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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > DC DC Switching Controllers

STMicroelectronics UC3844BD1

Name: UC3844BD1
Brand: STMicroelectronics
SKU: UC3844BD1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: UC3844BD1

Manufacturer:: STMicroelectronics

Category:: DC DC Switching Controllers

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

Datasheet:: UC3844BD1.pdf

Description:: IC REG CTRLR BST FLYBK ISO 8-SO

Quantity:: RFQ Add To RFQ list

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Inventory:2,000

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Product details

Overview

UC3844BD1 from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency off-line and DC-DC power supplies. It features a trimmed oscillator guaranteed at 250 kHz, <50% maximum duty cycle (due to internal toggle flip-flop), UVLO thresholds of 16 V (on) / 10 V (off), and a totem-pole output capable of ±1 A peak drive for N-channel MOSFETs - used in AC-DC adapters and isolated flyback converters.

For engineers reviewing the UC3844BD1 datasheet, UC3844BD1 pinout, UC3844BD1 application, or UC3844BD1 equivalent, key selection criteria include its 250 kHz oscillator guarantee, 47–50% max duty cycle limitation, 16 V/10 V UVLO hysteresis, 5 V ±2% reference accuracy, and SO8/Minidip package compatibility with gate-drive thermal and layout constraints.

Technical Context

The UC3844BD1 implements current-mode control using a sampled inductor current signal at the ISENSE pin, compared against a ramp derived from the oscillator's CT waveform to terminate each switching cycle. Its internal toggle flip-flop blanks the output every other clock cycle, enforcing ≤50% duty cycle - critical for forward converter stability and transformer reset assurance.

It integrates a precision 5 V reference (±2% over temperature), error amplifier with 65–90 dB open-loop gain and 0.7–1 MHz unity-gain bandwidth, and a high-current totem-pole output stage with 0.1–0.4 V low-level saturation at 20 mA sink. UVLO hysteresis prevents chatter during brown-out conditions, while start-up current remains below 0.5 mA.

Key Specifications

Parameter	Value and Actual Design Meaning
Oscillator Frequency	Guaranteed 250 kHz at T_J = 25°C; supports up to 500 kHz with external RT/CT tuning - sets primary switching rate and EMI profile.
Max Duty Cycle	47–50% due to internal toggle flip-flop - enforces safe transformer reset in forward/flyback topologies.
V_REF Output	5.00 V ±2% (4.90–5.10 V) at I_OUT = 1 mA - supplies stable bias for RT/CT timing network and feedback divider reference.
UVLO Thresholds	16 V turn-on / 10 V turn-off with hysteresis - ensures reliable startup after bulk capacitor charging and graceful shutdown during line sag.
Output Drive	±1 A peak source/sink capability with 0.4 V low-level saturation at 20 mA - directly drives medium-power MOSFET gates without buffer.
Current Sense Gain	3.0 V/V ±5% - converts sensed resistor voltage to precise comparator trip point for cycle-by-cycle current limiting.
Error Amp GBW	0.7–1 MHz unity-gain bandwidth - enables stable compensation for typical flyback control loops with Type II/III networks.

Pinout & Package

UC3844BD1 is available in SO8 and Minidip packages. Pin functions are electrically identical across both variants; SO8 offers superior thermal performance (R_θJA = 150 °C/W vs. 100 °C/W for Minidip) and surface-mount compatibility.

Pin/Terminal	Circuit Role	Design Meaning
1 - COMP	Error amplifier output	Provides access to EA output for loop compensation (Type II/III networks); high-impedance node requiring low-leakage capacitor.
2 - VFB	Inverting input of error amplifier	Receives feedback voltage from output divider; sets regulation point via 2.5 V internal reference comparison.
3 - ISENSE	Current sense comparator input	Accepts voltage from sense resistor; triggers PWM latch when ≥1.0 V (typical), enabling cycle-by-cycle current limiting.
4 - RT/CT	Oscillator timing interface	Connects external R (to VREF) and C (to GND) to set f_OSC and fine-tune dead time; determines max switching frequency and slope compensation.
5 - GROUND	Power and signal common reference	Single-point ground for control circuitry and power return; critical for noise immunity - must be routed separately from power ground.
6 - OUTPUT	Totem-pole gate driver output	Drives MOSFET gate directly; logic-high = ~13.5 V (at 20 mA), logic-low = ≤0.4 V (at 20 mA); fast rise/fall (<150 ns).
7 - VCC	Supply input	Accepts 10–30 V DC; powers internal bias, reference, and logic; UVLO monitors this pin to enable/disable operation.
8 - VREF	5 V precision reference output	Supplies regulated 5 V ±2% for RT/CT timing and optional auxiliary circuits; delivers up to 20 mA with <25 mV load regulation.

Key Features

Feature	Design Value
Latched PWM with cycle-by-cycle current limit	Prevents MOSFET overcurrent during fault conditions by disabling output until next clock cycle - eliminates need for external protection latches.
Internally trimmed 5 V reference	±2% accuracy over temperature and load eliminates external reference IC, reducing BOM count and improving long-term regulation stability.
Toggle flip-flop duty cycle clamp	Hard-limits max duty cycle to <50%, enabling safe operation in forward converters and simplifying transformer design and reset requirements.
Low start-up current (<0.5 mA)	Reduces HV startup resistor power loss and thermal stress in offline applications - supports high-impedance bias networks.
High-current totem-pole output (±1 A)	Eliminates need for external gate drivers in sub-100 W designs, reducing layout complexity and propagation delay in current-mode control loops.

Applications

AC-DC Adapter

Flyback SMPS

Use Scenario: 12 V / 2 A universal-input offline adapter for consumer electronics.

IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode flyback regulation with optocoupler feedback.

