ACE701C
High Efficiency Low Noise PFM Boost DC/DC Converter
Capacitor Selection
Ignore ESR of capacitor，the ripple of output voltage is:
R=ΔVout / Vout=D / R
load
Cf
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：
r'=r+Imax•R
ESR
/ Vout
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 (I
load
=1mA)
ACE701C
VER 1.3
6
ACE [ ACE TECHNOLOGY CO., LTD. ]
