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Texas Instruments UC3855BDW
- Part No.:
- UC3855BDW
- Manufacturer:
- Texas Instruments
- Category:
- PFC (Power Factor Correction)
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
UC3855BDW.pdf
- Description:
- IC PFC CTR AVERAGE 500KHZ 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,115
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Product details
Overview
UC3855BDW from Texas Instruments is a high-frequency average-current-mode PFC controller IC designed for active power factor correction in boost preregulators. It integrates ZVT (Zero Voltage Transition) drive, inductor current synthesizer, analog multiplier with line compensation, 7.5V ±1% reference, and dual gate drivers (GTOUT/ZVTOUT) - enabling stable operation up to 500kHz with low line current distortion in universal-input AC-DC supplies.
For engineers reviewing the UC3855BDW datasheet, UC3855BDW pinout, UC3855BDW application, or UC3855BDW equivalent, key selection considerations include its 0°C to 70°C operating range, SOIC-20 (DW) package, fixed-frequency average-current control architecture, ZVT timing thresholds (2.3–2.9V), and compatibility with single-current-transformer sensing for high-power industrial and telecom rectifiers.
Technical Context
The UC3855BDW implements fixed-frequency average-current-mode control using an internal current amplifier (5MHz GBW, 80–110dB open-loop gain) and voltage amplifier (65–80dB gain, soft-start enabled) to regulate boost output voltage while programming input current via a precision analog multiplier. Its ZVT block triggers resonant switching based on drain-voltage zero-crossing sensed at ZVS pin, reducing MOSFET turn-on loss and EMI.
Current sensing employs an inductor current synthesizer that reconstructs the full waveform using CI capacitor discharge and RVS/ION inputs - eliminating need for slope compensation and enabling accurate average-current control without shunt losses. The multiplier's gain constant (−0.95 to −0.75 V⁻¹) and VRMS feedforward (0–5.5V range) support universal input operation from 85–265VAC.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 160–240 kHz typical; sets PWM switching frequency up to 500kHz with external CT capacitor. |
| Voltage Reference | 7.5V ±1% at 25°C; powers external circuitry with 25mA sink/source capability and internal short-circuit limiting. |
| Current Amplifier GBW | 2.5–5 MHz; enables fast transient response in current loop for low THD line current regulation. |
| ZVT Drive Capability | ±0.25A continuous / ±0.75A peak; drives auxiliary MOSFET for zero-voltage turn-on of main boost switch. |
| Operating Temperature | 0°C to +70°C; defines ambient range for rated performance in commercial-grade power supplies. |
| UVLO Threshold | UC3855B variant: 10.5–10.8V turn-on, 9–10V turn-off; ensures controlled startup under brownout conditions. |
| Gate Driver Output | GTOUT: ±0.5A continuous / ±1.5A peak; drives main boost MOSFET gate directly with <35ns rise/fall time. |
Pinout & Package
UC3855BDW is housed in a 20-pin SOIC (DW) package per JEDEC MS-013, 7.5mm body width, 2.65mm max height, with standard 1.27mm pitch and RoHS-compliant NiPdAu lead finish (MSL Level-2, 260°C reflow).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CA | Inverting input of current amplifier | Accepts compensated feedback from CS; common-mode range −0.3V to 5V supports wide-swing error signal. |
| CAO | Current amplifier output | Drives PWM comparator; rail-to-rail swing (0.1–7.5V) enables precise duty-cycle control. |
| CI | Current synthesizer capacitor node | Integrates reconstructed inductor current; discharge rate proportional to dI/dt for accurate average sensing. |
| CS | Level-shifted current waveform output | Feeds CA input and peak-limit comparator; >1.5V disables GTOUT for overcurrent protection. |
| CT | Oscillator timing capacitor connection | Defines switching frequency via f ≈ 1/(11200·CT); min 200pF recommended for layout immunity. |
| GND | Signal and power ground reference | Common return for all analog/digital functions; requires low-inductance bypassing near VCC/REF pins. |
| GTOUT | Main MOSFET gate driver output | 1.5A peak totem-pole output; requires series gate resistor ≥10Ω and Schottky clamp to GND. |
| IAC | Multiplier current input | Accepts rectified line current sense; nominal 650mV offset eliminates zero-crossing compensation resistors. |
| IMO | Multiplier current output | Sinks current into CA resistor; gain constant K = −0.85 V⁻¹ enables line-voltage-compensated current command. |
| ION | Current transformer secondary input | Buffered level-shifted input to CI; source-only output drives CI capacitor during switch-on phase. |
| OVP | Overvoltage protection input | Hysteretic comparator (7.5–7.66V trip, 400mV hysteresis) disables GTOUT/ZVTOUT on boost OV fault. |
| REF | Precision 7.5V reference output | Stable reference for external circuits; disabled below UVLO and during OVP/EN disable. |
| RVS | Output voltage-derived current source | 3V buffered output; current into GND forms second synthesizer input for IAC scaling. |
