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Analog Devices Inc. LT3574IMS#PBF
- Part No.:
- LT3574IMS#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-TFSOP (0.118", 3.00mm Width)
- Datasheet:
-
LT3574IMS#PBF.pdf
- Description:
- IC REG FLYBACK 650MA 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,533
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Product details
Overview
LT3574IMS#PBF from Analog Devices (formerly Linear Technology) is a monolithic isolated flyback controller IC with integrated 0.65A/60V NPN power switch, designed for primary-side regulation without opto-coupler or third winding. It operates from 3V to 40V input, delivers up to 3W output power, and uses boundary mode control for improved load regulation in industrial and medical isolated power supplies.
For engineers reviewing the LT3574IMS#PBF datasheet, LT3574IMS#PBF pinout, LT3574IMS#PBF application, or LT3574IMS#PBF equivalent, key selection considerations include its 16-lead MSOP package, programmable current limit via RILIM, temperature-compensated feedback via TC pin, soft-start capability, and −40°C to 125°C operating junction temperature range.
Technical Context
The LT3574IMS#PBF implements boundary conduction mode (BCM) control to eliminate subharmonic oscillation and enable smaller magnetics. Its flyback error amplifier samples the SW node voltage at zero-secondary-current instants, deriving isolated output voltage information directly from the primary-side flyback waveform.
It integrates a 0.65A/60V NPN switch, internal bias regulator, programmable UVLO threshold (1.22V), soft-start current source (7µA), and temperature-compensation current source (27.5µA into RREF via TC pin). The VC pin provides error amplifier compensation, while RFB/RREF resistor ratio sets output voltage in conjunction with transformer turns ratio and diode forward drop.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3V to 40V - supports wide-input industrial and automotive supply rails without external pre-regulation. |
| Integrated Power Switch | 0.65A, 60V NPN - eliminates need for external high-voltage transistor in ≤3W isolated designs. |
| Switching Frequency | Up to 1000kHz - enables compact magnetics and fast transient response. |
| RREF Reference Voltage | 1.21V to 1.25V - precision bandgap reference used with RFB to set output voltage via transformer ratio. |
| Operating Temperature | −40°C to 125°C - qualified for harsh industrial and automotive environments. |
| Current Limit Range | 100mA to 1.1A - adjustable via RILIM resistor (10kΩ yields full 0.65A rating). |
| Soft-Start Threshold | 0.7V - controls ramp rate of output voltage during startup to limit inrush current. |
Pinout & Package
LT3574IMS#PBF is housed in a 16-lead plastic MSOP package (3mm × 4.9mm, 0.5mm pitch) with exposed pad for thermal performance. Pin functions are validated per Linear Technology's official pin configuration diagram.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pins 1,3,4,8,10,16) | Ground reference | Multiple ground pins reduce impedance and improve noise immunity in high-dI/dt flyback operation. |
| SW (Pin 5) | Collector of internal NPN switch | High-slew-rate node requiring short PCB traces to minimize EMI and voltage spikes. |
| VIN (Pin 6) | Main input supply | Supplies start-up circuitry and serves as DCM comparator reference; requires local bypass capacitor. |
| BIAS (Pin 7) | Internal bias supply | Provides current to switch driver and internal logic; may connect to VIN if ≤15V and no third winding used. |
| SHDN/UVLO (Pin 8) | Shutdown and undervoltage lockout | Resistor divider sets turn-on threshold (1.22V typical); 2.5µA hysteresis current ensures stable UVLO behavior. |
| RILIM (Pin 11) | Current limit programming | Resistor to GND sets peak switch current (e.g., 10kΩ → 0.65A); enables design flexibility across output power levels. |
| RFB (Pin 12) | Primary-side feedback sensing | Connects to SW node; forms voltage divider with RREF to derive output voltage information from flyback pulse amplitude. |
| RREF (Pin 13) | Reference resistor connection | Ground-referred resistor (typically 6.04kΩ) sets gain for feedback loop; internal 1.23V bandgap reference anchors regulation accuracy. |
| VC (Pin 14) | Error amplifier compensation | External RC network stabilizes control loop; 100pF parallel capacitor suppresses noise coupling. |
