UC3845

The UC1842/3/4/5 family of control ICs 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 than1mA,aprecision reference trimmed for ac curacyat the error ampinput,logic to insure latched operation,a PWM comparator which also provide scurrentl imit control,and a totem poleout put stage designed to source or sink high peak current.The out put stage,suit able 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 16V (on) and 10V (off),ideally suited to off-line applications.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 UC 1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.

The UC3845 is designed as current mode PWM controller which provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count.

UC3845 has eleven features. (1) Optimized for off-line and DC to DC converters. (2) Low start-up current (< 1 mA). (3) Automatic feed forward compensation. (4) Pulse-by-pulse current limiting. (5) Enhanced load response characteristics. (6) Under-voltage lockout with hysteresis. (7) Double pulse suppression. (8) High current totem pole output. (9) Internally trimmed bandgap reference. (10) 500 kHz operation. (11) Low Ro error AMP. That are all the main features.

Some absolute maximum ratings of UC3845 have been concluded into several points as follow. (1) Its supply voltage (low impedance source) would be 30V. (2) Its output current would be +/-1A. (3) Its output energy (capacitive load) would be 5uJ. (4) Its analog inputs pins 2,3 would be from -0.3V to 6.3V. (5) Its error amplifier output sink current would be 10mA. (6) Its power dissipation at Ta<=50°C (minidip, DIP-14) would be 1W. (7) Its power dissipation at Tamb <= 25°C (SO14) would be 725mW. (8) Its storage temperature range would be from -65 to 150°C. (9) Its lead temperature (soldering 10s) would be 300°C. It should be noted that stresses above those listed in absolute maximum ratings may cause permanent damage to device.

Also some electrical characteristics about UC3845. (1) Its output voltage would be min 4.9V and typ 5.0V and max 5.1V. (2) Its line regulation would be typ 6mV and max 20mV. (3) Its load regulation would be typ 6mV and max 25mV. (4) Its temperature stability would be typ 0.2mV/°C and max 0.4mV/°C. (5) Its total output variant would be min 4.82V and max 5.18V. And so on. If you have any question or suggestion or want to know more information please contact us for details. Thank you!