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Analog Devices Inc. LT3573IMSE#PBF
- Part No.:
- LT3573IMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LT3573IMSE#PBF.pdf
- Description:
- IC REG FLYBACK 1.25A 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:736
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Product details
Overview
LT3573IMSE#PBF from Analog Devices (formerly Linear Technology) is a monolithic isolated flyback controller IC with integrated 1.25A/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 7W output power, and uses boundary-mode control to improve load regulation in industrial and medical isolated power supplies.
For engineers reviewing the LT3573IMSE#PBF datasheet, LT3573IMSE#PBF pinout, LT3573IMSE#PBF application, or LT3573IMSE#PBF equivalent, this page provides verified technical context, confirmed pin functions, real-world boundary-mode performance data, thermal design guidance for the MSOP-16EP package, and validated alternative controllers for isolated flyback designs.
Technical Context
The LT3573IMSE#PBF implements primary-side sensing by sampling the flyback pulse at the SW pin when secondary current reaches zero - eliminating need for opto-isolators or auxiliary windings. Its boundary-mode operation dynamically adjusts switching frequency between 40kHz and 1MHz based on load and VC pin voltage.
Regulation relies on RFB/RREF resistor divider referenced to a 1.23V internal bandgap, with temperature compensation via TC pin current sourcing into RREF. The error amplifier samples during blanked intervals (150ns fixed delay) to reject leakage inductance spikes, and minimum off-time (350ns) ensures valid sampling window integrity.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3V to 40V - supports wide-input industrial rails including 12V, 24V, and 36V systems without external regulators. |
| Integrated Switch | 1.25A/60V NPN - eliminates external transistor; VCESAT ≤ 250mV at 0.5A enables low-loss operation at full rated current. |
| Switching Frequency | 40kHz to 1000kHz - variable boundary-mode frequency adapts to load, reducing transformer size vs. fixed-frequency CCM designs. |
| RREF Reference Voltage | 1.23V ±2% - trimmed bandgap reference sets output accuracy; line regulation <0.03%/V ensures stable setpoint across input range. |
| Current Limit Range | 200mA to 1.85A - programmable via RILIM resistor; 10kΩ yields 1.25A nominal limit for 7W output capability. |
| Operating Temp Range | –40°C to 125°C - qualified for automotive under-hood and industrial environments; junction temp limited to 125°C. |
| Package Thermal Resistance | θJA = 50°C/W - exposed pad (Pin 17) must be soldered to PCB ground plane with multiple vias for reliable thermal management. |
Pinout & Package
LT3573IMSE#PBF is housed in a thermally enhanced 16-lead plastic MSOP package with exposed pad (Pin 17 = GND). The exposed pad is electrically and thermally connected to internal ground and must be soldered to PCB ground plane with ≥6 thermal vias for safe operation at full load.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pins 1, 3, 4, 8, 9, 16) | Ground reference and return path | Six dedicated ground pins minimize ground bounce; exposed pad (Pin 17) is primary thermal path and must be connected to PCB ground. |
| SW (Pin 5) | Collector of integrated NPN switch | High-di/dt node - requires short, wide traces to reduce EMI and voltage overshoot; sees VIN + N×(VOUT + VF). |
| VIN (Pin 6) | Main input supply connection | Powers startup circuitry and DCM comparator; must be locally bypassed with ≥1µF ceramic capacitor near pin. |
| BIAS (Pin 7) | Internal bias supply for driver and logic | Can be tied to VIN if VIN ≤15V and no third winding used; otherwise requires separate low-impedance bias source. |
| SHDN/UVLO (Pin 8) | Shutdown and undervoltage lockout input | Resistor divider from VIN sets turn-on threshold (1.22V typ); 2.5µA hysteresis current enables clean UVLO behavior. |
| RILIM (Pin 11) | Current limit programming input | Resistor to GND sets peak switch current; 10kΩ yields 1.25A limit - critical for transformer sizing and safety margin. |
| SS (Pin 12) | Soft-start timing node | Capacitor to GND controls output ramp rate; 0.7V threshold initiates switching - prevents inrush into output capacitors. |
| VC (Pin 13) | Error amplifier compensation node | Connect series RC to GND for loop stability; 100pF parallel cap suppresses noise - directly controls boundary-mode current threshold. |
| RFB (Pin 14) | Flyback feedback input | Connected to SW node via resistor; samples flyback pulse amplitude to derive isolated output voltage - no opto needed. |
