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Analog Devices Inc. LT1247CS8#PBF
- Part No.:
- LT1247CS8#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1247CS8#PBF.pdf
- Description:
- IC REG CTRLR BUCK 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,356
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Product details
Overview
LT1247CS8#PBF from Analog Devices (formerly Linear Technology) is an 8-pin SOIC current-mode PWM controller IC designed for off-line and DC/DC converter applications. It features 1 MHz switching capability, 30 ns current sense delay, <250 µA start-up current, 1 A totem-pole output, and active pull-down during undervoltage lockout. It operates in fixed-frequency current-mode control with leading-edge blanking and is optimized for driving power MOSFETs in flyback and forward converters.
For engineers reviewing the LT1247CS8#PBF datasheet, LT1247CS8#PBF pinout, LT1247CS8#PBF application, or LT1247CS8#PBF equivalent, key selection criteria include UVLO thresholds (8.4 V start-up / 7.6 V operating), oscillator sink current (8.2 mA typ.), reference accuracy (±1% over temperature), current sense gain (3.00 V/V), and 100% maximum duty cycle - all critical for stable high-frequency SMPS design.
Technical Context
The LT1247CS8#PBF implements a fixed-frequency current-mode architecture with a trimmed oscillator (500 kHz typical at RT=6.2 kΩ, CT=500 pF) and tightly specified sink current (7.9–8.5 mA). Its error amplifier delivers 90 dB open-loop gain and 2 MHz unity-gain bandwidth, with internal 2.5 V feedback reference derived from the 5 V bandgap.
Current sensing uses a proportional comparator with 1 V clamp and 60 ns blanking time (at VFB = 2.5 V), eliminating external filtering. The totem-pole output provides ±1 A drive with 30 ns rise/20 ns fall times into 1 nF, and clamps high-level output at 18 V to protect MOSFET gates.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Operating Frequency | Up to 1 MHz; set by external RT/CT network with trimmed oscillator sink current for tight frequency stability. |
| UVLO Start Threshold | 8.4 V (typ); ensures reliable startup only after sufficient VCC rail stabilization in off-line designs. |
| Reference Voltage | 5.000 V ±1% (4.925–5.075 V); supplies timing resistor bias and internal reference levels with 50 µV RMS noise. |
| Current Sense Gain | 3.00 V/V (2.85–3.15 V/V); defines peak current threshold scaling from error amp output to ISENSE pin. |
| Output Drive Capability | ±1 A peak; enables direct gate drive of medium-power MOSFETs without external buffers in 1 MHz converters. |
| Start-Up Current | 250 µA max; minimizes power loss in high-impedance VCC startup networks for universal-input AC/DC supplies. |
| Current Sense Delay | 30 ns; enables fast fault response while maintaining stability under high di/dt conditions. |
Pinout & Package
LT1247CS8#PBF is housed in an 8-lead plastic SOIC (S8) package with standard SOIC-8 footprint (5.0 mm × 6.2 mm, 1.27 mm pitch), θJA = 150°C/W, rated for 0°C to 100°C junction temperature.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Provides loop compensation node; sources ≥0.5 mA / sinks ≥2 mA; used to clamp current sense threshold. |
| 2 - FB | Inverting input of error amplifier | Internally referenced to 2.5 V; accepts feedback voltage divider for output regulation. |
| 3 - ISENSE | Current sense comparator input | Receives sensed switch current; trip point proportional to COMP voltage with 1 V clamp and 60 ns blanking. |
| 4 - RT/CT | Oscillator timing node | Charged via RT from VREF; discharged by internal 8.2 mA sink; sets frequency and deadtime. |
| 5 - GND | Analog and power ground | Single-point return for feedback, oscillator, and output drive paths to minimize noise coupling. |
| 6 - OUTPUT | Totem-pole gate driver output | ±1 A capable; clamped to ≤18 V; actively pulled low (~1 V) during UVLO to hold MOSFET off. |
| 7 - VCC | Supply input | Operates from 7.6 V to 25 V; includes UVLO with 0.8 V hysteresis; powers internal circuitry. |
