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Analog Devices Inc. LT1725CGN#PBF
- Part No.:
- LT1725CGN#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
LT1725CGN#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:119
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Product details
Overview
LT1725CGN#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, 1.245 V feedback reference accuracy, 85–90% maximum duty cycle, 50–250 kHz programmable switching frequency via OSCAP pin, and integrated 3 V auxiliary output capable of 15 mA. It enables optocoupler-free regulation by sensing output voltage directly from the transformer's third winding.
For engineers reviewing the LT1725CGN#PBF datasheet, LT1725CGN#PBF pinout, LT1725CGN#PBF application, or LT1725CGN#PBF equivalent, key selection considerations include primary-side feedback timing constraints (enable delay, minimum enable time, collapse detect), load compensation capability via ROCMP/RCMPC pins, UVLO threshold programmability, soft-start control via SFST, and gate drive strength (11.8 V high-level at 500 mA sink).
Technical Context
The LT1725CGN#PBF implements a specialized flyback error amplifier that samples the reflected flyback pulse during a precisely timed window-enabled after a fixed delay (ENDLY) and held active for a minimum duration (MINENAB)-to reject leakage spikes and maintain regulation across continuous and discontinuous conduction modes. Its VC pin serves as both feedback amplifier output and current comparator input, with loop compensation applied externally between VC and SGND.
Control logic integrates dynamic timing functions including tON (minimum switch on time), collapse detection at ~0.8×VBG, and programmable soft-start via SFST capacitor. The 3VOUT pin provides a buffered, current-limited reference for biasing primary-side circuitry, while UVLO allows VIN-referenced undervoltage lockout using an external resistor divider tied to Pin 10.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VFB Reference | 1.245 V (typical); sets output voltage precision without trimming |
| Switching Frequency | 80–125 kHz (over temp); set by 33–200 pF OSCAP capacitor |
| GATE Drive High Level | 11.8 V at 500 mA sink; ensures robust MOSFET turn-on under load |
| VISENSE Limit | 250 mV (typical); defines peak primary current via external sense resistor |
| UVLO Threshold | 1.25 V (typical); enables VIN-based startup control independent of VCC |
| 3VOUT Current Limit | 15 mA (max); supports biasing of primary-side comparators or references |
| Max Duty Cycle | 90%; constrains minimum off-time and impacts transformer design |
Pinout & Package
LT1725CGN#PBF is housed in a 16-lead plastic SSOP (GN) package with exposed pad thermal enhancement (θJA = 110°C/W). Pin 1 (PGND) carries high-di/dt GATE discharge current and must connect directly to a low-inductance ground plane.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return | Carries transient GATE discharge current; requires direct low-inductance ground connection |
| ISENSE (2) | Current sense input | Monitors MOSFET source voltage drop; triggers current limit at 250 mV |
| SFST (3) | Soft-start capacitor | Controls startup ramp rate via external capacitor; charges at 40 µA (typ) |
| ROCMP (4) | Load compensation resistor | Adjusts feedback reference to compensate for secondary impedance effects |
| RCMPC (5) | Load compensation filter | Filters average switch current signal; typically 0.1 µF ceramic |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency; 100 pF yields ~100 kHz |
| VC (7) | Control voltage node | Feedback amplifier output and current comparator input; loop compensation applied here |
| FB (8) | Feedback input | Receives scaled flyback pulse; referenced to 1.245 V internal bandgap |
| 3VOUT (9) | Auxiliary reference output | Provides 3 V ±0.2 V at ≤15 mA for primary-side biasing |
| UVLO (10) | Undervoltage lockout input | Enables VIN-referenced shutdown; threshold 1.25 V with hysteresis |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, VC; must be isolated from PGND noise |
| MINENAB (12) | Minimum enable time resistor | Sets duration feedback amplifier remains active per cycle |
| ENDLY (13) | Enable delay resistor | Programs delay between MOSFET turn-off and feedback sampling start |
