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STMicroelectronics UC3843BD1
- Part No.:
- UC3843BD1
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
UC3843BD1.pdf
- Description:
- IC REG CTRLR BOOST/FLYBACK 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:11,531
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Product details
Overview
UC3843BD1 from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency DC-DC and off-line power supplies. It features an internally trimmed oscillator (guaranteed 250 kHz), latching PWM for cycle-by-cycle current limiting, under-voltage lockout with hysteresis (8.4 V turn-on / 7.6 V turn-off), and a totem-pole output capable of ±1 A peak drive - enabling direct N-channel MOSFET gate control in flyback, forward, and boost converters.
For engineers reviewing the UC3843BD1 datasheet, UC3843BD1 pinout, UC3843BD1 application, or UC3843BD1 equivalent, key selection criteria include its low start-up current (<0.5 mA), 5.0 V ±10 mV reference accuracy, 96% maximum duty cycle, current-sense gain of 3.0 V/V, and SO8 package compatibility with standard PCB layouts for cost-sensitive industrial and consumer SMPS designs.
Technical Context
The UC3843BD1 implements true current-mode control via a dedicated ISENSE input that feeds a comparator with a 1 V threshold, enabling precise per-cycle current limiting. Its error amplifier features 90 dB open-loop gain and 1 MHz unity-gain bandwidth, supporting stable loop compensation across wide load and line variations.
Oscillator frequency is set externally via RT/CT (e.g., 10 kΩ + 3.3 nF yields ~250 kHz), with internal discharge current trimmed to 7.8–8.8 mA and temperature-stable frequency variation (<0.5% over –40°C to +150°C). The UVLO circuit ensures reliable start-up only when VCC exceeds 8.4 V and remains active down to 7.6 V, preventing erratic operation during brownouts.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | Guaranteed 250 kHz at 25°C; supports up to 500 kHz with external RT/CT tuning for high-density converter designs. |
| Reference Voltage (VREF) | 5.00 V ±10 mV at 1 mA load; provides stable bias for CT charging and feedback divider reference. |
| Current Sense Gain | 3.0 V/V (2.85–3.15 V/V); converts sensed resistor voltage to precise 1 V trip point for PWM latch activation. |
| UVLO Thresholds | 8.4 V (turn-on) / 7.6 V (turn-off); enables reliable startup in low-input-voltage DC-DC applications like 12 V input adapters. |
| Output Drive Capability | ±1 A peak source/sink; directly drives medium-power MOSFET gates without external buffers in sub-100 W topologies. |
| Max Duty Cycle | 96% (typical); supports high step-up ratios in boost and flyback converters with minimal dead-time constraints. |
| Start-up Current | ≤0.5 mA at 6.5 V; reduces auxiliary winding losses and enables efficient high-impedance VCC startup circuits. |
Pinout & Package
UC3843BD1 is housed in an industry-standard SO8 (Small Outline 8-pin) package with 1.27 mm pitch, compliant with JEDEC MS-012, and rated for 800 mW power dissipation at Tamb ≤ 25°C.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error amplifier output | Provides access to EA output for Type II/III compensation network placement; high-impedance node requiring low-leakage capacitor. |
| 2 - VFB | Inverting input of error amplifier | Connects to output voltage divider; sets regulation point via 2.5 V internal reference comparison. |
| 3 - ISENSE | Current sense comparator input | Accepts voltage from sense resistor; triggers PWM shutdown when ≥1.0 V, enforcing cycle-by-cycle current limit. |
| 4 - RT/CT | Oscillator timing interface | RT connects to VREF (pin 8), CT to ground; sets fOSC and max duty cycle via RC time constant and internal discharge current. |
| 5 - GROUND | Signal and power return | Single-point analog/digital ground; must be routed separately from power ground to avoid noise coupling into ISENSE/VFB. |
| 6 - OUTPUT | Totem-pole gate driver output | Sources/sinks up to 1 A; logic-high = MOSFET on; low-impedance state minimizes switching losses in gate drive path. |
| 7 - VCC | Supply input | Accepts 7.6–30 V; powers internal bias, reference, and output stage; includes UVLO hysteresis and thermal foldback. |
| 8 - VREF | 5.0 V precision reference output | Supplies regulated 5 V at ≤20 mA; used to charge CT and bias external circuitry; ±0.2 mV/°C tempco ensures timing stability. |
Key Features
| Feature | Design Value |
|---|---|
| Latching PWM with cycle-by-cycle current limit | Prevents transformer saturation and MOSFET overstress by disabling output after each overcurrent event until next clock cycle. |
| Internally trimmed 5.0 V reference | Eliminates need for external reference IC; maintains ±2% total variation over line/load/temperature for stable feedback. |
| Low-startup-current UVLO (≤0.5 mA) | Enables use of high-value startup resistors, reducing standby power in offline adapters and extending hold-up time. |
| High-current totem-pole output (±1 A) | Drives 1000 pF gate capacitance with <150 ns rise/fall times, supporting fast-switching MOSFETs up to 500 kHz. |
| Automatic feed-forward compensation | Compensates for input voltage variations in real time via oscillator frequency modulation, improving transient response. |
Applications
| AC-DC Adapter | Flyback SMPS |
|---|---|
|
Use Scenario: 12 V/2 A wall adapter for consumer electronics with universal AC input (90–264 VAC). IC Role / Device Role / Timing Role: Primary-side PWM controller regulating output via optocoupler feedback; generates 250 kHz gate drive synchronized to current-sense zero-crossing. Use Value: Enables compact design with <150 mW no-load consumption and ±3% output regulation across line/load/temperature. |
