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Analog Devices Inc. LT1247CN8#PBF
- Part No.:
- LT1247CN8#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
LT1247CN8#PBF.pdf
- Description:
- IC REG CTRLR BUCK 8DIP
- Quantity:
- Payment:
- Shipping:
Inventory:4,780
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Product details
Overview
LT1247CN8#PBF from Analog Devices (formerly Linear Technology) is an 8-pin fixed-frequency current-mode PWM controller IC optimized for off-line and DC/DC converter applications. It features 100% maximum duty cycle, 8.4V start-up threshold, 7.6V minimum operating voltage, 1A totem-pole output, and integrated 5V reference with ±1% initial tolerance - enabling high-efficiency flyback and forward converter designs in industrial power supplies.
For engineers reviewing the LT1247CN8#PBF datasheet, LT1247CN8#PBF pinout, LT1247CN8#PBF application, or LT1247CN8#PBF equivalent, key selection criteria include undervoltage lockout hysteresis (0.4–0.8V), 30ns current sense delay, leading-edge blanking, oscillator sink current trim (8.2mA typ.), and compatibility with UC1843-based legacy designs requiring stable 1MHz-capable control.
Technical Context
The LT1247CN8#PBF implements a fixed-frequency current-mode architecture where peak switch current is controlled cycle-by-cycle via the ISENSE comparator, whose trip point is proportional to the error amplifier output. Its oscillator uses a trimmed 8.2mA discharge current and external RT/CT network to set frequency and deadtime independently.
It integrates a temperature-compensated 5V bandgap reference, high-gain error amplifier (90dB DC gain, 2MHz unity-gain bandwidth), active pull-down on VREF and OUTPUT during UVLO, and a 18V output clamp - all within an 8-lead PDIP package rated for 0°C to 100°C junction temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Start-Up Threshold | 8.4V (typical); enables reliable turn-on in low-voltage AC/DC adapters without premature oscillation |
| Minimum Operating Voltage | 7.6V (typical); sustains regulation during brownout conditions in universal-input offline converters |
| Oscillator Sink Current | 8.2mA (typical); tightly trimmed for ±5% frequency accuracy across RT/CT combinations |
| Current Sense Delay | 30ns; minimizes propagation latency for fast overcurrent response in high-frequency SMPS |
| Output Clamp Voltage | 18V (min); protects MOSFET gate oxide in 15V-biased drive circuits |
| Reference Output Accuracy | ±1% (initial); ensures precise feedback divider biasing and timing resistor current setting |
| Max Duty Cycle | 100%; supports zero-voltage-switching topologies and high step-down ratio converters |
Pinout & Package
LT1247CN8#PBF is housed in an 8-lead plastic DIP (N8) package with 0.300-inch wide body, 0.100-inch lead pitch, and JEDEC MS-001 compliant footprint. Thermal resistance θJA = 130°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (COMP) | Error amplifier output | Provides loop compensation node; sources ≥0.5mA / sinks ≥2mA for external RC networks |
| 2 (FB) | Inverting input of error amplifier | Receives resistive divider feedback; referenced to internal 2.5V; input bias ≤–2µA |
| 3 (ISENSE) | Current sense comparator input | Accepts MOSFET source/sense resistor voltage; includes 60ns blanking at VFB = 2.5V |
| 4 (RT/CT) | Oscillator timing node | Charged by VREF through RT; discharged by internal 8.2mA sink; sets frequency and deadtime |
| 5 (GND) | Analog/digital ground reference | Single-point return for feedback, oscillator, and output drive paths to minimize noise coupling |
| 6 (OUTPUT) | Totem-pole gate driver output | Delivers ±1A peak into MOSFET gate; rise/fall times ≤70ns/60ns with 1nF load; clamped to 18V |
| 7 (VCC) | Supply input | Operates from 7.6V to 25V; includes UVLO with 0.8V hysteresis; quiescent current <250µA at startup |
| 8 (VREF) | 5V bandgap reference output | Supplies RT charging current; powers internal circuitry; delivers up to 20mA with ±1% tolerance |
Key Features
| Feature | Design Value |
|---|---|
| Current mode operation to 1MHz | Enables stable high-frequency switching with inherent cycle-by-cycle current limiting |
| Leading edge blanking on ISENSE | Eliminates need for external RC filter, reducing current-sense loop delay to <30ns |
| Active pull-down on VREF and OUTPUT during UVLO | Removes requirement for external pull-down resistors on reference and gate drive lines |
| Trimmed oscillator sink current | Ensures ±5% oscillator frequency accuracy without calibration across temperature and supply |
| 18V output clamp | Prevents MOSFET gate overvoltage in 15V-biased systems without external Zener protection |
Applications
| AC/DC Flyback Adapters | Isolated DC/DC Converters |
|---|---|
Use Scenario: Universal-input (85–265VAC) 12W–65W wall adapters powering consumer electronics. IC Role / Device Role / Timing Role: Primary-side PWM controller regulating output via optocoupler feedback; generates 50–500kHz gate drive with current-mode stability. Use Value: 8.4V UVLO start-up enables reliable cold-start under low-line conditions; 100% duty cycle supports high step-down ratios in discontinuous conduction mode. | Use Scenario: Industrial 24V-to-5V/3.3V isolated DC/DC modules for PLC I/O and sensor interfaces. IC Role / Device Role / Timing Role: Secondary-side synchronous rectifier controller or primary-side flyback controller with transformer-isolated feedback. Use Value: 30ns current sense delay and blanking reduce false triggering from transformer leakage spikes; 5V reference powers optocoupler LED and feedback divider precisely. |
| Offline LED Drivers | Telecom DC/DC Modules |
Use Scenario: Constant-current LED drivers for commercial lighting with TRIAC dimming compatibility. IC Role / Device Role / Timing Role: High-voltage buck-boost or flyback controller modulating LED current via primary-side sensing. Use Value: 1A output drives large MOSFETs directly; 7.6V minimum operating voltage maintains regulation during phase-cut dimmer hold-off periods. | Use Scenario: 48V input telecom power modules delivering 12V/5V outputs with tight transient response. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller managing synchronous rectification and overcurrent protection. Use Value: Trimmed 8.2mA oscillator sink current ensures consistent deadtime across units; 18V output clamp safeguards 12V-gate MOSFETs during surge events. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar current-mode PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC1843N8 | Higher 16V start-up threshold; no leading-edge blanking; looser oscillator trim (±10%); 0.5A output | Requires external blanking RC filter; less suitable for >300kHz designs due to slower current sense path | Legacy drop-in where UVLO margin is sufficient and cost sensitivity outweighs performance gains |
| UCC38C43N | 8.4V start-up; 1A output; but lacks trimmed oscillator sink current and has 50ns sense delay | Needs external compensation for high-frequency stability; higher EMI risk without blanking | Acceptable for 200–400kHz applications where layout controls noise, but not recommended for 1MHz designs |
Compared with UC1843N8 and UCC38C43N, the LT1247CN8#PBF delivers tighter frequency control, lower propagation delay, and integrated blanking - enabling robust 1MHz operation without added components, while maintaining pin compatibility with UC1843 for upgrade paths.
