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Analog Devices Inc. LT1737CS#TRPBF
- Part No.:
- LT1737CS#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1737CS#TRPBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,116
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Product details
Overview
LT1737CS#TRPBF from Analog Devices (formerly Linear Technology) is a current-mode isolated flyback controller IC designed to drive an external N-channel MOSFET in primary-side regulated, transformer-isolated DC/DC converters. It operates from 4.5V to 20V supply, supports 50kHz–250kHz switching frequency via external OSCAP capacitor, delivers up to tens of watts, and achieves ±1.2% feedback voltage accuracy (1.245 V typical) without user trimming - enabling compact, optoisolator-free medical and instrumentation power supplies.
For engineers reviewing the LT1737CS#TRPBF datasheet, LT1737CS#TRPBF pinout, LT1737CS#TRPBF application, or LT1737CS#TRPBF equivalent, key selection considerations include primary-side sensing capability, discontinuous-mode regulation stability, UVLO programmability, soft-start control via SFST pin, and load compensation support through ROCMP/RCMPC pins for high-accuracy output regulation under variable load conditions.
Technical Context
The LT1737CS#TRPBF implements a specialized flyback error amplifier that samples the reflected flyback pulse from a third transformer winding (or primary), rejecting leakage spikes via timing-controlled enable window (ENDLY/MINENAB/tON pins). Its current-sense architecture uses an internal 250 mV threshold at ISENSE with external sense resistor, while VC pin serves as both feedback amplifier output and current-comparator input for loop compensation.
Control logic integrates collapse-detect comparator (triggered at ~0.8×VBG), minimum on-time enforcement (tON pin), and dual-function UVLO/shutdown (Pin 10), allowing robust start-up, latch-up immunity, and precise regulation across continuous and discontinuous conduction modes - all within a 16-pin SO package rated for 0°C to 100°C operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4.5 V to 20 V - powers internal bias regulator and gate driver; supports wide-input industrial and medical DC bus rails. |
| Feedback Reference Voltage | 1.245 V (typ), ±1.2% - enables accurate primary-side output voltage setting without optocoupler or secondary-side sensing. |
| Switching Frequency Range | 50 kHz to 250 kHz - set by external OSCAP capacitor (33 pF to 200 pF); balances EMI, transformer size, and efficiency. |
| Current Sense Threshold | 250 mV (typ) at ISENSE - defines peak switch current limit; sets power capability with external RSENSE. |
| Gate Drive Output | 12.1 V high / 0.45 V low (at 100 mA) - directly drives logic-level MOSFETs; rise/fall times ≤30 ns into 1000 pF. |
| UVLO Threshold | 1.25 V (typ) at UVLO pin - enables programmable input undervoltage lockout or shutdown via external resistor divider. |
| Operating Temperature | 0°C to 100°C (C-grade) - qualified for commercial/industrial instrumentation and medical auxiliary power applications. |
Pinout & Package
LT1737CS#TRPBF is housed in a 16-lead plastic SO (Small Outline) package with standard JEDEC MS-012AC footprint, 1.27 mm pitch, and exposed pad not present. Thermal resistance θJA = 110°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power ground return for GATE discharge current | Carries high di/dt spike (~hundreds of mA, tens of ns); must connect directly to low-inductance ground plane. |
| ISENSE (2) | Primary-side current sense input | Monitors external sense resistor voltage; triggers switch turn-off when ≥250 mV - sets peak current limit. |
| SFST (3) | Soft-start capacitor connection | Charges with 40 µA (typ); controls ramp rate of VC voltage during startup to limit inrush current. |
| ROCMP (4) | Load compensation resistor input | Accepts current proportional to average switch current; compensates for output impedance (ESR, diode VF, winding resistance). |
| RCMPC (5) | Load compensation filter capacitor | Filters ROCMP signal; 0.1 µF ceramic typical - stabilizes compensation loop against noise. |
| OSCAP (6) | Oscillator timing capacitor | Sets switching frequency (f = k/COSCAP); 100 pF yields ~100 kHz - determines transformer size and EMI profile. |
| VC (7) | Control voltage node | Output of feedback amplifier & input to current comparator; external RC network sets loop compensation and stability. |
| FB (8) | Feedback voltage input | Compares reflected flyback pulse to 1.245 V reference; Thevenin impedance ~3 kΩ optimal for bias cancellation. |
| 3VOUT (9) | Internal 3 V reference output | Stable 3.0 V (±0.2 V), 15 mA max - powers auxiliary circuits or bias for optocoupler if used externally. |
| UVLO (10) | Undervoltage lockout / shutdown control | Pull to <0.95 V to shut down (IQ ≈ 50 µA); resistor divider from VIN sets turn-on threshold with hysteresis. |
| SGND (11) | Signal ground reference | Reference for FB, OSCAP, VC; must be isolated from PGND currents to prevent noise coupling into control loop. |
