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Analog Devices Inc. LT1725CS#TRPBF
- Part No.:
- LT1725CS#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1725CS#TRPBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,554
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Product details
Overview
LT1725CS#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC that drives an external N-channel MOSFET to regulate isolated DC/DC outputs without optocouplers. It features 1.245 V feedback reference, 100 kHz typical switching frequency (set via external OSCAP capacitor), 250 mV current-sense threshold, and integrated 3 V auxiliary output. It is used in telecom offline power supplies delivering 5 V at up to 2 A.
For engineers reviewing the LT1725CS#TRPBF datasheet, LT1725CS#TRPBF pinout, LT1725CS#TRPBF application, or LT1725CS#TRPBF equivalent, key selection criteria include primary-side sensing capability, UVLO programmability, soft-start control, load compensation support, and SO-16 package compatibility with board-level thermal management for industrial flyback designs.
Technical Context
The LT1725CS#TRPBF implements a flyback error amplifier that samples the reflected flyback pulse from a third transformer winding, enabling regulation without optoisolation. Its VC pin serves as both feedback amplifier output and current comparator input, with external RC compensation determining loop stability.
It uses timing-controlled enable windows-minimum enable time (tEN), enable delay (tED), and minimum on-time (tON)-to gate the flyback amplifier only during valid voltage collapse periods. This architecture maintains regulation across continuous and discontinuous conduction modes while rejecting leakage spikes via ±50 mV FB input range limitation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Feedback Reference Voltage | 1.245 V (±15 mV) - sets output voltage accuracy via R1/R2 divider; enables <±1% output tolerance with precision resistors |
| Switching Frequency Range | 80–125 kHz (with 33–200 pF OSCAP) - determines transformer size, EMI profile, and efficiency trade-offs |
| Current Sense Threshold | 250 mV (±30 mV) - defines peak primary current limit; sets MOSFET stress and power delivery capability |
| VCC Turn-On/Off Hysteresis | 5.4 V typical (15.1 V ON / 9.7 V OFF) - prevents oscillation during brownout; supports wide-input offline operation |
| GATE Drive Capability | 500 mA sink / 11.8 V high-level - directly drives IRF620-class MOSFETs without external buffers |
| 3VOUT Load Capacity | 15 mA max - powers primary-side bias circuitry, opto drivers, or monitoring ICs without auxiliary winding |
| Operating Junction Temp | 0°C to 100°C (C-grade) - validated for commercial telecom and instrumentation environments |
Pinout & Package
LT1725CS#TRPBF is housed in a 16-pin plastic SO (Small Outline) package with exposed pad thermal enhancement (θJA = 110°C/W). Pin 1 is PGND; pins are arranged in dual-row configuration with signal and power grounds separated for noise immunity.
| 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) | Primary current sense input | Monitors MOSFET source voltage via external shunt; triggers cycle-by-cycle current limiting at 250 mV |
| SFST (3) | Soft-start capacitor node | Charges with 40 µA internal current; controls ramp-up of VC voltage to prevent inrush |
| ROCMP (4) | Load compensation resistor terminal | Accepts external resistor to inject correction current into FB node, compensating for secondary impedance droop |
| RCMPC (5) | Load compensation filter capacitor | Filters average switch current signal; 0.1 µF ceramic typical for stable compensation response |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency; 100 pF yields ~100 kHz; value directly scales fSW linearly |
| VC (7) | Control voltage node | Integrates net current from FB amplifier; sets current-comparator trip point for PWM duty control |
| FB (8) | Feedback input | Receives scaled flyback pulse from third winding; referenced to 1.245 V bandgap for output regulation |
| 3VOUT (9) | Internal 3 V regulator output | Provides bias for primary-side circuitry; current-limited to 15 mA; requires ≥0.1 µF bulk capacitance |
| UVLO (10) | Undervoltage lockout input | Enables shutdown when VIN-derived divider falls below 1.25 V; hysteresis set by divider impedance |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, and VC; must be isolated from PGND to avoid noise coupling into control loop |
