A7985ATR datasheet(36/44 Pages) STMICROELECTRONICS

tên linh kiện	A7985ATR

Giải thích chi tiết về linh kiện	2 A step-down switching regulator for automotive applications

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Application ideas

A7985A

36/44

DocID023128 Rev 5

Application ideas

7.1

Positive buck-boost

The A7985A can implement the step-up/down converter with a positive output voltage.

Figure 34 shows the schematic: one Power MOSFET and one Schottky diode are added to

the standard buck topology to provide a 12 V output voltage with input voltage from 4.5 V to

38 V.

Figure 34. Positive buck-boost regulator

The relationship between input and output voltage is:

Equation 40

so the duty cycle is:

Equation 41

The output voltage isn’t limited by the maximum operating voltage of the device (38 V),

because the output voltage is sensed only through the resistor divider. The external Power

MOSFET maximum drain to source voltage, must be higher than output voltage; the

maximum gate to source voltage must be higher than the input voltage (in Figure 34, if VIN is

higher than 16 V, the gate must be protected through a Zener diode and resistor).

VOUT

VIN

–

-------------



VOUT

VOUT VIN

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