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Analog Devices Inc. LT1737IS#PBF
- Part No.:
- LT1737IS#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1737IS#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:211
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Product details
Overview
LT1737IS#PBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed to drive an external N-channel MOSFET in high-efficiency, transformer-isolated DC/DC converters. It operates from 4.5V to 20V supply, supports 50kHz–250kHz switching frequency via external capacitor, delivers up to tens of watts, and enables primary-side regulation without optocoupler. It is used in medical instrument power supplies requiring reinforced isolation and stable output under variable load.
For engineers reviewing the LT1737IS#PBF datasheet, LT1737IS#PBF pinout, LT1737IS#PBF application, or LT1737IS#PBF equivalent, key selection criteria include its primary-side feedback architecture, discontinuous-mode regulation capability, UVLO and shutdown control, soft-start implementation, and SO-16 package compatibility with industrial temperature range (–40°C to 125°C).
Technical Context
The LT1737IS#PBF implements a specialized flyback error amplifier that samples the reflected flyback pulse from a third winding (or primary) to derive output voltage information-eliminating need for optoisolator or secondary-side sensing. Its control loop integrates VC pin-based current-mode regulation with programmable timing functions (tON, ENDLY, MINENAB) to manage minimum on-time, enable delay, and minimum enable time for robust operation across continuous and discontinuous conduction modes.
It features dual-function UVLO/shutdown pin, optional load compensation via ROCMP/RCMPC, and internal 3V reference (3VOUT). Gate driver delivers >500mA sink/source with <30ns rise/fall times, while ISENSE pin monitors switch current via external resistor with 250mV typical limit threshold and ±20mV tempco over –40°C to 125°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4.5V to 20V - powers internal bias circuitry and gate driver; supports wide-input industrial and medical DC bus rails. |
| Switching Frequency | 50kHz to 250kHz - set by external OSCAP capacitor; higher frequencies reduce transformer size but increase switching loss. |
| Feedback Reference Voltage | 1.245V (typ) at FB pin - sets output voltage via R1/R2 divider; ±1.5% tolerance over full temperature range ensures stable regulation. |
| Current Sense Threshold | 250mV (typ) at ISENSE - determines peak switch current limit; enables accurate overcurrent protection without additional sensing ICs. |
| Gate Drive Output | 11.8V high / 0.45V low (at 500mA) - directly drives logic-level MOSFETs; eliminates need for external level-shifting or buffer stages. |
| Operating Temperature | –40°C to 125°C - qualified for industrial and medical environments; junction max 125°C with θJA = 110°C/W in SO-16 package. |
| Shutdown Current | 50µA (typ) - reduces system standby power; activated by pulling UVLO pin to ground. |
Pinout & Package
LT1737IS#PBF is housed in a 16-lead plastic SO (Small Outline) package with standard JEDEC MS-012AC footprint, 1.27mm pitch, and exposed pad not present. Pin 1 is PGND, located at bottom-left corner when notch is up.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return for GATE discharge current | Carries high di/dt spikes during MOSFET turn-off; must connect directly to low-inductance ground plane. |
| ISENSE (2) | Current sense input | Monitors voltage across external sense resistor; triggers current-limit shutdown at ~250mV. |
| SFST (3) | Soft-start capacitor connection | Charges linearly to ramp up VC voltage; prevents inrush current during startup. |
| ROCMP (4) | Load compensation resistor input | Accepts current proportional to average switch current to correct for output impedance droop. |
| RCMPC (5) | Load compensation filter capacitor | Filters ROCMP signal; 0.1µF ceramic typical to stabilize compensation loop. |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency; 33pF–200pF range yields 80–125kHz over temperature. |
| VC (7) | Control voltage output/input | Integrates feedback error current; sets current-comparator trip point for duty cycle control. |
| FB (8) | Feedback voltage input | Compares reflected flyback voltage to 1.245V reference; primary-side regulation node. |
| 3VOUT (9) | Internal 3V reference output | Provides stable 3V rail for auxiliary circuits; current-limited to 15mA max. |
| UVLO (10) | Undervoltage lockout & shutdown | Pull to ground disables controller and reduces IQ to 50µA; resistor divider enables input-voltage monitoring. |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, VC; must be isolated from PGND to avoid noise coupling into control loop. |