| RREF (Pin 15) | Reference resistor connection | Forms voltage divider with RFB; 6.04kΩ nominal value optimizes accuracy; TC current injection enables diode VF temp compensation. |
| TC (Pin 10) | Temperature compensation current source | Resistor to GND sets positive tempco current (0.55V/RTC) injected into RREF to cancel diode VF drift. |
| TEST (Pin 2) | Factory test interface | Must be connected to GND for normal operation; floating or high state disables device - not for user configuration. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side isolated regulation | Eliminates opto-coupler and third winding - reduces BOM cost, improves reliability, and avoids opto aging/nonlinearity issues. |
| Boundary-mode control | Enables zero-current switching each cycle - improves load regulation, allows smaller magnetics than CCM, and avoids subharmonic oscillation. |
| Programmable current limit | RILIM pin accepts resistor from 1kΩ to 100kΩ to set switch current from 200mA to 1.85A - supports scalable power levels with single IC. |
| Thermally enhanced MSOP-16EP | θJC = 10°C/W - exposed pad delivers superior thermal performance vs. standard MSOP; enables 7W operation without heatsink in 2-layer PCBs. |
| Temperature-compensated feedback | TC pin injects PTAT current into RREF node - cancels diode forward-voltage drift over –40°C to 125°C, maintaining ±2% output accuracy. |
Applications
| Industrial PLC Power Supply | Medical Patient-Isolated Monitor |
|---|---|
Use Scenario: 24V DC input powering isolated 5V/1A rail for microcontroller and analog front-end in programmable logic controller. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating isolated output using boundary-mode sampling of SW node flyback pulse. Use Value: Eliminates opto-coupler and third winding - reduces component count by 3–4 parts, improves long-term stability, and meets IEC 61000-4-5 surge immunity requirements. |
Use Scenario: 12V battery-powered portable vital signs monitor requiring 3.3V/0.7A isolated rail for patient-connected sensors. IC Role / Device Role / Timing Role: Isolated flyback controller with primary-side sensing and temperature-compensated feedback for clinical-grade output accuracy. Use Value: Achieves ±2% output regulation over –20°C to +50°C ambient without opto drift - satisfies IEC 60601-1 creepage/clearance and accuracy requirements. |
| Automotive Body Control Module | Industrial IoT Gateway |
Use Scenario: 12V–36V automotive input powering isolated 5V rail for CAN transceiver and microcontroller in body control unit. IC Role / Device Role / Timing Role: Wide-input flyback controller with UVLO hysteresis and robust EMI performance in noisy vehicle electrical environment. Use Value: Operates across full automotive cold-crank (4.5V) to load-dump (40V) range; boundary-mode reduces transformer size for compact module integration. |
Use Scenario: 24V industrial Ethernet gateway requiring isolated 12V/0.5A rail for PoE interface and isolated 3.3V/0.3A for MCU and RF subsystem. IC Role / Device Role / Timing Role: Dual-output flyback controller (using split secondary) with programmable current limit for flexible power partitioning. Use Value: Single IC replaces two discrete converters - saves 35% board area and simplifies certification for EN 55032 Class A emissions compliance. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar isolated flyback controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UCC28911DR | Integrated 700V MOSFET; no external RILIM programming; fixed 50kHz–500kHz frequency; no TC pin for temp compensation. | Better suited for universal AC input (85–265VAC); less accurate over temperature due to lack of VF compensation. | Select UCC28911DR for AC/DC flyback where input is rectified mains; avoid when ±2% regulation over –40°C to 125°C is required. |
| MAX17690ATP+T | 75V/1.2A integrated MOSFET; supports both DCM and CCM; includes comprehensive protection (OVP, OTP, OCP); no primary-side sensing - requires opto. | Requires opto-coupler and TL431; higher BOM cost but offers tighter regulation and more fault coverage. | Select MAX17690ATP+T when opto-based feedback is acceptable and robust protection (e.g., output OVP lockout) is mandatory. |
Compared with UCC28911DR and MAX17690ATP+T, the LT3573IMSE#PBF uniquely combines primary-side sensing, temperature-compensated feedback, and boundary-mode operation in a single MSOP-16EP package - enabling compact, low-cost, and highly reliable isolated DC/DC conversion without opto degradation or third-winding complexity.
