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Analog Devices Inc. LT1725IS#TRPBF
- Part No.:
- LT1725IS#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1725IS#TRPBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,635
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Product details
Overview
LT1725IS#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed to drive an external N-channel MOSFET in telecom and industrial offline power supplies. It features primary-side sensing (no optoisolator), 3V auxiliary output, programmable soft-start, undervoltage lockout, and load compensation-enabling stable 5V/2A isolated output from 36V–72V input.
For engineers reviewing the LT1725IS#TRPBF datasheet, LT1725IS#TRPBF pinout, LT1725IS#TRPBF application, or LT1725IS#TRPBF equivalent, key selection considerations include its 16-pin SO package, VCC turn-on threshold of 15.1V (typ), 250mV current-sense limit, ±2mA FB pin current, and support for 50kHz–250kHz switching via OSCAP capacitor.
Technical Context
The LT1725IS#TRPBF implements a flyback-specific error amplifier that samples the reflected flyback pulse from a third transformer winding-not a continuous DC voltage-enabling regulation without optocouplers. Its control loop integrates VC node current from a transconductance amplifier (400–1800 µmho) and uses collapse-detect timing to gate feedback during valid flyback intervals.
It supports discontinuous conduction mode (DCM) operation with maintained regulation, employs minimum on-time (200 ns typ) and enable-delay (200 ns typ) timing functions set by external resistors, and includes dedicated pins (ROCMP/RCMPC) for compensating secondary-side impedance effects-including diode VF, winding resistance, and capacitor ESR-via average-current-derived correction.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Turn-On Voltage | 15.1 V (typ); ensures reliable startup above brownout threshold in high-voltage telecom inputs |
| ISENSE Threshold | 250 mV (typ); sets peak switch current limit using external sense resistor, enabling precise overcurrent protection |
| FB Reference Voltage | 1.245 V (typ); internal bandgap reference used with R1/R2 divider to determine output voltage via third-winding feedback |
| 3VOUT Load Capability | 15 mA (max); provides regulated auxiliary supply for biasing primary-side circuitry without secondary-side LDO |
| Switching Frequency Range | 50–250 kHz; set by OSCAP capacitor (33–200 pF), balancing efficiency, size, and EMI in isolated designs |
| UVLO Threshold | 1.25 V (typ); enables input-voltage-dependent shutdown via external resistor divider on UVLO pin |
| GATE Drive High Level | 12.1 V (typ at 100 mA); sufficient to fully enhance logic-level or standard N-MOSFETs like IRF620 in high-side flyback switches |
Pinout & Package
LT1725IS#TRPBF is housed in a 16-lead plastic SO (Small Outline) package with exposed pad thermal enhancement, rated for –40°C to 125°C operating junction temperature.
| 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 |
| ISENSE (2) | Current sense input | Monitors external sense resistor voltage; triggers switch turn-off when ≥250 mV (typ), defining peak primary current |
| SFST (3) | Soft-start capacitor connection | Charges with 40 µA (typ); controls ramp-up of VC voltage to limit inrush current during startup |
| ROCMP (4) | Load compensation resistor input | Accepts current proportional to average switch current; adjusts FB reference to compensate for output impedance droop |
| RCMPC (5) | Load compensation filter capacitor | Filters ROCMP signal; 0.1 µF ceramic typical; stabilizes compensation loop against noise |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency (e.g., 100 pF → 100 kHz); determines core reset time and transformer design constraints |
| VC (7) | Control voltage output/integrator node | Integrates error amplifier output; sets current-comparator trip point; requires external RC compensation to ground |
| FB (8) | Feedback input | Receives scaled flyback pulse from third winding; referenced to 1.245 V bandgap; Thevenin resistance ~3 kΩ recommended |
| 3VOUT (9) | Regulated auxiliary output | Provides 3.0 V ±0.2 V at ≤15 mA; powers op-amps, comparators, or logic on primary side without secondary winding |
| UVLO (10) | Undervoltage lockout input | Enables/disables switching based on VIN-derived voltage divider; bias current changes at threshold to create hysteresis |
| SGND (11) | Signal ground reference | Low-noise ground for FB, OSCAP, and VC compensation components; must be isolated from PGND currents |
| MINENAB (12) | Minimum enable time programming | Resistor sets minimum duration (≥200 ns) that flyback error amplifier remains active per cycle |
