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Analog Devices Inc. LT3574EMS#PBF
- Part No.:
- LT3574EMS#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-TFSOP (0.118", 3.00mm Width)
- Datasheet:
-
LT3574EMS#PBF.pdf
- Description:
- IC REG FLYBACK 650MA 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,477
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Product details
Overview
LT3574EMS#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 LT3574EMS#PBF datasheet, LT3574EMS#PBF pinout, LT3574EMS#PBF application, or LT3574EMS#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 UVLO threshold of 1.22V with hysteresis.
Technical Context
The LT3574EMS#PBF implements boundary-mode (BCM) current-mode control to sample the isolated output voltage directly from the primary-side flyback waveform at zero-secondary-current instants, eliminating need for opto-isolators or auxiliary windings. Its flyback error amplifier compares a pseudo-DC representation of VOUT-derived from RFB/RREF resistor ratio and transformer turns ratio-against a 1.23V internal bandgap reference.
Internal circuitry includes a DCM comparator detecting SW node voltage collapse to trigger switch turn-on, a programmable current limit set by RILIM (10kΩ yields 0.65A), and temperature compensation via TC pin sourcing proportional-to-absolute-temperature current into RREF to offset diode forward-voltage drift. The VC pin provides error amplifier compensation with external RC network.
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 external transistor, reduces BOM count, limits max SW pin stress to 60V absolute rating. |
| Switching Frequency | Up to 1000kHz - enables compact magnetics; minimum frequency 40kHz at light load for stable DCM operation. |
| RREF Reference Voltage | 1.23V ±2% - high-accuracy bandgap reference sets output voltage precision when used with RFB/RREF ratio. |
| SHDN/UVLO Threshold | 1.22V rising, 1.20V falling - ensures reliable start-up and brown-out protection across –40°C to 125°C junction range. |
| Soft-Start Threshold | 0.7V - defines ramp completion point; SS pin sinks 7µA to control output voltage slew rate and limit inrush. |
| Operating Temperature | –40°C to 125°C - qualified for harsh industrial and automotive under-hood environments. |
Pinout & Package
LT3574EMS#PBF is housed in a 16-lead plastic MSOP package (3mm × 4.9mm, 0.5mm pitch) with exposed pad for thermal dissipation. Pin 1 is located at top-left corner adjacent to dot marking; pin numbering proceeds counterclockwise.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pins 1, 3, 4, 8, 11, 16) | Ground reference | Multiple ground pins reduce PCB trace inductance and improve noise immunity for switching node and analog sections. |
| SW (Pin 5) | Collector of internal NPN switch | High-dI/dt node requiring short, low-inductance routing to transformer primary and snubber components. |
| VIN (Pin 6) | Main input supply | Supplies start-up bias and serves as reference for DCM comparator; requires local 1µF ceramic bypass. |
| BIAS (Pin 7) | Internal bias and driver supply | Can be tied to VIN if ≤15V or powered from third winding; must be bypassed with ≥1µF capacitor. |
| SHDN/UVLO (Pin 8) | Enable and undervoltage lockout | Resistor divider from VIN sets turn-on threshold; pulls 2.5µA hysteresis current below 1.22V. |
| RILIM (Pin 10) | Current limit programming | Resistor to GND sets peak switch current: 10kΩ = 0.65A; lower resistance increases limit. |
| RFB (Pin 11) | Flyback feedback sensing | Connects to SW node; forms voltage divider with RREF to derive output voltage information from flyback pulse amplitude. |
| RREF (Pin 12) | Reference resistor connection | Ground-referred resistor (typically 6.04kΩ) sets gain for feedback loop; TC pin injects temp-compensation current here. |
| VC (Pin 13) | Error amplifier compensation | External RC network (e.g., 100pF || 10kΩ to GND) stabilizes control loop and rejects noise. |
| SS (Pin 14) | Soft-start timing | Capacitor to GND controls voltage ramp rate; 7µA current charges it until 0.7V triggers full operation. |
| TC (Pin 15) | Temperature compensation | Resistor to GND sources PTAT current (0.55V/RTC) into RREF to cancel diode VF temperature drift. |
| TEST (Pin 2) | Factory test only | Must be connected to GND for normal operation; floating or driven causes undefined behavior. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side isolated regulation | Eliminates opto-coupler and third winding, reducing cost, size, and long-term drift issues in medical/industrial supplies. |