| MINENAB (12) | Minimum enable time programming | Resistor sets minimum duration FB amplifier stays active; prevents latch-up at light loads. |
| ENDLY (13) | Enable delay programming | Resistor delays FB amplifier activation after switch turn-off to reject leakage spike artifacts. |
| tON (14) | Minimum switch on-time programming | Resistor enforces shortest allowable MOSFET conduction period per cycle; maintains regulation at very light loads. |
| VCC (15) | Supply input | Requires ≥1µF local bypass; powers internal regulators, oscillator, and gate driver. |
| GATE (16) | MOSFET gate driver output | High-current push-pull stage; layout must minimize trace inductance to prevent ringing and EMI. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optocoupler | Uses third-winding or primary-referred flyback pulse sampling to eliminate optoisolator, reducing BOM cost and improving long-term reliability in medical systems. |
| Discontinuous mode regulation maintenance | Retains tight output regulation even below critical conduction threshold-enables stable operation down to ~10% load without secondary feedback. |
| Programmable timing functions | tON, ENDLY, and MINENAB pins allow precise tuning of minimum on-time, enable delay, and minimum enable time to match transformer leakage and load dynamics. |
| Integrated 3V reference with current limiting | 3VOUT pin provides regulated auxiliary supply for biasing sensors or logic; built-in 15mA current limit protects against short-circuit faults. |
| Load compensation for output impedance | ROCMP/RCMPC interface enables correction of voltage droop caused by secondary winding resistance, diode VF, and capacitor ESR-improving load regulation to ±1%. |
Applications
| Medical Isolated Power Supplies | Industrial Sensor Interface Power |
|---|---|
Use Scenario: Providing reinforced-isolation 15V/300mA output from 12V–18V input in portable ultrasound or patient-monitoring equipment. IC Role / Device Role / Timing Role: Flyback controller managing primary-side regulation, UVLO supervision, and soft-start sequencing during battery-powered startup. Use Value: Eliminates optocoupler and secondary-side TL431, reducing component count by 3–4 parts while meeting IEC 60601 creepage/clearance requirements. | Use Scenario: Generating isolated ±12V rails for precision analog front-ends in factory automation I/O modules. IC Role / Device Role / Timing Role: Primary-side controller implementing programmable tON and ENDLY to suppress transformer leakage-induced regulation error at 200kHz switching. Use Value: Achieves <±2% load regulation across –40°C to 85°C without trimming, using only primary-side components and no secondary feedback network. |
| Test Equipment Auxiliary Supplies | Isolated Communication Interface Power |
Use Scenario: Delivering 5V/1A isolated output from 24V DC input in benchtop oscilloscope auxiliary power domain. IC Role / Device Role / Timing Role: High-power flyback controller driving IRFL014 MOSFET with GATE pin delivering >500mA peak drive current. Use Value: Supports >10W output with SO-16 package thermal performance (θJA = 110°C/W), enabling compact PCB layout without heatsink. | Use Scenario: Powering isolated RS-485 transceivers in smart grid metering devices requiring 3.3V/200mA output. IC Role / Device Role / Timing Role: Controller using 3VOUT pin to bias isolated digital isolators and 3.3V LDO, reducing external regulator count. Use Value: Integrates 3V reference with ±2% accuracy and 15mA drive-replaces discrete 3.3V regulator and saves 25mm² board area. |
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 external MOSFET gate drive; requires transformer auxiliary winding for VDD. | Targets lower-cost consumer adapters; lacks primary-side sensing flexibility and load compensation. | Choose UCC28740DR for cost-sensitive, low-power (<5W) adapters where efficiency >88% is required and design cycle time is constrained. |
| MAX17595ATP+ | Current-mode flyback controller with integrated 1.5A gate driver; supports 4.5V–40V input; includes comprehensive fault protection (OVP, OTP, OCP). | Designed for industrial power supplies with wide VIN and harsh environment requirements; larger TQFN-20 package. | Choose MAX17595ATP+ when operating above 20V input or requiring overvoltage/overtemperature protection beyond LT1737IS#PBF's capabilities. |
Compared with UCC28740DR and MAX17595ATP+, the LT1737IS#PBF offers unique primary-side regulation without auxiliary winding dependency, programmable timing for leakage immunity, and SO-16 industrial-temperature packaging-making it optimal for medical and test equipment where isolation integrity and regulation stability under variable load are critical.
