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Analog Devices Inc. LT1243IS8#PBF
- Part No.:
- LT1243IS8#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1243IS8#PBF.pdf
- Description:
- IC REG CTRLR BUCK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:152
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Product details
Overview
LT1243IS8#PBF from Analog Devices is an 8-pin, fixed-frequency current-mode PWM controller optimized for off-line and DC/DC converters. It features 1A totem-pole output, <250µA start-up current, 50ns current sense delay, and operates up to 500kHz switching frequency in applications such as AC-DC adapters and isolated flyback supplies.
For engineers reviewing the LT1243IS8#PBF datasheet, LT1243IS8#PBF pinout, LT1243IS8#PBF application, or LT1243IS8#PBF equivalent, key selection criteria include undervoltage lockout threshold (8.4V start-up), 100% maximum duty cycle capability, active pull-down during UVLO, and compatibility with UC1843-based designs requiring extended temperature operation.
Technical Context
The LT1243IS8#PBF implements a fixed-frequency current-mode control architecture with oscillator frequency set by external RT/CT components and trimmed sink current (8.2mA typ). Its error amplifier delivers 90dB open-loop gain and 1MHz unity-gain bandwidth, with internal 2.5V reference tied to FB pin.
Current sensing includes leading-edge blanking (100ns at VFB = 2.5V), 1V clamp on ISENSE input, and cycle-by-cycle peak current limiting. The output stage provides ±1A drive with 40ns rise/30ns fall times into 1nF, clamped to 18V high-level output and actively pulled low (<1V) during undervoltage lockout.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Start-Up Current | <250µA - enables low-loss biasing in high-voltage off-line converters using high-value startup resistors |
| UVLO Start Threshold | 8.4V - ensures reliable turn-on after bulk capacitor charging in universal-input AC-DC supplies |
| Max Duty Cycle | 100% - supports continuous conduction mode (CCM) operation and zero-voltage switching topologies |
| Oscillator Sink Current | 8.2mA (typ) - tightly trimmed for stable frequency and deadtime control across temperature |
| Output Drive Capability | ±1A - directly drives power MOSFET gates without external buffer stages |
| Current Sense Delay | 50ns - minimizes propagation latency for fast overcurrent response in fault protection |
| Reference Voltage | 5.000V ±1% - powers timing network and serves as precision bias for feedback and current sense circuits |
Pinout & Package
S8 package: 8-lead plastic SOIC, –40°C to 100°C operating temperature range, JEDEC MS-012AC compliant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Provides loop compensation node; sources 0.5mA / sinks 2mA; used to clamp current sense threshold |
| 2 - FB | Inverting input of error amplifier | Internally referenced to 2.5V; accepts voltage feedback divider; sets blanking time (100ns at 2.5V) |
| 3 - ISENSE | Current sense comparator input | Accepts MOSFET source/sense resistor voltage; trip point proportional to COMP output; 1V internal clamp |
| 4 - RT/CT | Oscillator timing node | Connects external RT (to VREF) and CT (to GND); sets frequency and deadtime via RC + 8.2mA sink current |
| 5 - GND | Analog and power ground | Single-point return for feedback, oscillator, and current sense paths; critical for noise immunity |
| 6 - OUTPUT | Totem-pole gate driver output | ±1A capable; 18V high-level clamp; actively pulled low (~1V) during UVLO; no external pull-down required |
| 7 - VCC | Supply input | Operates from 7.6V to 25V; powers internal circuitry; bypass with ≥0.1µF near pin |
| 8 - VREF | 5V bandgap reference output | Supplies RT current and internal bias; delivers up to 20mA; actively pulled low during UVLO |
Key Features
| Feature | Design Value |
|---|---|
| Leading-edge blanking | 100ns fixed duration synchronized to OUTPUT turn-on, eliminating false triggering from transformer leakage spikes |
| Trimmed oscillator sink current | 8.2mA ±3% - ensures predictable deadtime and frequency stability across temperature and unit-to-unit variation |
| Active UVLO pull-down | Darlington PNP on both OUTPUT and VREF pins pulls each to ~1V, removing need for external gate discharge resistors |
| High-speed output stage | 40ns rise / 30ns fall into 1nF - enables clean 500kHz switching with minimal cross-conduction and EMI |
| 100% duty cycle support | Enables CCM operation in forward/flyback converters and supports soft-start sequencing without duty cycle limitation |
Applications
| Industrial AC-DC Adapters | Isolated DC-DC Converters |
|---|---|
|
Use Scenario: Universal-input (90–240VAC), 30W flyback converter powering industrial PLC I/O modules. IC Role / Device Role / Timing Role: Primary-side PWM controller regulating output via optocoupler feedback; sets 300kHz switching frequency via RT/CT network. Use Value: 8.4V UVLO start threshold ensures robust operation after bulk capacitor charge; 100% duty cycle accommodates wide line/load transients without dropout. |
Use Scenario: 48V-to-12V isolated half-bridge DC-DC converter for telecom shelf management systems. IC Role / Device Role / Timing Role: Current-mode modulator driving synchronous rectifiers; uses COMP pin for slope compensation injection at ISENSE. Use Value: 50ns current sense delay enables precise peak current limiting; 1A output drives gate capacitance without buffering, reducing BOM count. |
| Medical Power Supplies | Automotive Off-Board Chargers |
|
Use Scenario: 24V input, 5V/3A medical-grade isolated supply meeting IEC 60601-1 creepage requirements. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller implementing primary-side regulation with auxiliary winding feedback. Use Value: –40°C to 100°C S8 package rating supports extended ambient operation; 5V reference accuracy (±1%) ensures stable output tolerance over life. |
Use Scenario: 12V battery-powered 120W boost converter for portable EV charging units operating in vehicle cabins. IC Role / Device Role / Timing Role: High-efficiency PWM controller managing MOSFET gate drive in discontinuous conduction mode (DCM). Use Value: <250µA start-up current minimizes standby loss; active VREF pull-down during UVLO enables controlled soft-start reset via external capacitor. |
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 |
|---|---|---|---|
| UC1843N | Same pinout, but higher 16V UVLO start threshold and 10mA quiescent current; no leading-edge blanking or trimmed oscillator sink current | Requires external blanking circuit for noisy transformer designs; less suitable for low-standby or wide-input-range applications | Select UC1843N only when legacy design reuse is mandatory and thermal margin allows higher operating current |
| UCC3803D | Lower 8.4V UVLO start (same as LT1243), but 500µA start-up current and no active VREF pull-down; 500kHz max frequency limited by slower propagation delays | Lacks integrated blanking and active UVLO discharge, increasing risk of false triggering and requiring external reset circuitry | Prefer UCC3803D only if cost sensitivity outweighs reliability requirements and layout constraints prevent adding blanking components |
Compared with UC1843N and UCC3803D, LT1243IS8#PBF delivers lower start-up current, built-in blanking, tighter oscillator control, and active UVLO discharge - enabling simpler, more robust, and lower-power designs without external component additions.