| ENDLY (13) | Enable delay programming | Resistor sets fixed delay (≥200 ns) between MOSFET turn-off and flyback amplifier activation to reject leakage spikes |
| tON (14) | Minimum on-time programming | Resistor sets absolute minimum MOSFET conduction time per cycle to ensure flyback pulse generation |
| VCC (15) | Main supply input | Operates from 14–22 V; requires ≥1 µF ceramic bypass to PGND; powered from third winding or auxiliary supply |
| GATE (16) | MOSFET gate driver output | 12.1 V high-level drive (100 mA sink/source); rise/fall times <30 ns into 1 nF; series gate resistor ≥5 Ω recommended |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optoisolator | Uses third-winding flyback pulse sampling and collapse-detect timing to eliminate optocoupler, reducing cost and improving reliability in telecom converters |
| Discontinuous mode regulation maintenance | Retains tight output regulation even at light loads where energy transfer becomes intermittent-critical for standby power compliance |
| Programmable load compensation | ROCMP/RCMPC interface allows dynamic correction of output voltage droop caused by diode VF, winding resistance, and capacitor ESR across load range |
| Integrated 3V auxiliary regulator | Delivers up to 15 mA at 3.0 V from VCC rail-powers gate drivers, bias circuits, or monitoring ICs without requiring separate LDO or winding |
| Configurable undervoltage lockout | UVLO pin accepts external resistor divider tied to VIN; enables system-level brownout protection independent of VCC supply path |
Applications
| Telecom Isolated Converters | Offline Isolated Power Supplies |
|---|---|
Use Scenario: 48V telecom rectifier feeding isolated 5V/2A output for line-card digital logic and analog interfaces. IC Role / Device Role / Timing Role: Flyback controller managing primary-side switching, third-winding feedback sampling, and gate drive timing with 200 ns minimum on-time enforcement. Use Value: Eliminates optoisolator and secondary-side TL431, reducing BOM count and improving long-term stability under temperature cycling. | Use Scenario: Universal-input (85–265 VAC) offline SMPS delivering isolated 12V/1A for industrial PLC I/O modules. IC Role / Device Role / Timing Role: Primary-side controller implementing programmable soft-start (SFST), UVLO (UVLO pin), and load compensation (ROCMP/RCMPC) for wide-line and load variation. Use Value: Maintains ±1% output regulation from full load to 10% load without secondary feedback components, simplifying certification. |
| Instrumentation Power Supplies | Medical Isolated Auxiliary Rails |
Use Scenario: Low-noise 24V-to-isolated ±15V dual-output supply for precision ADC/DAC signal conditioning circuits. IC Role / Device Role / Timing Role: Controller enforcing strict timing windows (ENDLY, MINENAB, tON) to reject transformer leakage spikes and ensure accurate flyback pulse capture. Use Value: Enables clean, ripple-free isolated rails without optocoupler-induced latency or gain drift-critical for 16-bit+ data acquisition systems. | Use Scenario: Patient-connected medical device requiring reinforced isolation and <10 µA creepage current, powering isolated microcontroller and sensor interface. IC Role / Device Role / Timing Role: Safety-critical flyback controller providing galvanic isolation via transformer, with 3VOUT powering isolated watchdog timer and status LEDs. Use Value: Reduces reliance on secondary-side components, lowering risk of isolation barrier failure and easing IEC 60601-1 creepage/clearance validation. |
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 700V MOSFET; no external gate driver required; lacks 3VOUT and load compensation pins | Better suited for lower-power (<15W), cost-sensitive consumer adapters; not ideal for telecom 36–72V input or precision load regulation | Select UCC28740DR only if integrating high-voltage switch and reducing component count outweighs need for primary-side load compensation and auxiliary 3V rail |
| ICE3B0565J | Fixed-frequency current-mode controller with integrated 650V MOSFET; no third-winding feedback support; requires optocoupler for regulation | Targeted at universal-input offline SMPS with opto-based feedback; higher integration but less flexibility in transformer design and regulation architecture | Choose ICE3B0565J when designing for cost-driven, non-telecom applications where optocoupler use is acceptable and third-winding feedback is unnecessary |
Compared with UCC28740DR and ICE3B0565J, the LT1725IS#TRPBF uniquely supports primary-side regulation without optoisolator, offers dedicated load compensation for tight load regulation, and provides a buffered 3V auxiliary output-making it optimal for telecom, industrial, and instrumentation flyback supplies demanding precision, reliability, and design flexibility.
