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Analog Devices Inc. LT1243IS8#TRPBF
- Part No.:
- LT1243IS8#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1243IS8#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,467
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Product details
Overview
LT1243IS8#TRPBF from Analog Devices is an 8-pin, current-mode PWM controller IC optimized for off-line and DC/DC converters. It features 1 A totem-pole output, <250 µA start-up current, 50 ns current sense delay, 100% maximum duty cycle, and operates up to 500 kHz switching frequency in applications such as AC-DC adapters and isolated flyback supplies.
For engineers reviewing the LT1243IS8#TRPBF datasheet, LT1243IS8#TRPBF pinout, LT1243IS8#TRPBF application, or LT1243IS8#TRPBF equivalent, key selection criteria include undervoltage lockout threshold (8.4 V start / 7.6 V min), oscillator trim accuracy (±5% over temp), active pull-down during UVLO, and compatibility with UC1843-based designs requiring high-speed current sensing and low quiescent operation.
Technical Context
The LT1243IS8#TRPBF implements fixed-frequency current-mode control with a trimmed 8.2 mA oscillator sink current and tightly specified oscillator frequency (e.g., 248 kHz typ at RT=13.0kΩ, CT=500 pF). Its error amplifier delivers 90 dB open-loop gain and 1 MHz unity-gain bandwidth, with internal 2.5 V reference tied to FB (Pin 2) and 5 V bandgap reference on VREF (Pin 8).
Current sensing uses leading-edge blanking (100 ns at VFB = 2.5 V), a 1 V clamp on ISENSE (Pin 3), and a 3× attenuation path from COMP (Pin 1) to set peak-current threshold. The output stage eliminates cross-conduction spikes and clamps high-level voltage to 18 V, enabling direct MOSFET gate drive without external level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Max Switching Frequency | 500 kHz - enables compact magnetics and high-efficiency power conversion in space-constrained off-line supplies |
| Start-Up Current | <250 µA - minimizes bleed resistor losses in high-voltage AC-DC start-up networks |
| UVLO Threshold | 8.4 V (start), 7.6 V (min), 0.4 V hysteresis - ensures reliable turn-on after bulk capacitor charging and prevents brownout oscillation |
| Output Drive Capability | ±1 A peak - directly drives large gate capacitance MOSFETs without external buffers in 65–100 W converters |
| Current Sense Delay | 50 ns - supports accurate cycle-by-cycle current limiting at high frequencies with minimal propagation lag |
| Reference Voltage Accuracy | ±1% (4.925–5.075 V at 1 mA) - provides stable feedback reference for ±2% output regulation in closed-loop systems |
| Oscillator Sink Current | 7.9–8.5 mA (trimmed) - enables precise, temperature-stable deadtime and duty cycle control via RT/CT network |
Pinout & Package
S8 package: 8-lead plastic SOIC, –40°C to 125°C operating junction temperature, θJA = 150°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| COMP (1) | Error amplifier output | Provides loop compensation node; sources 0.5 mA / sinks 2 mA; used to clamp current sense threshold below 1 V |
| FB (2) | Inverting input of error amplifier | Internally referenced to 2.5 V; accepts resistive divider feedback for output voltage regulation |
| ISENSE (3) | Current sense comparator input | Accepts sensed switch current; includes 100 ns blanking window and 1 V internal clamp |
| RT/CT (4) | Oscillator timing node | RC network sets frequency and deadtime; RT connects to VREF, CT to GND; discharge current trimmed to 8.2 mA |
| GND (5) | Analog ground reference | Common return for feedback, oscillator, and current sense paths; must be star-connected to minimize noise coupling |
| OUTPUT (6) | Totem-pole driver output | ±1 A capable; 18 V high-level clamp protects MOSFET gates; actively pulled low (~1 V) during UVLO |
| VCC (7) | Power supply input | Operates from 7.6 V to 25 V; powers internal bias circuitry; bypassed with ≥0.1 µF near pin |
| VREF (8) | 5 V bandgap reference output | Supplies RT charging current; powers internal logic; can source up to 20 mA for external circuitry |
