ACE707C

0.9 V startup, 1MHz, 300mA Iout, Low Iq, Synchronous Boost Converter

VER 1.1

4

Detail Description

ACE707C is a low input voltage start up, current mode DC-DC step up converter. It’s operation can be

best understood by referring to the block diagram. Upon starting up, the low voltage startup circuitry drives

SW with on-off cycles, transferring energy from input to OUT by storing energy in the inductor during

on-time and releasing it to the output during off-time. When OUT reaches 2V, the startup circuit turns off

and the main controller takes over. The main control loop consists of a reference, a GM error amplifier, a

PWM controller, a current sense amplifier, an oscillator, a PWM logic control, and it is power stage

including its driver. The main control loop is a classic current mode control loop. The GM stage integrates

the error between FB and REF, and its output is used to compare with a triangular wave which the

summing result of the current sense amplifier output and a slope compensation voltage. The output of the

comparator is used to drive the power stage to reach regulation.

Application Information

Inductor selection

With switching frequency up to 1MHz, small surface mount inductors can be used with values from

2.2uH to 4.7uH. For a given chosen inductor value and application conditions make sure the peak

inductor current does not exceed the maximum current rating of the selected vendor's inductor.

Input and output capacitor selection

The ACE707C's bootstrap architecture allows the use of very small input capacitor. For applications

that only need to drive small output load current, the input capacitor is optional, because once output is

started up, the IC's is powered by OUT, a quiet power supply.

The output capacitor is used to stabilize the loop and provide ac current to the load. A low ESR ceramic

cap with values from 2.2uF to 22uF can be used. Smaller value capacitors are generally cheaper with

small footprints, while larger capacitor provides lower ripples and better transient load responses. Also,

when extreme low startup voltage is needed, larger output capacitors are needed for the part to startup

under heavy load condition.