UC3856Q

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The UC3856Q is a member of the versatile high performance Pulse Width Modulation (PWM) pulse-by-pulse current mode control family of PWM Controller ICs. These PWM controllers are designed to precisely control and regulate the output voltage and current of dc-to-dc converters, such as synchronous buck, boost, flyback and forward converters.

The UC3856Q can operate in both current mode control and voltage mode control for high performance closed loop control. The PWM control IC has internal circuitry specifically designed to allow flexible control of soft start and ramping.

In terms of its application field, the UC3856Q is especially suited for driving N-channel MOSFETs in a switching mode power supply for use with mobile devices like cellular phones, PDAs and other portable devices, which require a very low current standby mode as well as high efficiency in the middle/high load operation conditions.

The operating principle of the UC3856Q is based on a pulse by pulse current mode control. It has a dedicated internal sensing circuit that monitors the load current and results in controlling the switching frequency and integrated over current protection. It also has an output voltage regulation buffered voltage feedback loop which provides tight regulation of the output voltage.

It also provides internal Under Voltage Lock Out (UVLO) and Over Voltage Detection/Protection (OVDP) functions as well as cycle-by-cycle current limit protection and an Output Voltage Position (OVP) detection circuit to provide over current protection functions. In addition, there is a Thermal Shutdown (TSD) circuit to protect against IC over temperature condition.

The UC3856Q also has a feedback input which is used to sense the output voltage of the switching supply for regulation. It also includes a resistor divider network for setting the output voltage. When connected to an opto-coupler for regulation, the UC3856Q provides a very high accuracy voltage source. This can also be used for both routine monitoring and under overvoltage/overcurrent protection.

In addition, the IC also features a very low power standby mode control with little or no audible noise. This makes it suitable for low current applications that require low noise, such as LCD display and discrete component power supply.

Overall, the UC3856Q is an ideal Pulse Width Modulation (PWM) controller for driving N-channel MOSFETs in a switching mode power supply. It is suitable for use with mobile devices such as cellular phones, PDAs and other portable devices, as well as LCD displays and discrete component power supplies, which require a very low current standby mode as well as high efficiency in middle/high load operation condition.

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