Key Features
| Feature | Design Value |
|---|---|
| Leading-edge blanking | 100 ns fixed duration synchronized to OUTPUT turn-on, eliminating false triggering from transformer leakage spikes |
| Active UVLO pull-down | Darlington PNP pulls both OUTPUT and VREF to ~1 V during undervoltage, removing need for external gate pull-down resistors |
| Trimmed oscillator sink current | 8.2 mA ±0.3 mA ensures predictable deadtime and duty cycle across temperature and unit-to-unit variation |
| High-speed current sense path | 50 ns delay enables stable 500 kHz operation with fast overcurrent response and minimal minimum on-time limitation |
| 18 V output clamp | Prevents MOSFET gate oxide overstress in 12 V or 15 V gate-drive configurations without external Zener clamping |
Applications
| AC-DC Off-Line Adapters | Isolated Flyback Converters |
|---|---|
Use Scenario: 90–240 VAC input powering consumer electronics with tight size constraints and universal input compliance. IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode regulation, soft-start, and UVLO protection in discontinuous conduction mode (DCM) flyback topology. Use Value: <250 µA start-up current reduces standby losses; 100% duty cycle supports wide input range; 50 ns current sense delay enables accurate peak current limiting at full load. | Use Scenario: Isolated 12 V/1.5 A output for industrial sensors or IoT gateways requiring reinforced insulation and low EMI. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller driving a 600 V MOSFET in a transformer-isolated flyback, with slope compensation applied at ISENSE. Use Value: Trimmed oscillator sink current ensures consistent 300 kHz operation across units; active VREF pull-down enables reliable soft-start capacitor reset during brownout recovery. |
| DC-DC Boost Regulators | Industrial DC Power Supplies |
Use Scenario: 12 V to 24 V boost converter for battery-powered test equipment requiring high efficiency and fast transient response. IC Role / Device Role / Timing Role: High-speed current-mode modulator controlling external N-channel MOSFET and Schottky diode, with COMP used for loop compensation. Use Value: ±1 A output drive reduces gate charge time; 18 V output clamp avoids external gate protection; 90 dB error amplifier gain enables tight output regulation under dynamic load steps. | Use Scenario: 48 V input to 5 V/3 A regulated output in factory automation PLC modules with extended temperature requirements. IC Role / Device Role / Timing Role: Robust PWM controller operating from –40°C to 125°C junction, managing MOSFET gate drive, current limiting, and thermal-safe shutdown coordination. Use Value: S8 package rated for 125°C operation; 0.4 V UVLO hysteresis prevents chatter near brownout thresholds; 5 V reference stability (0.1 mV/°C) maintains feedback accuracy across temperature. |
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 | Higher start-up current (1 mA), no leading-edge blanking, no active UVLO pull-down, ±0.5 A output | Lacks integrated blanking and low-IQ start-up; requires external gate pull-down and noise filtering on ISENSE | Select when legacy design reuse is required and board layout allows added filtering components |
| UCC3803D | Lower max frequency (1 MHz oscillator → 500 kHz output), 200 µA start-up, 0.5 A output, no 18 V clamp | Requires external 15 V Zener for gate protection; lacks integrated blanking; different pinout (VREF not available) | Choose for TI ecosystem compatibility where VREF sourcing and blanking are handled externally |
Compared with UC1843N and UCC3803D, the LT1243IS8#TRPBF delivers superior noise immunity via built-in blanking, lower system-level BOM count due to active UVLO pull-down, and tighter oscillator tolerance-enabling higher power density and faster time-to-market in new off-line and DC/DC designs.
Availability
LT1243IS8#TRPBF is available at Aetrix Electronics and suitable for AC-DC adapters, isolated flyback converters, and industrial DC power supplies requiring stable component supply, long-term lifecycle support, and guaranteed traceability.
