16-pin SSOP packaging, 50kHz–250kHz programmable switching frequency, ±2mA FB pin input current, 1.245V typical feedback reference voltage, and integrated 3V auxiliary output capable of 8–15mA. It enables optoisolator-free regulation via third-winding flyback pulse sensing in 36V–72V input converters delivering up to 2A at 5V.
For engineers reviewing the LT1725IGN#PBF datasheet, LT1725IGN#PBF pinout, LT1725IGN#PBF application, or LT1725IGN#PBF equivalent, key selection considerations include primary-side feedback timing parameters (tON, ENDLY, MINENAB), load compensation interface (ROCMP/RCMPC), UVLO threshold (1.25V), gate drive capability (500mA sink, 11.8V high-level), and discontinuous-mode regulation stability.
Technical Context
The LT1725IGN#PBF implements a specialized flyback error amplifier that samples the transformer's third-winding flyback pulse-rather than secondary voltage-to derive regulation feedback without optocouplers. Its control loop uses VC as the integrator node between the feedback amplifier output and current comparator input, with external capacitor compensation.
Timing functions are resistor-programmable: tON (Pin 14) sets minimum switch-on time (200ns typ.), ENDLY (Pin 13) sets enable delay (200ns typ.), and MINENAB (Pin 12) sets minimum enable time (200ns typ.). Load compensation is implemented via ROCMP (Pin 4) and RCMPC (Pin 5) to correct for secondary impedance effects including diode VF, winding resistance, and capacitor ESR.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VFB Reference | 1.245V typical; sets output voltage accuracy via R1/R2 divider on FB pin (Pin 8) |
| Switching Frequency | 80–125kHz (full temp range); set by OSCAP (Pin 6) capacitor (33–200pF) |
| ISENSE Threshold | 250mV typical; limits peak primary current via external sense resistor on Pin 2 |
| VUVLO Threshold | 1.25V typical; disables switching when VIN-derived UVLO pin voltage falls below threshold |
| GATE Drive | 11.8V high-level / 0.45V low-level at 500mA; drives external MOSFET gate directly |
| 3VOUT Current Limit | 15mA max; powers auxiliary circuitry (e.g., bias rails, monitoring ICs) without external regulator |
| Operating Temp Range | –40°C to +125°C; specified for industrial and telecom environments |
Pinout & Package
LT1725IGN#PBF is housed in a 16-lead plastic SSOP (GN) package with 0.65mm lead pitch and exposed pad thermal enhancement. Pin 1 is PGND; pin 16 is GATE. The package is RoHS-compliant and lead-free (#PBF suffix).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return | Carries high-di/dt GATE discharge current; must connect directly to low-inductance ground plane |
| ISENSE (2) | Current sense input | Monitors MOSFET source voltage via external sense resistor; triggers current limit at 250mV |
| SFST (3) | Soft-start capacitor | Connects to external capacitor to ramp VC voltage linearly at startup (25–50µA charging current) |
| ROCMP (4) | Load compensation resistor | Adjusts feedback reference to compensate for output impedance (diode VF, ESR, winding R) |
| RCMPC (5) | Load compensation filter cap | 0.1µF ceramic capacitor filters compensation signal; stabilizes loop under load transients |
| OSCAP (6) | Oscillator timing capacitor | 33–200pF capacitor sets switching frequency (80–125kHz over temp) |
| VC (7) | Control voltage integrator | Output of feedback amplifier; integrates net current to set current-mode trip point |
| FB (8) | Feedback input | Receives scaled flyback pulse from third winding; referenced to 1.245V internal bandgap |
| 3VOUT (9) | 3V auxiliary output | Stable 3V rail (±0.2V) for biasing primary-side circuitry; internally current-limited to 15mA |
| UVLO (10) | Undervoltage lockout input | Resistor-divider from VIN enables/disables operation based on input rail level (1.25V threshold) |
| SGND (11) | Signal ground reference | Low-noise analog ground for FB, OSCAP, and VC; isolate from PGND to prevent noise coupling |
| MINENAB (12) | Minimum enable time resistor | Programs fixed duration (≥200ns) that flyback amplifier remains active per cycle |
| ENDLY (13) | Enable delay resistor | Introduces fixed delay (≥200ns) between MOSFET turn-off and flyback amplifier activation |
