UC3856QG3

The UC3856QG3 is a low-cost, high-efficiency PWM current-mode controller from Microchip. It is designed to regulate the output voltage of a switch mode power supply (SMPS) using a fixed frequency, voltage-mode control algorithm. The output waveforms are digitally generated, providing excellent control flexibility. This controller is capable of outputting current up to 3 A in continuous mode and up to 6 A in pulse-by-pulse-mode operation.

The UC3856QG3 is optimized for efficiency and can operate with reduced switching losses. It can provide a wide input operating range and regulated output voltages up to 15 V. With its low memory-requirement and logic-based startup, the UC3856QG3 simplifies the development of precision power supplies. It also features programmable overload protection, allowing it to protect the power supply from excessive overload and correct faults.

The UC3856QG3 operates in a Current-Mode PWM or PWM for voltage mode control. In Current-Mode PWM, a trapezoidal modulation law is used to control the output current by varying the duty cycle of the switching transistor. The output voltage is thereby set by controlling the current and playing into effect the output inductor-capacitor combination—a process called Magamp control. V/I (voltage-to-current) –mode control, or alternatively PWM for voltage mode control, is used to regulate the output voltage by varying the duty cycle of the switching transistor directly. The output current is thereby driven by the voltage, capacitance and inductance—a process called Vamp (voltage-mode) control.

The UC3856QG3 features overcurrent protection, undervoltage protection, and programmable soft-start. In addition, a frequency-mode control select pin allows rapid switching between frequencies, allowing for a tailored solution for each application. The UC3856QG3 also includes an advanced fault protection system to protect against over-voltage and over-current conditions.

The UC3856QG3 is well suited for a wide array of switches mode power supplies, from controllable transformers to small linear regulators. It is best suited for applications where efficiency is paramount and a wide input range of voltages is required, such as in tablet PCs, notebooks, and other mobile devices. Comparatively, the UC3856QG3 achieves higher efficiency with a significantly lower cost. This makes it an ideal solution for cost-sensitive applications.