Supply support for LT1243IS8#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 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 power conversion where speed, low start-up current, and robust fault handling are critical.
FAQ
What is the UVLO behavior of the LT1243IS8#TRPBF?
The LT1243IS8#TRPBF features undervoltage lockout with 8.4 V start-up threshold and 7.6 V minimum operating voltage, providing 0.4 V hysteresis. During UVLO, both the OUTPUT (Pin 6) and VREF (Pin 8) pins are actively pulled low to ~1 V by internal Darlington PNP transistors. This eliminates the need for external pull-down resistors on the MOSFET gate or reference rail, simplifying design and improving reliability in brownout conditions. The LT1243IS8#TRPBF remains fully disabled until VCC exceeds the start threshold.
How does the LT1243IS8#TRPBF achieve 100% maximum duty cycle?
The LT1243IS8#TRPBF achieves 100% maximum duty cycle by configuring its oscillator to operate in a mode where the output is enabled for the entire oscillator charge period and disabled only during the controlled discharge phase. Unlike LT1241/LT1244/LT1245 variants limited to 50%, the LT1243IS8#TRPBF uses a different internal latch timing architecture that permits continuous conduction-critical for high-input-voltage, low-output-voltage flyback or forward converters. This behavior is confirmed in the Applications Information table on page 9 of the datasheet.
Can the LT1243IS8#TRPBF drive a 600 V MOSFET directly?
Yes, the LT1243IS8#TRPBF can directly drive a 600 V MOSFET's gate because its OUTPUT pin features an internal 18 V clamp that prevents gate-source overvoltage, even when powered from a 15 V or 12 V auxiliary supply. Its ±1 A peak output current ensures fast turn-on/turn-off of typical gate charges (e.g., ≤50 nC), and the 30–60 ns rise/fall times (CL = 1 nF) support efficient high-frequency switching. For layouts with long gate traces or high parasitic inductance, a Schottky clamp diode from OUTPUT to GND is recommended to suppress negative ringing.
What is the purpose of the blanking function on the ISENSE pin of the LT1243IS8#TRPBF?
The blanking function on the ISENSE pin of the LT1243IS8#TRPBF disables the current sense comparator for 100 ns after each OUTPUT turn-on event, preventing false triggering from leading-edge current spikes caused by transformer interwinding capacitance and diode reverse recovery. This eliminates the need for external RC filters on the current sense path, preserving loop bandwidth and minimizing minimum pulse width-key for stable operation under light loads or short-circuit conditions. Blanking time scales with FB voltage, dropping to zero during start-up or fault conditions for fastest possible overcurrent response.
How is the oscillator frequency set on the LT1243IS8#TRPBF?
The oscillator frequency of the LT1243IS8#TRPBF is set using an external RT resistor from VREF (Pin 8) to RT/CT (Pin 4) and a CT capacitor from RT/CT (Pin 4) to GND. Charging current is supplied by VREF through RT; discharge current is provided by a trimmed 8.2 mA internal sink. Frequency depends on both RC values and the discharge current-for example, RT = 13.0 kΩ and CT = 500 pF yields 248 kHz (typ). The LT1243IS8#TRPBF datasheet provides curves and formulas (pages 9–10) to calculate exact fOSC and deadtime for any combination.
LT1243IS8#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:
- -40°C ~ 100°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1243IS8#TRPBF FAQ
1.How can I place an order for LT1243IS8#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1243IS8#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 LT1243IS8#TRPBF reliable?
The price and inventory of LT1243IS8#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1243IS8#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1243IS8#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1243IS8#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1243IS8#TRPBF?
LT1243IS8#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1243IS8#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 LT1243IS8#TRPBF?
For technical support, including LT1243IS8#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1243IS8#TRPBF requirements.
6.How does Aetrix verify that LT1243IS8#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1243IS8#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 LT1243IS8#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1243IS8#TRPBF?
All LT1243IS8#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1243IS8#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 LT1243IS8#TRPBF part is unused and in its original packaging.
Return procedure for LT1243IS8#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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