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Analog Devices Inc. LT1737IGN#PBF
- Part No.:
- LT1737IGN#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
LT1737IGN#PBF.pdf
- Description:
- IC REG CTRLR FLYBACK 16SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:778
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Product details
Overview
LT1737IGN#PBF 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 capacitor, delivers up to tens of watts, and enables optoisolator-free regulation using primary-side flyback pulse sensing. It is used in medical instrument power supplies and isolated instrumentation converters.
For engineers reviewing the LT1737IGN#PBF datasheet, LT1737IGN#PBF pinout, LT1737IGN#PBF application, or LT1737IGN#PBF equivalent, key selection considerations include its primary-side feedback architecture, UVLO and shutdown control, soft-start implementation, load compensation capability, and GN package thermal performance (θJA = 110°C/W).
Technical Context
The LT1737IGN#PBF implements a specialized flyback error amplifier that samples the reflected flyback voltage pulse on a third winding (or primary), comparing it to a 1.245V internal bandgap reference. Its control loop integrates current-mode operation with dynamic enable timing-minimum on-time (200ns), enable delay (200ns), and minimum enable time (200ns)-to maintain regulation across continuous and discontinuous conduction modes.
It features dual-function UVLO/shutdown pin, optional external load compensation (via ROCMP/RCMPC), soft-start (SFST), and programmable oscillator frequency (OSCAP). The VC pin serves as both feedback amplifier output and current comparator input, enabling loop compensation via external capacitor to ground.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 4.5V to 20V - powers internal bias circuitry and gate driver; absolute max 22V limits external supply design headroom. |
| Switching Frequency | 50kHz to 250kHz - set by external OSCAP capacitor; typical 100kHz at 100pF enables compact magnetics and EMI control. |
| Feedback Reference Voltage | 1.245V (±15mV) - precise internal bandgap sets output voltage accuracy; determines R1/R2 divider ratio for target VOUT. |
| Current Sense Threshold | 250mV (±30mV) - internal comparator trips when ISENSE × RSENSE reaches this level, defining peak switch current limit. |
| Gate Drive Output | 12.1V high / 0.45V low (at 100mA) - drives external MOSFET with fast rise/fall times (30ns) for efficient switching. |
| UVLO Threshold | 1.25V (±0.04V) - halts operation below input supply threshold; hysteresis enabled via external resistor divider. |
| Shutdown Current | 50µA typical - reduces system standby power; activated by pulling UVLO pin near ground. |
Pinout & Package
The LT1737IGN#PBF is housed in a 16-lead plastic SSOP (GN) package with exposed pad for thermal enhancement and 110°C/W junction-to-ambient thermal resistance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| PGND (1) | Power Ground | Carries high-current GATE discharge spikes; must connect directly to low-inductance ground plane. |
| ISENSE (2) | Current Sense Input | Monitors MOSFET source current via external sense resistor; 250mV threshold triggers cycle-by-cycle current limiting. |
| SFST (3) | Soft-Start Capacitor | Charges external capacitor to ramp VC voltage linearly at startup, preventing output overshoot and inrush stress. |
| ROCMP (4) | Load Compensation Resistor | Accepts current proportional to average switch current to offset secondary impedance effects on regulation. |
| RCMPC (5) | Load Compensation Filter | Filters ROCMP signal with 0.1µF ceramic capacitor to stabilize compensation loop response. |
| OSCAP (6) | Oscillator Timing Capacitor | Sets switching frequency; 100pF yields ~100kHz, enabling predictable transformer design and EMI filtering. |
| VC (7) | Control Voltage Node | Output of feedback amplifier and input to current comparator; compensated externally for stable loop gain and phase margin. |
| FB (8) | Feedback Input | Receives scaled flyback pulse voltage; closed-loop regulation achieved when FB ≈ 1.245V. |
| 3VOUT (9) | 3V Reference Output | Stable 3.0V (±0.2V) output capable of driving small capacitive loads; useful for auxiliary bias or sensing circuits. |
| UVLO (10) | Undervoltage Lockout / Shutdown | Dual-function pin: resistor divider enables input UVLO; direct grounding forces shutdown and reduces IQ to 50µA. |
| SGND (11) | Signal Ground | Reference for internal analog blocks (oscillator, FB amp, references); must be isolated from PGND noise paths. |
| MINENAB (12) | Minimum Enable Time Resistor | Programs fixed duration the flyback amplifier stays active after enable delay; prevents lockup during low-load or start-up. |
