ACE722E datasheet(13/16 Pages) ACE

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ACE722E

3MHz 2A Step-Down Converter

VER 1.1

UVLO and

Thermal Shutdown

If IN drops below 1.9V, the UVLO circuit inhibits switching. Once IN rises above 2.1V, the UVLO clears,

and the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the

device. When the junction temperature exceeds TJ= +160°C, a thermal sensor forces the device into

shutdown, allowing the die to cool. The thermal sensor turns the device on again after the junction

temperature cools by 15°C, resulting in a pulsed output during continuous overload conditions. Following

a thermal- shutdown condition, the soft-start sequence begins.

DESIGN PROCEDURE

Setting Output Voltages

Output voltages are set by external resistors. The FB threshold is 0.6V.

RTOP = RBOTTOM x [(VOUT / 0.6) - 1]

Inductor Selection

The peak-to-peak ripple is limited to 30% of the maximum output current. This places the peak current

far enough from the minimum overcurrent trip level to ensure reliable operation while providing enough

current ripples for the current mode converter to operate stably. In this case, for 2A maximum output

current, the maximum inductor ripple current is 667 mA. The inductor size is estimated as following

equation:

LIDEAL=(VIN(MAX)-VOUT)/IRIPPLE*DMIN*(1/FOSC)

Therefore, for VOUT=1.8V,

The inductor values is calculated to be L = 0.6

0μH.

Chose 1

Μh.

For VOUT =1.2V,

The inductor values is calculated to be L = 0.469μH.

Chose 0.47μH

The resulting ripple is

IRIPPLE =(VIN(MAX)-VOUT)/LACTUAL*DMIN*(1/FOSC)

When,

VOUT=1.8V, IRIPPLE = 403mA

VOUT=1.2V, IRIPPLE = 665mA

Output Capacitor Selection

For most applications a nominal 10

μ F or 22μ F capacitor is suitable. The ACE722E internal

compensation is designed for a fixed corner frequency that is equal to

FC= 1 2∗ π√COUT∗ L = 50Khz

For example, for VOUT=1.8V, L=1μ H, COUT=10μ F, for VOUT =1.2V, L=0.47μ H, COUT=22μ F

The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor

must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are

suitable, with ceramic exhibiting the lowest ESR and

high-frequency impedance. Output ripple with a

ceramic output capacitor is approximately as follows: VRIPPLE = IL(PEAK)[1 / (2π

x f

OSC x COUT)]

If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:

VRIPPLE(ESR) = IL(PEAK) x ESR

ACE722E Datasheet(PDF) 13 Page - ACE Technology Co., LTD.

ACE722E Datasheet(HTML) 13 Page - ACE Technology Co., LTD.

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