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Analog Devices Inc. LT1725CGN#TRPBF
- Part No.:
- LT1725CGN#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
LT1725CGN#TRPBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,305
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Product details
Overview
LT1725CGN#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed for primary-side regulation in telecom and 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 at 50kHz–250kHz with external timing capacitor.
For engineers reviewing the LT1725CGN#TRPBF datasheet, LT1725CGN#TRPBF pinout, LT1725CGN#TRPBF application, or LT1725CGN#TRPBF equivalent, key selection considerations include its primary-side feedback architecture, UVLO programmability via external resistor divider, soft-start implementation using SFST pin, load compensation capability (ROCMP/RCMPC), and guaranteed operation across 0°C to 100°C junction temperature.
Technical Context
The LT1725CGN#TRPBF implements a specialized flyback error amplifier that samples the reflected flyback pulse during a precisely timed window-enabled after a programmable delay (ENDLY) and held for a minimum duration (MINENAB)-to derive output voltage information without secondary-side sensing. Its control loop integrates VC pin current from feedback amplifier output and current-sense comparator, with frequency compensation applied externally between VC and SGND.
It uses current-mode control with fixed 250mV ISENSE threshold, supports discontinuous conduction mode regulation via collapse-detect circuitry, and includes dedicated circuitry for load compensation (via ROCMP/RCMPC) and undervoltage lockout (UVLO) referenced to VIN-not VCC-enabling precise input rail monitoring independent of internal bias supply.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Turn-On Voltage | 15.1 V typical - ensures reliable startup only when auxiliary winding provides sufficient bias voltage |
| ISENSE Threshold | 250 mV ±30 mV - sets peak switch current limit; determines maximum power delivery with external sense resistor |
| FB Reference Voltage | 1.245 V ±15 mV - precision bandgap reference used with external R1/R2 divider to set output voltage |
| Switching Frequency Range | 50 kHz to 250 kHz - adjustable via OSCAP capacitor; higher frequencies reduce transformer size but increase switching loss |
| GATE Drive High Level | 12.1 V at 100 mA - sufficient to fully enhance standard logic-level MOSFETs with low gate charge |
| 3VOUT Load Capability | 15 mA max - powers auxiliary circuitry (e.g., bias regulators, monitoring ICs) without external LDO |
| UVLO Threshold | 1.25 V ±0.04 V - enables precise input under-voltage cutoff using external resistor divider on UVLO pin |
| Operating Junction Temp | 0°C to 100°C - specified for commercial-grade performance; matches LT1725C grade designation |
Pinout & Package
LT1725CGN#TRPBF is housed in a 16-lead plastic SSOP (GN) package with exposed pad for thermal enhancement. Pin pitch is 0.65 mm; body dimensions are 5.0 mm × 6.2 mm × 1.75 mm (L × W × H). Recommended PCB layout isolates PGND and SGND planes, routes GATE trace short and wide, and places OSCAP/VC/RCMPC capacitors close to respective pins.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return for GATE discharge current | Carries high di/dt spikes; must connect directly to low-inductance ground plane to prevent noise coupling |
| ISENSE (2) | Current sense input | Monitors voltage across external sense resistor; triggers cycle-by-cycle current limiting at ~250 mV |
| SFST (3) | Soft-start capacitor connection | Charges linearly to ramp up VC voltage; controls startup slew rate and inrush current |
| ROCMP (4) | Load compensation resistor input | Accepts current proportional to average switch current; adjusts FB reference to compensate for output impedance |
| RCMPC (5) | Load compensation filter capacitor | Filters ROCMP current; sets time constant for dynamic load compensation response |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency; 100 pF yields ~100 kHz; smaller values increase frequency |
| VC (7) | Control voltage output/input node | Integrates error amplifier output current; sets current-comparator trip point; requires external compensation capacitor to SGND |
| FB (8) | Feedback amplifier inverting input | Receives scaled flyback pulse from third winding; compared to 1.245 V reference to regulate output |
| 3VOUT (9) | Internal 3V regulator output | Provides stable 3V supply for auxiliary circuits; internally current-limited to 15 mA |
| UVLO (10) | Undervoltage lockout input | Enables/disables switching based on VIN-derived threshold; bias current varies to create user-adjustable hysteresis |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, VC; must be isolated from PGND to avoid noise injection into sensitive analog nodes |