| tON (14) | Minimum on-time resistor | Enforces absolute minimum switch conduction time (≥200ns) to maintain regulation at light loads |
| VCC (15) | Supply input | 14–22V operating range; bypass with ≥1µF ceramic capacitor near pin |
| GATE (16) | MOSFET gate driver output | High-current push-pull driver (500mA sink/11.8V high) with 30ns rise/fall times |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation | Eliminates optoisolator and secondary-side TL431 by sampling third-winding flyback pulse |
| Discontinuous mode stability | Maintains regulation down to zero load via programmable minimum on-time and enable timing |
| Load compensation interface | ROCMP/RCMPC pins allow dynamic correction of output voltage droop due to secondary impedance |
| Integrated 3V auxiliary supply | Delivers up to 15mA at 3V from VCC rail-reduces need for external LDO in primary-side bias networks |
| UVLO with user-adjustable hysteresis | External resistor divider on UVLO pin sets turn-on/turn-off thresholds; hysteresis controlled by divider impedance |
Applications
| Telecom Isolated Converters | Offline Isolated Power Supplies |
|---|---|
Use Scenario: 48V telecom input converted to isolated 5V/2A output for line card power in central office equipment. IC Role / Device Role / Timing Role: LT1725IGN#PBF acts as primary-side flyback controller, using third-winding feedback to regulate output without optocoupler while managing UVLO for brownout protection. Use Value: Enables compact, high-reliability 48V-to-5V conversion meeting GR-1089 immunity requirements with no secondary-side feedback components. | Use Scenario: Universal AC-input (85–265VAC) offline SMPS delivering 12V/1A to industrial I/O modules. IC Role / Device Role / Timing Role: LT1725IGN#PBF controls flyback power stage with programmable soft-start (SFST), load compensation (ROCMP/RCMPC), and precise 1.245V reference for tight output tolerance. Use Value: Achieves <±1% output regulation across line/load/temperature with reduced BOM count versus optocoupler-based solutions. |
| Instrumentation Power Supplies | Medical Isolated Auxiliary Rails |
Use Scenario: Low-noise 24V-to-±15V dual-output isolated supply for precision ADC front-ends in test equipment. IC Role / Device Role / Timing Role: LT1725IGN#PBF provides primary-side regulation with SGND-isolated analog ground and VC-loop compensation for low ripple and fast transient response. Use Value: Delivers <10mVpp output ripple and <50µs transient recovery-critical for 16-bit+ data acquisition systems. | Use Scenario: Patient-connected medical device requiring reinforced isolation and 5V/500mA auxiliary rail for microcontroller and sensor interface. IC Role / Device Role / Timing Role: LT1725IGN#PBF implements creepage/clearance-compliant flyback control with 3VOUT powering isolated communication ICs and UVLO ensuring safe shutdown during input faults. Use Value: Meets IEC 60601-1 2× MOPP requirements while simplifying certification via single-chip primary-side regulation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar isolated flyback controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UCC28740DR | Fixed-frequency quasi-resonant controller with integrated HV start-up; no 3VOUT or ROCMP interface | Better efficiency at light loads; lacks primary-side load compensation and auxiliary 3V rail | Select UCC28740DR when optimizing for no-load power and QR topology; choose LT1725IGN#PBF when needing programmable timing, load compensation, or 3V bias rail |
| LNK364PG | Integrated MOSFET flyback switcher with <100mW standby; no external MOSFET drive or timing resistors | Lower component count but limited to <10W output; no programmable tON/ENDLY/MINENAB | Select LNK364PG for cost-sensitive sub-10W designs; choose LT1725IGN#PBF when requiring >10W output, external MOSFET flexibility, or precise timing control |
Compared with UCC28740DR and LNK364PG, the LT1725IGN#PBF offers unique primary-side load compensation, a dedicated 3V auxiliary output, and fully resistor-programmable timing (tON, ENDLY, MINENAB), making it optimal for industrial and telecom flyback designs demanding tight regulation across wide load ranges without optocouplers.