Availability
LT1247CN8#PBF is available at Aetrix Electronics and suitable for AC/DC flyback adapters, isolated DC/DC converters, and offline LED drivers requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LT1247CN8#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 and continues its legacy of precision analog and power management ICs for industrial, automotive, and communications markets.
The LT1247CN8#PBF belongs to the LT124x family of current-mode PWM controllers designed specifically for high-reliability off-line and isolated DC/DC converter applications demanding tight regulation, fast transient response, and robust fault handling.
FAQ
What is the start-up threshold voltage for LT1247CN8#PBF?
The LT1247CN8#PBF has a typical start-up threshold voltage of 8.4V, with a guaranteed range of 7.8V to 9.0V across temperature. This lower threshold compared to LT1246 (16V) allows reliable operation in low-input-voltage offline applications such as 12V DC-powered converters or brownout-prone AC/DC adapters. The LT1247CN8#PBF remains latched off below this threshold, drawing less than 250µA.
Does LT1247CN8#PBF support 1MHz switching operation?
Yes, the LT1247CN8#PBF is explicitly characterized for stable operation up to 1MHz, enabled by its 30ns current sense delay, eliminated cross-conduction in the totem-pole output stage, and leading-edge blanking circuit. When paired with appropriate RT/CT values (e.g., RT = 6.2kΩ, CT = 500pF), it achieves 500kHz typical frequency with ±5% accuracy - and scales linearly to 1MHz with verified waveform integrity per datasheet Figure 21.
How does the leading-edge blanking function in LT1247CN8#PBF?
The LT1247CN8#PBF incorporates internal leading-edge blanking that disables the current sense comparator output for 60ns after each OUTPUT turn-on event when FB = 2.5V. This duration scales down to zero as FB approaches 0V, ensuring minimal blanking during short-circuit faults. It eliminates external RC filters, preserving current-loop bandwidth and reducing peak fault currents - a feature absent in UC1843 and critical for >300kHz designs.
What is the purpose of the 18V output clamp in LT1247CN8#PBF?
The 18V output clamp in the LT1247CN8#PBF limits the high-side voltage of the OUTPUT pin to prevent gate oxide damage in standard 15V-rated MOSFETs. During turn-on transients or capacitive loading, the clamp activates to hold VOUT ≤ 19V (max), eliminating the need for external Zener diodes. This design choice directly supports robust gate drive in high-voltage offline converters without adding bill-of-materials cost or PCB area.
Is LT1247CN8#PBF pin-compatible with UC1843?
Yes, the LT1247CN8#PBF is pin-compatible with UC1843 in the 8-lead DIP package (N8), sharing identical pin functions: COMP, FB, ISENSE, RT/CT, GND, OUTPUT, VCC, and VREF. However, LT1247CN8#PBF improves upon UC1843 with tighter oscillator trim, lower start-up current (<250µA vs. ~500µA), integrated blanking, and active pull-down during UVLO - making it a direct functional upgrade without layout changes.
LT1247CN8#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 8.4V ~ 25V
- Frequency - Switching:
- 1MHz
- Duty Cycle (Max):
- 100%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 8-PDIP
LT1247CN8#PBF FAQ
1.How can I place an order for LT1247CN8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1247CN8#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 LT1247CN8#PBF reliable?
The price and inventory of LT1247CN8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1247CN8#PBF is usually 5 days.
3.What payment methods are accepted for LT1247CN8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1247CN8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1247CN8#PBF?
LT1247CN8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1247CN8#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 LT1247CN8#PBF?
For technical support, including LT1247CN8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1247CN8#PBF requirements.
6.How does Aetrix verify that LT1247CN8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1247CN8#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 LT1247CN8#PBF meets industry standards.
7.What is the process for return or replacement of LT1247CN8#PBF?
All LT1247CN8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1247CN8#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 LT1247CN8#PBF part is unused and in its original packaging.
Return procedure for LT1247CN8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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