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Analog Devices Inc. LT1243CS8#TRPBF
- Part No.:
- LT1243CS8#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1243CS8#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,623
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Product details
Overview
LT1243CS8#TRPBF from Analog Devices is an 8-pin, fixed-frequency, current-mode PWM controller IC optimized for off-line and DC/DC converters. It delivers 1A totem-pole output drive, supports up to 500kHz switching frequency, features 50ns current sense delay with leading-edge blanking, and operates with start-up current <250µA. It serves as a high-speed, low-quiescent-current replacement for UC1843 in flyback and forward converter control circuits.
For engineers reviewing the LT1243CS8#TRPBF datasheet, LT1243CS8#TRPBF pinout, LT1243CS8#TRPBF application, or LT1243CS8#TRPBF equivalent, key selection criteria include its 8.4V undervoltage lockout threshold, 100% maximum duty cycle capability, active pull-down during UVLO, and tight oscillator sink current trim (8.2mA typ) - all critical for stable high-frequency power supply design.
Technical Context
The LT1243CS8#TRPBF implements a fixed-frequency current-mode control architecture where the oscillator sets both switching frequency and deadtime via external RT/CT components, with trimmed 8.2mA discharge current ensuring ±5% frequency accuracy. Its error amplifier (90dB DC gain, 1MHz unity-gain bandwidth) feeds a scaled version of its output into the current sense comparator, enabling cycle-by-cycle peak current limiting.
Unlike voltage-mode controllers, it uses real-time inductor current feedback to directly regulate switch conduction time. The built-in 100ns blanking window (voltage-dependent, zero at VFB = 0V) suppresses noise-induced false triggering during MOSFET turn-on transients, eliminating need for external RC filters while preserving fast fault response.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Max Output Frequency | 500kHz - enables compact magnetics and high-power-density SMPS designs without requiring external clock division. |
| UVLO Start Threshold | 8.4V - ensures reliable startup after bulk capacitor charges above brownout level in universal-input AC/DC supplies. |
| Max Duty Cycle | 100% - supports forward and push-pull topologies requiring full-on conduction without deadtime limitation. |
| Output Drive Capability | ±1A - directly drives large gate capacitance MOSFETs (e.g., >2nF) without external buffers, reducing BOM count. |
| Current Sense Delay | 50ns - minimizes minimum on-time limitation, critical for high-frequency operation with low-duty-cycle requirements. |
| Oscillator Sink Current | 8.2mA (typ) - tightly trimmed parameter enabling precise, temperature-stable deadtime and frequency setting with RT/CT network. |
| Start-Up Current | <250µA - reduces power loss in high-impedance start-up resistors, improving light-load efficiency in offline converters. |
Pinout & Package
S8 package: 8-lead plastic SOIC, surface-mount, 1.27mm pitch, JEDEC MS-012AC compliant, rated for –40°C to 100°C operating junction temperature.
