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Analog Devices Inc. LT1245IS8#TRPBF
- Part No.:
- LT1245IS8#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1245IS8#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,175
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Product details
Overview
LT1245IS8#TRPBF from Analog Devices is an 8-pin, fixed-frequency, current-mode PWM controller optimized for off-line and DC/DC converters. It delivers 1A totem-pole output drive, operates up to 500kHz switching frequency, features 50ns current sense delay with leading-edge blanking, and includes active pull-down during undervoltage lockout (UVLO) at 8.4V start-up threshold. It drives power MOSFETs in isolated flyback and forward converters.
For engineers reviewing the LT1245IS8#TRPBF datasheet, LT1245IS8#TRPBF pinout, LT1245IS8#TRPBF application, or LT1245IS8#TRPBF equivalent, key selection criteria include UVLO hysteresis (0.4V), ±1A output drive capability, 50ns current sense propagation delay, trimmed oscillator sink current (8.2mA typ), and compatibility with UC1845-based designs requiring extended temperature range support.
Technical Context
The LT1245IS8#TRPBF implements a fixed-frequency current-mode control architecture where the oscillator sets both switching frequency and deadtime via external RT/CT network, with trimmed 8.2mA discharge current enabling tight frequency tolerance. Its error amplifier provides 90dB DC gain and 1MHz unity-gain bandwidth, referenced to an internal 2.5V node derived from the 5V bandgap reference.
Current sensing uses a comparator with 100ns blanking time (at VFB = 2.5V), clamped input threshold (0.9–1.1V), and 70dB PSRR. The output stage eliminates cross-conduction spikes and clamps high-level voltage to 18V, while UVLO actively pulls down both OUTPUT (Pin 6) and VREF (Pin 8) to ~1V during undervoltage conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switching Frequency | 500kHz max output frequency (oscillator runs at 1MHz); enables compact magnetics in high-density SMPS designs. |
| UVLO Start Threshold | 8.4V with 0.4V hysteresis; ensures reliable startup after bulk capacitor charging in universal-input AC/DC supplies. |
| Output Drive Current | ±1A peak; directly drives large gate capacitance of 600V+ MOSFETs without external buffer stages. |
| Current Sense Delay | 50ns typical; minimizes minimum on-time limitation and improves light-load regulation in high-frequency converters. |
| Reference Voltage | 5.000V ±1% (4.925–5.075V); powers RT resistor and provides stable bias for feedback divider and clamp circuitry. |
| Start-Up Current | <250µA (170µA typ); reduces bleed resistor power loss in high-voltage offline applications. |
| Oscillator Sink Current | 8.2mA ±0.3mA; tightly trimmed to ensure consistent deadtime and duty cycle accuracy across temperature and unit variance. |
Pinout & Package
S8 package: 8-lead plastic SOIC, –40°C to 125°C operating temperature range, 150°C/W thermal resistance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| COMP (1) | Error amplifier output | Provides loop compensation node; sources 0.5mA / sinks 2mA; used to adjust current sense clamp level below 1V. |
| FB (2) | Inverting input of error amplifier | Internally referenced to 2.5V; accepts resistive feedback from output to regulate voltage with 2.42–2.58V input window. |
| ISENSE (3) | Current sense comparator input | Trips at 0.9–1.1V threshold; blanked for 100ns after switch turn-on to reject transformer leakage spikes. |
| RT/CT (4) | Oscillator timing node | Connects external RT (to VREF) and CT (to GND); sets frequency and deadtime via RC time constant and 8.2mA sink current. |
| GND (5) | Analog ground reference | Common return for feedback network, oscillator capacitor, and power stage; must be star-connected to minimize noise coupling. |
| OUTPUT (6) | Totem-pole driver output | Delivers ±1A into MOSFET gate; clamped to 18V max; actively pulled low (~1V) during UVLO to prevent unintended FET turn-on. |
| VCC (7) | Supply input | Operates from 7.6V to 25V; powers internal circuitry; bypassed with ≥0.1µF ceramic capacitor placed adjacent to pin. |
| VREF (8) | 5V bandgap reference output | Supplies charging current to RT; powers internal logic; can source up to 20mA but increases die temperature if heavily loaded. |