| ENDLY (13) | Enable Delay Resistor | Delays flyback amplifier activation post-switch-off to avoid leakage spike interference; critical for accurate VOUT sampling. |
| tON (14) | Minimum On-Time Resistor | Ensures MOSFET conducts for ≥200ns per cycle to sustain feedback information flow and prevent regulation loss at light loads. |
| VCC (15) | Supply Input | Requires ≥1µF local bypass to PGND; powers all internal circuitry except gate driver (which draws from VCC). |
| GATE (16) | MOSFET Gate Driver Output | High-current push-pull output; trace must be short and low-inductance to minimize ringing and EMI. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side regulation without optoisolator | Eliminates optocoupler cost, aging drift, and bandwidth limitations; uses third-winding or primary-referred flyback pulse for feedback. |
| Discontinuous mode regulation maintenance | Unique timing control (ENDLY/MINENAB/tON) ensures stable loop behavior even when transformer energy fully depletes each cycle. |
| Programmable load compensation | External ROCMP/RCMPC network actively corrects for output impedance errors caused by diode VF, winding resistance, and capacitor ESR. |
| Integrated 3V reference output | Provides precision 3.0V (±0.2V) rail for auxiliary circuitry without requiring external regulator or divider. |
| UVLO with user-adjustable hysteresis | Hysteresis magnitude set by Thevenin impedance of external UVLO divider; avoids oscillation near turn-on/turn-off thresholds. |
Applications
| Medical Isolated Power Supplies | Industrial Instrumentation Converters |
|---|---|
Use Scenario: Providing galvanically isolated 15V/300mA output from 12V–18V input in portable diagnostic equipment where creepage/clearance and safety certification (IEC 60601) are mandatory. IC Role / Device Role / Timing Role: LT1737IGN#PBF acts as primary-side controller, sampling flyback pulse to regulate output without optocoupler; tON and ENDLY ensure reliable startup and transient immunity. Use Value: Reduces BOM count and improves long-term reliability versus optocoupler-based solutions while meeting stringent isolation and leakage current requirements. | Use Scenario: Generating isolated ±12V rails for precision analog front-ends in data acquisition systems operating in electrically noisy factory environments. IC Role / Device Role / Timing Role: LT1737IGN#PBF controls external MOSFET to deliver tightly regulated outputs; ROCMP/RCMPC compensates for variable load-induced voltage droop across transformer secondary impedance. Use Value: Achieves <±1% load regulation over 10–100% load range without secondary-side sensing components, simplifying layout and certification. |
| Isolated Sensor Interface Supplies | Low-Power Telecom Isolation |
Use Scenario: Powering isolated current/voltage sensors in motor drive feedback loops where ground potential differences exceed 1kV. IC Role / Device Role / Timing Role: LT1737IGN#PBF implements flyback topology with SGND/PGND separation to reject common-mode noise; SFST ensures controlled startup into capacitive sensor loads. Use Value: Maintains regulation stability despite wide input voltage variation (12V–18V) and high dv/dt transients on isolated grounds. | Use Scenario: Providing 5V isolated bias for RS-485 transceivers in distributed building automation nodes powered from 24V PoE-derived rails. IC Role / Device Role / Timing Role: LT1737IGN#PBF operates at 200kHz (via OSCAP) to minimize transformer size; UVLO pin enables brownout protection aligned with upstream PoE controller. Use Value: Enables compact, certified isolation solution with <50µA shutdown current to meet Energy Star standby requirements. |
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 different transformer design. | Targets higher efficiency (>90%) at medium loads; lacks primary-side load compensation and 3VOUT reference. | Choose UCC28740DR for lower no-load power and simpler BOM where load compensation isn't required. |
| MAX17595ATP+T | Current-mode flyback controller with integrated 1.5A gate driver; supports wider VCC (8V–36V); no 3VOUT pin or ROCMP interface. | Designed for industrial 24V/48V inputs; includes comprehensive fault protection (OVP, OTP, OCP) not present in LT1737IGN#PBF. | Choose MAX17595ATP+T for higher input voltage robustness and built-in protection where space allows larger SO-16 package. |
Compared with UCC28740DR and MAX17595ATP+T, the LT1737IGN#PBF uniquely combines primary-side load compensation, a dedicated 3V reference, and precise programmable timing (ENDLY/MINENAB/tON) for demanding medical and instrumentation applications requiring tight regulation under variable loads and input conditions.
