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Texas Instruments UC3855BNG4
- Part No.:
- UC3855BNG4
- Manufacturer:
- Texas Instruments
- Category:
- PFC (Power Factor Correction)
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
UC3855BNG4.pdf
- Description:
- IC PFC CTR AV CURR 500KHZ 20DIP
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
UC3855BNG4 from Texas Instruments is a high-frequency average current-mode PFC controller IC designed for boost-type power factor correction preregulators. It delivers fixed-frequency control up to 500 kHz, integrates active snubbing (ZVT) for zero-voltage switching, features a 7.5 V ±1% precision reference, and supports universal AC input via analog multiplier with line compensation. It is used in industrial and telecom AC-DC front-end supplies requiring >95% efficiency and low THD.
For engineers reviewing the UC3855BNG4 datasheet, UC3855BNG4 pinout, UC3855BNG4 application, or UC3855BNG4 equivalent, this page provides verified technical context, validated pin functions, real-world application mappings, and two confirmed alternative parts with documented functional and thermal differences - all specific to the UC3855BNG4's 0°C to 70°C operating range and PDIP-20 package.
Technical Context
The UC3855BNG4 implements average current mode control using an internal current synthesizer that reconstructs inductor current from a single current sense transformer signal, eliminating slope compensation. Its integrated ZVT circuitry senses MOSFET drain voltage via the ZVS pin and drives the ZVTOUT gate driver to enable resonant turn-on, reducing diode recovery loss and EMI.
It employs a single-quadrant analog multiplier with VRMS feedforward to maintain constant power across universal AC inputs (85–265 VAC), while its voltage amplifier (5 MHz GBW, 80 dB open-loop gain) and current amplifier (2.5–5 MHz gain-bandwidth product, <4 mV offset) jointly regulate output voltage and shape input current waveform.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Turn-On Threshold | 10.5 V (UC3855B variant; enables startup at lower supply voltage than UC3855A) |
| Oscillator Frequency Range | 160–240 kHz (total variation over line/temp; CT = 470 pF yields ~200 kHz nominal) |
| Reference Voltage | 7.5 V ±1% (precision internal bandgap reference; stable under 1–10 mA load) |
| Current Amplifier GBW | 2.5–5 MHz (enables fast response to current transients in high-frequency PFC designs) |
| ZVTOUT Peak Current | 0.75 A (drives auxiliary ZVT MOSFET; sufficient for typical 1/3-size snubber switch) |
| Operating Temperature | 0°C to +70°C (industrial-grade rating; distinct from UC2855A/B's −40°C to +85°C) |
| Startup Supply Current | 150 µA typical (low ICC(OFF) enables efficient biasing from HV startup resistor) |
Pinout & Package
UC3855BNG4 is housed in a 20-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width, 0.1-inch lead pitch, and through-hole mounting. Pin 1 is identified by a notch or dot; leads are tin-lead (NIPDAU) finish, RoHS-compliant, and rated for 300°C soldering (10 sec).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CA | Inverting input of current amplifier | Accepts compensated feedback from CS; common-mode range −0.3 V to 5 V |
| CAO | Current amplifier output | Drives PWM comparator; rail-to-rail swing (0.1–7.5 V); sinks/source up to 0.5 mA |
| CI | Current synthesizer capacitor node | Charged/discharged to reconstruct inductor current waveform using IAC and RVS inputs |
| CS | Level-shifted current synthesizer output | Feeds CA input and peak-limit comparator; >1.5 V disables GTOUT |
| CT | Oscillator timing capacitor connection | Set frequency via f ≈ 1/(11200·CT); min 200 pF for accuracy and layout immunity |
| GND | Signal and power ground reference | All voltages referenced here; bypass capacitors must connect with shortest possible leads |
| GTOUT | Main boost MOSFET gate driver output | 1.5 A peak totem-pole drive; requires series gate resistor ≥10 Ω and Schottky clamp |
| IAC | Multiplier line-voltage current input | Accepts rectified AC line current proportional signal; nominal 650 mV offsets zero-crossing |
| IMO | Multiplier output current | Sinks current into CA resistor; gain constant −0.85 ±0.1 V⁻¹ at VRMS = 1.5 V |
| ION | Current sense transformer secondary input | Buffered and level-shifted to CI; source-only output; 10–15 µA bias current |
| OVP | Overvoltage protection input | Hysteretic comparator (7.5 V trip, 400 mV hysteresis); disables GTOUT/ZVTOUT on fault |
| REF | Precision 7.5 V reference output | Supplies 25 mA max; disabled during UVLO or OVP; requires 0.1 µF ceramic bypass |
| RVS | Output voltage-sensing buffer output | Provides 3 V nominal signal; forms second input to current synthesizer with IAC |
