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STMicroelectronics UC3842BN
- Part No.:
- UC3842BN
- Manufacturer:
- STMicroelectronics
- Category:
- DC DC Switching Controllers
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
UC3842BN.pdf
- Description:
- IC REG CTRLR PWM CM 8-MINIDIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,589
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Product details
Overview
UC3842BN 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 250 kHz oscillator, latching PWM for cycle-by-cycle current limiting, 5 V ±1% internal reference with UVLO (16 V on / 10 V off), and a totem-pole output capable of ±1 A peak drive for N-channel MOSFETs.
For engineers reviewing the UC3842BN datasheet, UC3842BN pinout, UC3842BN application, or UC3842BN equivalent, key selection criteria include its 100% max duty cycle capability, <0.5 mA start-up current, 2.5 V error amplifier input threshold, 3 V/V current sense gain, and SO8/Minidip package compatibility in industrial and consumer SMPS designs.
Technical Context
The UC3842BN implements current-mode control using a comparator that compares sensed inductor current against an error-amplifier-derived ramp reference. Its oscillator uses RT/CT network to set frequency up to 500 kHz, with internal trimming ensuring ±3% tolerance at 250 kHz under nominal conditions.
UVLO hysteresis (16 V ON / 10 V OFF) ensures reliable start-up and brown-out recovery; the 5 V reference (±20 mV line/load regulation) feeds both CT charging and external compensation networks, while the COMP pin provides direct access to the error amplifier output for loop stabilization.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Oscillator Frequency | 250 kHz guaranteed - enables stable switching in universal-input AC-DC adapters without external frequency calibration. |
| Max Duty Cycle | 96–100% - supports high step-down ratio topologies like flyback and forward converters with minimal dead time. |
| Start-up Current | <0.5 mA at 6.5 V - reduces auxiliary winding losses and enables direct HV startup from rectified AC lines. |
| Output Drive | ±1 A peak sink/source - directly drives gate capacitance of ≤1 nF MOSFETs without external buffers in sub-100 W designs. |
| Current Sense Gain | 3 V/V - converts 1 V across sense resistor to 3 V at comparator input, enabling precise 0.33 V current limit threshold setting. |
| Reference Voltage | 5.00 V ±100 mV - powers RT/CT timing network and serves as stable bias for feedback divider and compensation circuits. |
| UVLO Threshold | 16 V (ON) / 10 V (OFF) - prevents erratic operation during low-line brownouts and ensures clean restart after AC dropout. |
Pinout & Package
UC3842BN is available in 8-pin Minidip (PDIP-8) and SO8 packages. Pin functions are electrically identical across variants; mechanical dimensions differ per JEDEC MS-012 (SO8) and standard PDIP-8 outlines.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - COMP | Error Amplifier Output | Provides open-collector output for Type II/III compensation networks; requires external RC network to stabilize voltage-mode or current-mode loops. |
| 2 - VFB | Inverting Input of Error Amplifier | Receives feedback voltage from output divider; 2.5 V internal reference sets regulation point when VFB = 2.5 V. |
| 3 - ISENSE | Current Sense Input | Accepts voltage proportional to primary-side current; comparator trips at ~1 V, enabling cycle-by-cycle overcurrent shutdown. |
| 4 - RT/CT | Oscillator Timing Node | Connects external resistor to VREF and capacitor to GND; sets fOSC and maximum duty cycle via discharge current (7.8–8.8 mA). |
| 5 - GROUND | Signal & Power Ground | Single-point return for control circuitry and power stage; critical for noise immunity in high di/dt SMPS layouts. |
| 6 - OUTPUT | Totem-Pole Gate Driver | Sources/sinks ≥200 mA continuously; logic-high state pulls gate to ~13.5 V, low state discharges to ≤0.4 V for fast MOSFET turn-off. |
| 7 - VCC | Supply Input | Operates from 10–30 V; internal zener clamps at 36 V; draws 12–17 mA during operation and <0.5 mA at startup. |
| 8 - VREF | 5 V Reference Output | Supplies 50 mA max; charges CT through RT; used for biasing feedback dividers and external circuitry requiring stable 5 V. |
Key Features
| Feature | Design Value |
|---|---|
| Latching PWM with cycle-by-cycle current limit | Prevents MOSFET destruction during overload by disabling output until next clock cycle reset - no external latch required. |
| Internally trimmed 5 V reference | ±20 mV line/load regulation enables accurate feedback scaling without external precision references in cost-sensitive adapters. |
| Automatic feed-forward compensation | Input voltage variation directly modulates oscillator timing, improving transient response to line changes without extra components. |
| Low-startup current (<0.5 mA) | Reduces dissipation in startup resistors and allows use of high-value resistors (>1 MΩ) for direct AC-line connection. |
| High-current totem-pole output | ±1 A peak drive eliminates need for external driver stages in ≤100 W applications, reducing BOM count and layout area. |
Applications
| AC-DC Adapter | PC ATX Standby Supply |
|---|---|
|
Use Scenario: 5–24 V isolated output from universal AC input (85–265 VAC) in wall-wart and laptop chargers. IC Role / Device Role / Timing Role: Primary-side PWM controller implementing current-mode flyback topology with fixed 250 kHz switching. Use Value: Enables compact design with <0.5 mA start-up current, eliminating dedicated startup ICs and reducing transformer auxiliary winding complexity. |
Use Scenario: +5 VSB generation in desktop PC power supplies operating continuously at light load. IC Role / Device Role / Timing Role: Constant-frequency current-mode controller managing low-power standby rail with tight regulation and fast transient response. Use Value: 5 V reference stability (±100 mV) and 2.5 V error amp threshold ensure ±3% output accuracy across temperature and line variations. |
