ACE705

High efficiency, multi-funtion step-up

DC/DC Controller

VER 1.2

5

(2) Application with external NPN transistor

ACE705

Fig3

be smaller. )

Detailed Description

The ACE705 series are boost structure, voltage-type pulse-frequency modulation(PFM) step-up DC-DC

controller. Only four external components are necessary: an inductor, a schottky diode, an output filter

capacitor and a NMOSFET or a NPN transistor. The step-up DC-DC converter, constructed by ACE705,

can be adjusted from 2.5V to 6.0V, 0.1V step. By using the depletion technics, the quiescent current

drawn from power source is lower than 8uA. The high efficiency device consists of resistors for output

voltage detection and trimming, a start-up voltage circuit, an oscillator, a reference circuit, a PFM control

circuit, a switch protection circuit and a driver transistor.

ACE705 integrates PFM control system. This system controls fixed power switch on duty cycle

frequency to stabilize output voltage by calculating results of other blocks which sense input voltage,

output voltage, output current and load conditions. In PFM modulation system, the frequency and pulse

width is fixed. The duty cycle is adjusted by skipping pulses, so that switch on-time is changed based on

the conditions such as input voltage, output current and load. The oscillate block inside ACE705 provides

fixed frequency and pulse width wave.

The reference circuit provides stable reference voltage to output stable output voltage. Because internal

trimming technology is used, the chip output change less than ±2%. At the same time，the problem of

temperature-drift coefficient of output voltage is considered in design, so temperature-drift coefficient of

output voltage is less than 100ppm/℃。

High-gain differential error amplifier guarantees stable output voltage at difference input voltage

and load. In order to reduce ripple and noise, the error amplifier is designed with high band-with.

ACE705 has a drive pin (EXT) for external transistor. So it is possible to load a large output current with

a power transistor and a low saturation voltage. At very light load condition, the switch current and

quiescent current of chip will effect efficiency certainly. So in very light load condition, the efficiency will

drop. Therefore, it is recommended that user use ACE705 in the condition of load current as large as

several tens of mA to several hundreds of mA