| SS | Soft-start control voltage node | Charged by internal current source; controls PWM duty ramp-up; discharges on VCC dropout |
| VAO | Voltage amplifier output | Drives multiplier non-inverting input; swing limited to 0.1–6 V; used for loop compensation |
| VCC | Positive supply input | Internally clamped at 20 V; UVLO threshold 10.5 V (on), 10.0 V (off); 25 mA operating current |
| VRMS | Line RMS voltage feedforward input | 0–5.5 V range; scales multiplier gain as 1/VRMS² for universal input operation |
| VSENSE | Voltage amplifier inverting input | Feedback node for boost output; nominal 3 V from divider; must exceed 1.5 V for synthesizer operation |
| ZVS | ZVT zero-voltage sense input | Detects MOSFET drain near 0 V (≈0.7 V threshold); resets ZVT latch; requires blocking diode |
| ZVTOUT | ZVT auxiliary MOSFET gate driver | 750 mA peak drive; supports soft-switching of snubber FET; same layout rules as GTOUT |
Key Features
| Feature | Design Value |
|---|---|
| Average current mode control | Stable, low-distortion AC line current without slope compensation; uses reconstructed inductor current from CI/CS |
| Integrated ZVT (Zero Voltage Transition) | Reduces MOSFET turn-on loss and diode reverse-recovery EMI; enables reliable 500 kHz operation with external resonant components |
| Inductor current synthesizer | Enables single current transformer sensing; eliminates shunt loss and improves noise margin in >300 W PFC stages |
| Analog multiplier with line compensation | VRMS feedforward ensures constant power delivery across 85–265 VAC input; supports universal-input SMPS front-ends |
| High-bandwidth current amplifier | 5 MHz gain-bandwidth product and <4 mV input offset enable fast transient response and accurate current regulation at high switching frequencies |
Applications
| Server Power Supply | Industrial Motor Drive Front-End |
|---|---|
|
Use Scenario: 1 kW AC-DC front-end in 1U server PSU with 80 PLUS Titanium compliance requirement. IC Role / Device Role / Timing Role: Primary PFC controller regulating boost stage; sets 200 kHz switching frequency via CT pin; synchronizes ZVT timing to main switch dead-time. Use Value: Enables >96% efficiency and <5% THD at full load by combining average current control with ZVT, meeting strict energy standards without additional DSP overhead. |
Use Scenario: 3-phase rectified input PFC stage in variable-frequency drive for HVAC compressors. IC Role / Device Role / Timing Role: Controls interleaved boost converter; VRMS input derived from DC bus ripple; VSENSE monitors regulated 750 V DC link. Use Value: Maintains unity power factor across wide input voltage range (400–690 VAC rectified) using multiplier feedforward, reducing upstream transformer sizing and harmonic filtering cost. |
| Telecom Rectifier | Medical Imaging Power System |
|
Use Scenario: -48 V telecom rectifier with hot-swap and hold-up capability, requiring low EMI and high reliability. IC Role / Device Role / Timing Role: Manages boost PFC before LLC resonant converter; OVP pin tied to DC bus monitor; SS pin coordinated with system enable sequencing. Use Value: ZVT reduces EMI below CISPR-32 Class B limits without large filter inductors, easing enclosure shielding and saving board space in dense rack-mount units. |
Use Scenario: High-stability X-ray generator power supply demanding low output ripple and rapid load transient response. IC Role / Device Role / Timing Role: Regulates 1.2 kV PFC output; REF pin supplies precision bias to downstream error amplifiers; CAO output feeds analog current loop of final regulation stage. Use Value: 1% reference and 80 dB open-loop voltage amplifier gain ensure <±0.5% output voltage regulation over line/load/temperature, critical for consistent X-ray dose delivery. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PFC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UC3855ADW | SOIC-20 package; higher VCC turn-on threshold (15.5 V); −40°C to +85°C temp range | Better suited for extended-temperature industrial environments; incompatible with UC3855BNG4's low-VCC startup profile | Select UC3855ADW only if board design supports SOIC footprint and requires wider temperature range. |
| L6562A | Fixed-frequency average current mode; no ZVT; 650 kHz max; 8-pin SO; 12 V VCC start | Lacks active snubbing; requires external slope compensation; lower integration (no multiplier feedforward or current synthesizer) | Choose L6562A for cost-sensitive, lower-power (<300 W) designs where ZVT and universal input are not required. |
Compared with UC3855ADW and L6562A, the UC3855BNG4 uniquely combines PDIP-20 robustness, 10.5 V UVLO for low-input startups, and integrated ZVT-making it optimal for legacy-compatible, medium-power telecom and industrial PFC designs where layout simplicity and EMI reduction are prioritized over package miniaturization.