| MINENAB (12) | Minimum enable time programming | Resistor sets minimum duration the flyback amplifier remains active per cycle; prevents latch-up at light loads |
| ENDLY (13) | Enable delay programming | Resistor sets delay between MOSFET turn-off and flyback amplifier activation; avoids leakage spike corruption |
| tON (14) | Minimum switch-on time programming | Resistor sets shortest allowable on-time; ensures minimum energy transfer and stable regulation at low loads |
| VCC (15) | Supply voltage input | Powered from auxiliary winding; bypassed with ≥1 µF ceramic capacitor to suppress ripple and transients |
| GATE (16) | MOSFET gate driver output | High-current push-pull driver; capable of sourcing 500 mA and sinking 2.5 mA; requires series gate resistor for ringing control |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optoisolator | Uses third-winding flyback pulse sampling to eliminate secondary-side feedback components and associated latency/complexity |
| Programmable UVLO referenced to VIN | Allows system-level brown-out protection tied directly to input bus, independent of VCC bias stability |
| Discontinuous mode regulation maintenance | Retains tight output regulation even as load drops below critical conduction threshold, via collapse-detect timing |
| External load compensation interface | ROCMP/RCMPC pins enable correction of output voltage droop caused by transformer secondary ESR and diode VF |
| Integrated 3V auxiliary supply | Eliminates need for external LDO to power monitoring or sequencing circuitry on primary side |
| Adjustable soft-start and timing parameters | All key timing functions (fSW, tON, ENDLY, MINENAB) set via external passive components for design flexibility |
Applications
| Telecom Isolated Converters | Offline Isolated Power Supplies |
|---|---|
Use Scenario: 48V DC input telecom shelf power feeding distributed 5V/2A loads across backplane. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating output via third-winding feedback; manages gate drive timing, current limiting, and UVLO shutdown during input dips. Use Value: Enables compact, cost-effective isolation without optocouplers or secondary-side controllers-reducing BOM count and improving reliability in -40°C to +70°C operating environments. | Use Scenario: Universal-input (85–265V AC) offline adapter delivering isolated 5V/2A for industrial IoT gateway. IC Role / Device Role / Timing Role: Core controller implementing primary-side regulation, programmable soft-start, and load-compensated feedback to maintain ±2% output accuracy across line/load/temperature. Use Value: Meets IEC 62368-1 creepage/clearance requirements while achieving >85% efficiency and <100 mW no-load consumption via precise gate drive and low ICC quiescent current. |
| Instrumentation Power Supplies | Medical Isolated Auxiliary Rails |
Use Scenario: Precision lab equipment requiring clean, low-noise ±15V and +5V isolated rails from 24V DC input. IC Role / Device Role / Timing Role: Flyback controller managing dual-output topology with cross-regulation via third-winding sensing; coordinates timing of synchronous rectification (if used) and load compensation. Use Value: Delivers <10 mVpp output ripple and <0.1% load regulation drift over 0–100°C-critical for ADC reference and op-amp bias stability. | Use Scenario: Patient-connected medical device needing reinforced isolation for 3.3V microcontroller rail derived from 24V system bus. IC Role / Device Role / Timing Role: Safety-critical isolated controller ensuring galvanic separation per IEC 60601-1; implements mandatory UVLO, soft-start, and fault-safe shutdown on VCC undervoltage. Use Value: Achieves 4 kV AC isolation rating with certified transformer design, while maintaining 200 ns minimum tON to guarantee regulation during transient load steps. |
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 rail; requires optocoupler for tight regulation | Better light-load efficiency via QR operation; lacks primary-side compensation and auxiliary 3V supply | Select UCC28740DR when optimizing for <30 mW no-load power and accepting optocoupler dependency |
| MAX17690ATP+T | Current-mode flyback controller with integrated 700V MOSFET; no external gate drive; supports 3.3V/5V selectable VREF | Reduces component count but limits max output power to ~15W; no programmable UVLO or load compensation | Select MAX17690ATP+T for space-constrained designs where integrated FET suffices and load compensation is unnecessary |
Compared with UCC28740DR and MAX17690ATP+T, the LT1725CGN#TRPBF uniquely combines primary-side regulation without optoisolator, user-programmable timing/compensation, and an integrated 3V auxiliary supply-making it optimal for mid-power (10–30W), cost-sensitive, and thermally constrained telecom and industrial flyback designs.
