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Ver1.0

4/14

BL8530

NOTE：

1、Diode：Schottky type, such as：1N5817,1N5819,1N5822

2、Inductor：27uH(R<0.5

Ω)

3、Capacitor：100uF(Tantalum type)

TYPICAL APPLICATIONS：

DETAILED DESCRIPTION

The BL8530 series are boost structure, voltage-type pulse-frequency modulation(PFM) step-up

DC-DC converter. Only three external components are necessary: an inductor, a output filter

capacitor and a schottky diode. And the converter’s low noise and low ripple output voltage can be

adjusted from 2.5V to 5.0V, 0.1V step. By using the depletion technics, the quiescent current drawn

from power source is lower than 7uA. 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.

The PFM control circuit is the core of the BL8530 IC. This block controls power switch on duty

cycle 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

BL8530 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.

Though at very low load condition, the quiescent current of chip do effect efficiency certainly.

The four main energy loss of Boost structure DC-DC converter in full load are the ESR of inductor,

the voltage of Schottky diode, on resistor of internal N-channel MOSFET and its driver. In order to

improve the efficiency, BL8530 integrates low on-resistor N-channel MOSFET and well design driver

circuits. The switch energy loss is limited at very low level.

SELECTION OF THE EXTERNAL COMPONENTS

Thus it can be seen, the inductor and schottky diode affect the conversion efficiency greatly.

The inductor and the capacitor also have great influence on the output voltage ripple of the converter.

So it is necessary to choose a suitable inductor, a capacitor and a right schottky diode, to obtain high

efficiency, low ripple and low noise.