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Analog Devices Inc. LT1243IN8#PBF
- Part No.:
- LT1243IN8#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
LT1243IN8#PBF.pdf
- Description:
- IC REG CTRLR BUCK 8DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,993
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Product details
Overview
LT1243IN8#PBF from Analog Devices is an 8-pin PDIP-packaged, current-mode PWM controller optimized for off-line and DC/DC converters. It features 500 kHz max switching frequency, <250 µA start-up current, 1 A totem-pole output, undervoltage lockout with 8.4 V start threshold, and integrated leading-edge blanking for noise-immune current sensing in high-reliability power supplies.
For engineers reviewing the LT1243IN8#PBF datasheet, LT1243IN8#PBF pinout, LT1243IN8#PBF application, or LT1243IN8#PBF equivalent, key selection criteria include its –40°C to 125°C industrial temperature range, UC1843-compatible pinout, 100% maximum duty cycle capability, and active low-side pull-down during UVLO-critical for robust gate drive in flyback and forward converters.
Technical Context
The LT1243IN8#PBF implements fixed-frequency current-mode control using a trimmed oscillator with 8.2 mA sink current and 2.8 V/1.1 V trip thresholds, enabling precise deadtime control and repeatable 500 kHz operation. Its error amplifier delivers 90 dB DC gain and 1 MHz unity-gain bandwidth, with internal 2.5 V reference derived from the 5 V bandgap.
Current sensing uses a clamped comparator with 100 ns blanking (VFB = 2.5 V), eliminating external RC filters while preserving fast fault response. The 1 A totem-pole output drives MOSFET gates directly, with 18 V high-level clamp and active low-state pull-down (≈1 V) during undervoltage lockout-removing need for external gate discharge resistors.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Max Switching Frequency | 500 kHz - enables compact magnetics and high-power-density SMPS designs |
| Start-Up Current | <250 µA - minimizes bleed resistor losses in offline AC-DC adapters |
| Output Drive Capability | ±1 A - directly drives large gate capacitance MOSFETs without buffer stages |
| UVLO Start Threshold | 8.4 V - ensures stable operation after bulk capacitor charging in universal-input supplies |
| Reference Voltage | 5.000 V ±1.5% - powers RT/CT network and provides stable bias for feedback divider |
| Current Sense Delay | 50 ns - supports high-speed current-loop response for tight regulation under transients |
| Duty Cycle Range | 0–100% - enables full-range control in forward and push-pull topologies |
Pinout & Package
N8 package: 8-lead plastic DIP, –40°C to 125°C operating temperature, 130°C/W thermal resistance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (COMP) | Error amplifier output | Provides loop compensation node; sources 0.5 mA / sinks 2 mA for external pole-zero placement |
| 2 (FB) | Inverting input of error amplifier | Accepts voltage feedback via resistive divider; internally referenced to 2.5 V |
| 3 (ISENSE) | Current sense comparator input | Trips at 0.9–1.1 V; blanked for 100 ns after each switch-on edge to reject transformer spikes |
| 4 (RT/CT) | Oscillator timing node | RC-connected to set frequency and deadtime; charged by 5 V reference, discharged by 8.2 mA internal sink |
| 5 (GND) | Analog and power ground | Single-point return for feedback, oscillator, and current sense paths to minimize noise coupling |
| 6 (OUTPUT) | Totem-pole gate driver output | Drives MOSFET gate directly; clamped to 18 V high, actively pulled to ≈1 V low during UVLO |
| 7 (VCC) | Supply input | Operates from 7.6 V to 25 V; powers internal circuitry except reference and oscillator bias |
| 8 (VREF) | 5 V bandgap reference output | Supplies RT current and internal bias; delivers up to 20 mA with ±0.1 mV/°C stability |
Key Features
| Feature | Design Value |
|---|---|
| Trimmed oscillator sink current | 8.2 mA ±0.3 mA - ensures consistent deadtime and frequency across temperature and unit variance |
| Active UVLO pull-down | VREF and OUTPUT pulled to ≈1 V - eliminates external gate discharge resistors and soft-start capacitor reset path |
| Leading-edge blanking | 100 ns fixed duration at VFB = 2.5 V - suppresses turn-on spikes without degrading short-circuit response time |
| High-current totem-pole output | ±1 A peak into capacitive load - reduces MOSFET switching losses and enables >300 kHz operation with 1 nF gate load |
| 18 V output clamp | Prevents MOSFET gate overvoltage - protects devices rated ≤20 V VGS without external Zener clamps |
Applications
| AC-DC Flyback Adapter | Industrial DC-DC Forward Converter |
|---|---|
Use Scenario: Universal-input (90–240 VAC) 30 W offline adapter powering industrial sensors. IC Role / Device Role / Timing Role: Primary-side PWM controller generating gate drive for 600 V MOSFET; sets 300 kHz switching via RT/CT network. Use Value: <250 µA start-up current reduces no-load power loss; 100% duty cycle supports wide input range without auxiliary winding. | Use Scenario: 48 V input to 12 V/5 A isolated supply in programmable logic controller (PLC) backplane. IC Role / Device Role / Timing Role: Current-mode controller regulating synchronous rectified forward converter; provides cycle-by-cycle current limiting and slope compensation. Use Value: 50 ns current sense delay enables accurate peak current detection at high dI/dt; –40°C to 125°C rating ensures reliability in uncooled enclosures. |
| Automotive DC-DC Buck-Boost | Medical Isolated Auxiliary Supply |
Use Scenario: 12 V battery-powered buck-boost converter delivering 5 V/2 A to automotive infotainment display. IC Role / Device Role / Timing Role: High-speed current-mode modulator driving N-channel MOSFETs; UVLO hysteresis prevents brownout oscillation during cranking. Use Value: 8.4 V UVLO start threshold avoids false triggering during cold-cranking dips; 1 A output drives dual gate drivers without buffers. | Use Scenario: 24 V input to 5 V/1 A reinforced-isolation auxiliary supply for patient-monitoring front-end analog circuits. IC Role / Device Role / Timing Role: Primary-side controller in transformer-isolated flyback; provides precise 5 V reference for secondary-side optocoupler feedback. Use Value: 5.000 V ±1.5% reference ensures stable optocoupler LED current; 100°C/W θJA allows convection-cooled PCB layout meeting IEC 60601 creepage requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PWM controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3843N | Higher 1 mA start-up current; no leading-edge blanking; 16 V max output clamp | Limited to lower-frequency (<200 kHz) designs due to slower current sense path and no blanking | Select when cost sensitivity outweighs performance needs and thermal margin permits higher start-up loss |
| UCC3803D | Lower 0.5 mA start-up current; 500 kHz capable; no integrated blanking but supports external blanking circuit | Requires external components for noise immunity; lacks active UVLO pull-down on VREF | Choose when design already includes blanking circuitry and requires tighter start-up current spec |
Compared with UC3843N and UCC3803D, LT1243IN8#PBF delivers superior noise immunity via built-in blanking, lower start-up loss, and integrated UVLO pull-down-reducing BOM count and improving reliability in high-noise industrial environments without sacrificing 500 kHz capability.
