ACE707A

Micro Power Step-up DC-DC Converter

 

VER 1.2

6

Junction Temperature (℃)

Junction Temperature (℃)

Figure 7. Saturation Voltage vs. Junction Temperature

Figure 8. Saturation Voltage vs. Junction Temperature

Load Current (mA)

Load Current (mA)

Figure 9. Efficiency

Figure 10. Efficiency

Application Information

Operating Principles

ACE707A feature a constant off-time control scheme. Refer to Figure 3， the bandgap voltage VREF

(1.23V typical) is used to control the output voltage.

When the voltage at the FB pin drops below the lower hysteresis point of Feedback Comparator (typical

hysteresis is 8mV), the Feedback Comparator enables the chip and the NPN power switch is turned on,

the current in the inductor begins to ramp up and store energy in the coil while the load current is supplied

by the output capacitor. Once the current in the inductor reaches the current limit, the Current-Limit

Comparator resets the 400ns One-Shot which turns off the NPN switch for 400ns. The SW voltage rises

to the output voltage plus a diode drop and the inductor current begins to ramp down. During this time the

energy stored in the inductor is transferred to COUT and the load. After the 400ns off-time, the NPN

switch is turned on and energy will be stored in the inductor again.

This cycle will continue until the voltage at FB pin reaches 1.23V, the Feedback Comparator disables

the chip and turns off the NPN switch. The load current is then supplied solely by output capacitor and the

output voltage will decrease. When the FB pin voltage drops below the lower hysteresis point of

Feedback Comparator, the Feedback Comparator enables the device and repeats the cycle described

previously. Under not switching condition, the IQ of the device is about 17μA.