Availability
LT1725IS#TRPBF is available at Aetrix Electronics and suitable for telecom isolated converters, offline isolated power supplies, and instrumentation power supplies requiring stable component supply, long-lifecycle assurance, and traceable sourcing.
Supply support for LT1725IS#TRPBF 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#TRPBF belongs to Linear's legacy isolated power controller product line, engineered specifically for high-reliability, primary-side-regulated flyback topologies in telecom and industrial environments where optocoupler elimination and load regulation accuracy are critical.
FAQ
What is the operating temperature range for the LT1725IS#TRPBF?
The LT1725IS#TRPBF is specified for an industrial operating junction temperature range of –40°C to 125°C. This rating is confirmed in the Absolute Maximum Ratings table and Electrical Characteristics section of the official datasheet, where parameters marked with ● apply across this full range. The "I" grade suffix in LT1725IS#TRPBF explicitly denotes this extended temperature capability, distinguishing it from the commercial-grade LT1725CS#TRPBF (0°C to 100°C).
Does the LT1725IS#TRPBF require an optoisolator for feedback?
No, the LT1725IS#TRPBF does not require an optoisolator. It achieves isolated output regulation by sampling the reflected flyback pulse from a dedicated third transformer winding and processing it through its internal flyback error amplifier and collapse-detect circuitry. This primary-side sensing architecture eliminates the need for optocouplers or secondary-side references like TL431, as explicitly stated in the Features and Typical Application sections of the LT1725 datasheet.
How is the switching frequency set on the LT1725IS#TRPBF?
The switching frequency of the LT1725IS#TRPBF is set by an external capacitor connected to the OSCAP pin (Pin 6). The datasheet specifies a range of 50 kHz to 250 kHz, corresponding to OSCAP values from 200 pF down to 33 pF. For example, a 100 pF capacitor yields a typical frequency of 100 kHz. This capacitor directly programs the oscillator timing and must be placed close to OSCAP and SGND with low-ESR characteristics.
What is the purpose of the ROCMP and RCMPC pins on the LT1725IS#TRPBF?
The ROCMP (Pin 4) and RCMPC (Pin 5) pins implement optional load compensation on the LT1725IS#TRPBF. ROCMP accepts a resistor that develops a voltage proportional to average switch current, while RCMPC connects to a filter capacitor (typically 0.1 µF) to smooth that signal. Together, they inject correction current into the FB node to counteract output voltage droop caused by secondary-side impedances-including diode forward voltage, winding resistance, and capacitor ESR-thereby improving load regulation without secondary feedback.
Can the LT1725IS#TRPBF drive a high-side N-channel MOSFET directly?
Yes, the LT1725IS#TRPBF can directly drive a high-side N-channel MOSFET via its GATE pin (Pin 16), which delivers a 12.1 V (typ) high-level output capable of sinking and sourcing up to 500 mA. The datasheet confirms compatibility with devices like the IRF620 and specifies gate drive rise/fall times under 30 ns with 1 nF load. A series gate resistor (≥5 Ω) is recommended to damp ringing, and the GATE trace must be kept short to minimize EMI and voltage spikes.
LT1725IS#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LT1725IS#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725IS#TRPBF 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#TRPBF reliable?
The price and inventory of LT1725IS#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725IS#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1725IS#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725IS#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725IS#TRPBF?
LT1725IS#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725IS#TRPBF 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#TRPBF?
For technical support, including LT1725IS#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725IS#TRPBF requirements.
6.How does Aetrix verify that LT1725IS#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1725IS#TRPBF 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#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1725IS#TRPBF?
All LT1725IS#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725IS#TRPBF, 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#TRPBF part is unused and in its original packaging.
Return procedure for LT1725IS#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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