| 8 - VREF | 5 V bandgap reference output | Supplies RT bias current; powers internal logic; can source up to 20 mA for external circuitry. |
Key Features
| Feature | Design Value |
|---|---|
| Leading-edge blanking | 60 ns fixed blanking window (at VFB = 2.5 V) eliminates need for external RC filter on ISENSE, reducing current-sense loop delay. |
| Trimmed oscillator sink current | 8.2 mA (7.9–8.5 mA) enables precise, temperature-stable frequency setting independent of VCC variations. |
| Active UVLO pull-down | Darlington PNP pulls both OUTPUT and VREF low to ~1 V during undervoltage, removing need for external gate pull-down resistors. |
| 100% maximum duty cycle | Enables zero-voltage-switching topologies and high step-down ratios without duty-cycle limiting artifacts. |
| 1 A totem-pole output | Drives MOSFET gates directly at 1 MHz with 30 ns rise/20 ns fall into 1 nF, minimizing external component count. |
Applications
| AC/DC Flyback Adapter | Isolated DC/DC Converter |
|---|---|
|
Use Scenario: Universal-input (85–265 VAC) 12 W adapter powering IoT sensors with tight no-load consumption requirements. IC Role / Device Role / Timing Role: Primary-side current-mode PWM controller regulating output via optocoupler feedback; sets 500 kHz switching frequency and controls MOSFET gate drive timing. Use Value: 250 µA start-up current minimizes standby losses; 30 ns current sense delay enables accurate peak-current limiting during line transients. |
Use Scenario: Industrial 24 V to 5 V isolated DC/DC module requiring high reliability and EMI robustness in motor drive systems. IC Role / Device Role / Timing Role: Secondary-side synchronous rectifier controller with current-mode feedback; manages gate timing for primary MOSFET and secondary SR FET. Use Value: 18 V output clamp protects MOSFET gate oxide; active VREF pull-down ensures clean soft-start reset during brownout recovery. |
| Offline LED Driver | High-Frequency Forward Converter |
|
Use Scenario: Dimmable constant-current LED driver for commercial lighting, operating from 120/230 VAC with TRIAC dimmer compatibility. IC Role / Device Role / Timing Role: Primary-side PWM modulator implementing valley-switching control; senses primary current to regulate LED current without secondary sensing. Use Value: Leading-edge blanking suppresses diode reverse-recovery noise; 100% duty cycle supports deep dimming at low line voltages. |
Use Scenario: 48 V input telecom DC/DC brick delivering 12 V/20 A with >92% efficiency and fast transient response. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller managing transformer reset and synchronous rectification timing in forward topology. Use Value: Trimmed 500 kHz oscillator enables compact magnetics; 2 MHz error amp bandwidth supports tight load regulation under dynamic current steps. |
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 UVLO (8.5 V start / 7.6 V op), but no leading-edge blanking, no trimmed oscillator sink, ±0.5 A output. | Lacks integrated blanking and precision oscillator; requires external filter and tighter RT/CT tolerance for same frequency stability. | Choose UC1843N8 only if legacy compatibility or cost sensitivity outweighs need for 1 MHz operation and noise immunity. |
| UCC3803D | Lower start-up current (100 µA), 1 A output, but 500 kHz max frequency, no 18 V output clamp, different pinout. | Not pin-compatible; lacks output clamp and blanking; limited to lower-frequency designs where gate protection is handled externally. | Select UCC3803D when ultra-low start-up power is critical and 1 MHz operation is unnecessary; verify PCB layout changes required. |
Compared with UC1843N8 and UCC3803D, the LT1247CS8#PBF delivers superior high-frequency stability via trimmed oscillator sink current, eliminates external current-sense filtering through integrated blanking, and ensures MOSFET gate safety with its 18 V output clamp - making it optimal for compact, noise-sensitive 500 kHz–1 MHz SMPS designs.