Availability
LT1737IGN#PBF is available at Aetrix Electronics and suitable for medical instrument power supplies, industrial instrumentation converters, isolated sensor interface supplies, and low-power telecom isolation requiring stable component supply, long-lifecycle support, and consistent parametric performance.
Supply support for LT1737IGN#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.
The LT1737IGN#PBF belongs to ADI's legacy Linear Technology power management portfolio, engineered specifically for primary-side regulated isolated flyback converters where optoisolator elimination, load regulation accuracy, and robust timing control are critical design objectives.
FAQ
What is the maximum recommended switching frequency for LT1737IGN#PBF?
The LT1737IGN#PBF supports switching frequencies from 50kHz to 250kHz, set by the external OSCAP capacitor. At 100pF, it operates at approximately 100kHz (typical), which balances transformer size, core losses, and EMI filter requirements. Frequencies above 200kHz may increase gate drive losses and require tighter layout control but are permissible per datasheet specifications. Always verify MOSFET switching losses and transformer saturation margins at the chosen frequency.
Does LT1737IGN#PBF require an optoisolator for feedback?
No, the LT1737IGN#PBF does not require an optoisolator. It achieves isolated output regulation by sensing the reflected flyback voltage pulse on a third transformer winding or directly from the primary winding. This primary-side sensing architecture eliminates optocoupler cost, aging drift, and bandwidth limitations while maintaining safety isolation through transformer design.
How is load regulation improved using the ROCMP and RCMPC pins on LT1737IGN#PBF?
The ROCMP and RCMPC pins implement active load compensation on the LT1737IGN#PBF. An external resistor (ROCMP) and capacitor (RCMPC) form a network that injects a correction current into the FB node, proportional to average switch current. This offsets voltage errors caused by secondary-side impedance (diode VF, winding resistance, capacitor ESR), improving load regulation from typically ±5% to <±1% across full load range without secondary sensing components.
What is the purpose of the ENDLY, MINENAB, and tON pins on LT1737IGN#PBF?
These pins configure critical timing parameters for stable flyback operation: ENDLY sets the delay between MOSFET turn-off and flyback amplifier enable (to avoid leakage spike interference); MINENAB defines the minimum duration the amplifier stays active; tON enforces a minimum MOSFET on-time per cycle. Together, they ensure reliable regulation in both continuous and discontinuous conduction modes and prevent lockup during start-up or light-load conditions on the LT1737IGN#PBF.
Can LT1737IGN#PBF operate with input voltages below 4.5V?
No, the LT1737IGN#PBF has a specified minimum supply voltage of 4.5V (typical 4.1V absolute min). Operation below this risks improper gate drive strength, unstable oscillator frequency, and degraded feedback amplifier performance. For sub-4.5V applications, consider controllers with lower VCC minima or use an auxiliary bias supply. The UVLO pin can be configured to disable the LT1737IGN#PBF before VCC drops to the operational threshold.
LT1737IGN#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SSOP (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-SSOP
LT1737IGN#PBF FAQ
1.How can I place an order for LT1737IGN#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1737IGN#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 LT1737IGN#PBF reliable?
The price and inventory of LT1737IGN#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1737IGN#PBF is usually 5 days.
3.What payment methods are accepted for LT1737IGN#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1737IGN#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1737IGN#PBF?
LT1737IGN#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1737IGN#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 LT1737IGN#PBF?
For technical support, including LT1737IGN#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1737IGN#PBF requirements.
6.How does Aetrix verify that LT1737IGN#PBF is sourced from the original manufacturer or authorized distributors?
All LT1737IGN#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 LT1737IGN#PBF meets industry standards.
7.What is the process for return or replacement of LT1737IGN#PBF?
All LT1737IGN#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1737IGN#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 LT1737IGN#PBF part is unused and in its original packaging.
Return procedure for LT1737IGN#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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