| Boundary mode operation | Enables zero-current switching detection per cycle, improving load regulation and allowing smaller transformers vs CCM. |
| Programmable current limit | RILIM pin accepts resistor to GND (10kΩ standard) to set switch current limit from 100mA to 1.1A, supporting diverse output power levels. |
| Temperature-compensated feedback | TC pin injects PTAT current into RREF to offset diode forward-voltage drift, maintaining ±1% output accuracy over –40°C to 125°C. |
| 16-lead MSOP package | Compact 3mm × 4.9mm footprint with exposed pad enables high-power-density designs while supporting automated assembly. |
Applications
| Industrial Isolated Sensors | Medical Patient Monitoring |
|---|---|
Use Scenario: Isolated 5V supply for analog front-end of pressure/temperature sensors in PLC I/O modules. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating isolated output without opto-coupler, using boundary-mode sampling for tight load regulation. Use Value: Enables compact, long-life isolated power with no opto aging or unit-to-unit variation, meeting IEC 61000-4-5 surge immunity requirements. | Use Scenario: 3.3V isolated rail powering ADC and microcontroller in ECG patient interface circuits. IC Role / Device Role / Timing Role: Flyback controller delivering medically certified isolation (reinforced per IEC 60601-1) with precise output voltage tracking over temperature. Use Value: TC pin compensation maintains <±1% output accuracy across body-temperature operating range, critical for signal integrity. |
| Automotive Body Control | Industrial Field Transmitters |
Use Scenario: 12V isolated output for CAN transceiver and microcontroller in battery management system slave nodes. IC Role / Device Role / Timing Role: Boundary-mode controller operating from 12V–40V automotive input, with UVLO set to 9V to prevent brown-out during cranking. Use Value: Wide input range and robust 125°C junction rating ensure reliable operation in under-hood environments without derating. | Use Scenario: 5V isolated supply for 4–20mA loop-powered transmitter with HART modulation capability. IC Role / Device Role / Timing Role: Primary-side regulated flyback IC delivering low-noise, tightly regulated output despite varying loop voltage (12–42V). Use Value: Programmable soft-start prevents current surges during hot-plug events, protecting sensitive 4–20mA DAC and sensor interfaces. |
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 2.5A/100V MOSFET driver; requires external FET; supports higher output power (>10W); no integrated NPN switch. | Suitable for >5W isolated supplies where efficiency and thermal headroom are critical; not drop-in compatible due to different pinout and external switch requirement. | Select LT3748IMS#PBF when scaling beyond 3W or needing higher voltage/current capability; redesign required. |
| UCC28911DR | 65V integrated MOSFET; primary-side regulation; fixed 60kHz frequency; no RILIM or TC pins; lower quiescent current (200µA). | Better suited for cost-sensitive consumer/industrial SMPS where temperature compensation and fine current limiting are not required. | Choose UCC28911DR for simpler, lower-cost designs with fixed-frequency operation and reduced component count. |
Compared with LT3574EMS#PBF, LT3748IMS#PBF offers higher power scalability but demands external FET layout and compensation redesign, while UCC28911DR simplifies design at the expense of programmability and precision temperature compensation-making LT3574EMS#PBF optimal for mid-power, high-accuracy isolated supplies.
Availability
LT3574EMS#PBF is available at Aetrix Electronics and suitable for industrial sensors, medical monitoring equipment, and automotive body control modules requiring stable component supply, long lifecycle support, and guaranteed RoHS-compliant lead-free packaging.
Supply support for LT3574EMS#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, Inc. (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 LT3574EMS#PBF belongs to Linear's isolated power controller product line, engineered specifically for primary-side regulated flyback converters targeting space-constrained, reliability-critical applications where opto-coupler elimination improves long-term stability.