Availability
LT1247CS8#PBF is available at Aetrix Electronics and suitable for AC/DC adapters, isolated DC/DC modules, offline LED drivers, and high-frequency forward converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LT1247CS8#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT1247CS8#PBF belongs to Linear's legacy current-mode PWM controller product line, specifically engineered for high-efficiency, high-frequency switched-mode power supplies where precision timing, low start-up current, and robust noise immunity are essential.
FAQ
What is the UVLO behavior of the LT1247CS8#PBF?
The LT1247CS8#PBF features undervoltage lockout with a typical start-up threshold of 8.4 V and minimum operating voltage of 7.6 V, plus 0.8 V hysteresis. During UVLO, both the OUTPUT and VREF pins are actively pulled low to approximately 1 V by internal Darlington PNP transistors - eliminating the need for external pull-down resistors and ensuring safe MOSFET gate discharge. This behavior is fully specified in the Electrical Characteristics table and confirmed across temperature.
How does the LT1247CS8#PBF implement leading-edge blanking?
The LT1247CS8#PBF integrates a fixed-duration blanking circuit that disables the current sense comparator output for 60 ns after each OUTPUT turn-on edge (at nominal VFB = 2.5 V). Blanking time scales linearly with VFB voltage and drops to zero at 0 V, enabling faster fault response during short-circuit events. This eliminates the need for external RC filters on the ISENSE pin, preserving current-loop bandwidth and reducing component count - a key differentiator versus UC1843.
Can the LT1247CS8#PBF drive a MOSFET directly without a gate driver?
Yes, the LT1247CS8#PBF provides a ±1 A totem-pole output stage with 30 ns rise and 20 ns fall times into a 1 nF load, enabling direct gate drive of medium-power MOSFETs (e.g., ≤5 nC gate charge) in 500 kHz–1 MHz converters. Its 18 V output clamp protects against gate overvoltage, and active pull-down during UVLO ensures fail-safe gate discharge - verified in Typical Performance Characteristics TPC20–TPC22.
What is the purpose of the COMP pin on the LT1247CS8#PBF?
The COMP pin on the LT1247CS8#PBF is the error amplifier output, made accessible for external loop compensation (e.g., Type II or III networks). It sources ≥0.5 mA and sinks ≥2 mA, and is used to adjust the current sense clamp voltage: clamping COMP below 4.4 V reduces the maximum ISENSE threshold below 1 V, allowing precise control of peak switch current and sense resistor power dissipation - detailed in Applications Information section "Adjustable Clamp Level with Soft Start".
How does the oscillator frequency depend on RT and CT in the LT1247CS8#PBF?
Oscillator frequency in the LT1247CS8#PBF is set by RT (connected from VREF to RT/CT) and CT (from RT/CT to GND). Charging current is determined by RT; discharging current is trimmed to 8.2 mA. Frequency formulas are provided in the datasheet: tr = 0.583·R·C, td = R·C·(3.46 − 0.0164/R − 11.73/C), f = 1/(tr + td). At RT = 6.2 kΩ and CT = 500 pF, typical frequency is 500 kHz with ±5% accuracy - validated in TPC19 and Electrical Characteristics tables.
LT1247CS8#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
- 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:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1247CS8#PBF FAQ
1.How can I place an order for LT1247CS8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1247CS8#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 LT1247CS8#PBF reliable?
The price and inventory of LT1247CS8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1247CS8#PBF is usually 5 days.
3.What payment methods are accepted for LT1247CS8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1247CS8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1247CS8#PBF?
LT1247CS8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1247CS8#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 LT1247CS8#PBF?
For technical support, including LT1247CS8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1247CS8#PBF requirements.
6.How does Aetrix verify that LT1247CS8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1247CS8#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 LT1247CS8#PBF meets industry standards.
7.What is the process for return or replacement of LT1247CS8#PBF?
All LT1247CS8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1247CS8#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 LT1247CS8#PBF part is unused and in its original packaging.
Return procedure for LT1247CS8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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