Availability
LT1737IS#PBF is available at Aetrix Electronics and suitable for medical instrumentation, industrial sensor interfaces, and test equipment power supplies requiring stable component supply, long lifecycle support, and guaranteed industrial temperature grade performance.
Supply support for LT1737IS#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. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies. Formerly Linear Technology, ADI acquired the LT product line in 2017.
The LT1737IS#PBF belongs to ADI's isolated power controller family, engineered specifically for primary-side regulated flyback converters in safety-critical applications such as medical, industrial, and test equipment where optocoupler-free design and robust discontinuous-mode operation are essential.
FAQ
What is the maximum recommended switching frequency for LT1737IS#PBF?
The LT1737IS#PBF supports switching frequencies from 50kHz to 250kHz, set by the external OSCAP capacitor. At 250kHz, typical operation requires OSCAP ≈ 33pF, but thermal and EMI constraints may limit practical use to ≤200kHz in densely packed layouts. The datasheet specifies 80–125kHz over full temperature range with 33–200pF capacitor values, and LT1737IS#PBF maintains stable regulation across this band without external compensation.
Does LT1737IS#PBF require an optocoupler for regulation?
No, LT1737IS#PBF does not require an optocoupler. It achieves isolated output regulation by sensing the reflected flyback voltage from a third transformer winding or the primary winding, comparing it to its internal 1.245V reference at the FB pin. This primary-side sensing architecture eliminates optocoupler dependency, reducing component count, improving long-term reliability, and simplifying certification for medical and industrial isolation standards.
How is load regulation improved using the ROCMP pin on LT1737IS#PBF?
The ROCMP pin on LT1737IS#PBF accepts a current proportional to average MOSFET switch current, which is used to offset voltage droop caused by secondary-side impedance (diode VF, winding resistance, capacitor ESR). By connecting an external resistor (ROCMP) and capacitor (RCMPC), the LT1737IS#PBF injects compensating current into the FB node, effectively raising the target flyback voltage under load-improving load regulation from ±5% to ±1% without secondary feedback components.
What is the purpose of the ENDLY and MINENAB pins on LT1737IS#PBF?
The ENDLY pin on LT1737IS#PBF programs a fixed delay between MOSFET turn-off and activation of the flyback error amplifier, rejecting transformer leakage spikes. The MINENAB pin sets the minimum duration the amplifier remains enabled. Together, they ensure the FB amplifier samples only the true flyback pulse-not artifacts-enabling stable regulation in discontinuous mode and preventing bistable behavior under high-leakage conditions.
Can LT1737IS#PBF operate with input voltages below 4.5V?
No, LT1737IS#PBF has a minimum specified supply voltage of 4.5V (VCC(MIN) = 4.1V min, 4.5V typ). Operation below 4.5V risks improper gate drive strength, unstable oscillator frequency, and failure of the internal bias regulator. The UVLO function (threshold 1.25V at UVLO pin) can be configured to disable the part before VCC drops to 4.5V, but the controller itself cannot sustain regulation or gate drive below that supply rail.
LT1737IS#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- 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):
- 4.1V ~ 20V
- Frequency - Switching:
- 90kHz ~ 115kHz
- Duty Cycle (Max):
- 90%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Enable, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SO
LT1737IS#PBF FAQ
1.How can I place an order for LT1737IS#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1737IS#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 LT1737IS#PBF reliable?
The price and inventory of LT1737IS#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1737IS#PBF is usually 5 days.
3.What payment methods are accepted for LT1737IS#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1737IS#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1737IS#PBF?
LT1737IS#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1737IS#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 LT1737IS#PBF?
For technical support, including LT1737IS#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1737IS#PBF requirements.
6.How does Aetrix verify that LT1737IS#PBF is sourced from the original manufacturer or authorized distributors?
All LT1737IS#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 LT1737IS#PBF meets industry standards.
7.What is the process for return or replacement of LT1737IS#PBF?
All LT1737IS#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1737IS#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 LT1737IS#PBF part is unused and in its original packaging.
Return procedure for LT1737IS#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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