UC2846Q

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UC2846Q Application Field and Working Principle

UC2846Q is a monolithic integrated circuit for pulse width modulation (PWM) controllers in DC/DC conversion applications, which belongs to the PMIC (Power Management Integrated Circuit) voltage regulators category. It is designed particularly for on-board switching power supplies in laptop computer, personal computers and other portable device applications.

Apart from its high operating frequency, high efficiency, and simple circuit construction features, UC2846Q particularly features programmable on-chip compensation and shutdown/restart. The integration of all of these functions into a single chip makes it a highly-desirable product for DC/DC converters.

In this section, we will examinethe working principle and application field of UC2846Q.

Working Principle

UC2846Q is a monolithic integrated dual pulse width modulation (PWM) controller intended for use in DC/DC converters. It combines a temperature compensated bandgap reference with an oscillator, a timer and three error amplifiers on a single monolithic CMOS chip. The oscillator frequency can be programmed with an external resistor to accommodate changing board layout requirements. It is composed of two independently functioning error amplifiers with common reference input.

The error amplifiers are basically magnitude comparators with positive feedback that are connected such that their outputs are complementary. The UC2846Q has two error amplifiers (each with separate ref and inv inputs) that only interact in the presence of skip pulses. This set of amplifiers is designed to generate a pulses width modulation (PWM) signal that replaces a traditional on/off or pulse-by-pulse type of switching control.

Apart from built-in compensation, UC2846Q also provide a built-in thermal shutdown and latch-up protection circuit that can protect against over-current and over-temperature conditions. It also includes a main output (MOUT) to enable voltage readout loop. To enable quick and regulated transient response, the chip also contains an internal current limiter in the main output.

Application Field

UC2846Q is an ideal choice for off-line switching power supplies or DC/DC converters in portable applications that are poweredfrom a wide range of supply voltages. It has been primarily designed for use in laptop computer, personal computer and other portable devices, but is also suitable for use in other off-line switching power supplies. Since its high frequency operation results in small component solutions, the UC2846Q ishighly suitable for board space-critical applications. On-chip compensation eliminates the need for externalcomponent compensation and can substantially reduce design time and costs.

In particular, it has been designed with the following application areas in mind:

• DC/DC converters - Especially laptop computer and personal computerequipment.
• Communications equipment - Switching power supplies for cellular phones and pagers.
• Consumer appliances - Switching power supplies for hairdryers, irons, etc.
• Computer peripherals -USB hubs, printers, scanners, etc.
• Audio equipment - Switching power supplies for amplifiers, etc.

In conclusion, UC2846Q makes an excellent choice for DC/DC switching controllers, and its on-board features make it an attractive solution for many applications.

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