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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Power Supply Controllers, Monitors

Texas Instruments UC3843AD8G4

Name: UC3843AD8G4
Brand: Texas Instruments
SKU: UC3843AD8G4
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: UC3843AD8G4

Manufacturer:: Texas Instruments

Category:: Power Supply Controllers, Monitors

Package:: 8-SOIC (0.154", 3.90mm Width)

Datasheet:: UC3843AD8G4.pdf

Description:: IC REG CTRLR MULT TOPOLOGY 8SOIC

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Product details

Overview

UC3843AD8G4 from Texas Instruments is a fixed-frequency current-mode PWM controller IC designed for DC-DC converter applications, featuring 8.4 V turn-on/7.6 V turn-off UVLO thresholds, up to 500 kHz switching frequency, 100% maximum duty cycle, and ±1 A peak totem-pole output drive capability. It operates across 0°C to 70°C and targets regulated-input isolated/non-isolated switch-mode power supplies.

For engineers reviewing the UC3843AD8G4 datasheet, UC3843AD8G4 pinout, UC3843AD8G4 application, or UC3843AD8G4 equivalent, key selection criteria include its low-startup-current (<1 mA), pulse-by-pulse current limiting, internal 5-V reference with ±2% tolerance, and compatibility with N-channel MOSFET gate driving in voltage-mode or current-mode topologies.

Technical Context

The UC3843AD8G4 implements a current-mode control architecture with an integrated PWM comparator, error amplifier, oscillator (RT/CT-based), undervoltage lockout with hysteresis, and latched logic for stable operation. Its oscillator supports precise frequency setting via external R_RT and C_CT, and its high-current totem-pole output directly drives N-MOSFET gates without external buffers.

Unlike UC3844/UC3845 variants, UC3843AD8G4 lacks internal toggle flip-flop logic-enabling full 0–100% duty cycle operation-and uses a dedicated GROUND pin (not split PWRGND/ANALOG GND) in its 8-pin SOIC package. Its UVLO thresholds (8.4 V ON / 7.6 V OFF) are optimized for regulated DC input rails rather than off-line AC-derived supplies.

Key Specifications

Parameter	Value and Actual Design Meaning
Operating Temp Range	0°C to 70°C - suitable for commercial-grade DC-DC power supplies, not extended industrial or automotive environments
UVLO Thresholds	8.4 V turn-on / 7.6 V turn-off - enables reliable startup and shutdown on stable DC bus voltages like 12 V or 24 V systems
Max Switching Frequency	500 kHz - supports compact magnetics and high-power-density designs while maintaining controllable gate drive timing
Output Drive Capability	±1 A peak sink/source - directly drives medium-size N-channel MOSFETs without external drivers or level shifters
Reference Voltage	5.0 V ±2% - provides stable bias for oscillator timing and error amplifier feedback, reducing need for external references
Duty Cycle Range	0–100% - supports forward, flyback, push-pull, and half-bridge topologies requiring full-range PWM control
Start-up Current	<1 mA - minimizes auxiliary supply burden during initial power-up, easing design of low-power bias networks

Pinout & Package

UC3843AD8G4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with GND, VCC, VREF, RT/CT, ISENSE, VFB, COMP, and OUTPUT terminals arranged per JEDEC MS-012 standard.

Pin/Terminal	Circuit Role	Design Meaning
1 - COMP	Error amplifier output	Open-collector node with internal current limit; externally compensated to stabilize voltage loop and command zero duty cycle when pulled to GND
2 - VFB	Inverting error amp input	Receives feedback signal from output divider; sets regulation point at 2.5 V threshold, enabling precise output voltage control
3 - ISENSE	Current sense input	Terminates PWM pulse when sensed voltage reaches ~1 V; supports slope compensation and voltage-mode operation via injected ramp
4 - RT/CT	Oscillator timing node	Accepts external R_RT (to VREF) and C_CT (to GND); sets f_SW = 1.72/(R_RT×C_CT) with typical range 100 kHz–500 kHz
5 - GROUND	Analog & power return	Single-reference ground for all analog circuits and output stage; requires low-impedance PCB connection to minimize noise coupling
6 - OUTPUT	MOSFET gate driver	Totem-pole output sourcing/sinking up to 1 A peak; actively held low during UVLO; compatible with standard N-MOSFET gate capacitances
7 - VCC	Supply input	Bias rail accepting 12–28 V; includes internal 34 V clamp; average current depends on f_SW and MOSFET Q_g (I_OUT = Q_g × f_SW)
8 - VREF	5-V reference output	Stable 5 V ±2% source for RT/CT charging and external circuitry; requires ≥0.1 µF ceramic bypass directly at pin

