ACE7215C

1.5A 1.5MHz Synchronous Buck Converter

VER 1.1

5

Detailed Description

The ACE7215C uses a constant frequency, current mode step-down architecture. Both the main

(P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. During normal

operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch,

and turned off when the current comparator, ICOMP, resets the RS latch. The peak inductor current at

which ICOMP resets the RS latch, is controlled by the output of error amplifier EA. When the load current

increases, it causes a slight decrease in the feedback voltage, FB, relative to the 0.6V reference, which in

turn, causes the EA amplifier’s output voltage to increase until the average inductor current matches the

new load current. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor

current starts to reverse, as indicated by the current reversal comparator IRCMP, or the beginning of the

next clock cycle.

Applications Information

Setting the Output Voltage

In the adjustable version, the output voltage is set by a resistive divider according to the following formula:

The external resistive divider is connected to the output, allowing remote voltage sensing as shown in on

page 1.

Inductor Selection

For most designs, the ACE7215C operates with inductors of 1µH to 4.7µH. Low inductance values are

physically smaller but require faster switching, which results in some efficiency loss. The inductor value

can be derived from the following equation:

Where

I

L

is inductor Ripple Current. Large value inductors result in lower ripple current and small value

inductors result in high ripple current. For optimum voltage-positioning load transients, choose an inductor

with DC series resistance in

the 50mΩ to 150mΩ range.