| Industrial DC-DC Converter | LED Driver (Constant Current) |
|
Use Scenario: 12–48 V input to 3.3/5/12 V isolated outputs in PLC and sensor interface modules. IC Role / Device Role / Timing Role: Fixed-frequency current-mode controller in forward or half-bridge topology with programmable fOSC up to 500 kHz. Use Value: 100% max duty cycle and 3 V/V current sense gain allow precise current limiting and high efficiency at partial load. |
Use Scenario: Constant-current LED driver for signage or architectural lighting using buck-boost or SEPIC topology. IC Role / Device Role / Timing Role: Current-mode PWM controller regulating LED string current via primary-side sensing and error amplifier feedback. Use Value: Latching overcurrent protection and <150 ns current sense delay prevent LED thermal runaway during short-circuit events. |
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 |
|---|---|---|---|
| UC3842D8TR | SO8 package, tape-and-reel, same electrical specs but qualified for extended temperature range (–40°C to 105°C). | Preferred for automotive or industrial environments where ambient exceeds 70°C. | Select when production volume requires reel packaging and higher temperature grade is mandatory. |
| NCP1200DR2G | Fixed-frequency current-mode controller with integrated HV startup, lower start-up current (50 µA), but no 5 V reference output. | Eliminates startup resistor but requires external reference for feedback; lacks VREF pin functionality. | Choose for ultra-low standby power designs where VREF is not needed and HV startup integration reduces component count. |
Compared with UC3842BN, UC3842D8TR offers identical performance in a more manufacturable package with wider temperature support, while NCP1200DR2G trades VREF availability and pin compatibility for significantly lower no-load consumption and integrated HV startup - making it suitable only when reference output is unused and energy efficiency dominates layout simplicity.
Availability
UC3842BN is available at Aetrix Electronics and suitable for AC-DC adapters, PC standby supplies, industrial DC-DC converters, and LED drivers requiring stable component supply, long-term lifecycle continuity, and traceable sourcing.
Supply support for UC3842BN 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-effective, high-reliability current-mode switch-mode power supplies - targeting consumer, industrial, and computing power conversion where minimal external parts and robust fault handling are essential.
FAQ
What is the maximum recommended oscillator frequency for UC3842BN?
The UC3842BN supports oscillator frequencies up to 500 kHz, verified by test conditions in the datasheet using RT = 6.2 kΩ and CT = 1 nF. At 250 kHz (guaranteed spec), timing accuracy is ±3%; above 350 kHz, propagation delays and layout parasitics may reduce effective duty cycle resolution and require careful PCB grounding near pins 4 and 5.
Can UC3842BN drive a P-channel MOSFET directly?
No - UC3842BN's OUTPUT pin is a totem-pole stage optimized for sinking current into an N-channel MOSFET gate. Driving a P-channel device would require level-shifting circuitry or an external inverter, as the output does not swing above VCC nor provide high-side gate drive capability. Its logic-high state reaches ~13.5 V (at 20 mA), insufficient for full enhancement of most P-MOSFETs.
How does the UVLO hysteresis affect system behavior during brown-out conditions?
With 16 V turn-on and 10 V turn-off thresholds, UC3842BN remains active down to 10 V, then shuts down completely until VCC rises above 16 V. This 6 V hysteresis prevents oscillatory restart during marginal AC line sags, ensuring clean re-initiation only after sufficient bulk capacitor recharge - critical for avoiding repeated MOSFET stress in offline converters.
Is the 5 V reference (pin 8) internally buffered for driving external circuitry?
Yes - the VREF pin delivers up to 50 mA with ±100 mV regulation over line, load, and temperature. It is internally buffered and intended to power RT/CT networks, feedback dividers, and low-current external comparators. Loading beyond 50 mA risks reference droop and oscillator frequency drift; for >50 mA loads, an external buffer amplifier is required.
UC3842BN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- Series:
- -
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- 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):
- 96%
- Synchronous Rectifier:
- No
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Frequency Control
- Operating Temperature:
- 0°C ~ 70°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 8-Mini DIP
UC3842BN FAQ
1.How can I place an order for UC3842BN through Aetrix?
Please submit a Request for Quotation (RFQ) for UC3842BN 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 UC3842BN reliable?
The price and inventory of UC3842BN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for UC3842BN is usually 5 days.
3.What payment methods are accepted for UC3842BN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for UC3842BN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for UC3842BN?
UC3842BN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your UC3842BN 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 UC3842BN?
For technical support, including UC3842BN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your UC3842BN requirements.
6.How does Aetrix verify that UC3842BN is sourced from the original manufacturer or authorized distributors?
All UC3842BN 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 UC3842BN meets industry standards.
7.What is the process for return or replacement of UC3842BN?
All UC3842BN units undergo pre-shipment inspection (PSI). If there is an issue with UC3842BN, 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 UC3842BN part is unused and in its original packaging.
Return procedure for UC3842BN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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