Availability
LT1725CGN#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-term lifecycle support, and consistent parametric performance across production batches.
Supply support for LT1725CGN#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 leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, formed through the acquisition of Linear Technology in 2017.
The LT1725CGN#TRPBF belongs to ADI's legacy Linear Technology power management portfolio, specifically engineered for primary-side regulated isolated flyback topologies in telecom, industrial, and medical applications where optocoupler elimination and design flexibility are critical.
FAQ
What is the recommended minimum value for the OSCAP capacitor on LT1725CGN#TRPBF?
The LT1725CGN#TRPBF datasheet specifies a minimum OSCAP capacitor value of 33 pF to ensure stable oscillator operation across temperature and process variation. Using less than 33 pF may cause frequency instability or erratic switching behavior. For nominal 100 kHz operation, a 100 pF ±5% NP0 ceramic capacitor placed within 2 mm of OSCAP and SGND pins is recommended to minimize parasitic inductance and maintain accuracy.
Can LT1725CGN#TRPBF operate without an external MOSFET?
No, the LT1725CGN#TRPBF cannot operate without an external MOSFET. It is a controller-only IC with a dedicated GATE pin designed to drive the gate of an external N-channel power MOSFET. The IC does not integrate any power switch; all energy transfer occurs through the external MOSFET and transformer. Attempting to use LT1725CGN#TRPBF without an external MOSFET will result in no output regulation or power delivery.
How does the LT1725CGN#TRPBF achieve primary-side regulation without an optoisolator?
The LT1725CGN#TRPBF achieves primary-side regulation by sampling the reflected flyback voltage from a dedicated third winding on the transformer. This voltage-proportional to the isolated output-is fed into the FB pin via a resistor divider. Internal circuitry enables the feedback amplifier only during a precise window after MOSFET turn-off, rejecting leakage spikes and enabling accurate output voltage reconstruction without secondary-side components. This eliminates optoisolator latency, aging, and cost.
What is the function of the ROCMP and RCMPC pins on LT1725CGN#TRPBF?
The ROCMP and RCMPC pins on LT1725CGN#TRPBF implement optional load compensation to correct output voltage droop caused by transformer secondary resistance, diode forward voltage, and capacitor ESR. ROCMP accepts a current proportional to average switch current, while RCMPC connects a filter capacitor to smooth that current. Together, they dynamically raise the effective FB reference voltage under increasing load, counteracting output impedance effects and improving load regulation to <±1% across 0–2A.
Is LT1725CGN#TRPBF RoHS compliant and lead-free?
Yes, LT1725CGN#TRPBF is RoHS compliant and lead-free. The "#TRPBF" suffix explicitly denotes tape-and-reel packaging with lead-free (Pb-free) finish per JEDEC J-STD-020. The SSOP package uses matte tin lead plating, and the device meets EU RoHS Directive 2011/65/EU and China RoHS II requirements. Full compliance documentation, including material declarations and test reports, is available from Analog Devices' product page for LT1725CGN#TRPBF.
LT1725CGN#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SSOP (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-SSOP
LT1725CGN#TRPBF FAQ
1.How can I place an order for LT1725CGN#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1725CGN#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 LT1725CGN#TRPBF reliable?
The price and inventory of LT1725CGN#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1725CGN#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1725CGN#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1725CGN#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1725CGN#TRPBF?
LT1725CGN#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1725CGN#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 LT1725CGN#TRPBF?
For technical support, including LT1725CGN#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1725CGN#TRPBF requirements.
6.How does Aetrix verify that LT1725CGN#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1725CGN#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 LT1725CGN#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1725CGN#TRPBF?
All LT1725CGN#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1725CGN#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 LT1725CGN#TRPBF part is unused and in its original packaging.
Return procedure for LT1725CGN#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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