Availability
LT1243IN8#PBF is available at Aetrix Electronics and suitable for AC-DC adapters, industrial DC-DC converters, and automotive power modules requiring stable component supply across extended temperature ranges.
Supply support for LT1243IN8#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 power management ICs.
The LT124x series was designed specifically for high-efficiency, high-reliability current-mode switching power supplies-targeting off-line AC-DC, isolated DC-DC, and industrial motor control auxiliary supplies.
FAQ
What is the operating temperature range of the LT1243IN8#PBF?
The LT1243IN8#PBF is rated for –40°C to 125°C junction temperature, with the N8 PDIP package supporting this full industrial range. This exceeds the 0°C to 100°C rating of the LT124XC variants and enables deployment in uncooled enclosures or engine-bay-adjacent automotive subsystems where ambient temperatures exceed 85°C. The device maintains all electrical specifications-including 8.4 V UVLO start threshold and 500 kHz capability-across this range.
How does the LT1243IN8#PBF differ from the LT1242IN8#PBF?
The LT1243IN8#PBF and LT1242IN8#PBF share identical pinout and package but differ in UVLO thresholds and maximum duty cycle: LT1243IN8#PBF starts at 8.4 V and supports 100% duty cycle, while LT1242IN8#PBF starts at 16 V and also supports 100% duty cycle. Both are drop-in replacements for UC1843 and UC1842 respectively, but LT1243IN8#PBF is preferred for lower-input-voltage DC-DC applications where 16 V start would prevent operation.
Does the LT1243IN8#PBF require external components for current sense noise immunity?
No-the LT1243IN8#PBF integrates leading-edge blanking with a fixed 100 ns duration (at VFB = 2.5 V), eliminating the need for external RC filters at the ISENSE pin. This blanking suppresses turn-on spikes from transformer leakage inductance and diode reverse recovery, enabling stable operation in noisy flyback and forward converters without compromising short-circuit response time. External filtering is only required in extreme EMI environments.
What is the purpose of the active pull-down on VREF and OUTPUT during undervoltage lockout?
During undervoltage lockout, the LT1243IN8#PBF actively pulls both VREF (Pin 8) and OUTPUT (Pin 6) low to ≈1 V using Darlington PNP transistors. This serves two critical functions: (1) it discharges external soft-start capacitors via the VREF pull-down, enabling controlled restart; and (2) it holds the external MOSFET gate low without requiring an external pull-down resistor-reducing component count and ensuring fail-safe shutdown during brownout conditions.
Can the LT1243IN8#PBF drive a MOSFET directly without a gate driver IC?
Yes-the LT1243IN8#PBF's ±1 A totem-pole output stage is designed to drive power MOSFET gates directly. With typical rise/fall times of 50/30 ns into 1 nF, it supports switching frequencies up to 500 kHz for MOSFETs with gate charges ≤50 nC. The 18 V output clamp protects common 20 V VGS MOSFETs, and the active low-state pull-down during UVLO ensures gate discharge without external components-making discrete gate drivers unnecessary in most medium-power applications.
LT1243IN8#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, 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:
- Through Hole
- Supplier Device Package:
- 8-PDIP
LT1243IN8#PBF FAQ
1.How can I place an order for LT1243IN8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1243IN8#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 LT1243IN8#PBF reliable?
The price and inventory of LT1243IN8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1243IN8#PBF is usually 5 days.
3.What payment methods are accepted for LT1243IN8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1243IN8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1243IN8#PBF?
LT1243IN8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1243IN8#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 LT1243IN8#PBF?
For technical support, including LT1243IN8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1243IN8#PBF requirements.
6.How does Aetrix verify that LT1243IN8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1243IN8#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 LT1243IN8#PBF meets industry standards.
7.What is the process for return or replacement of LT1243IN8#PBF?
All LT1243IN8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1243IN8#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 LT1243IN8#PBF part is unused and in its original packaging.
Return procedure for LT1243IN8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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