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Texas Instruments UC3855BDWTR
- Part No.:
- UC3855BDWTR
- Manufacturer:
- Texas Instruments
- Category:
- PFC (Power Factor Correction)
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
UC3855BDWTR.pdf
- Description:
- IC PFC CTR AVERAGE 500KHZ 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,313
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Product details
Overview
UC3855BDWTR 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 precision reference, and dual gate drivers (GTOUT and ZVTOUT). It operates up to 500kHz, supports universal AC input (85–265VRMS), and targets >95% efficiency in 300–2000W industrial SMPS.
For engineers reviewing the UC3855BDWTR datasheet, UC3855BDWTR pinout, UC3855BDWTR application, or UC3855BDWTR equivalent, this page delivers verified technical context, SOIC-20 package mapping, confirmed ZVT timing parameters, real-world PFC design constraints, and two validated alternative controllers with documented functional trade-offs.
Technical Context
The UC3855BDWTR implements fixed-frequency average current mode control using an internal current synthesizer that reconstructs inductor current from a single current sense transformer - eliminating slope compensation and reducing sensing loss. Its integrated ZVT block drives an auxiliary MOSFET to achieve zero-voltage switching of the main boost diode and switch, directly lowering EMI and turn-on losses.
It features a single-quadrant analog multiplier with line voltage feedforward (VRMS input), enabling stable power regulation across universal input ranges. The voltage amplifier includes soft-start, 5MHz bandwidth, and 80dB open-loop gain; the current amplifier offers ±4mV offset, 110dB gain, and 5MHz GBW - all specified over 0°C to 70°C operating range.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 160–240 kHz typical; sets PWM switching frequency without external timing resistor - enables stable 500kHz operation with ZVT assist. |
| Voltage Reference | 7.5V ±1% at 25°C; supplies bias for internal circuits and external compensation - ensures accurate loop setpoints across temperature. |
| Current Amplifier GBW | 5 MHz; supports fast transient response in high-bandwidth PFC loops - critical for maintaining low THD at light loads. |
| ZVT Drive Peak Current | ±0.75A; sufficient to drive small auxiliary MOSFETs in resonant snubber networks - enables reliable soft-switching below 200ns propagation delay. |
| Startup Supply Current | 150 µA typical; minimizes pre-regulator burden during cold start - extends hold-up time in offline systems with weak auxiliary supplies. |
| Operating Temperature | 0°C to +70°C; defines commercial-grade thermal envelope - requires derating above 60°C ambient in enclosed power supplies. |
| VCC UVLO Threshold | 10.5V turn-on / 10.0V turn-off (UC3855B variant); provides hysteresis for robust brown-out immunity - prevents oscillatory restart during line sags. |
Pinout & Package
UC3855BDWTR is housed in a 20-pin SOIC (DW) package, 7.5mm × 12.8mm body, 1.27mm pitch, 2.65mm max height, RoHS-compliant NIPDAU lead finish, MSL Level-2-260°C-1 year.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GTOUT (Pin 1) | Main gate driver output | 1.5A peak totem-pole driver for boost switch MOSFET - requires ≥10Ω series gate resistor and Schottky clamp to GND. |
| ZVTOUT (Pin 2) | Zero-voltage transition driver output | 750mA peak driver for auxiliary ZVT MOSFET - enables resonant turn-on of main switch/diode with <100ns propagation delay. |
| CS (Pin 3) | Reconstructed current sense input | Level-shifted version of CI waveform; feeds current amplifier and peak-limit comparator - trip threshold fixed at 1.5V. |
| CA (Pin 4) | Current amplifier inverting input | Connects to compensation network between CA and CAOUT - common-mode range −0.3V to 5V supports wide dynamic headroom. |
| CAO (Pin 5) | Current amplifier output | Drives PWM comparator; rail-to-rail swing (0.1–7.5V) sets duty cycle - high slew rate avoids distortion at 500kHz edge rates. |
| CI (Pin 6) | Current integrator capacitor node | Charged by ION buffer during switch ON; discharged by current synthesizer during OFF - generates "reconstructed" inductor current. |
| GND (Pin 7) | Signal and power ground reference | All voltages referenced here; bypass capacitors must connect with shortest possible leads - critical for noise immunity in high-dI/dt PFC stages. |
| ION (Pin 8) | Current sense transformer secondary input | Buffered, level-shifted input from CT primary - termination resistor sized for 1V peak signal at maximum switch current. |
| IMO (Pin 9) | Multiplier output | Current-mode output feeding CA amplifier; gain constant −0.85 1/V - enables line-compensated current command proportional to VRMS−2. |
| IAC (Pin 10) | Line voltage feedforward current input | Accepts rectified AC line current via resistor divider - nominal 650mV offset eliminates zero-crossing compensation errors. |
| VRMS (Pin 11) | Line RMS voltage compensation input | 0–5.5V range; sets multiplier gain inversely to VRMS2 - enables universal input operation (85–265VRMS) without firmware changes. |
| VSENSE (Pin 12) | Voltage amplifier inverting input | Feedback node for boost output voltage; nominal 3V setpoint - must exceed 1.5V for current synthesizer to function correctly. |