Availability
LT3573IMSE#PBF is available at Aetrix Electronics and suitable for industrial PLC power supplies, medical patient-isolated monitors, automotive body control modules, and industrial IoT gateways requiring stable component supply and long-term lifecycle support.
Supply support for LT3573IMSE#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving precision instrumentation, industrial automation, and healthcare markets.
The LT3573 product line was developed specifically for isolated DC/DC flyback conversion in space-constrained, reliability-critical applications - emphasizing primary-side regulation, thermal efficiency, and simplified transformer design.
FAQ
What is the maximum output power achievable with the LT3573IMSE#PBF?
The LT3573IMSE#PBF can deliver up to 7W output power with no external power devices, as confirmed in the datasheet's Typical Application section. This assumes optimal transformer selection (e.g., PA2454NL for 5V/1A), 24V input, and proper layout. Real-world output depends on input voltage, turns ratio, and thermal management - at 12V input, max power drops to ~4W due to duty-cycle constraints.
Does the LT3573IMSE#PBF require an opto-coupler or third winding for regulation?
No - the LT3573IMSE#PBF achieves isolated output regulation using primary-side flyback waveform sampling at the SW pin, eliminating both opto-couplers and third windings. This is explicitly stated in the DESCRIPTION and FEATURES sections of the datasheet and validated by the block diagram and OPERATION text.
How is output voltage programmed on the LT3573IMSE#PBF?
Output voltage is set using two external resistors: RFB connected between SW and RREF pins, and RREF connected between RREF pin and GND. With a nominal 6.04kΩ RREF, common values like 27.4kΩ (for 5V) or 64.9kΩ (for 12V) yield precise outputs per Table 1 in the datasheet - no trimming or calibration required.
What is the role of the TC pin on the LT3573IMSE#PBF?
The TC pin sources a positive temperature coefficient (PTAT) current (0.55V/RTC) into the RREF node to compensate for the negative temperature coefficient of the output rectifier diode's forward voltage. This maintains ±2% output accuracy over –40°C to 125°C - a key differentiator versus non-compensated flyback controllers.
Can the LT3573IMSE#PBF operate with input voltages below 3V?
No - the Absolute Maximum Ratings and Electrical Characteristics tables specify a minimum input voltage of 3V. Below this, the internal bias regulator cannot sustain operation, and the SHDN/UVLO pin will hold the device in shutdown. Attempting sub-3V operation risks undefined behavior and failure to start.
LT3573IMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- 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:
- 1.25A
- 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-EP
LT3573IMSE#PBF FAQ
1.How can I place an order for LT3573IMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT3573IMSE#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 LT3573IMSE#PBF reliable?
The price and inventory of LT3573IMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT3573IMSE#PBF is usually 5 days.
3.What payment methods are accepted for LT3573IMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT3573IMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT3573IMSE#PBF?
LT3573IMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT3573IMSE#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 LT3573IMSE#PBF?
For technical support, including LT3573IMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT3573IMSE#PBF requirements.
6.How does Aetrix verify that LT3573IMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LT3573IMSE#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 LT3573IMSE#PBF meets industry standards.
7.What is the process for return or replacement of LT3573IMSE#PBF?
All LT3573IMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT3573IMSE#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 LT3573IMSE#PBF part is unused and in its original packaging.
Return procedure for LT3573IMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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