| SS | Soft-start control voltage | Charges external capacitor to ramp PWM duty cycle; discharges rapidly during VCC dropout. |
| VCC | Positive supply input | Internally clamped at 18–22V; 150µA startup current enables low-power auxiliary supply design. |
| VAO | Voltage amplifier output | 100mV–6V swing; controls multiplier gain based on load; <1.5V inhibits multiplier output. |
| VSENSE | Voltage amplifier inverting input | Feedback node for boost output; nominal 3V input requires voltage divider; must exceed 1.5V for synthesizer enable. |
| VRMS | Line RMS voltage feedforward | 0–5.5V input scales multiplier gain as 1/VRMS²; enables universal input and fast line transient response. |
| VZS | ZVT zero-voltage sense input | Detects main MOSFET drain ≈0V via blocking diode; threshold 2.3–2.9V triggers ZVTOUT pulse. |
| ZVTOUT | ZVT auxiliary MOSFET driver | 750mA peak totem-pole output; drives smaller ZVT switch; supports sync-out functionality. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated ZVT (Zero Voltage Transition) control | Reduces MOSFET turn-on loss and diode reverse-recovery EMI by enabling resonant switching at up to 500kHz. |
| Inductor current synthesizer | Reconstructs full inductor current waveform from single current transformer, eliminating shunt losses and improving SNR. |
| Accurate analog multiplier with line compensation | Uses VRMS feedforward (0–5.5V) and gain constant −0.85 V⁻¹ to maintain constant power across 85–265VAC input. |
| High-bandwidth current amplifier | 5MHz gain-bandwidth product and 80–110dB open-loop gain ensure fast current-loop response and low THD. |
| Two UVLO thresholds (A/B variants) | UC3855B version provides 10.5–10.8V startup for applications requiring lower-voltage auxiliary supply compatibility. |
| 1% precision 7.5V reference | Stable reference with ±15mV load regulation and ±10mV line regulation supports accurate voltage loop calibration. |
Applications
| Industrial AC-DC Power Supplies | Telecom Rectifier Modules |
|---|---|
Use Scenario: 3kW front-end rectifier in 48V telecom system with universal AC input (85–265VAC) and strict EN61000-3-2 Class A harmonic limits. IC Role / Device Role / Timing Role: UC3855BDW serves as the primary PFC controller, executing average-current-mode PWM with ZVT to achieve >98% efficiency and <5% THD at full load. Use Value: Enables compliance with harmonic standards without external slope compensation or complex current sensing, reducing BOM count and layout area. |
Use Scenario: High-density server PSU requiring compact, high-efficiency PFC stage operating continuously at 70°C ambient. IC Role / Device Role / Timing Role: UC3855BDW manages boost converter switching at 300kHz using SOIC-20 package and integrated current synthesizer for thermal robustness. Use Value: Delivers stable operation across 0–70°C with 150µA startup current and internal 7.5V reference, minimizing auxiliary supply complexity. |
| Medical Imaging Power Systems | LED Driver Front-Ends |
Use Scenario: MRI or CT scanner power supply needing ultra-low EMI and high reliability under variable line conditions. IC Role / Device Role / Timing Role: UC3855BDW implements fixed-frequency average-current control with active snubbing to suppress high-frequency noise radiated from boost diode recovery. Use Value: Reduces conducted EMI by >10dB compared to conventional controllers, easing EMC filter design and certification effort. |
Use Scenario: Outdoor LED streetlight driver with wide input range (90–305VAC) and requirement for >95% efficiency at 50% load. IC Role / Device Role / Timing Role: UC3855BDW regulates boost output using VSENSE feedback and VRMS feedforward to maintain constant power across input variation. Use Value: Maintains power factor >0.99 and efficiency >94% from 10–100% load via accurate analog multiplier and low-offset current amplifier. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PFC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3855ADW | Wider temperature range (−40°C to +85°C); higher UVLO (15.5–17.5V turn-on) and different oscillator accuracy (170–230kHz). | Suitable for industrial environments requiring extended temp operation; not drop-in due to UVLO mismatch with UC3855BDW. | Select UC3855ADW only when −40°C operation or higher startup voltage is required; verify OVP and soft-start timing compatibility. |
| L6562A | Fixed-frequency average-current controller with 600kHz max, no integrated ZVT drive; uses external op-amp for current amplification. | Requires discrete ZVT circuit and additional compensation components; lacks current synthesizer and integrated multiplier. | Choose L6562A when cost sensitivity outweighs integration benefits and board space allows added discretes for ZVT implementation. |
Compared with UC3855ADW and L6562A, the UC3855BDW offers optimized commercial-temperature operation with built-in ZVT drive and current synthesizer - reducing component count and layout complexity for 300–500kHz PFC designs where 0–70°C ambient suffices.
