Current-Mode PWM Controller - UC3843

UC3843 (ACTIVE)

Current-Mode PWM Controller

Description

The UC1842/3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include under-voltage lockout featuring start up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off state.

Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have UVLO thresholds of 16 VON and 10 VOFF, ideally suited to off-line applications. The corresponding thresholds for the UC1843 and UC1845 are 8.4 V and 7.6 V. The UC1842 and UC1843 can operate to duty cycles approaching 100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.

Features

  • Optimized For Off-line and DC-to-DC Converters
  • Low Start-Up Current (<1 mA)
  • Automatic Feed ForwardCompensation
  • Pulse-by-Pulse Current Limiting
  • Enhanced Load Response Characteristics
  • Under-Voltage Lockout With Hysteresis
  • Double Pulse Suppression
  • High Current Totem Pole Output
  • Internally Trimmed Bandgap Reference
  • 500-kHz Operation
  • Low RO Error Amp

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Parametrics Compare all products in PWM and Resonant Controller

 
Topology
Control Method
Vin (Min) (V)
Vin (Max) (V)
Frequency (Max) (kHz)
UVLO Thresholds On/Off (V)
Duty Cycle (Max) (%)
Gate Drive (Typ) (A)
Special Features
Rating
Operating Temperature Range (C)
Pin/Package
UC3843 LM5021 LM5021-Q1 UC1843 UC2843 UC3842 UC3845
Boost
Buck
Flyback
Forward    
Boost
Flyback    
Flyback     Boost
Flyback
Forward    
Boost
Flyback
Forward    
Boost
Buck
Flyback
Forward    
Boost
Buck
Flyback
Forward    
Current         Current     Current     Current     Current    
7.6     8     8     7.6     7.6     10     7.6    
30     30     30     30     30     30     30    
500         500     500     500     500    
8.4/7.6         8.4/7.6     8.4/7.6     16/10     8.4/7.6    
100     80     80     100     100     100     50    
1     0.7       1     1     1     1    
Error Amplifier     Frequency Synchronization     Frequency Synchronization     Error Amplifier     Error Amplifier     Error Amplifier     Error Amplifier    
Catalog     Catalog     Automotive     Military     Military     Catalog     Catalog    
0 to 70     -40 to 125     -40 to 125     -55 to 125     -40 to 85     0 to 70     0 to 70    
14SOIC
8PDIP
8SOIC    
8PDIP
8VSSOP    
8VSSOP     20LCCC
8CDIP    
14SOIC
8PDIP
8SOIC    
14SOIC
8PDIP
8SOIC    
14SOIC
8PDIP
8SOIC    

Other qualified versions of UC3843

Version Part Number Definition
Military UC1843 QML certified for Military and Defense Applications

WEBENCH® Designer UC3843

 AC  DC  
AC Frequency  60 Hz  50 Hz
Use Isolated Output?
  Min   Max Range
VinRMS  V 20.00 to 300.00V
Vout  V 3.3 to 50.0V
Iout  A ≤ 20.0A
Ambient Temp  °C 0 to 70°C