| TC (Pin 15) | Temperature compensation | Resistor to GND injects positive TC current into RREF to cancel diode VF drift over temperature. |
| SS (Pin 9) | Soft-start timing | Capacitor to GND sets output voltage ramp time; 7µA current charges SS until 0.7V triggers switching. |
| TEST (Pin 2) | Factory test | Must be tied to GND for normal operation; not intended for system use. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation | Eliminates opto-coupler and third winding, reducing BOM cost, board area, and long-term reliability risk from opto aging. |
| Boundary mode operation | Enables zero-current switching on secondary side, improving load regulation and allowing smaller transformer core size vs CCM. |
| Programmable current limit | RILIM pin allows precise setting of switch current threshold to match transformer saturation and output power requirements. |
| Temperature-compensated feedback | TC pin current source offsets diode forward voltage drift, maintaining ±1% output accuracy over −40°C to 125°C. |
| Integrated 60V NPN switch | Supports 40V max input with margin for flyback voltage spikes, enabling robust operation in noisy industrial environments. |
Applications
| Industrial Isolated Sensors | Automotive Body Control Modules |
|---|---|
Use Scenario: Isolated 5V supply for analog sensor front-ends in factory automation systems with 24V DC bus and stringent EMC requirements. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating isolated 5V rail using PA2626NL transformer and boundary-mode switching. Use Value: Eliminates opto-coupler drift and aging, ensuring stable sensor bias over 10+ year service life in unattended equipment. | Use Scenario: Compact 3.3V isolated power for CAN transceiver and microcontroller in vehicle door module with 9V–16V battery input. IC Role / Device Role / Timing Role: Flyback controller operating in boundary mode to maintain tight load regulation across cold-crank (6.5V) to load-dump (18V) conditions. Use Value: −40°C to 125°C rating and integrated switch enable single-chip solution meeting AEC-Q100 Grade 1 requirements without external HV FET. |
| Medical Patient Monitoring | Industrial PLC I/O Isolation |
Use Scenario: Reinforced-isolation 5V supply for ECG front-end ADC in portable patient monitor powered by Li-ion battery pack (10V–12.6V). IC Role / Device Role / Timing Role: Regulates isolated output using 3:1 transformer and TC-compensated feedback to meet IEC 60601-1 creepage/clearance and accuracy specs. Use Value: No opto-coupler simplifies safety certification and avoids lifetime degradation affecting measurement stability. | Use Scenario: 12V isolated auxiliary supply for digital I/O modules in programmable logic controllers with 24V DC field bus. IC Role / Device Role / Timing Role: Boundary-mode flyback controller driving PA3020NL transformer to deliver 12V/0.25A with <±1.5% line/load regulation. Use Value: Programmable RILIM and soft-start prevent inrush tripping of upstream 24V power supply during hot-plug insertion. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar isolated flyback controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT3748IMS#PBF | Higher 1.2A/100V MOSFET switch; supports up to 10W; requires external gate driver for synchronous rectification. | Targets higher-power isolated supplies (>5W); lacks integrated NPN but offers wider VIN range (4.5V–100V). | Choose LT3748IMS#PBF when >3W output or >40V input is required; LT3574IMS#PBF remains optimal for cost-sensitive ≤3W designs. |
| UCC28911DR | 65V integrated MOSFET; proprietary constant-on-time quasi-resonant control; no RILIM or TC pins; fixed 1.25V reference. | Optimized for low-noise consumer AC/DC adapters; lacks temperature compensation and programmable current limit. | UCC28911DR suits high-volume, low-cost AC/DC; LT3574IMS#PBF preferred where precision, temperature stability, and design flexibility are critical. |
Compared with LT3748IMS#PBF and UCC28911DR, the LT3574IMS#PBF uniquely combines integrated NPN switching, primary-side regulation without opto-coupler, temperature-compensated feedback, and −40°C to 125°C operation-making it ideal for precision, medium-reliability isolated DC/DC in industrial and medical settings.
Availability
LT3574IMS#PBF is available at Aetrix Electronics and suitable for industrial sensors, automotive body electronics, medical monitoring devices, and PLC I/O modules requiring stable component supply and long-term lifecycle support.