| tON (14) | Minimum on-time resistor | Ensures minimum conduction period to sustain regulation at light loads |
| VCC (15) | Supply input | Operates up to 22 V; requires ≥1 µF local bypass to PGND |
| GATE (16) | MOSFET gate driver output | Drives external N-MOSFET; 11.8 V high level, 0.45 V low level at 100 mA |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation | Eliminates optoisolator and secondary-side TL431, reducing BOM count and improving reliability |
| Programmable timing windows | Independent adjustment of enable delay (ENDLY), minimum enable time (MINENAB), and minimum on-time (tON) optimizes regulation across load and line ranges |
| Load compensation | ROCMP/RCMPC interface corrects for output impedance errors caused by diode VF, winding resistance, and capacitor ESR |
| VIN-referenced UVLO | Allows precise input voltage brownout protection without sensing VCC rail |
| Integrated 3 V reference | Supplies up to 15 mA for primary-side monitoring circuits, reducing need for auxiliary LDOs |
Applications
| Telecom Isolated Converters | Offline Isolated Power Supplies |
|---|---|
Use Scenario: 48 V telecom input converted to isolated 5 V/2 A output for line card power. IC Role / Device Role / Timing Role: LT1725CGN#PBF acts as primary-side flyback controller, sampling third-winding flyback pulse to regulate output without optocoupler. Use Value: Enables compact, high-reliability 48 V DC-DC conversion meeting GR-1089 immunity requirements with no secondary feedback components. | Use Scenario: Universal AC input (85–265 VAC) rectified to 36–72 VDC powering isolated 5 V/2 A output for industrial control I/O modules. IC Role / Device Role / Timing Role: LT1725CGN#PBF controls external IRF620 MOSFET, using UVLO to prevent startup below 36 VDC and soft-start to limit inrush. Use Value: Delivers stable 5 V output across wide input range with <±1% load regulation (0–2 A) and no optoisolator aging concerns. |
| Instrumentation Power Supplies | Medical Isolated Auxiliary Rails |
Use Scenario: Precision analog front-end requiring clean, isolated ±15 V and +5 V rails derived from 24 VDC input. IC Role / Device Role / Timing Role: LT1725CGN#PBF regulates main 5 V output; its 3VOUT pin powers isolated op-amp bias networks and ADC references. Use Value: Reduces component count by integrating auxiliary bias generation and eliminates separate LDOs while maintaining low-noise performance. | Use Scenario: Patient-connected medical device needing reinforced isolation for 3.3 V microcontroller supply derived from 24 V system bus. IC Role / Device Role / Timing Role: LT1725CGN#PBF implements creepage/clearance-compliant flyback stage with primary-side feedback, avoiding optocoupler certification burden. Use Value: Meets IEC 60601-1 isolation requirements while simplifying safety validation through elimination of secondary-side feedback components. |
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 pin; different timing architecture (no ENDLY/MINENAB) | Optimized for higher efficiency at light loads; lacks primary-side load compensation | Prefer UCC28740DR when ZVS operation and >90% efficiency at 10% load are critical; avoid if transformer leakage spike rejection or secondary impedance compensation is required. |
| ICE3B0565J | Fixed-frequency current-mode controller with integrated 650 V MOSFET; no programmable timing pins; no 3VOUT or load compensation | Single-chip solution reduces board space but limits design flexibility and thermal management | Choose ICE3B0565J for cost-sensitive, low-power (<15 W) applications where integration outweighs timing control needs; use LT1725CGN#PBF when discrete MOSFET selection, layout optimization, or advanced regulation features are prioritized. |
Compared with UCC28740DR and ICE3B0565J, the LT1725CGN#PBF offers unique primary-side timing programmability (ENDLY, MINENAB, tON) and load compensation-critical for stable regulation with high-leakage transformers or variable-output systems-while its 3VOUT pin simplifies auxiliary biasing not available in either alternative.
Availability
LT1725CGN#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 consistent parametric performance across temperature.
Supply support for LT1725CGN#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 digital signal processing semiconductors.