Availability
UC3855BDW is available at Aetrix Electronics and suitable for industrial AC-DC power supplies, telecom rectifier modules, and medical imaging power systems requiring stable component supply and long-term manufacturability.
Supply support for UC3855BDW 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 leader specializing in analog, embedded processing, and power management technologies with decades of power conversion IP.
The UC3855 family was developed specifically for high-efficiency, high-frequency active PFC in commercial and industrial AC-DC front-ends - emphasizing integration of ZVT, current synthesis, and line-compensated multiplier functions.
FAQ
What is the operating temperature range specified for the UC3855BDW?
The UC3855BDW is rated for operation from 0°C to +70°C ambient temperature, as confirmed in the Electrical Characteristics table under "UC3855A/B" test conditions. This distinguishes it from the UC3855ADW variant, which supports −40°C to +85°C. The UC3855BDW's thermal specification aligns with commercial-grade power supply requirements and is validated across all electrical parameters in this range.
Does the UC3855BDW support ZVT (Zero Voltage Transition) operation out of the box?
Yes, the UC3855BDW includes fully integrated ZVT control logic and dedicated ZVTOUT driver (±0.25A continuous / ±0.75A peak). It senses zero voltage at the main MOSFET drain via the ZVS pin and generates precisely timed pulses on ZVTOUT to drive an auxiliary switch - enabling resonant turn-on without external timing circuitry. The ZVT threshold is fixed at 2.3–2.9V per datasheet.
Can the UC3855BDW be used with a resistive current shunt instead of a current transformer?
Yes, the UC3855BDW supports both sensing methods. While the current synthesizer (ION/CI/CS path) is optimized for transformer-based sensing, the CA/CAO amplifier accepts direct shunt voltage signals applied to CA. The datasheet explicitly states "average current sensing can be employed using a simple resistive shunt or a current sense transformer", and CA's −0.3V to 5V common-mode range accommodates typical shunt voltages.
What is the purpose of the VRMS pin on the UC3855BDW?
The VRMS pin on the UC3855BDW provides line-voltage feedforward to the internal analog multiplier, accepting a DC voltage (0–5.5V) proportional to the AC input RMS value. This enables the multiplier to scale the current command as 1/VRMS², ensuring constant output power across universal input ranges (85–265VAC) and improving dynamic response to line fluctuations - a core feature for PFC compliance.
How does the UC3855BDW handle overvoltage protection?
The UC3855BDW implements hardware-based overvoltage protection via the OVP pin: when voltage exceeds 7.5–7.66V (with 200–600mV hysteresis), the internal comparator disables both GTOUT and ZVTOUT outputs until the sensed voltage falls below the hysteresis threshold. Propagation delay is 200ns, and the OVP input bias current is ≤10µA - ensuring fast, reliable shutdown without software intervention.
UC3855BDW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Mode:
- Average Current
- Frequency - Switching:
- 500kHz
- Current - Startup:
- 150 µA
- Voltage - Supply:
- 10.5V ~ 20V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
UC3855BDW FAQ
1.How can I place an order for UC3855BDW through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3855BDW 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 UC3855BDW reliable?
The price and inventory of UC3855BDW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3855BDW is usually 5 days.
3.What payment methods are accepted for UC3855BDW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3855BDW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3855BDW?
UC3855BDW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3855BDW 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 UC3855BDW?
For technical support, including UC3855BDW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3855BDW requirements.
6.How does Aetrix verify that UC3855BDW is sourced from the original manufacturer or authorized distributors?
All UC3855BDW 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 UC3855BDW meets industry standards.
7.What is the process for return or replacement of UC3855BDW?
All UC3855BDW units undergo pre-shipment inspection (PSI). If there is an issue with UC3855BDW, 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 UC3855BDW part is unused and in its original packaging.
Return procedure for UC3855BDW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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