5B High Performance Current Mode PWM Controller Datasheet

Category: Electronics, Other Semiconductors, STMicroelectronics Inc

Overview of UC2842B/3B/4B/5B UC3842B/3B/4B/5B PWM Controllers

The datasheet presents the UC2842B/3B/4B/5B UC3842B/3B/4B/5B series of high performance current mode PWM controllers used primarily in off-line and DC to DC fixed frequency applications. The key feature of these controllers includes an internally trimmed oscillator for precise frequency control and PWM operation up to 500kHz, latching PWM for cycle-by-cycle current limiting and an internal reference with undervoltage lockout. There are features to enable controlled operations such as automatic feed forward compensation, high current totem pole output, and under voltage lockout with hysteresis. A low operating current makes these controllers particularly suitable for power-efficient applications.

Functional Differences and Description

Variations among the series members are primarily the under-voltage lockout thresholds and the maximum duty cycle ranges. For instance, the UC3842B and UC3844B are designed for applications requiring UVLO thresholds of 16V (on) and 10V (off), while the UC3843B and UC3845B cater to thresholds of 8.5V and 7.9V respectively. Additionally, the UC3842B and UC3843B support duty cycles close to 100%, whereas the UC3844B and UC3845B have a range of 0% to 50% thanks to an internal toggle flip flop that adjusts the output.

Circuitry and Pin Configuration

The UC384xB control ICs minimize the need for external parts due to the integration of necessary circuit features. These features include a trimmed oscillator for duty cycle control, under voltage lockout with low start-up current, precision reference, latched operation, and a PWM comparator that controls current limits.

The provided block diagram illustrates the internal configuration, highlighting components such as the undervoltage lockout (UVLO), voltage reference (VREF), oscillator (OSC), error amplifier, PWM latch, and the current sense comparator. The datasheet specifies pin functions including the error amplifier output (COMP), inverting input (VFB), current sense input (ISENSE), oscillator timing (RT/CT), power ground (GROUND), output drive for a power MOSFET (OUTPUT), control IC supply voltage (Vcc), and the reference output (VREF).

Absolute Maximum Ratings and Ordering Information

The datasheet details absolute maximum ratings for parameters such as supply voltage, output current and energy, input voltages for analog inputs, error amplifier output current, power dissipation for different operating temperatures, storage temperature range, junction operating temperature, and lead temperature during soldering.

Ordering numbers are provided for both SO8 and Minidip packages for each member of the UC2842B/3B/4B/5B UC3842B/3B/4B/5B series, facilitating an easier selection process for various application needs.