Supply support for LT3574IMS#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 and maintains full product support, documentation, and manufacturing continuity for all Linear ICs including the LT3574 series.
The LT3574 product line was designed specifically for isolated flyback power conversion with primary-side regulation, targeting applications where opto-coupler elimination, small footprint, and wide temperature operation are essential.
FAQ
What is the maximum output power achievable with the LT3574IMS#PBF?
The LT3574IMS#PBF delivers up to 3W of isolated output power without an external power switch. This assumes proper transformer selection (e.g., PA2626NL for 5V/0.5A), boundary mode operation, and input voltage within 3V–40V. Output power scales with input voltage and transformer turns ratio-higher VIN or larger NPS increases available power but must keep SW pin voltage below 50V to avoid breakdown. Real-world derating for thermal and efficiency should be applied.
Does the LT3574IMS#PBF require an opto-coupler for regulation?
No, the LT3574IMS#PBF does not require an opto-coupler. It achieves isolated output voltage regulation by sampling the flyback pulse amplitude at the SW pin during zero-secondary-current intervals. This primary-side sensing method eliminates opto-coupler drift, aging, and bandwidth limitations-key advantages for long-life industrial and medical power supplies.
How is output voltage set on the LT3574IMS#PBF?
Output voltage on the LT3574IMS#PBF is set using two external resistors: RFB connected between SW and RREF pins, and RREF connected between RREF pin and GND. The ratio RFB/RREF, multiplied by the internal 1.23V bandgap reference and transformer turns ratio (NPS), determines VOUT. For example, a 3:1 transformer with RREF = 6.04kΩ and RFB = 80.6kΩ yields ~5V output. Tables in the datasheet provide standard values for common voltages and ratios.
What is the purpose of the TC pin on the LT3574IMS#PBF?
The TC (Temperature Compensation) pin on the LT3574IMS#PBF sources a positive temperature coefficient current into the RREF node to counteract the negative temperature coefficient of the output rectifier diode's forward voltage (VF). A resistor from TC to GND sets this current (ITC = 0.55V / RTC). Proper TC compensation maintains output voltage accuracy within ±1% over the full −40°C to 125°C operating range.
Can the LT3574IMS#PBF operate with a 1:1 transformer?
Yes, the LT3574IMS#PBF can operate with a 1:1 transformer, as confirmed in Table 1 of the datasheet which lists resistor values for 1:1 configurations (e.g., 5V output uses RFB = 27.4kΩ, RREF = 6.04kΩ). However, 1:1 operation limits maximum output power and requires careful attention to SW pin voltage: VSW(MAX) = VIN(MAX) + VOUT + VF must remain ≤50V. For higher power or lower VIN, higher turns ratios (e.g., 2:1, 3:1) are typically preferred.
LT3574IMS#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TFSOP (0.118", 3.00mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive or Negative, Isolation Capable
- Topology:
- Flyback
- Output Type:
- -
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 3V
- Voltage - Input (Max):
- 40V
- Voltage - Output (Min/Fixed):
- -
- Voltage - Output (Max):
- -
- Current - Output:
- 650mA
- Frequency - Switching:
- 40kHz ~ 1MHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-MSOP
LT3574IMS#PBF FAQ
1.How can I place an order for LT3574IMS#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3574IMS#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 LT3574IMS#PBF reliable?
The price and inventory of LT3574IMS#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3574IMS#PBF is usually 5 days.
3.What payment methods are accepted for LT3574IMS#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3574IMS#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3574IMS#PBF?
LT3574IMS#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3574IMS#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 LT3574IMS#PBF?
For technical support, including LT3574IMS#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3574IMS#PBF requirements.
6.How does Aetrix verify that LT3574IMS#PBF is sourced from the original manufacturer or authorized distributors?
All LT3574IMS#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 LT3574IMS#PBF meets industry standards.
7.What is the process for return or replacement of LT3574IMS#PBF?
All LT3574IMS#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3574IMS#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 LT3574IMS#PBF part is unused and in its original packaging.
Return procedure for LT3574IMS#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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