LTC3787IGN

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Linear Technology\'s LTC3787IGN is a high frequency PWM controller, designed for off-line and DC/DC converter applications. This highly integrated IC device includes a 550V/4A SenseFET with internally set current limit, and a PWM controller driving a low Rds(on) N-Channel MOSFET with low output voltage switching ripple and low component count.

Application Field

The LTC3787IGN is highly suitable for applications that require a high efficiency supply with low voltage ripple. It handles input and output voltages ranging from 3.5V to 16V. The LTC3787IGN can generate output power from 10W to 30W and provides a wide range of features to satisfy many types of applications. It can be used in off-line power supplies, DC/DC converters, 3.3V/5V to 5V/12V/15V conversion, adaptive-mode converters, fixed frequency converters, adapter/chargers for portable equipment and notebook computers, motor controls, lighting, induction heating, and polymer/battery charger LED.

Working Principle

The LTC3787IGN works by employing a pulse width modulation (PWM) control scheme. PWM is a technique used to acquire precise digital or analog output by quickly turning a digital or analog signal on or off over a fixed period of time. The frequency of this fixed period is determined by a frequency-setting resistor, and it is inversely proportional to the value of the resistor. In the case of the LTC3787IGN, the output voltage is regulated using a voltage feedback signal taken from the output side.

In the feedback loop, a voltage divider R7 and R8 creates the feedback signal that is compared to the reference voltage (Vref). When the output voltage is lower than the reference voltage, the PWM signal becomes longer and the switch is on for some more time. On the contrary, when the output voltage is higher than the reference voltage, the PWM signal becomes shorter and the switch is on for some less time. This control loop also regulates the switching current, making it constant and synchronous with the PWM switch.Moreover, the LTC3787IGN also features a fixed frequency of 180kHz, allowing the PWM cycle to adjust the on-time quickly while at the same time limiting the noise and EMI radiated by the converter.

Conclusion

The LTC3787IGN is a highly integrated IC device for off-line and DC/DC converter applications. It includes a 550V/4A SenseFET with internally set current limit, and a PWM controller driving a low Rds(on) N-Channel MOSFET. It is suitable for applications requiring a high efficiency supply with low voltage ripple and can generate output power of ranging from 10W to 30W. The LTC3787IGN employs a pulse width modulation (PWM) control scheme with a frequency of 180kHz, allowing the PWM cycle to adjust the on-time quickly while at the same time limiting the noise and EMI radiated by the converter.

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