Availability
LT1243IS8#PBF is available at Aetrix Electronics and suitable for industrial AC-DC adapters, isolated DC-DC converters, and medical power supplies requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT1243IS8#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 (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 LT1243IS8#PBF belongs to the LT124x series of current-mode PWM controllers, designed specifically for high-reliability, high-efficiency off-line and isolated DC-DC power conversion where low start-up current, tight frequency control, and robust fault handling are critical.
FAQ
What is the UVLO start-up threshold voltage for LT1243IS8#PBF?
The LT1243IS8#PBF has a guaranteed UVLO start-up threshold of 8.4V (min) and 9.0V (max), with 0.4V hysteresis. This ensures reliable activation after bulk capacitor charging in universal-input AC-DC supplies while preventing chatter near the threshold. The LT1243IS8#PBF maintains this specification across its full –40°C to 100°C operating range.
Does LT1243IS8#PBF support 100% duty cycle operation?
Yes, the LT1243IS8#PBF supports 100% maximum duty cycle, unlike the LT1241/LT1244/LT1245 variants limited to 46–48%. This enables continuous conduction mode (CCM) operation in forward and flyback topologies, improves light-load efficiency, and simplifies soft-start implementation. The LT1243IS8#PBF achieves this via internal oscillator timing architecture optimized for full-cycle enablement.
How does the leading-edge blanking function in LT1243IS8#PBF?
The LT1243IS8#PBF incorporates a fixed 100ns blanking window triggered at OUTPUT turn-on, synchronized to suppress false current-sense trips caused by transformer leakage spikes or diode reverse recovery. Blanking duration scales inversely with FB pin voltage - dropping to zero at 0V - ensuring responsiveness during short-circuit faults. This eliminates the need for external RC filters that degrade current-loop bandwidth. The LT1243IS8#PBF implements this entirely internally with no user configuration required.
What is the purpose of the active pull-down on VREF and OUTPUT during UVLO?
During undervoltage lockout, the LT1243IS8#PBF actively pulls both VREF (Pin 8) and OUTPUT (Pin 6) low via integrated Darlington PNP transistors, sinking several milliamps to ~1V. This eliminates external pull-down resistors previously needed to hold MOSFET gates low and discharge soft-start capacitors. The LT1243IS8#PBF's active pull-down ensures predictable, rapid shutdown and enables direct reset of external timing networks without additional components.
Can LT1243IS8#PBF drive a power MOSFET directly without a gate driver?
Yes, the LT1243IS8#PBF integrates a ±1A totem-pole output stage with 40ns rise and 30ns fall times into 1nF, sufficient to drive typical power MOSFET gates (e.g., Qg ≤ 30nC) in sub-500kHz applications. Its 18V output clamp protects MOSFET gates from overvoltage, and active UVLO pull-down prevents unintended turn-on. For high-Qg devices (>50nC) or >300kHz operation, a dedicated gate driver remains recommended - but the LT1243IS8#PBF itself requires no buffer stage in most standard implementations.
LT1243IS8#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- 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):
- 96%
- 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
LT1243IS8#PBF FAQ
1.How can I place an order for LT1243IS8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1243IS8#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 LT1243IS8#PBF reliable?
The price and inventory of LT1243IS8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1243IS8#PBF is usually 5 days.
3.What payment methods are accepted for LT1243IS8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1243IS8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1243IS8#PBF?
LT1243IS8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1243IS8#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 LT1243IS8#PBF?
For technical support, including LT1243IS8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1243IS8#PBF requirements.
6.How does Aetrix verify that LT1243IS8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1243IS8#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 LT1243IS8#PBF meets industry standards.
7.What is the process for return or replacement of LT1243IS8#PBF?
All LT1243IS8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1243IS8#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 LT1243IS8#PBF part is unused and in its original packaging.
Return procedure for LT1243IS8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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