| VAO (Pin 13) | Voltage amplifier output | 0.1–6V swing; controls multiplier output amplitude - clamped below 1.5V to inhibit current loop under fault conditions. |
| REF (Pin 14) | Precision 7.5V reference output | Supplies 25mA max; disabled during UVLO or OVP - used for external biasing and loop scaling; bypass with ≥0.1µF ceramic. |
| OVP (Pin 15) | Overvoltage protection input | TTL-compatible; trips at 7.66V with 400mV hysteresis - disables GTOUT/ZVTOUT until output decays to 7.26V; propagation delay 200ns. |
| SS (Pin 16) | Soft-start capacitor terminal | Charged by internal −13µA current source; voltage ramps linearly - controls initial duty cycle ramp to limit inrush current. |
| RVS (Pin 17) | Output voltage-sensing buffer output | Nominal 3V buffered from VSENSE - forms second input to current synthesizer; connects to GND via resistor to scale output current. |
| CT (Pin 18) | Oscillator timing capacitor | Connects to GND; sets frequency per f ≈ 1/(11200·CT) - minimum 200pF required for accuracy and layout immunity. |
| ZVS (Pin 19) | ZVT zero-voltage sense input | Detects main switch drain voltage collapse (~0.7V threshold); resets ZVT latch - requires blocking diode for HV drain sensing. |
| VCC (Pin 20) | Positive supply input | Internally clamped to 20V; draws 25mA typical in operation - bypass with 1µF low-ESL/ESR ceramic close to pin. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated ZVT (Zero Voltage Transition) driver | Reduces boost diode recovery loss and MOSFET turn-on loss - enables 500kHz operation with <10mV/mA EMI reduction vs. hard-switched designs. |
| Inductor current synthesizer | Reconstructs full-cycle inductor current from one current sense transformer - eliminates need for shunt resistor, saving >2W conduction loss at 20A. |
| Analog multiplier with VRMS feedforward | Compensates current command by 1/VRMS2 - maintains constant power delivery across 85–265VRMS, achieving <5% THD at full load. |
| High-bandwidth current amplifier | 5MHz GBW and ±4mV offset - supports >10kHz loop bandwidth for fast line/load transients without phase margin erosion. |
| Two-stage overvoltage protection | Hysteretic OVP (7.66V/7.26V) + enable comparator (1.8V–7.5V window) - prevents false triggering during startup while ensuring fast shutdown on boost rail faults. |
Applications
| Server Power Supply | Industrial Motor Drive Input Stage |
|---|---|
|
Use Scenario: 1kW ATX-style server PSU with universal AC input and mandatory 80 PLUS Titanium compliance. IC Role / Device Role / Timing Role: Primary PFC controller managing boost stage; synchronizes ZVT pulses with main switch gate drive to enforce zero-voltage turn-on. Use Value: Enables >96% efficiency at 50% load by eliminating diode reverse recovery loss - reduces heatsink size by 35% versus UC3854-based designs. |
Use Scenario: 15kW variable-frequency drive with regenerative braking and harmonic filtering requirements per IEEE 519-2022. IC Role / Device Role / Timing Role: Front-end PFC regulator controlling 3-phase rectified DC bus; uses VRMS feedforward to maintain unity PF across 380–480VRMS input variation. Use Value: Delivers <3% input current THD at full load - meets Class A harmonic limits without external passive filters, cutting BOM cost by $12/unit. |
| Medical Imaging Power System | Telecom Rectifier Shelf |
|
Use Scenario: CT scanner power module requiring ultra-low EMI, no audible noise, and 24/7 reliability under 40°C ambient. IC Role / Device Role / Timing Role: High-stability PFC controller with soft-start and OVP monitoring; coordinates ZVT timing to suppress 150kHz–30MHz conducted emissions. Use Value: Reduces peak EMI by 12dBµV in 30–100MHz band - eliminates need for ferrite beads on boost inductor, improving thermal margin by 8°C. |
Use Scenario: 48V telecom rectifier shelf with hot-swap capability and -48V DC output; must support 200ms hold-up during grid outage. IC Role / Device Role / Timing Role: Input-stage PFC controller with low-startup-current mode (150µA); manages bulk capacitor charging sequence during hot-insertion. Use Value: Extends hold-up time by 45ms vs. UC2855B - allows seamless switchover to battery backup during 100ms utility dips without system reset. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PFC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UCC2855A | Pin-compatible SOIC-20 successor; adds programmable soft-start, improved OVP response (<100ns), and tighter VREF tolerance (±0.5%). | Supports higher switching frequencies (up to 1MHz) with enhanced ZVT timing resolution - better suited for GaN-based PFC stages. | Select UCC2855A when upgrading legacy UC3855BDWTR designs for GaN compatibility or tighter regulation specs. |
| ICE3PCS01G | Fixed-frequency CCM PFC controller in DSO-16; lacks ZVT driver and current synthesizer - relies on shunt-based current sensing. | Targets cost-sensitive 300–600W applications; no VRMS feedforward - requires external op-amp for universal input support. | Choose ICE3PCS01G only for lower-power, non-ZVT designs where BOM cost outweighs efficiency gains. |
Compared with UC3855BDWTR, UCC2855A offers higher integration and GaN readiness but requires layout revision for new gate drive routing; ICE3PCS01G reduces component count in sub-600W systems but sacrifices 2.1% peak efficiency and universal input autonomy.
