Image UC3843
型号: UC3843
厂商: Texas Instruments Texas Instruments
标准:
分类: 半导体
描述: current mode pwm controller
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UC3843的详细信息

Feature: Current-Mode PWM Controller
UC1842/3/4/5  
UC2842/3/4/5  
UC3842/3/4/5  
Current Mode PWM Controller  
FEATURES  
DESCRIPTION  
Optimized For Off-line And DC  
To DC Converters  
The UC1842/3/4/5 family of control ICs provides the necessary features to im-  
plement off-line or DC to DC fixed frequency current mode control schemes  
with a minimal external parts count. Internally implemented circuits include un-  
der-voltage lockout featuring start up current less than 1mA, a precision refer-  
ence 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 out-  
put stage, suitable for driving N Channel MOSFETs, is low in the off state.  
Low Start Up Current (<1mA)  
Automatic Feed Forward  
Compensation  
Pulse-by-pulse Current Limiting  
Enhanced Load Response  
Characteristics  
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 16V (on) and 10V (off), ideally suited to off-line applica-  
tions. The corresponding thresholds for the UC1843 and UC1845 are 8.4V  
and 7.6V. 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.  
Under-voltage Lockout With  
Hysteresis  
Double Pulse Suppression  
High Current Totem Pole  
Output  
Internally Trimmed Bandgap  
Reference  
500khz Operation  
Low RO Error Amp  
BLOCK DIAGRAM  
Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.  
Note 2: Toggle flip flop used only in 1844 and 1845.  
4/97  

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