SLUS224H September   1994  – October 2024 UC1842A , UC1843A , UC1844A , UC1845A , UC2842A , UC2843A , UC2844A , UC2845A , UC3842A , UC3843A , UC3844A , UC3845A

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Pin Configuration and Functions
  6. Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Pulse-by-Pulse Current Limiting
      2. 6.3.2 Current Sense Circuit
      3. 6.3.3 Error Amplifier Configuration
      4. 6.3.4 Undervoltage Lockout
      5. 6.3.5 Oscillator
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Undervoltage Lockout (UVLO) Start-Up
      3. 6.4.3 UVLO Turnoff Mode
  8. Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Custom Design With WEBENCH® Tools
        2. 7.2.2.2 UC2842A Design Procedure
      3. 7.2.3 Application Curves
  9. Power Supply Recommendations
  10. Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
        1. 10.1.1.1 Custom Design With WEBENCH® Tools
      2. 10.1.2 Device Nomenclature
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Related Links
    4. 10.4 Receiving Notification of Documentation Updates
    5. 10.5 Support Resources
    6. 10.6 Trademarks
    7. 10.7 Electrostatic Discharge Caution
    8. 10.8 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Electrical Characteristics

Unless otherwise stated, these specifications apply for TA = –55°C to 125°C (UC184xA), TA = –40°C to 125°C (UC284xAQ), TA = –40°C to 85°C (UC284xA), TA = 0°C to 70°C (UC384xA); TA = TJ; VCC = 15 V(4); RT = 10 kΩ; CT = 3.3 nF.
PARAMETERTEST CONDITIONSMINTYPMAXUNIT
REFERENCE
Output voltageTJ = 25°C, IO = 1 mAUC184xA, UC284xA4.9555.05V
UC384xA4.955.1
Line regulation12 ≤ VIN ≤ 25 V620mV
Load regulation1 ≤ IO ≤ 20 mA625mV
Temperature stabilitySee (1)(6)0.20.4mV/°C
Total output variationLine, Load, TemperatureUC184xA, UC284xA4.95.1V
UC384xA4.825.18
Output noise voltage10 Hz ≤ f ≤ 10 kHz; TJ = 25°C(1)50µV
Long-term stabilityTA = 125°C, 1000 hrs(1)525mV
Output short circuit–30–100–180mA
OSCILLATOR
Initial accuracyTJ = 25°C(5)475257kHz
Voltage stability12 ≤ VCC ≤ 25 V0.2%1%
Temperature stabilityTMIN ≤ TA ≤ TMAX(1)5%
AmplitudeVRT/CT peak to peak(1)1.7V
Discharge currentTJ = 25°C, VRT/CT = 2 V(7)7.88.38.8mA
VRT/CT = 2 V(7)UC184xA, UC284xA7.58.8
UC384xA7.68.8
ERROR AMPLIFIER
Input voltageVCOMP = 2.5 VUC184xA, UC284xA2.452.52.55V
UC384xA2.422.52.58
Input bias current–0.3–1µA
–0.3–2
AVOLOpen-loop gain2 ≤ VO ≤ 4 V6590dB
Unity gain bandwidthTJ = 25°C(1)0.71MHz
CMRRCommon mode rejection ratio12 ≤ VCC ≤ 25 V6070dB
Output sink currentVFB = 2.7 V, VCOMP = 1.1 V26mA
Output source currentVFB = 2.3 V, VCOMP = 5 V–0.5–0.8mA
VOUT highVFB = 2.3 V, RL = 15 kΩ to ground56V
VOUT lowVFB = 2.7 V, RL = 15 kΩ to VREF0.71.1V
CURRENT SENSE
GainSee (2)(3)2.8533.15V/V
Maximum input signalVCOMP = 5 V(2)0.911.1V
PSRRPower supply rejection ratio12 ≤ VCC ≤ 25 V(2)70dB
Input bias current–2–10µA
Delay to outputVISENSE = 0 to 2 V(1)150300ns
OUTPUT
Output low levelISINK = 20 mA0.10.4V
ISINK = 200 mA1.52.2
Output high levelISOURCE = 20 mA1313.5V
ISOURCE = 200 mA1213.5
Rise timeTJ = 25°C, CL = 1 nF(1)25150ns
Fall timeTJ = 25°C, CL = 1 nF(1)25150ns
UVLO saturationVCC = 5 V, ISINK = 10 mA0.71.2V
UNDERVOLTAGE LOCKOUT
Start thresholdUC1842A, UC1844A, UC2842A, and UC2844A151617V
UC3842A and UC3844A14.51617.5
UCx843A and UCx845A7.88.49
Minimum operation voltage after turnonUC1842A, UC1844A, UC2842A, and UC2844A91011V
UC3842A and UC3844A8.51011.5
UCx843A and UCx845A77.68.2
PWM
Maximum duty cycleUCx842A, UCx843A92%96%100%
UCx844A, UCx845A46%48%50%
Minimum duty cycle0%
TOTAL STANDBY CURRENT
Start-up current0.30.5mA
Operating supply currentVFB = VISENSE = 0 V1117mA
VCC Zener voltageICC = 25 mA3039V
Verified by design, but not 100% production tested.
Parameter measured at trip point of latch with VFB = 0.
Gain defined as: A = ΔVCOMP / ΔVISENSE; 0 ≤ VISENSE ≤ 0.8 V.
Adjust VCC above the start threshold before setting at 15 V.
Output frequency equals oscillator frequency for the UCx842A and UCx843A. Output frequency is one half oscillator frequency for the UCx844A and UCx845A.
Temperature stability, sometimes referred to as average temperature coefficient, is described by: Temperature stability = ( VREF(max) – VREF(min)) / (TJ(max) – TJ(min) ). VREF(max) and VREF(min) are the maximum and minimum reference voltage measured over the appropriate temperature range. Note that the extremes in voltage do not necessarily occur at the extremes in temperature.
This parameter is measured with RT = 10 kΩ to VREF. This contributes approximately 300 µA of current to the measurement. The total current flowing into the RT/CT pin is approximately 300 µA higher than the measured value.