Key Features
| Feature | Design Value |
|---|---|
| Leading-edge blanking | 100ns fixed blanking window synchronized to OUTPUT turn-on, eliminating need for RC filter at ISENSE and preserving fast fault response. |
| Trimmed oscillator sink current | 8.2mA ±0.3mA specification ensures <±5% oscillator frequency variation across units and temperature without external calibration. |
| Active UVLO pull-down | Darlington PNP transistors pull OUTPUT and VREF to ~1V during undervoltage, removing need for external gate pull-down resistors and enabling soft-start capacitor reset. |
| High-current totem-pole output | ±1A drive capability with 40ns rise / 30ns fall times into 1nF load enables direct driving of high-Qg MOSFETs at 500kHz without gate drivers. |
| 18V output clamp | Internal clamp prevents OUTPUT from exceeding 18V, protecting MOSFET gate oxide in high-side configurations with bootstrap or isolated gate drive. |
Applications
| Isolated Flyback Converter | Forward Converter |
|---|---|
Use Scenario: Universal-input (90–240VAC) 30W adapter with primary-side regulation and Y-capacitor EMI filtering. IC Role / Device Role / Timing Role: Primary-side PWM controller generating gate drive for 600V MOSFET; regulates output via optocoupler feedback to FB pin. Use Value: 50ns current sense delay and 100ns blanking enable stable operation at 300kHz with minimal minimum on-time distortion and no external noise filters. | Use Scenario: 48V input telecom DC/DC module delivering 12V@5A with synchronous rectification. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller managing main switch and reset winding timing; coordinates with external SR controller via OUTPUT waveform. Use Value: ±1A output drive directly switches high-side MOSFET with 40ns rise time, reducing conduction losses and enabling >92% efficiency at full load. |
| Offline AC/DC Power Supply | Industrial DC/DC Converter |
Use Scenario: DIN-rail mounted 24V/10A industrial power supply with wide input range (85–305VAC) and reinforced isolation. IC Role / Device Role / Timing Role: Core PWM controller implementing current-mode control with slope compensation; interfaces with overvoltage/overcurrent protection circuits via COMP and ISENSE pins. Use Value: 8.4V UVLO start threshold with 0.4V hysteresis ensures robust startup after bulk capacitor charging while preventing brownout oscillation. | Use Scenario: Railway or factory automation system requiring –40°C to 125°C operation with 28V input and 5V/3A output. IC Role / Device Role / Timing Role: High-reliability PWM controller in non-isolated buck-derived topology; leverages S8 package's extended temperature rating and 150°C/W θJA. Use Value: Active VREF pull-down during UVLO allows integration with external soft-start circuit using a single capacitor tied to VREF, simplifying BOM and layout. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC1845N | Same pinout and basic function; higher start-up current (500µA vs 250µA), no leading-edge blanking, no trimmed oscillator sink current. | Legacy design replacement only; lacks 50ns current sense delay and blanking, limiting usable frequency to ≤200kHz in noisy environments. | Select UC1845N only for cost-sensitive, low-frequency (<150kHz), non-extended-temp replacements where layout cannot accommodate LT1245IS8#TRPBF's tighter tolerances. |
| LT3748IS8#TRPBF | Primary-side flyback controller with integrated 60V MOSFET driver; includes built-in soft-start, fault latching, and 1MHz max frequency; not pin-compatible. | Targeted specifically for isolated flyback topologies with secondary-side regulation; requires different feedback architecture (no optocoupler needed). | Choose LT3748IS8#TRPBF when designing new flyback supplies requiring enhanced protection, lower component count, and higher integration - not for drop-in UC1845 upgrades. |
Compared with UC1845N, LT1245IS8#TRPBF offers 50% lower start-up current and built-in blanking for noise immunity, while LT3748IS8#TRPBF trades pin compatibility for integrated protection and flyback-specific features - making LT1245IS8#TRPBF the optimal choice for high-frequency, extended-temperature, UC1845-replacement designs requiring proven reliability.
