Features: ·TRIMMED OSCILLATOR FOR PRECISE FREQUENCY CONTROL
·OSCILLATOR FREQUENCY GUARANTEED AT 250kHz
·CURRENT MODE OPERATION TO 500kHz
·AUTOMATIC FEED FORWARD COMPENSATION
·LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING
·INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT
·HIGH CURRENT TOTEM POLE OUTPUT
·UNDERVOLTAGE LOCKOUT WITH HYSTERESIS
·LOW START-UP AND OPERATING CURRENTPinout
Specifications
| Symbol |
Parameter |
Value |
Unit |
| Vi |
Supply Voltage (low impedance source) |
30 |
V |
| Vi |
Supply Voltage (Ii < 30mA) |
Self Limiting |
|
| IO |
Output Current |
±1 |
A |
| EO |
Output Energy (capacitive load) |
5 |
J |
|
Analog Inputs (pins 2, 3) |
0.3 to 5.5 |
V |
|
Error Amplifier Output Sink Current |
10 |
mA |
| Ptot |
Power Dissipation at Tamb 25 °C (Minidip) |
1.25 |
W |
| Ptot |
Power Dissipation at Tamb 25 °C (SO8) |
800 |
mW |
| Tstg |
Storage Temperature Range |
65 to 150 |
|
| TL |
Lead Temperature (soldering 10s) |
300 |
|
All voltages are with respect to pin 5, all currents are positive into the specified terminal.DescriptionThe UC384XT 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 a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5mA, 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 offstate.
Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842T and UC3844T have UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applications The corresponding thresholds for the UC3843T and UC3845T are 8.5 V and 7.9 V. The UC3842T and UC3843T can operate to duty cycles approaching 100%. A range of zero to < 50 % is obtained by the UC3844T and UC3845T by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.
Here is the description about UC3845T of the HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER. The UC384XT 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 implmented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5mA, 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 sourceor sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the offstate.
Here are the features: TRIMMED OSCILLATOR FOR PRECISE FREQUENCY CONTROL; OSCILLATOR FREQUENCY GUARANTEEDAT 250kHz; CURRENT MODE OPERATION TO 500kHzAUTOMATIC FEED FORWARD COMPENSATION; LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING; INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT; HIGH CURRENT TOTEM POLE OUTPUT; UNDERVOLTAGE LOCKOUT WITH HYSTERESIS; LOW START-UP AND OPERATING CURRENT.
Here are the absolute Maximum Ratings (TA = 25). Supply Voltage (low impedance source) is 30V. Supply Voltage (Ii < 30mA) is Self Limiting. Output Current is ±1A. Output Energy (capacitive load) is 5uJ. Analog Inputs (pins 2, 3) is from 0.3 to 5.5V. Error Amplifier Output Sink Current is 10mA. Power Dissipation at T amb 25 C (Minidip) is 1.25W. The lead Temperature is 300C. The Storage Temperature is from 65 to +150C.
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UC3845T Data Sheet