| 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 below 1V. |
| 2 - FB | Inverting input of error amplifier | Receives voltage feedback via resistor divider; internally referenced to 2.5V; blanking time varies with voltage here (100ns at 2.5V). |
| 3 - ISENSE | Current sense comparator input | Detects MOSFET source current via sense resistor; trip threshold proportional to COMP voltage; clamped at 1V max. |
| 4 - RT/CT | Oscillator timing node | Connects external RT (to VREF) and CT (to GND); sets frequency and deadtime; oscillator ramp rises at ~0.583·RT·CT rate. |
| 5 - GND | Analog and power ground reference | Single-point return for feedback, oscillator, and current sense paths; layout separation from high-di/dt traces is mandatory. |
| 6 - OUTPUT | High-current totem-pole driver | Drives MOSFET gate directly; clamped to ≤18V; actively pulled low (~1V) during UVLO; rise/fall times ≤80/60ns @ 1nF. |
| 7 - VCC | Positive supply input | Operates from 7.6V to 25V; powers internal bias, reference, and logic; requires local 0.1µF bypass near pin. |
| 8 - VREF | 5V bandgap reference output | Stable 5.000V ±1% output; supplies RT charging current; powers internal circuitry; can source up to 20mA. |
Key Features
| Feature | Design Value |
|---|---|
| Leading-edge blanking | 100ns fixed blanking window (at VFB = 2.5V), dynamically reduced during startup/short-circuit to preserve fast fault response. |
| Active UVLO pull-down | Both OUTPUT and VREF pins actively pulled low (~1V) during undervoltage lockout, eliminating need for external gate pull-down resistors. |
| Trimmed oscillator sink current | 8.2mA ±0.3mA tolerance ensures predictable deadtime and frequency across temperature and unit-to-unit variation. |
| 1A totem-pole output stage | Capable of ±1A transient drive into capacitive loads; eliminates external driver stages in medium-power applications (≤150W). |
| Low start-up current | 170µA typical start-up current minimizes bleed resistor losses in high-voltage offline supplies, improving no-load efficiency. |
Applications
| Universal Input AC/DC Adapters | Industrial DC/DC Converters |
|---|---|
Use Scenario: 90–264VAC input, 12V/3A isolated flyback supply for industrial HMIs. 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: 8.4V UVLO start threshold ensures robust startup after rectified bulk capacitor reaches ~12V; 100% duty cycle supports wide input range regulation without auxiliary winding dependency. | Use Scenario: 24V–48V DC input, 5V/10A non-isolated buck-derived converter for PLC I/O modules. IC Role / Device Role / Timing Role: Current-mode controller driving synchronous MOSFET pair; senses high-side current via Rsense at ISENSE pin. Use Value: 50ns current sense delay enables stable operation at 350kHz with <100ns minimum on-time; active OUTPUT pull-down prevents shoot-through during brownout recovery. |
| Telecom Power Supplies | LED Driver Controllers |
Use Scenario: -48V telecom rectifier with 3.3V/20A output using forward topology. IC Role / Device Role / Timing Role: Primary-side controller managing duty cycle and current limit; synchronized to system clock via RT/CT node. Use Value: Trimmed 8.2mA oscillator sink current allows precise deadtime control to prevent transformer saturation; 1A output drives dual-gate MOSFETs without buffering. | Use Scenario: Constant-current LED driver for street lighting with analog dimming interface. IC Role / Device Role / Timing Role: PWM modulator regulating LED string current via sense resistor; FB pin biased by dimming voltage for adjustable setpoint. Use Value: COMP pin clamping enables programmable current limit (0–1A range); blanking suppression prevents false overcurrent trips during PWM dimming transitions. |
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 start-up current (1mA), no leading-edge blanking, 16V output clamp, ±0.5A drive | Lacks integrated blanking and active UVLO pull-down; requires external blanking RC and gate pull-down resistor | Choose UC3843N only if legacy compatibility or cost sensitivity outweighs performance gains in noise immunity and startup efficiency. |
| UCC2802DR | Fixed 1MHz oscillator, no RT/CT programming, 500mA output, 7.6V UVLO start, no active VREF pull-down | Designed for lower-power applications; lacks programmable frequency and full 100% duty cycle support | Select UCC2802DR when board space is constrained and fixed-frequency operation suffices; avoid for variable-frequency or high-duty-cycle designs. |
Compared with UC3843N and UCC2802DR, the LT1243CS8#TRPBF provides superior noise immunity via blanking, lower start-up loss, higher drive strength, and tighter oscillator control - making it optimal for high-reliability, high-frequency, and universal-input power supplies where stability under transient conditions is critical.
Availability
LT1243CS8#TRPBF is available at Aetrix Electronics and suitable for universal-input AC/DC adapters, industrial DC/DC converters, and telecom power supplies requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.
Supply support for LT1243CS8#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 power management semiconductors.