The LT1725CGN#PBF belongs to Linear Technology's legacy isolated power controller product line, engineered specifically for primary-side regulated flyback topologies in telecom, industrial, and medical applications where optocoupler elimination and transformer leakage resilience are essential.
FAQ
What is the operating temperature range for the LT1725CGN#PBF?
The LT1725CGN#PBF is rated for 0°C to 100°C junction temperature (C-grade), with guaranteed electrical performance over this full range. Its 16-pin SSOP package has a thermal resistance θJA of 110°C/W. Derating guidelines and thermal layout recommendations-including PGND copper area and SGND isolation-are provided in the LT1725 datasheet to ensure reliable operation within this range. The LT1725CGN#PBF does not require external thermal shutdown circuitry under normal conditions.
How does the LT1725CGN#PBF achieve optocoupler-free regulation?
The LT1725CGN#PBF achieves optocoupler-free regulation by sampling the reflected flyback voltage from the transformer's third winding and feeding it into the FB pin. Internal circuitry enables the flyback error amplifier only during a precisely timed window-after a programmable enable delay (ENDLY) and for a minimum duration (MINENAB)-to reject leakage spikes and capture the true output-referred voltage. This sampled signal is compared to the 1.245 V internal reference, and the resulting error drives the VC node to adjust MOSFET conduction. The LT1725CGN#PBF thus maintains tight regulation without secondary-side components.
Can the LT1725CGN#PBF drive high-side or low-side MOSFET configurations?
The LT1725CGN#PBF is designed exclusively for low-side N-channel MOSFET drive in flyback topologies. Its GATE pin outputs a ground-referenced drive signal, and PGND serves as the power ground return path for the MOSFET source. It cannot drive high-side configurations or P-channel devices. The gate driver delivers 11.8 V at 500 mA sink capability, supporting fast turn-on of standard logic-level MOSFETs like the IRF620 referenced in typical applications. Layout best practices-such as short GATE traces and series damping resistors-must be followed to minimize ringing.
What is the purpose of the ROCMP and RCMPC pins on the LT1725CGN#PBF?
The ROCMP and RCMPC pins implement load compensation to correct for output voltage droop caused by secondary-side impedance (diode VF, winding resistance, capacitor ESR). ROCMP accepts an external resistor that adjusts the effective feedback reference voltage in proportion to average switch current, while RCMPC connects to a 0.1 µF capacitor that filters the current-sense signal before it modulates the reference. Together, they enable the LT1725CGN#PBF to maintain <±1% load regulation across 0–2 A output current without requiring secondary-side compensation networks.
Does the LT1725CGN#PBF support programmable soft-start, and how is it implemented?
Yes, the LT1725CGN#PBF supports programmable soft-start via the SFST pin. An external capacitor connected between SFST and PGND sets the startup ramp time: the internal 40 µA (typical) charging current linearly raises the SFST voltage, which modulates the VC node to gradually increase the current limit threshold and duty cycle. This prevents inrush current and transformer saturation during startup. Discharge occurs at 1.5 mA when UVLO is active, ensuring rapid shutdown recovery. The LT1725CGN#PBF datasheet provides capacitor value guidelines for target startup times.
LT1725CGN#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:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SSOP
LT1725CGN#PBF FAQ
1.How can I place an order for LT1725CGN#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725CGN#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 LT1725CGN#PBF reliable?
The price and inventory of LT1725CGN#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725CGN#PBF is usually 5 days.
3.What payment methods are accepted for LT1725CGN#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725CGN#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725CGN#PBF?
LT1725CGN#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725CGN#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 LT1725CGN#PBF?
For technical support, including LT1725CGN#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725CGN#PBF requirements.
6.How does Aetrix verify that LT1725CGN#PBF is sourced from the original manufacturer or authorized distributors?
All LT1725CGN#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 LT1725CGN#PBF meets industry standards.
7.What is the process for return or replacement of LT1725CGN#PBF?
All LT1725CGN#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725CGN#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 LT1725CGN#PBF part is unused and in its original packaging.
Return procedure for LT1725CGN#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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