Key Features

Feature	Design Value
Automatic feedforward compensation	Compensates for input voltage variations in real time, improving transient response without additional external components
Pulse-by-pulse current limiting	Prevents MOSFET overcurrent on every switching cycle using ISENSE threshold detection, enabling robust short-circuit protection
Enhanced load-response characteristics	Combines fast error amplifier (1 MHz GBW) and low-output-impedance COMP stage to reduce output voltage deviation under step-load changes
Internally trimmed bandgap reference	Delivers 5.0 V ±2% accuracy over temperature and line, eliminating need for external trimming or calibration in most applications
Double-pulse suppression	Latched PWM logic prevents multiple output pulses per clock cycle, ensuring clean single-pulse gating and avoiding shoot-through risk

Applications

Isolated DC-DC Converter	Non-Isolated Buck Regulator
Use Scenario: 24 V input to 5 V/3 A isolated flyback supply for industrial I/O modules. IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode feedback, providing gate drive timing and cycle-by-cycle current limiting. Use Value: Enables stable regulation under variable load and input conditions using only one optocoupler and minimal compensation components.	Use Scenario: 12 V automotive subsystem supply stepping down to 3.3 V for microcontroller domain. IC Role / Device Role / Timing Role: Fixed-frequency current-mode buck controller managing MOSFET switching, sensing inductor current, and regulating output voltage. Use Value: Delivers tight output regulation (±1%) and fast transient recovery (<50 µs) due to high-bandwidth error amplifier and low-latency current sensing.
AC-DC Adapter Auxiliary Supply	LED Driver Constant-Current Source
Use Scenario: Standby 5 V/0.5 A auxiliary winding supply in 65 W laptop adapter. IC Role / Device Role / Timing Role: Secondary-side controller regulating auxiliary output via opto-feedback, operating in discontinuous conduction mode. Use Value: Maintains regulation across wide input voltage swings (90–264 VAC rectified) using UVLO hysteresis and low start-up current.	Use Scenario: 24 V input constant-current LED driver delivering 350 mA to 12 V string in signage application. IC Role / Device Role / Timing Role: Current-mode PWM controller sensing LED string current via shunt resistor and modulating MOSFET duty cycle. Use Value: Achieves <±3% current accuracy over temperature using internal 1 V ISENSE threshold and stable 5 V reference for sensing amplifier bias.

Isolated DC-DC Converter

Non-Isolated Buck Regulator

Use Scenario: 24 V input to 5 V/3 A isolated flyback supply for industrial I/O modules.

IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode feedback, providing gate drive timing and cycle-by-cycle current limiting.

Use Value: Enables stable regulation under variable load and input conditions using only one optocoupler and minimal compensation components.

Use Scenario: 12 V automotive subsystem supply stepping down to 3.3 V for microcontroller domain.

IC Role / Device Role / Timing Role: Fixed-frequency current-mode buck controller managing MOSFET switching, sensing inductor current, and regulating output voltage.

Use Value: Delivers tight output regulation (±1%) and fast transient recovery (<50 µs) due to high-bandwidth error amplifier and low-latency current sensing.

AC-DC Adapter Auxiliary Supply

LED Driver Constant-Current Source

Use Scenario: Standby 5 V/0.5 A auxiliary winding supply in 65 W laptop adapter.

IC Role / Device Role / Timing Role: Secondary-side controller regulating auxiliary output via opto-feedback, operating in discontinuous conduction mode.

Use Value: Maintains regulation across wide input voltage swings (90–264 VAC rectified) using UVLO hysteresis and low start-up current.

Use Scenario: 24 V input constant-current LED driver delivering 350 mA to 12 V string in signage application.

IC Role / Device Role / Timing Role: Current-mode PWM controller sensing LED string current via shunt resistor and modulating MOSFET duty cycle.

Use Value: Achieves <±3% current accuracy over temperature using internal 1 V ISENSE threshold and stable 5 V reference for sensing amplifier bias.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PWM controller applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
UC3843D8	Same pinout, identical electrical specs, but rated for 0°C to 70°C and packaged in standard SOIC (no G4 suffix indicating tape-and-reel or green compliance)	No functional difference; used in same DC-DC topologies but may lack RoHS/lead-free certification required for new designs	Select UC3843AD8G4 when lead-free compliance and guaranteed green material content are mandatory per IPC-1752A.
TL494CN	Dual-output, fixed-frequency voltage-mode controller with 50% max duty cycle per channel, no integrated current sense comparator or UVLO hysteresis	Suitable for push-pull or dual-MOSFET topologies where independent channel control is needed, but requires external current sensing and startup circuitry	Choose TL494CN only when dual-output timing or adjustable dead time is required; otherwise UC3843AD8G4 offers simpler current-mode implementation with fewer external parts.

