PFM STEP-UP DC/DC CONVERTER WITH HIGH EFFICIENCY AND LOW NOISE

HT9261(A)

第 5 页共 13 页

TYPICAL APPLICATIONS

SOT-89-3 and SOT-23-3 Package

SOT-23-5 Package

DETAILED DESCRIPTION

The HT9261 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 drawnfrom 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 HT9261 IC. This block controls power switch on dutycycle 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 HT9261 providesfixed 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.

Vout

Iout

Cout

100uF Tan

Rload

Cin

47uF

LX

OUT

GND

LX

Vin

L

D 1N5819

Vout

Iout

Cout

100uF Tan

Rload

Cin

47uF

LX

OUT

GND

LX

Vin

L

D 1N5817

27uH

OFF

ON

CE