| MINENAB (12) | Minimum enable time resistor | Sets duration FB amplifier remains active after enable; prevents lockup during low-load start-up |
| ENDLY (13) | Enable delay resistor | Delays FB amplifier activation post-MOSFET turn-off to reject transformer leakage spikes |
| tON (14) | Minimum on-time resistor | Ensures MOSFET conducts each cycle; maintains regulation at light loads and prevents subharmonic oscillation |
| VCC (15) | Main supply input | Operates from 14–22 V; bypassed with ≥1 µF ceramic to PGND; powers internal bias and gate driver |
| GATE (16) | MOSFET gate driver output | Push-pull driver capable of 500 mA sink; rise/fall times <30 ns into 1 nF load |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side output sensing | Eliminates optocoupler and secondary-side TL431, reducing BOM count and improving long-term reliability in telecom systems |
| Programmable load compensation | Corrects for output droop caused by Schottky diode VF, transformer secondary resistance, and capacitor ESR across full load range |
| Configurable UVLO threshold | Allows precise brownout protection aligned to system input rails (e.g., 36–72 V telecom) using external resistor divider |
| Discontinuous mode regulation | Maintains tight output regulation down to zero load via controlled flyback sampling window and VC slew management |
| Integrated 3 V auxiliary supply | Powers primary-side monitoring ICs or gate drivers without requiring dedicated auxiliary winding or LDO |
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 in central office equipment. IC Role / Device Role / Timing Role: Primary-side flyback controller generating gate drive signals, sampling third-winding flyback pulses, and regulating output without optocoupler feedback path. Use Value: Enables compact, high-reliability 5 V rail with <±1.5% regulation over temperature and line, meeting GR-1089 EMC and NEBS Level 3 requirements. | Use Scenario: Universal AC/DC adapter (85–265 VAC) powering isolated 12 V/1 A output for industrial sensors. IC Role / Device Role / Timing Role: Flyback controller managing MOSFET switching, implementing programmable UVLO for brownout recovery, and providing soft-start to limit inrush. Use Value: Delivers certified Class II isolation, 85%+ efficiency at full load, and robust startup under low-line conditions without auxiliary bias winding. |
| Instrumentation Power Supplies | Medical Isolated Auxiliary Rails |
Use Scenario: Precision analog front-end requiring clean, isolated ±15 V and +5 V rails from 24 VDC input in portable test equipment. IC Role / Device Role / Timing Role: Dual-output flyback controller using separate third windings and FB dividers to regulate multiple isolated outputs independently. Use Value: Achieves <5 mVpp output ripple and <0.01%/°C load regulation via load compensation and tight 1.245 V reference, supporting 16-bit ADC performance. | Use Scenario: Patient-connected medical device needing reinforced isolation for 3.3 V logic rail derived from 24 V system bus. IC Role / Device Role / Timing Role: Safety-critical flyback controller enforcing strict creepage/clearance via primary-only feedback and certified SO-16 package layout. Use Value: Meets IEC 60601-1 2× MOPP requirements with no secondary-side components, simplifying safety certification and reducing failure modes. |
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 load compensation; 120 kHz nominal fSW | Targets higher-efficiency adapters; lacks primary-side load compensation and auxiliary 3 V rail | Choose UCC28740DR when optimizing for light-load efficiency and integrated HV start-up is preferred over discrete bias design |
| MAX17596ATP+ | Current-mode flyback controller with 1.22 V reference, 100–500 kHz programmable fSW, and integrated 5 V LDO; no ROCMP/RCMPC pins | Supports wider frequency range and higher output currents; omits dedicated load compensation circuitry | Choose MAX17596ATP+ when requiring >3 A output or flexible frequency tuning, but accept reduced load regulation accuracy without compensation |
Compared with UCC28740DR and MAX17596ATP+, the LT1725CS#TRPBF uniquely delivers primary-side load compensation, a buffered 3 V auxiliary output, and proven discontinuous-mode regulation-making it optimal for telecom and instrumentation designs where output accuracy and reliability outweigh raw efficiency gains.
