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Analog Devices Inc. LT1725IS#PBF
- Part No.:
- LT1725IS#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1725IS#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,154
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Product details
Overview
LT1725IS#PBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed for primary-side regulation in telecom and industrial offline power supplies. It drives an external N-channel MOSFET, senses output voltage directly from the transformer's third winding (eliminating optoisolators), supports 36V–72V input, delivers up to 2A at 5V output, and operates with 80–125kHz switching frequency via external OSCAP capacitor.
For engineers reviewing the LT1725IS#PBF datasheet, LT1725IS#PBF pinout, LT1725IS#PBF application, or LT1725IS#PBF equivalent, this page provides verified functional identity, confirmed 16-pin SSOP package mapping, validated pin roles including FB, GATE, ISENSE, UVLO, and 3VOUT, real-world load regulation behavior across discontinuous/continuous modes, and two field-validated alternative controllers for isolated flyback designs.
Technical Context
The LT1725IS#PBF implements a specialized flyback error amplifier that samples the reflected flyback pulse-not a DC voltage-enabling primary-side regulation without optocouplers. Its control loop uses VC as integrated control voltage, FB as high-impedance reference node (1.245V typical), and ROCMP/RCMPC pins for optional secondary impedance compensation.
It features programmable timing functions: tON (min on-time), ENDLY (enable delay), MINENAB (min enable time), and OSCAP (frequency setting). The gate driver delivers 500mA sink/source capability with 30ns rise/fall times into 1000pF, and includes undervoltage lockout (UVLO threshold 1.25V ±0.04V) referenced to VIN-not VCC.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VFB | 1.245V typical; sets output voltage accuracy via R1/R2 divider on FB pin; ±1.5% over temperature ensures stable regulation without trimming. |
| fSW | 80–125kHz (typical 100kHz); set by 33–200pF OSCAP capacitor; enables EMI control and transformer size optimization. |
| IGATE | 500mA sink/source; drives IRF620-class MOSFETs directly; eliminates need for external gate driver in ≤20W designs. |
| VISENSE | 250mV typical current limit threshold; allows precise 0.18Ω sense resistor for 2A max load; supports accurate overcurrent protection. |
| V3VOUT | 3.0V ±0.2V at 1mA; powers auxiliary circuitry (e.g., bias rails, monitoring ICs); internally current-limited to 15mA for robustness. |
| VUVLO | 1.25V ±0.04V threshold; enables VIN-referenced startup control; hysteresis adjustable via external resistor divider for clean brownout recovery. |
| TJ Range | –40°C to +125°C; qualified for industrial and telecom environments; SSOP package offers θJA = 100°C/W for thermal reliability. |
Pinout & Package
LT1725IS#PBF is housed in a 16-lead plastic SSOP (GN) package with exposed pad thermal enhancement. Pin 1 is PGND; pin 16 is GATE; pin 9 is 3VOUT; pin 10 is UVLO; pin 11 is SGND (signal ground, separate from PGND).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return for GATE discharge current | Carries high di/dt spikes (hundreds of mA, tens of ns); must connect directly to low-inductance ground plane to prevent noise coupling. |
| ISENSE (2) | Current sense input | Monitors external sense resistor voltage; internal 250mV comparator triggers shutdown if exceeded-critical for overcurrent safety. |
| SFST (3) | Soft-start capacitor connection | Charges with 40µA typical current; controls ramp-up of VC to prevent inrush; 1nF yields ~25ms soft-start time. |
| ROCMP (4) | Load compensation resistor input | Enables secondary impedance compensation; adjusts FB reference dynamically with load to improve line/load regulation. |
| RCMPC (5) | Load compensation filter capacitor | 0.1µF ceramic stabilizes compensation loop; works with ROCMP to cancel ESR-induced output droop under load steps. |
| OSCAP (6) | Oscillator timing capacitor | 33–200pF sets switching frequency; 100pF yields 100kHz; critical for EMI compliance and transformer design. |
| VC (7) | Control voltage output/integrator node | Integrates error amplifier output; connects to compensation capacitor to ground; defines current-mode trip point. |
| FB (8) | Feedback input | High-impedance node (±500nA bias); compares reflected flyback pulse to 1.245V bandgap; sets output voltage via R1/R2 ratio. |
| 3VOUT (9) | Internal 3V regulator output | Stable 3V supply for auxiliary circuits; limited to 15mA; decoupling with ≥0.1µF ceramic required for stability. |
| UVLO (10) | Undervoltage lockout input | VIN-referenced threshold (1.25V); enables brownout protection independent of VCC; 100pF bypass recommended. |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, VC; must be isolated from PGND currents to avoid feedback loop corruption. |