| MINENAB (12) | Minimum enable time programming | Resistor sets duration FB amplifier stays active after enable - prevents lockup during low-load or startup. |
| ENDLY (13) | Enable delay time programming | Resistor delays FB amplifier activation post-switch-turnoff - rejects transformer leakage spikes. |
| tON (14) | Minimum switch on-time programming | Resistor enforces absolute minimum MOSFET conduction per cycle - ensures flyback pulse availability for regulation. |
| VCC (15) | Supply input | 4.5–20 V input; requires ≥1 µF ceramic bypass to PGND close to pin for stable gate drive. |
| GATE (16) | MOSFET gate driver output | High-current source/sink (500 mA peak); short trace + series resistor (≥5 Ω) recommended to damp ringing. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optocoupler | Uses third-winding or primary-referred flyback pulse sampling - eliminates isolation barrier component count and aging drift. |
| Discontinuous mode regulation stability | Maintains tight output regulation even at light loads where energy transfer becomes intermittent - critical for standby power compliance. |
| Programmable load compensation | ROCMP/RCMPC pins allow dynamic correction of output voltage droop due to secondary ESR, diode VF, and winding resistance - improves line/load regulation to <±2%. |
| Configurable timing control | ENDLY, MINENAB, and tON pins enable precise tuning of feedback window timing - rejects leakage spikes and ensures reliable collapse detection across operating conditions. |
| Low-quiescent shutdown | Reduces supply current to 50 µA (typ) when UVLO pin pulled low - supports energy-efficient system-level power sequencing and sleep modes. |
Applications
| Medical Isolated Auxiliary Power | Industrial Instrumentation Supply |
|---|---|
Use Scenario: Providing isolated 15 V @ 300 mA for analog front-end circuitry in patient-connected diagnostic equipment (e.g., ECG, EEG amplifiers), meeting IEC 60601 creepage/clearance requirements. IC Role / Device Role / Timing Role: LT1737CS#TRPBF acts as primary-side flyback controller, using third-winding feedback to regulate output without optocoupler - reducing BOM cost and long-term calibration drift. Use Value: Enables certified 4 kV reinforced isolation with <±1.5% output accuracy over temperature and load, eliminating secondary-side sensing components and simplifying safety certification. | Use Scenario: Generating isolated ±12 V rails for precision ADC/DAC reference buffers and sensor excitation in programmable logic controller (PLC) I/O modules. IC Role / Device Role / Timing Role: LT1737CS#TRPBF manages flyback timing and load compensation to maintain regulation despite varying sensor loading and ambient temperature shifts (0°C–70°C). Use Value: Achieves <±2% total output variation across full load range and temperature via ROCMP-based impedance compensation - ensuring 16-bit measurement integrity. |
| 12V–18V to Isolated 15V Converter | Low-Power Telecom Interface Supply |
Use Scenario: Converting unregulated 12 V–18 V DC input (e.g., from PoE midspan or battery backup) to isolated 15 V @ 200 mA for RS-485 transceivers and isolated CAN nodes. IC Role / Device Role / Timing Role: LT1737CS#TRPBF provides primary-side regulation with UVLO set to 13 V to prevent brownout operation during PoE voltage sag. Use Value: Delivers stable 15 V output with <100 mV ripple and fast transient response (<50 µs recovery) - ensuring robust communication link integrity under dynamic load steps. | Use Scenario: Powering isolated Ethernet PHY interfaces in industrial gateways where EMI-sensitive 100BASE-TX signaling coexists with noisy 24 V DC field power. IC Role / Device Role / Timing Role: LT1737CS#TRPBF operates at 200 kHz (via 47 pF OSCAP) to shift switching noise above sensitive 30–60 MHz Ethernet bands and reduce conducted emissions. Use Value: Meets CISPR 22 Class B conducted EMI limits without additional filtering - reducing board area and BOM cost in space-constrained gateway designs. |
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 | Integrated high-voltage start-up, quasi-resonant control, no external MOSFET gate driver - requires HV FET; lacks ROCMP load compensation. | Better light-load efficiency in QR mode; unsuitable for fixed-frequency designs requiring precise timing control. | Select UCC28740DR only when optimizing for ultra-low standby power (<30 mW) and accepting trade-offs in load regulation accuracy and design flexibility. |
| MAX17595ATP+T | Includes integrated 0.5 Ω MOSFET driver, higher VCC rating (28 V), but no 3VOUT pin or dedicated load compensation inputs. | Supports wider input range and faster gate drive; lacks primary-side impedance compensation needed for <±1% load regulation. | Choose MAX17595ATP+T for ruggedized 24 V input systems where simplicity outweighs need for fine-grained load compensation. |
Compared with UCC28740DR and MAX17595ATP+T, the LT1737CS#TRPBF uniquely combines programmable timing (ENDLY/MINENAB/tON), dedicated load compensation (ROCMP/RCMPC), and a buffered 3 V reference - making it the preferred choice for high-accuracy, fixed-frequency isolated supplies where regulation stability across variable loads and temperatures is critical.