Availability
LT1245IS8#TRPBF is available at Aetrix Electronics and suitable for offline AC/DC power supplies, isolated flyback converters, and industrial DC/DC converters requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT1245IS8#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 (now part of Analog Devices, Inc., following merger with Linear Technology) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors.
The LT1241 series - including LT1245IS8#TRPBF - was designed as a performance-enhanced, plug-compatible upgrade to UC184x controllers for high-efficiency, high-frequency switch-mode power supplies in industrial and telecom infrastructure.
FAQ
What is the maximum operating junction temperature for LT1245IS8#TRPBF?
The LT1245IS8#TRPBF has a specified operating junction temperature range of –40°C to 125°C. This is enabled by its S8 plastic SOIC package with 150°C/W thermal resistance. Derating curves in the datasheet confirm continuous operation up to TJ = 125°C under appropriate PCB copper area and airflow conditions. The device enters thermal shutdown only if internal die temperature exceeds absolute maximum limits, which are not specified for LT1245IS8#TRPBF but align with standard Linear Technology process safety margins.
Does LT1245IS8#TRPBF support synchronization to an external clock?
No, LT1245IS8#TRPBF does not support external clock synchronization. Its oscillator is internally generated and set solely by the RT/CT network on Pin 4. Unlike some later-generation controllers (e.g., LT3748 or LT8316), the LT1245IS8#TRPBF lacks an external sync input pin or programmable clock divider. Synchronization requires replacing the RT/CT network with a precision current source or using a separate master oscillator - neither method is supported natively by LT1245IS8#TRPBF.
How does the current sense blanking time vary with feedback voltage in LT1245IS8#TRPBF?
In LT1245IS8#TRPBF, blanking time is inversely proportional to FB pin voltage: it is 100ns at VFB = 2.5V (normal regulation), decreases linearly as VFB drops, and reaches zero when VFB = 0V. This behavior ensures minimal blanking during startup or output short-circuit faults - preserving fast current-limit response - while providing full noise immunity during steady-state operation. The relationship is monotonic and specified in the Applications Information section of the datasheet.
Can LT1245IS8#TRPBF drive a MOSFET directly without a gate driver IC?
Yes, LT1245IS8#TRPBF can drive power MOSFETs directly due to its ±1A totem-pole output stage and 40ns rise time into 1nF. It is routinely used to drive Qg ≤ 25nC MOSFETs (e.g., MPT2N60, STP16NF20) in 300–500kHz flyback and forward converters. For MOSFETs with Qg > 30nC or layouts with >5cm gate trace length, a dedicated gate driver is recommended to maintain switching speed and reduce gate ringing.
What is the purpose of the active pull-down on VREF during undervoltage lockout in LT1245IS8#TRPBF?
The active pull-down on VREF (Pin 8) during UVLO in LT1245IS8#TRPBF serves two purposes: (1) it discharges external soft-start capacitors connected between VREF and GND, enabling controlled ramp-up of duty cycle at startup; and (2) it disables external circuitry powered from VREF (e.g., RT biasing, auxiliary references), preventing erratic behavior during brownout. This eliminates the need for external transistor-based reset circuits required by older UC184x controllers.
LT1245IS8#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive, Isolation Capable
- Topology:
- Buck
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 8.2V ~ 25V
- Frequency - Switching:
- 500kHz
- Duty Cycle (Max):
- 48%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- -40°C ~ 100°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1245IS8#TRPBF FAQ
1.How can I place an order for LT1245IS8#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1245IS8#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 LT1245IS8#TRPBF reliable?
The price and inventory of LT1245IS8#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1245IS8#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1245IS8#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1245IS8#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1245IS8#TRPBF?
LT1245IS8#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1245IS8#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 LT1245IS8#TRPBF?
For technical support, including LT1245IS8#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1245IS8#TRPBF requirements.
6.How does Aetrix verify that LT1245IS8#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1245IS8#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 LT1245IS8#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1245IS8#TRPBF?
All LT1245IS8#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1245IS8#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 LT1245IS8#TRPBF part is unused and in its original packaging.
Return procedure for LT1245IS8#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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