LT3845AMPFE#TRPBF

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The LT3845AMPFE#TRPBF is a high-voltage, wide-VIN, high-switching frequency synchronous step-down DC-DC controller with integrated FETs and a few small external components. It is capable of operating with an input voltage ranging from 2.6V to 72V and provides output voltages as low as 0.5V. It is an ideal solution for high power density applications, such as servers, storage, telecommunications and electric vehicles.

The LT3845AMPFE#TRPBF features a low quiescent current of 500nA operating at 2.6V to 4.5V and 150uA operating from 4.5V to 60V, allowing for extremely low power consumption. The device also includes an advanced current mode control to provide fast transient response, good current-sharing accuracy, and an adjustable soft-start. The device incorporates integrated FETs capable of up to 8A continuous minimum output current and 10A surge current rating.

The LT3845AMPFE#TRPBF operates in a PWM mode at a switch frequency of 800kHz and includes an adjustable deadtime to minimize switching losses. The device also includes over-current protection, over-temperature protection, and pulse-by-pulse current limit scheme. The operating temperature range extends from -40°C to +125°C.

The LT3845AMPFE#TRPBF has a variety of applications and is a perfect choice for high current, high voltage supply applications. It is ideal for powering FPGAs, microprocessors and DSPs. It is also suitable for designs requiring a high-efficiency and small solution size such as battery powered, automotive and industrial environments.

Working Principle

The LT3845AMPFE#TRPBF operates by regulating the output voltage over a variety of input voltage conditions. A high-speed, high-side switch (MOSFET) and a low-side switch (MOSFET) are employed to generate pulses of current. The PWM control regulates the pulses of current to maintain the input voltage (Vin) and the output voltage (Vout). The amount of time the high side switch is on is referred to as the ON-time and the amount of time the low side switch is on is referred to as the OFF-time.

The ON-time and OFF-time of the switch is regulated to the ratio required to maintain the regulated output voltage. This ratio is depicted by the equation below:

[ON-time/ (ON-time + OFF-time)] = 1 – (Vout/Vin)

The ON-time, OFF-time and the load current (Iout) determines the amount of energy transferred from the input voltage (Vin) to the output voltage (Vout). The energy transfer from Vin to Vout is determined by the equation below:

Energy Transfer = (ON-time/Fsw) * Vin * Iout

Fsw is the switching frequency of the LT3845AMPFE#TRPBF. The real-time output voltage (Vout) is sensed after each switching cycle and compared to the reference voltage. The error between the sensed and the reference is used to control the ON/ OFF time ratio of the switches.

Conclusion

The LT3845AMPFE#TRPBF is a high-voltage, high-current DC-DC synchronous step-down controller. It includes an integrated FET, low quiescent current, advanced current mode control and over-temperature protection. The device operates by regulating the ON/OFF times of the high-side and low-side switches to maintain the desired output voltage and can operate from 2.6V to 72V. It is an ideal solution for high power density applications such as FPGAs, microprocessors, DSPs, and automotive and industrial applications.

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