Use Value: 250 kHz fixed frequency enables compact transformer and EMI filter design; 5 V reference stabilizes feedback divider; UVLO ensures clean startup above rectified line minimum.

Use Scenario: Isolated 5 V / 3 A medical-grade power supply meeting IEC 60601 creepage requirements.

IC Role / Device Role / Timing Role: Current-sense-based primary-side controller with cycle-by-cycle limiting and soft-start via COMP pin.

Use Value: ≤50% duty cycle guarantees safe transformer reset under all load/transient conditions; low start-up current minimizes HV resistor dissipation.

Forward Converter

Industrial DC-DC Module

Use Scenario: 48 V input to 12 V / 5 A telecom forward converter with synchronous rectification.

IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller with external slope compensation and duty-cycle clamping.

Use Value: Internal toggle flip-flop enforces strict ≤50% duty cycle, preventing core saturation and enabling reliable transformer reset via auxiliary winding.

Use Scenario: DIN-rail mounted 24 V input to ±15 V dual-output industrial module for PLC I/O.

IC Role / Device Role / Timing Role: Core PWM engine for dual-output forward-derived topology with independent secondary regulation.

Use Value: High-accuracy 5 V reference ensures tight cross-regulation; ±1 A output drives multiple parallel MOSFETs without buffering; UVLO hysteresis prevents restart oscillation during brownouts.

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
UC3844N	DIP-8 package only; no SO8 option; identical electrical specs and pinout.	Suitable for through-hole prototyping or legacy board rework where SO8 footprint is unavailable.	Select when manual assembly or socketing is required; thermal resistance higher (R_θJA = 100 °C/W) limits high-power use.
TL494CN	Fixed-frequency voltage-mode controller; dual-output; adjustable dead time; no integrated current sense comparator or 5 V reference.	Used in push-pull, half-bridge, or dual-rail supplies where independent output control is needed.	Choose only if voltage-mode control suffices and external current sensing + reference are acceptable; not drop-in compatible.

Compared with UC3844N, the UC3844BD1 offers SO8 packaging for automated assembly and better thermal performance; versus TL494CN, it provides integrated current-mode control and reference but lacks dual outputs and dead-time adjustment - making it more compact for single-switch flyback/forward designs.

Availability

UC3844BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, isolated flyback SMPS, and forward converters requiring stable component supply, consistent parametric performance, and long-term industrial lifecycle support.

Supply support for UC3844BD1 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in power management, analog, microcontrollers, and automotive ICs.

The UC384xB series was developed specifically for cost-sensitive, high-reliability current-mode switch-mode power supplies - targeting offline AC-DC, DC-DC conversion, and industrial power modules where minimal external components and robust fault handling are essential.

FAQ

What is the maximum operating frequency of the UC3844BD1?

The UC3844BD1 oscillator is guaranteed at 250 kHz under standard test conditions (T_J = 25°C, RT = 6.2 kΩ, CT = 1 nF), but supports operation up to 500 kHz with optimized RT/CT values and proper PCB layout. Frequency stability degrades above 350 kHz due to propagation delays and oscillator discharge current variation with temperature.

Why does the UC3844BD1 have a maximum duty cycle of only 50%?

The UC3844BD1 includes an internal toggle flip-flop that disables the OUTPUT pin every other clock cycle, limiting maximum duty cycle to 47–50%. This is intentional to ensure safe transformer reset in forward converters and prevent core saturation - distinguishing it from the UC3842BD1/UC3843BD1, which support near-100% duty.

Can the UC3844BD1 drive a P-channel MOSFET directly?

No - the UC3844BD1 OUTPUT pin is a totem-pole stage referenced to GROUND (Pin 5), sourcing current when high and sinking when low. It is designed to drive N-channel MOSFET gates with source tied to ground. Driving a P-channel device would require level-shifting or an external inverter, as the output cannot swing above VCC or below GND.

How is the current sense threshold set on the UC3844BD1?

The current sense comparator trips when the voltage at ISENSE (Pin 3) reaches 1.0 V (typical), with ±0.1 V tolerance over temperature. This threshold is fixed and internally generated; users select the sense resistor value (R_SENSE) based on peak inductor current: R_SENSE ≈ 1.0 V / I_PEAK. An RC filter is recommended to suppress switching noise.

UC3844BD1 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Active

Output Type:: Transistor Driver

Function:: Step-Up, Step-Up/Step-Down

Output Configuration:: Positive, Isolation Capable

Topology:: Boost, Flyback

Number of Outputs:: 1

Output Phases:: 1

Voltage - Supply (Vcc/Vdd):: 10V ~ 30V

Frequency - Switching:: Up to 500kHz

Duty Cycle (Max):: 48%

Synchronous Rectifier:: No

Clock Sync:: No

Serial Interfaces:: -

Control Features:: Frequency Control

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

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 8-SOIC

UC3844BD1 FAQ

1.How can I place an order for UC3844BD1 through Aetrix?

Please submit a Request for Quotation (RFQ) for UC3844BD1 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 UC3844BD1 reliable?

The price and inventory of UC3844BD1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3844BD1 is usually 5 days.

3.What payment methods are accepted for UC3844BD1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3844BD1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for UC3844BD1?

UC3844BD1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your UC3844BD1 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 UC3844BD1?

For technical support, including UC3844BD1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3844BD1 requirements.

6.How does Aetrix verify that UC3844BD1 is sourced from the original manufacturer or authorized distributors?

All UC3844BD1 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 UC3844BD1 meets industry standards.

7.What is the process for return or replacement of UC3844BD1?

All UC3844BD1 units undergo pre-shipment inspection (PSI). If there is an issue with UC3844BD1, 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 UC3844BD1 part is unused and in its original packaging.

Return procedure for UC3844BD1:

1.Submit a request within 90 days.

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

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