UC2844B ST High Performance Current Mode PWM Controller Data Sheet

Download Datasheet for STMicroelectronics UC2844B High Performance Current Mode PWM Controller [15 pages 1999 pdf/zip]

SKU: UC2844BSTDS1999 Category: Brand:

Description

* 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
* Lowstart-Up And Operating Current

The UC384xB 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.

DATASHEET CONTAINS:

BLOCK DIAGRAM

ABSOLUTE MAXIMUM RATINGS

PIN CONNECTION (PINOUT)

PIN FUNCTIONS

ORDERING NUMBERS

THERMAL DATA

ELECTRICAL CHARACTERISTICS
– REFERENCE SECTION
– OSCILLATOR SECTION
– ERROR AMP SECTION
– CURRENT SENSE SECTION
– OUTPUT SECTION
– UNDER-VOLTAGE LOCKOUT SECTION
– PWM SECTION
– TOTAL STANDBY CURRENT

Figure 1: Open Loop Test Circuit.
Figure 2: Timing Resistor vs. Oscillator Frequency
Figure 3: Output Dead-Time vs. Oscillator Frequency
Figure 4: Oscillator Discharge Current vs. Temperature.
Figure 5: Maximum Output Duty Cycle vs. Timing Resistor.
Figure 6: Error Amp Open-Loop Gain and Phase vs. Frequency.
Figure 7: Current Sense Input Threshold vs. Error Amp Output Voltage.
Figure 8: Reference Voltage Change vs. Source Current.
Figure 9: Reference Short Circuit Current vs. Temperature.
Figure 10: Output Saturation Voltagevs. Load Current.
Figure 11: Supply Current vs. Supply Voltage.
Figure 12: Output Waveform.
Figure 13: Output Cross Conduction.
Figure 14: Oscillator and Output Waveforms.
Figure 15: ErrorAmp Configuration.
Figure 16: Under Voltage Lockout.
Figure 17: Current Sense Circuit.
Figure 18: SlopeCompensation Techniques.
Figure 19: IsolatedMOSFET Drive and Current Transformer Sensing.
Figure 20: Latched Shutdown.
Figure 21: Error Amplifier Compensation.
Figure 22: External Clock Synchronization.
Figure 23: External Duty Cycle Clamp and Multi Unit Synchronization.
Figure 24: Soft-Start Circuit.
Figure 25: Soft-Start and Error Amplifier Output Duty Cycle Clamp.

OUTLINE AND MECHANICAL DATA