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

HT9261(A)

第 7 页共 13 页

Consider all above，inductor value of 47uH、

ESR<0.5Ω is recommended in most applications.Large

value is recommended in high efficiency applications and smaller value is recommended.

Capacitor Selection

Ignore ESR of capacitor，the ripple of output voltage is:

Cf

R

D

r

load





Vout

ΔVout

So large value capacitor is needed to reduce ripple. But too large capacitor value will slow down

system reaction and cost will improve. So 100uF capacitor is recommended. Larger capacitor value will

be used in large output current system. If output current is small (<10mA), small value is needed.

Consider ESR of capacitor，ripple will increase：

Vout

R

ax

r

r

ESR







Im

'

When current is large, ripple caused by ESR will be main factor. It may be greater than 100mV。

The ESR will affects efficiency and increase energy loss. So low-ESR capacitor (for example: tantalum

capacitor) is recommend or connect two or more filter capacitors in parallel.

Diode Selection

Rectifier diode will affects efficiency greatly，Though a common diode (such as 1N4148)will work

well for light load，it will reduce about 5%~10% efficiency for heavy load，For optimum performance,

a Schottky diode (such as 1N5817、1N5819、1N5822) is recommended.

Input Capacitor

If supply voltage is stable, the DC-DC circuit can output low ripple, low noise and stable voltage

without input capacitor. If voltage source is far away from DC-DC circuit, input capacitor value greater

than 10uF is recommended.

TEST CIRCUITS

（1）Output voltage test circuit（Iload=1mA）

SOT-89-3&SOT-23-3 Package

SOT-23-5 Package

C1=47uF

Vin=1.8V

L

Dlode

LX

OUT

GND

CO

Vout

Rbxl

Vin