ACE709

0.9V startup, 1A True Shut-Off Synchronous Boost DC/DC Converter

VER 1.2

6

Detailed description

General description

The ACE709 is a high-efficiency, Boost DC/DC converter, with input current limit at 1.5A. It integrates an

150mΩ high side MOSFET and an 150 mΩ low side MOSFET. It employs PWM/PFM auto-switch control

mode.

Short circuit protection

ACE709 emplo

ys a “Hiccup” mode of short-circuit protection, which enables output voltage auto recover

when short-circuit is removed.

True shut off function

ACE709 offers a true shut off function, which means it can really shut off output (make output voltage to

zero) when CE is pull low (chip turns off). Normally, there is a schottky diode (or MOSFET body diode)

existed between LX and Vout for a normal boost converter, and thus, when CE is pull low, though the chip

is turned off, the Vin is connected to Vout thru inductor and schottky diode. So we still can detect a voltage

at Vout terminal. ACE709, with its proprietary design skill, can truly shut down the output when chip is

turned off.

Design Procedure

Setting Output Voltages

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

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

Capacitor Selection

A 22uF ceramic capacitor is demanded on output terminal, while 4.7uF is good enough for input.

Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their

high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications.

Using ceramic capacitors can achieve very low output ripple and small circuit size. When choosing the

input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics

have the best temperature and voltage characteristics of all the ceramics for a given value and size.

Application Information

Layout is critical to achieve clean and stable operation. The switching power stage requires particular

attention. Follow these guidelines for good PC board layout:

1. Place 22uF output capacitors as close to the IC VOUT and GND pins as possible

2. Connect input and output capacitors to the same power ground node with a star ground configuration

then to IC ground.

3. Keep the high-current paths as short and wide as possible. Keep the path of switching current short.

Avoid vias in the switching paths.

4. If possible, connect VIN, SW, and GND separately to a large copper area to help cool the IC to further

improve efficiency and long-term reliability.

5. Ensure all feedback connections are short and direct. Place the feedback resistors as close to the IC

as possible.

6. Route high-speed switching nodes away from sensitive analog areas