Use Scenario: Isolated 5 V/3 A flyback supply for industrial PLC I/O modules operating from 24 VDC input. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller implementing primary-side sensing with auxiliary winding feedback. Use Value: Provides inherent short-circuit protection and stable regulation without secondary-side TL431, reducing BOM count by 2 components. |
| Boost PFC Pre-regulator | DC-DC Buck Converter |
|
Use Scenario: 300 VDC boost PFC stage in LED driver with 85–265 VAC input and >0.95 PF. IC Role / Device Role / Timing Role: Average-current-mode controller using ISENSE for inductor current sensing and VFB for output voltage regulation. Use Value: Delivers >92% efficiency at full load with THD <10% due to precise 1 V current threshold and feed-forward line compensation. |
Use Scenario: 12 V to 3.3 V/5 A buck converter for FPGA core power in telecom baseband cards. IC Role / Device Role / Timing Role: Secondary-side synchronous buck controller with external high-side MOSFET drive and current-sense resistor feedback. Use Value: Supports 96% duty cycle for low dropout operation and ±1% output accuracy over –40°C to +85°C ambient. |
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 |
|---|---|---|---|
| UC3842BD1 | Higher UVLO (16 V on / 10 V off); same oscillator, reference, and output specs. | Designed for universal offline AC-DC where bulk cap charges above 16 V; unsuitable for low-Vin DC-DC. | Select UC3842BD1 only when input voltage reliably exceeds 16 V; otherwise UC3843BD1 avoids startup failure. |
| NCP1200DR2G | Fixed 65 kHz frequency; built-in soft-start; lower start-up current (100 µA); no VREF output. | Optimized for cost-sensitive, low-power adapters; lacks programmable oscillator and external reference utility. | Choose NCP1200DR2G for <15 W applications needing integrated soft-start and minimal external parts; UC3843BD1 preferred for design flexibility and higher power. |
Compared with UC3842BD1, UC3843BD1 enables reliable operation from lower input voltages (≥8.4 V), while NCP1200DR2G trades programmability for integration and ultra-low start-up current - making UC3843BD1 optimal for mid-power DC-DC and adjustable-frequency designs requiring VREF sourcing and precise current sensing.
Availability
UC3843BD1 is available at Aetrix Electronics and suitable for AC-DC adapters, flyback SMPS, boost PFC pre-regulators, and DC-DC buck converters requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.
Supply support for UC3843BD1 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, delivering innovative silicon solutions for automotive, industrial, and power management applications.
The UC384xB family was developed specifically for cost-effective, high-reliability current-mode switch-mode power supply control - targeting industrial power supplies, consumer adapters, and embedded DC-DC conversion where precision timing, robust fault protection, and minimal external component count are critical.
FAQ
What is the minimum recommended VCC startup voltage for UC3843BD1?
The UC3843BD1 begins operation when VCC rises above 8.4 V (typical), with hysteresis ensuring it remains active down to 7.6 V. Startup circuits must deliver ≥8.4 V before enabling the output stage; using a 1 MΩ resistor from bulk capacitor to VCC is common in 12 V input DC-DC designs.
Can UC3843BD1 drive a high-side N-channel MOSFET directly?
No - UC3843BD1's OUTPUT pin is a ground-referenced totem-pole driver optimized for low-side N-MOSFETs. Driving a high-side N-channel requires a floating gate driver (e.g., IR2110) or bootstrap circuit; the IC lacks high-side level-shifting capability or dedicated high-side output.
How does the UC3843BD1 implement automatic feed-forward compensation?
It modulates oscillator frequency in proportion to VCC changes: higher input voltage increases discharge current into CT, raising fOSC, which shortens on-time and maintains constant output power - effectively rejecting line-induced ripple without additional compensation components.
Is external slope compensation required when using UC3843BD1 in continuous conduction mode?
Yes - for duty cycles >50% in CCM flyback or boost topologies, external ramp injection (e.g., via resistor from VREF to ISENSE) is required to prevent subharmonic oscillation; the IC lacks internal slope compensation, unlike later-generation controllers such as UC3845B.
UC3843BD1 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):
- 7.6V ~ 30V
- Frequency - Switching:
- Up to 500kHz
- Duty Cycle (Max):
- 96%
- 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
UC3843BD1 FAQ
1.How can I place an order for UC3843BD1 through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3843BD1 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 UC3843BD1 reliable?
The price and inventory of UC3843BD1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3843BD1 is usually 5 days.
3.What payment methods are accepted for UC3843BD1?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3843BD1 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3843BD1?
UC3843BD1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3843BD1 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 UC3843BD1?
For technical support, including UC3843BD1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3843BD1 requirements.
6.How does Aetrix verify that UC3843BD1 is sourced from the original manufacturer or authorized distributors?
All UC3843BD1 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 UC3843BD1 meets industry standards.
7.What is the process for return or replacement of UC3843BD1?
All UC3843BD1 units undergo pre-shipment inspection (PSI). If there is an issue with UC3843BD1, 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 UC3843BD1 part is unused and in its original packaging.
Return procedure for UC3843BD1:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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