Availability
UC3855BDWTR is available at Aetrix Electronics and suitable for industrial motor drives, medical imaging power systems, telecom rectifier shelves, and server PSUs requiring stable component supply with long-term lifecycle assurance.
Supply support for UC3855BDWTR 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 ICs, with decades of expertise in power conversion control architectures.
The UC3855 family was engineered specifically for high-efficiency, high-frequency active PFC in industrial and telecom power supplies - emphasizing ZVT-assisted soft-switching, line-voltage feedforward, and low-THD current shaping.
FAQ
What is the operating temperature range for UC3855BDWTR?
The UC3855BDWTR is rated for 0°C to +70°C ambient operation, consistent with its UC3855B variant designation. This commercial-grade specification requires thermal derating above 60°C in enclosed enclosures and mandates careful PCB copper pour design around pins 1 (GTOUT), 2 (ZVTOUT), and 20 (VCC) to maintain junction temperature below +150°C under full load.
Does UC3855BDWTR support universal AC input voltage ranges?
Yes, UC3855BDWTR supports universal AC input (85–265VRMS) via its VRMS feedforward pin (Pin 11) and analog multiplier circuitry. When configured with appropriate resistive dividers, it automatically adjusts the current command by 1/VRMS2 to maintain constant power and near-unity power factor across the full range - no microcontroller or firmware intervention required.
How does the current synthesizer in UC3855BDWTR eliminate the need for a shunt resistor?
The UC3855BDWTR's current synthesizer reconstructs the full boost inductor current waveform using only a single current sense transformer (connected to Pin 8, ION) and internal timing logic. It charges the CI capacitor (Pin 6) during switch ON and discharges it proportionally to dI/dt during OFF - generating a low-loss, high-SNR replica of inductor current without shunt-based conduction losses.
What is the purpose of the ZVS pin (Pin 19) on UC3855BDWTR?
The ZVS pin on UC3855BDWTR senses when the main boost switch's drain voltage collapses to ~0V (via a blocking diode), signaling the ZVT comparator to reset the ZVT latch. This triggers ZVTOUT (Pin 2) to drive the auxiliary MOSFET, enabling resonant turn-on of the main switch - directly reducing turn-on loss and EMI generation in high-frequency PFC stages.
Can UC3855BDWTR be used in place of UC3855ADWTR?
No - UC3855BDWTR and UC3855ADWTR are not interchangeable due to differing UVLO thresholds: UC3855B turns on at 10.5V (500mV hysteresis), while UC3855A requires 15.5V (6V hysteresis). Substituting UC3855BDWTR into a UC3855ADWTR-designed board may cause premature startup or instability during brown-out conditions unless the VCC bias network is re-optimized.
UC3855BDWTR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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
UC3855BDWTR FAQ
1.How can I place an order for UC3855BDWTR through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3855BDWTR 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 UC3855BDWTR reliable?
The price and inventory of UC3855BDWTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3855BDWTR is usually 5 days.
3.What payment methods are accepted for UC3855BDWTR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3855BDWTR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3855BDWTR?
UC3855BDWTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3855BDWTR 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 UC3855BDWTR?
For technical support, including UC3855BDWTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3855BDWTR requirements.
6.How does Aetrix verify that UC3855BDWTR is sourced from the original manufacturer or authorized distributors?
All UC3855BDWTR 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 UC3855BDWTR meets industry standards.
7.What is the process for return or replacement of UC3855BDWTR?
All UC3855BDWTR units undergo pre-shipment inspection (PSI). If there is an issue with UC3855BDWTR, 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 UC3855BDWTR part is unused and in its original packaging.
Return procedure for UC3855BDWTR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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