Compared with UC3843D8, UC3843AD8G4 adds RoHS-compliant packaging and traceability; compared with TL494CN, it delivers integrated current-mode control, lower component count, and superior transient response in single-switch DC-DC converters.

Availability

UC3843AD8G4 is available at Aetrix Electronics and suitable for isolated flyback converters, non-isolated buck regulators, AC-DC auxiliary supplies, and LED constant-current drivers requiring stable component supply across production lifecycles.

Supply support for UC3843AD8G4 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

Texas Instruments is a global semiconductor company specializing in analog and embedded processing technologies, with leadership in power management ICs and industrial-grade controllers.

The UC384x product line was designed specifically for cost-sensitive, high-reliability DC-DC and off-line power supply applications requiring minimal external components and robust current-mode control.

FAQ

What is the UVLO behavior of UC3843AD8G4?

The UC3843AD8G4 features undervoltage lockout with 8.4 V turn-on and 7.6 V turn-off thresholds and built-in hysteresis. This ensures clean startup and shutdown on regulated DC inputs such as 12 V or 24 V rails. During UVLO, the OUTPUT pin is actively held low to prevent unintended MOSFET conduction. The UC3843AD8G4's hysteresis avoids oscillatory behavior near threshold and improves noise immunity in noisy power environments.

Can UC3843AD8G4 drive a MOSFET directly?

Yes, UC3843AD8G4 integrates a high-current totem-pole output stage capable of sourcing and sinking up to 1 A peak current, enabling direct gate drive of medium-size N-channel MOSFETs. Its OUTPUT pin is designed for low-impedance switching and includes active pull-down during UVLO. For optimal performance, use a gate resistor (typically 10–100 Ω) and ensure proper PCB layout with short, low-inductance paths to minimize ringing and EMI.

How is switching frequency set on UC3843AD8G4?

Switching frequency on UC3843AD8G4 is set using external components on the RT/CT pin: a resistor (R_RT) from VREF to RT/CT and a capacitor (C_CT) from RT/CT to GROUND. The oscillator frequency follows f_OSC = 1.72 / (R_RT × C_CT). For example, R_RT = 10 kΩ and C_CT = 3.3 nF yields ~500 kHz. UC3843AD8G4's OUTPUT frequency equals f_OSC, supporting up to 100% duty cycle without internal division.

What is the role of the COMP pin on UC3843AD8G4?

The COMP pin on UC3843AD8G4 is the open-collector output of the internal error amplifier, internally current-limited to ~6 mA sink capability. It serves as the control node for the voltage feedback loop: external RC compensation networks connect here to shape loop stability. Pulling COMP to GROUND forces zero duty cycle, enabling soft-start or fault shutdown. Its low output impedance and 1 MHz unity-gain bandwidth allow precise regulation in dynamic load conditions.

Does UC3843AD8G4 support voltage-mode control?

Yes, UC3843AD8G4 supports voltage-mode control by applying a sawtooth ramp signal to the ISENSE pin, overriding its default current-sense function. This allows traditional voltage-mode PWM operation while retaining the IC's oscillator, error amplifier, and output driver. The internal current-sense comparator gain remains ~3 V/V, so ramp amplitude must be scaled accordingly. This flexibility makes UC3843AD8G4 usable in both current-mode and voltage-mode topologies without hardware change.

UC3843AD8G4 Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: UCx84xA

Package/Case:: 8-SOIC (0.154", 3.90mm Width)

Packaging:: Tube

Product Status:: Obsolete

Programmable:: -

Applications:: PWM Controller

Voltage - Input:: -0.3V ~ 6.3V

Voltage - Supply:: 7.6V ~ 30V

Current - Supply:: 11 mA

Operating Temperature:: 0°C ~ 70°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 8-SOIC

UC3843AD8G4 FAQ

1.How can I place an order for UC3843AD8G4 through Aetrix?

Please submit a Request for Quotation (RFQ) for UC3843AD8G4 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 UC3843AD8G4 reliable?

The price and inventory of UC3843AD8G4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3843AD8G4 is usually 5 days.

3.What payment methods are accepted for UC3843AD8G4?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3843AD8G4 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for UC3843AD8G4?

UC3843AD8G4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your UC3843AD8G4 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 UC3843AD8G4?

For technical support, including UC3843AD8G4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3843AD8G4 requirements.

6.How does Aetrix verify that UC3843AD8G4 is sourced from the original manufacturer or authorized distributors?

All UC3843AD8G4 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 UC3843AD8G4 meets industry standards.

7.What is the process for return or replacement of UC3843AD8G4?

All UC3843AD8G4 units undergo pre-shipment inspection (PSI). If there is an issue with UC3843AD8G4, 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 UC3843AD8G4 part is unused and in its original packaging.

Return procedure for UC3843AD8G4:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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