FAQ
What is the maximum output power achievable with the LT3574EMS#PBF?
The LT3574EMS#PBF delivers up to 3W of isolated output power without an external power switch. This assumes optimal transformer selection (e.g., PA2626NL for 5V/0.5A), proper snubber design, and operation within the 3V–40V input range. At 24V input and 3:1 turns ratio, typical output is 2.5W; power scales with input voltage and transformer turns ratio, but SW pin voltage must remain below 60V absolute maximum rating to avoid damage. The LT3574EMS#PBF datasheet Figure 2 confirms this 3W limit for common 5V outputs.
How does the LT3574EMS#PBF achieve regulation without an opto-coupler?
The LT3574EMS#PBF samples the isolated output voltage indirectly by measuring the amplitude of the primary-side flyback pulse at the SW pin when secondary current reaches zero. This pseudo-DC value-scaled by transformer turns ratio and diode forward voltage-is converted to a feedback current via RFB and compared against the 1.23V internal reference through the RREF resistor. Boundary-mode timing ensures accurate sampling, eliminating need for opto-isolators or auxiliary windings. This method is implemented entirely within the LT3574EMS#PBF die.
What is the purpose of the TC pin on the LT3574EMS#PBF?
The TC (Temperature Compensation) pin on the LT3574EMS#PBF sources a proportional-to-absolute-temperature (PTAT) current into the RREF node to counteract the negative temperature coefficient of the output rectifier diode's forward voltage. By connecting a resistor (e.g., 28.7kΩ for 5V/3:1 design) from TC to GND, the LT3574EMS#PBF injects ~27.5µA at 25°C, improving output voltage stability over –40°C to 125°C. This feature is critical for medical and industrial applications where output accuracy must remain within ±1% across temperature.
Can the LT3574EMS#PBF operate with a 1:1 transformer?
Yes, the LT3574EMS#PBF can operate with a 1:1 transformer, as confirmed in Table 1 of the datasheet for 3.3V, 5V, 12V, and 15V outputs. However, 1:1 operation limits maximum output power and requires careful attention to SW pin voltage: VSW(MAX) = VIN(MAX) + VOUT + VF must stay below 60V. For example, at VIN = 40V and VOUT = 5V, even a 1:1 ratio exceeds the 60V SW rating. Thus, 1:1 is practical only for low-input, low-output-voltage designs (e.g., 12V input → 5V output). The LT3574EMS#PBF supports ratios up to 4:1 per Table 4.
What is the recommended snubber configuration for the LT3574EMS#PBF?
The LT3574EMS#PBF requires an RCD snubber (resistor-capacitor-diode) across the primary winding to clamp leakage inductance spikes at the SW pin. Per datasheet Figure 4 and Section "Leakage Inductance", the clamp diode must be fast Schottky (e.g., PMEG6010) to limit spike duration to <150ns and peak voltage to <55V during clamping. Capacitor value is typically 1nF–10nF; resistor value is selected to dissipate leakage energy without excessive loss. Failure to implement this snubber risks exceeding the 60V SW absolute maximum rating, potentially damaging the LT3574EMS#PBF internal NPN switch.
LT3574EMS#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
LT3574EMS#PBF FAQ
1.How can I place an order for LT3574EMS#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3574EMS#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 LT3574EMS#PBF reliable?
The price and inventory of LT3574EMS#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3574EMS#PBF is usually 5 days.
3.What payment methods are accepted for LT3574EMS#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3574EMS#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3574EMS#PBF?
LT3574EMS#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3574EMS#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 LT3574EMS#PBF?
For technical support, including LT3574EMS#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3574EMS#PBF requirements.
6.How does Aetrix verify that LT3574EMS#PBF is sourced from the original manufacturer or authorized distributors?
All LT3574EMS#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 LT3574EMS#PBF meets industry standards.
7.What is the process for return or replacement of LT3574EMS#PBF?
All LT3574EMS#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3574EMS#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 LT3574EMS#PBF part is unused and in its original packaging.
Return procedure for LT3574EMS#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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