| MINENAB (12) | Minimum enable time programming | Resistor sets minimum duration the flyback amplifier stays active; prevents latchup during startup or light-load conditions. |
| ENDLY (13) | Enable delay programming | Resistor delays flyback amplifier activation after switch turn-off; rejects leakage spike artifacts from transformer parasitics. |
| tON (14) | Minimum switch on-time programming | Resistor enforces absolute minimum conduction time per cycle; maintains regulation down to ~10% load in discontinuous mode. |
| VCC (15) | Supply voltage input | Operates from 14–22V; requires ≥1µF ceramic bypass; start-up current 280µA typical enables trickle-charge bootstrap operation. |
| GATE (16) | MOSFET gate driver output | 12V swing into 500mA load; 30ns edges; series 5Ω+ resistor recommended to damp ringing in high-dV/dt layouts. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optoisolator | Uses third-winding flyback pulse sampling (via FB pin) to achieve <±1.5% output regulation across line/load/temperature-reducing BOM cost and improving reliability. |
| Programmable timing architecture | Independent resistor-programmed tON, ENDLY, MINENAB, and OSCAP enable precise control of switching behavior, enabling optimization for EMI, efficiency, and transient response. |
| Integrated 3V auxiliary supply | Delivers up to 15mA at 3.0V ±0.2V from VCC; powers monitoring ICs, bias networks, or level-shifters-eliminating need for external LDO in many designs. |
| VIN-referenced UVLO | UVLO pin thresholds (1.25V ±0.04V) track input rail directly-not VCC-ensuring predictable startup/shutdown behavior even during VCC bootstrap transients. |
| Load compensation interface | ROCMP/RCMPC pins allow dynamic correction of output voltage droop caused by secondary winding resistance, diode VF, and capacitor ESR-improving load regulation to <±2%. |
Applications
| Telecom Isolated Converters | Offline Isolated Power Supplies |
|---|---|
Use Scenario: 48V telecom rectifier feeding isolated 5V/2A output for base station control logic. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating output via third-winding feedback; manages 100kHz switching, 250mV current limit, and 1.245V FB reference. Use Value: Eliminates optoisolator and TL431, reducing component count by 3–4 parts while maintaining ±1.5% regulation across –40°C to +85°C ambient. |
Use Scenario: AC/DC adapter with universal input (85–265VAC) delivering 5V/2A using flyback topology with 36–72V DC bus stage. IC Role / Device Role / Timing Role: Isolated flyback controller driving IRF620 MOSFET; uses UVLO for brownout protection and SFST for controlled startup. Use Value: Enables single-stage isolated conversion with no secondary-side feedback components-cutting bill-of-materials cost and improving long-term reliability. |
| Instrumentation Power Supplies | Industrial Control Modules |
Use Scenario: Precision sensor module requiring low-noise, isolated 5V supply with <10mV ripple and ±2% load regulation. IC Role / Device Role / Timing Role: Flyback controller implementing ROCMP/RCMPC-based load compensation to counteract secondary impedance effects. Use Value: Achieves <±2% load regulation across 0–2A by dynamically adjusting FB reference-replacing manual trimmer resistors and improving production yield. |
Use Scenario: PLC I/O module needing robust 5V/2A isolated supply operating continuously at 70°C ambient. IC Role / Device Role / Timing Role: Industrial-grade flyback controller (LT1725IS#PBF, –40°C to +125°C) managing thermal derating, UVLO, and gate drive integrity. Use Value: SSOP package with θJA = 100°C/W and guaranteed operation to 125°C junction enables reliable 24/7 operation without forced air cooling. |
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; integrates HV start-up; no 3VOUT or ROCMP pins; 1.22V FB reference. | Better light-load efficiency; lacks primary-side load compensation; requires external HV start-up circuit if used with DC bus. | Prefer UCC28740DR for ultra-low standby power (<30mW); choose LT1725IS#PBF when load compensation, 3V auxiliary supply, or wide VIN range (36–72V) are required. |
| ICE2QS03G | Current-mode PWM controller with integrated 650V MOSFET; fixed 65kHz frequency; no programmable timing or 3VOUT. | Lower system cost (integrated FET); limited to ≤15W; no primary-side regulation-requires optocoupler + TL431. | Select ICE2QS03G for cost-sensitive <15W designs where optocoupler use is acceptable; retain LT1725IS#PBF for >15W, opto-free, and programmable timing needs. |
Compared with UCC28740DR and ICE2QS03G, the LT1725IS#PBF uniquely combines primary-side regulation, programmable timing, integrated 3V auxiliary supply, and load compensation-making it optimal for industrial and telecom flyback supplies demanding precision, flexibility, and component count reduction.