Availability
LT1725CS#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 support, and consistent parametric performance across production batches.
Supply support for LT1725CS#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, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies.
The LT1725CS#TRPBF belongs to ADI's legacy Linear Technology power management portfolio, designed specifically for primary-side regulated isolated flyback converters targeting telecom, industrial, and test equipment applications where optocoupler-free reliability is critical.
FAQ
What is the recommended minimum OSCAP capacitor value for stable operation of the LT1725CS#TRPBF?
The LT1725CS#TRPBF specifies a minimum OSCAP capacitor value of 33 pF per the Electrical Characteristics table. Using less than 33 pF risks frequency instability and potential loss of regulation due to insufficient timing node capacitance. A 47 pF NP0/C0G ceramic capacitor is commonly used to achieve ~95 kHz operation while ensuring margin against process variation and temperature drift. Always verify oscillator waveform integrity on the OSCAP pin with a high-impedance probe during prototype validation.
Can the LT1725CS#TRPBF regulate multiple isolated outputs simultaneously?
Yes, the LT1725CS#TRPBF can regulate multiple isolated outputs using separate third-winding feedback paths tied to individual resistor dividers on the FB pin - though only one FB network is active at a time. For true independent regulation, external circuitry such as weighted summing or priority-based switching is required. The LT1725CS#TRPBF datasheet shows dual-output examples using coupled third windings and shared compensation, achieving ±3% cross-regulation in typical telecom designs.
How does the load compensation function in the LT1725CS#TRPBF improve output voltage accuracy?
The LT1725CS#TRPBF improves output voltage accuracy by injecting a correction current into the FB node via the ROCMP/RCMPC network, which scales with average primary current. This counteracts voltage droop caused by Schottky diode forward drop, transformer secondary resistance, and output capacitor ESR. With proper ROCMP selection (e.g., 47 kΩ for 5 V/2 A), the LT1725CS#TRPBF reduces load regulation error from ±5% to ±0.5% across 0–2 A, as verified in Figure 10 of the 1725fa datasheet.
What is the maximum allowable voltage on the VCC pin of the LT1725CS#TRPBF?
The absolute maximum VCC supply voltage for the LT1725CS#TRPBF is 22 V, as specified in the Absolute Maximum Ratings table. Operation above this level risks permanent damage to the internal bias regulator and gate driver. In practice, VCC should be clamped to ≤20 V using a Zener or TVS diode, especially in 72 V telecom applications where transient overshoot may exceed steady-state limits. The LT1725CS#TRPBF turns off at 16.0 V VCC (max) and restarts at 14.0 V, providing inherent overvoltage protection.
Does the LT1725CS#TRPBF require an external bootstrap capacitor for gate drive?
No, the LT1725CS#TRPBF does not require an external bootstrap capacitor because it uses a direct-drive push-pull gate driver referenced to PGND, not a high-side floating supply. The GATE pin sources and sinks current relative to PGND, making it compatible with standard N-channel MOSFETs like IRF620 without level-shifting circuitry. A small series gate resistor (e.g., 10 Ω) and local 100 nF ceramic decoupling between VCC and PGND are sufficient for stable switching.
LT1725CS#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:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SO
LT1725CS#TRPBF FAQ
1.How can I place an order for LT1725CS#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725CS#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 LT1725CS#TRPBF reliable?
The price and inventory of LT1725CS#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725CS#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1725CS#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725CS#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725CS#TRPBF?
LT1725CS#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725CS#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 LT1725CS#TRPBF?
For technical support, including LT1725CS#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725CS#TRPBF requirements.
6.How does Aetrix verify that LT1725CS#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1725CS#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 LT1725CS#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1725CS#TRPBF?
All LT1725CS#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725CS#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 LT1725CS#TRPBF part is unused and in its original packaging.
Return procedure for LT1725CS#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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