The LT1243CS8#TRPBF belongs to the LT124x series of current-mode PWM controllers, designed specifically for high-efficiency, high-reliability off-line and isolated DC/DC power conversion with emphasis on noise immunity, startup efficiency, and gate drive capability.
FAQ
What is the undervoltage lockout behavior of the LT1243CS8#TRPBF?
The LT1243CS8#TRPBF features an undervoltage lockout (UVLO) with 8.4V start threshold and 7.6V minimum operating voltage, providing 0.8V hysteresis. During UVLO, both the OUTPUT (Pin 6) and VREF (Pin 8) pins are actively pulled low to ~1V by internal Darlington PNP transistors - eliminating need for external pull-down resistors and ensuring safe MOSFET gate state during brownout conditions. This behavior is confirmed in the Absolute Maximum Ratings and Electrical Characteristics tables of the official LT1241 Series datasheet.
Can the LT1243CS8#TRPBF be used in a 100% duty cycle application?
Yes, the LT1243CS8#TRPBF supports 100% maximum duty cycle, unlike the LT1241/LT1244/LT1245 variants limited to 46–48%. This is explicitly stated in the Applications Information table (page 9) and enables use in forward, push-pull, and other topologies requiring continuous conduction. The 100% capability arises from its oscillator architecture, which disables deadtime enforcement for this variant - verified across oscillator timing equations and typical performance curves in the datasheet.
How does the current sense blanking function in the LT1243CS8#TRPBF?
The LT1243CS8#TRPBF incorporates a voltage-dependent blanking circuit at the ISENSE comparator output, with nominal duration of 100ns when FB pin voltage is at 2.5V. Blanking time scales linearly down to zero as FB voltage drops to 0V - ensuring minimal delay during startup and short-circuit events. This feature suppresses leading-edge spikes from transformer leakage and diode reverse recovery, eliminating need for external RC filters while maintaining fast fault response - detailed in the Applications Information section (page 11) and TPC24 waveform data.
What is the purpose of the COMP pin on the LT1243CS8#TRPBF?
The COMP pin (Pin 1) on the LT1243CS8#TRPBF is the error amplifier output, made available for external loop compensation and current limit adjustment. It sources ≥0.5mA and sinks ≥2mA, and is used to scale the current sense threshold - clamping COMP below 4.4V reduces the maximum ISENSE trip voltage below 1V, enabling programmable peak current limiting. This functionality is documented in the Pin Functions section (page 8) and Applications Information (page 10), where equations define the relationship between COMP voltage and current sense threshold.
Does the LT1243CS8#TRPBF require an external oscillator capacitor?
Yes, the LT1243CS8#TRPBF requires an external capacitor (CT) connected from RT/CT (Pin 4) to GND, along with a timing resistor (RT) from VREF (Pin 8) to RT/CT, to set oscillator frequency and deadtime. The oscillator is not crystal-based or internal-only; its frequency is programmable via the RT/CT network - confirmed in the Block Diagram, Pin Configuration, and Oscillator section (pages 1, 2, and 9). Typical values include RT = 13.0kΩ and CT = 500pF for 248kHz operation.
LT1243CS8#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):
- 96%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1243CS8#TRPBF FAQ
1.How can I place an order for LT1243CS8#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1243CS8#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 LT1243CS8#TRPBF reliable?
The price and inventory of LT1243CS8#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1243CS8#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1243CS8#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1243CS8#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1243CS8#TRPBF?
LT1243CS8#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1243CS8#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 LT1243CS8#TRPBF?
For technical support, including LT1243CS8#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1243CS8#TRPBF requirements.
6.How does Aetrix verify that LT1243CS8#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1243CS8#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 LT1243CS8#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1243CS8#TRPBF?
All LT1243CS8#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1243CS8#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 LT1243CS8#TRPBF part is unused and in its original packaging.
Return procedure for LT1243CS8#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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