Availability
LT1725IS#PBF is available at Aetrix Electronics and suitable for telecom isolated converters, offline isolated power supplies, and instrumentation power supplies requiring stable component supply, extended temperature operation, and long-term lifecycle support.
Supply support for LT1725IS#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT1725IS#PBF belongs to Linear's legacy isolated power controller family, engineered specifically for primary-side regulated flyback topologies in telecom and industrial applications where optoisolator elimination, wide input range, and load regulation accuracy are critical.
FAQ
What is the function of the ROCMP and RCMPC pins on the LT1725IS#PBF?
The ROCMP and RCMPC pins on the LT1725IS#PBF implement optional load compensation to correct output voltage droop caused by secondary-side impedance (winding resistance, diode VF, capacitor ESR). ROCMP accepts an external resistor that scales a current proportional to average switch current, while RCMPC connects to a 0.1µF filter capacitor to stabilize the compensation loop. This feature enables LT1725IS#PBF to maintain tighter load regulation-typically <±2% across 0–2A-without secondary-side sensing components.
Does the LT1725IS#PBF require an optoisolator for feedback?
No, the LT1725IS#PBF does not require an optoisolator. It achieves primary-side regulation by sampling the reflected flyback pulse from the transformer's third winding and applying it to the FB pin. The internal flyback error amplifier compares this pulse to a 1.245V bandgap reference, enabling accurate output voltage control (±1.5%) without secondary-side feedback components-reducing cost, size, and failure points in the LT1725IS#PBF design.
What is the purpose of the UVLO pin on the LT1725IS#PBF, and how is it different from standard VCC UVLO?
The UVLO pin on the LT1725IS#PBF provides VIN-referenced undervoltage lockout-distinct from VCC-based UVLO found in most controllers. With a precise 1.25V ±0.04V threshold, it monitors the main input rail directly, ensuring startup only when sufficient input energy is available. This prevents erratic operation during brownouts and enables clean shutdown even when VCC is bootstrapped. For LT1725IS#PBF, this means robust behavior in telecom 48V systems where input voltage sags are common.
Can the LT1725IS#PBF drive a MOSFET directly, and what are its gate drive specifications?
Yes, the LT1725IS#PBF drives external N-channel MOSFETs directly via its GATE pin. It delivers 500mA sink and source current with 30ns rise/fall times into 1000pF, supporting fast-switching devices like the IRF620. Output high level is 11.8V (at 500mA), low level is 1.0V (at 500mA), and the driver is rated for 12V swing. A series gate resistor (≥5Ω) is recommended to suppress ringing-making LT1725IS#PBF suitable for 20W+ flyback designs without external drivers.
What is the role of the 3VOUT pin on the LT1725IS#PBF, and what load can it support?
The 3VOUT pin on the LT1725IS#PBF provides a regulated 3.0V ±0.2V auxiliary supply, capable of delivering up to 15mA. It is intended to power low-current circuitry on the primary side-such as bias networks, monitoring ICs, or level shifters-eliminating the need for an external LDO. The output is internally current-limited and requires ≥0.1µF ceramic decoupling; loads exceeding 15mA will cause voltage droop, so LT1725IS#PBF users must verify auxiliary current draw remains within specification.
LT1725IS#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SOIC (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-SO
LT1725IS#PBF FAQ
1.How can I place an order for LT1725IS#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725IS#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 LT1725IS#PBF reliable?
The price and inventory of LT1725IS#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725IS#PBF is usually 5 days.
3.What payment methods are accepted for LT1725IS#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725IS#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725IS#PBF?
LT1725IS#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725IS#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 LT1725IS#PBF?
For technical support, including LT1725IS#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725IS#PBF requirements.
6.How does Aetrix verify that LT1725IS#PBF is sourced from the original manufacturer or authorized distributors?
All LT1725IS#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 LT1725IS#PBF meets industry standards.
7.What is the process for return or replacement of LT1725IS#PBF?
All LT1725IS#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725IS#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 LT1725IS#PBF part is unused and in its original packaging.
Return procedure for LT1725IS#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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