Availability
LT1725IGN#PBF is available at Aetrix Electronics and suitable for telecom isolated converters, offline isolated power supplies, and instrumentation power supplies requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant sourcing.
Supply support for LT1725IGN#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.
The LT1725IGN#PBF belongs to Linear's legacy isolated power controller product line, engineered specifically for primary-side regulated flyback topologies in telecom, industrial, and medical applications where optoisolator elimination and robust discontinuous-mode operation are critical.
FAQ
What is the maximum recommended switching frequency for LT1725IGN#PBF?
The LT1725IGN#PBF supports a switching frequency range of 80kHz to 125kHz over its full –40°C to +125°C operating temperature range. At 25°C, typical frequency is 100kHz with a 100pF OSCAP capacitor. Frequencies above 125kHz are not guaranteed across temperature and may reduce gate drive strength or compromise timing accuracy. Always verify stability with actual layout and transformer parasitics when operating near the upper limit.
Does LT1725IGN#PBF require an optoisolator for output voltage regulation?
No, the LT1725IGN#PBF does not require an optoisolator. It achieves output regulation by sensing the flyback voltage pulse from a third transformer winding connected to the FB pin. This primary-side sensing architecture eliminates the need for secondary-side feedback components like optocouplers or TL431 shunt regulators, reducing component count, improving reliability, and simplifying certification for isolated power supplies.
How is the 3VOUT pin on LT1725IGN#PBF intended to be used in a design?
LT1725IGN#PBF's 3VOUT pin delivers a regulated 3V reference (2.8–3.2V) capable of sourcing up to 15mA. It is designed to power primary-side auxiliary circuitry such as bias rails for gate drivers, monitoring comparators, or communication ICs-eliminating the need for a separate LDO. For stable operation, connect only moderate capacitive loads (<100pF) or large bulk capacitors (≥0.1µF); avoid mid-range values that may cause instability.
Can LT1725IGN#PBF operate in discontinuous conduction mode (DCM) with stable regulation?
Yes, LT1725IGN#PBF maintains stable regulation well into discontinuous conduction mode (DCM) thanks to its proprietary flyback error amplifier architecture and programmable timing features. Minimum on-time (tON), enable delay (ENDLY), and minimum enable time (MINENAB) are all resistor-programmable to ensure consistent loop behavior across light-load and no-load conditions-enabling reliable DCM operation without output voltage drift or burst-mode artifacts.
What is the purpose of the ROCMP and RCMPC pins on LT1725IGN#PBF?
The ROCMP (Pin 4) and RCMPC (Pin 5) pins implement load compensation on LT1725IGN#PBF to correct for output voltage droop caused by secondary-side impedance-including Schottky diode forward voltage, transformer winding resistance, and output capacitor ESR. ROCMP accepts an external resistor to scale compensation current, while RCMPC connects to a 0.1µF capacitor to filter the compensation signal, enabling tight load regulation across 0–2A output current in isolated flyback designs.
LT1725IGN#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SSOP (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive or Negative, Isolation Capable
- Topology:
- Flyback
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 9.7V ~ 22V
- Frequency - Switching:
- 90kHz ~ 115kHz
- Duty Cycle (Max):
- 90%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Enable, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SSOP
LT1725IGN#PBF FAQ
1.How can I place an order for LT1725IGN#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725IGN#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 LT1725IGN#PBF reliable?
The price and inventory of LT1725IGN#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725IGN#PBF is usually 5 days.
3.What payment methods are accepted for LT1725IGN#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725IGN#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725IGN#PBF?
LT1725IGN#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725IGN#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 LT1725IGN#PBF?
For technical support, including LT1725IGN#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725IGN#PBF requirements.
6.How does Aetrix verify that LT1725IGN#PBF is sourced from the original manufacturer or authorized distributors?
All LT1725IGN#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 LT1725IGN#PBF meets industry standards.
7.What is the process for return or replacement of LT1725IGN#PBF?
All LT1725IGN#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725IGN#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 LT1725IGN#PBF part is unused and in its original packaging.
Return procedure for LT1725IGN#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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