Availability
UC3855BNG4 is available at Aetrix Electronics and suitable for server power supplies, industrial motor drive front-ends, telecom rectifiers, medical imaging systems, and test equipment requiring stable component supply and long-term industrial lifecycle support.
Supply support for UC3855BNG4 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 expertise in power conversion ICs and industrial-grade reliability.
The UC3855BNG4 belongs to TI's legacy high-performance PFC controller family, engineered specifically for high-efficiency, high-frequency boost preregulators in AC-DC power supplies targeting telecom, server, and industrial applications.
FAQ
What is the operating temperature range of the UC3855BNG4?
The UC3855BNG4 is specified for operation from 0°C to +70°C ambient temperature. This distinguishes it from the UC2855A/B variants, which support −40°C to +85°C. The UC3855BNG4's temperature grade aligns with commercial and light-industrial applications where extended cold-start capability is not required. Thermal derating guidelines apply above 70°C.
Does the UC3855BNG4 support zero-voltage switching (ZVS) natively?
Yes, the UC3855BNG4 integrates dedicated ZVT (Zero Voltage Transition) circuitry, including ZVS input sensing and ZVTOUT gate driver output. It detects MOSFET drain voltage collapse via the ZVS pin and triggers resonant turn-on using external auxiliary components - enabling true ZVS in boost PFC topologies without external controllers or complex timing logic.
How does the UC3855BNG4 achieve universal AC input compatibility?
The UC3855BNG4 achieves universal AC input (85–265 VAC) through its analog multiplier with VRMS feedforward. The VRMS pin accepts a voltage proportional to input RMS, scaling the multiplier gain as 1/VRMS² to maintain constant output power. Combined with the IAC current input and line-compensated multiplier, this ensures near-unity power factor across the full input range.
What is the function of the CI and CS pins on the UC3855BNG4?
The CI pin hosts the capacitor where the current synthesizer charges and discharges to reconstruct the boost inductor current waveform. The CS pin outputs a level-shifted version of that waveform, feeding both the current amplifier (CA) and the peak current limit comparator. Together, they enable accurate average current mode control using only one current sense transformer - reducing loss and improving noise immunity.
Is the UC3855BNG4 pin-compatible with other UC3855 variants?
The UC3855BNG4 shares identical pinout and electrical functionality with UC3855BN (same PDIP-20 package), but differs from UC3855ADW/BDW in package type and thermal specs. It is not pin-compatible with UC2855 variants due to differing UVLO thresholds and temperature grades - though PCB layout may be reused with verification of startup behavior and thermal margins.
UC3855BNG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Discontinued at Digi-Key
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
UC3855BNG4 FAQ
1.How can I place an order for UC3855BNG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3855BNG4 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 UC3855BNG4 reliable?
The price and inventory of UC3855BNG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3855BNG4 is usually 5 days.
3.What payment methods are accepted for UC3855BNG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3855BNG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3855BNG4?
UC3855BNG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3855BNG4 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 UC3855BNG4?
For technical support, including UC3855BNG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3855BNG4 requirements.
6.How does Aetrix verify that UC3855BNG4 is sourced from the original manufacturer or authorized distributors?
All UC3855BNG4 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 UC3855BNG4 meets industry standards.
7.What is the process for return or replacement of UC3855BNG4?
All UC3855BNG4 units undergo pre-shipment inspection (PSI). If there is an issue with UC3855BNG4, 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 UC3855BNG4 part is unused and in its original packaging.
Return procedure for UC3855BNG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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