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MA5609

Major Power Technology Co., Ltd.

Rev.1.3 Apr. 12 , 2017



FUNCTION DESCRIPTIONS

The MA5609 is a synchronous rectified, current-mode, step-down regulator. It regulates

load current.

The MA5609 uses current-mode control to regulate the output voltage. The output voltage is

measured at FB through a resistive voltage divider and amplified through the internal Tran

conductance error amplifier.

The converter uses internal N-Channel MOSFET switches to step-down the input voltage to

the regulated output voltage. Since the high side MOSFET requires a gate voltage greater than

the input voltage, a boost capacitor connected between SW and BS is needed to drive the high

side gate. The boost capacitor is charged from the internal 5V rail when SW is low.

voltage comparator is tripped and the COMP pin is discharged to GND, forcing the high-side

switch off.



APPLICATION INFORMATION

Setting the Output Voltage

The output voltage is set using a resistive voltage divider from the output voltage to FB pin.

The voltage divider divides the output voltage down to the feedback voltage by the ratio.

Thus the output voltage is:

2

2

1

R

R

R 

Ω, and R1 is 40kΩ.

Inductor Selection

The inductor is required to supply constant current to the output load while being driven by

the switched input voltage. A larger value inductor will result in less ripple current that will result in

lower output ripple voltage. However, the larger value inductor will have a larger physical size,

higher series resistance, and/or lower saturation current. A good rule for determining the

inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately

30% of the maximum switch current limit.

VIN

<28V

<35V

Inductor

33uH

47uH

The choice of which style inductor to use mainly depends on the price vs. size requirements

and any EMI requirements.