Availability
LT1737CS#TRPBF is available at Aetrix Electronics and suitable for medical auxiliary power, industrial instrumentation supplies, and isolated interface converters requiring stable component supply, long-lifecycle support, and guaranteed traceable sourcing.
Supply support for LT1737CS#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 LT1737CS#TRPBF belongs to ADI's legacy Linear Technology power management portfolio, specifically engineered for precision primary-side regulated isolated flyback converters in safety-critical and low-noise applications such as medical diagnostics and test equipment.
FAQ
What is the maximum output power achievable with the LT1737CS#TRPBF?
The LT1737CS#TRPBF itself does not define maximum output power - it is a controller IC whose delivered power depends on the selected external MOSFET, transformer, and layout. With appropriate components (e.g., IRFL014 MOSFET, COILTRONICS CTX150-4 transformer), the LT1737CS#TRPBF has been validated to deliver up to 15 W (15 V @ 1 A) in typical designs. Higher power (tens of watts) is feasible with optimized magnetics and thermal management, but requires careful attention to gate drive strength, snubber design, and leakage inductance control.
Does the LT1737CS#TRPBF require an optocoupler for isolation?
No, the LT1737CS#TRPBF does not require an optocoupler. It achieves isolated output voltage regulation using primary-side sensing - either via a third transformer winding or direct sampling of the primary-side flyback pulse. This eliminates optocoupler-related aging, gain drift, and CMTI limitations, simplifying design and improving long-term reliability in medical and industrial applications.
How is the switching frequency set on the LT1737CS#TRPBF?
The switching frequency of the LT1737CS#TRPBF is set by an external capacitor connected to the OSCAP pin (Pin 6). Frequency scales inversely with capacitance: 100 pF yields ~100 kHz, 33 pF yields ~250 kHz, and 200 pF yields ~50 kHz. The relationship is approximately f = 10⁷ / COSCAP(pF) kHz. A stable, low-ESR ceramic capacitor (e.g., X7R, 0805) placed close to Pin 6 is required for accurate and jitter-free operation.
Can the LT1737CS#TRPBF operate in discontinuous conduction mode (DCM)?
Yes, the LT1737CS#TRPBF is explicitly designed to maintain stable regulation in discontinuous conduction mode. Its unique flyback error amplifier and collapse-detect comparator ensure consistent feedback sampling even when energy transfer becomes intermittent at light loads. This capability is confirmed in the datasheet's "Regulation Maintained Well into Discontinuous Mode" feature and validated across temperature and line variations - making it suitable for applications with wide dynamic load ranges.
What is the purpose of the ROCMP and RCMPC pins on the LT1737CS#TRPBF?
The ROCMP (Pin 4) and RCMPC (Pin 5) pins implement optional load compensation to correct output voltage droop caused by real-world secondary-side impedances - including Schottky diode forward voltage, transformer winding resistance, and output capacitor ESR. ROCMP accepts a resistor that develops a current proportional to average switch current; RCMPC filters this signal with a capacitor (typically 0.1 µF) before injecting correction into the FB node - improving load regulation from >±5% to <±2% in demanding applications.
LT1737CS#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SOIC (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):
- 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:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SO
LT1737CS#TRPBF FAQ
1.How can I place an order for LT1737CS#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1737CS#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 LT1737CS#TRPBF reliable?
The price and inventory of LT1737CS#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1737CS#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1737CS#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1737CS#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1737CS#TRPBF?
LT1737CS#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1737CS#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 LT1737CS#TRPBF?
For technical support, including LT1737CS#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1737CS#TRPBF requirements.
6.How does Aetrix verify that LT1737CS#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1737CS#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 LT1737CS#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1737CS#TRPBF?
All LT1737CS#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1737CS#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 LT1737CS#TRPBF part is unused and in its original packaging.
Return procedure for LT1737CS#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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