ZXSC400
APPLICATIONS INFORMATION
Sw itching transistor selection
Capacitor Selection
The choice of switching transistor has a m ajor im pact A sm all value, low ESR ceram ic capacitor is required to
on the converter efficiency. For optim um perform ance, filter the output, typically 1F to 4.7F.
a bipolar transistor with low VCE(SAT) and high gain is
required. The VCEO of the switching transistor is also an
im portant param eter as this sees the full output
voltage when the transistor is switched off. Zetex
SuperSOT™ transistors are an ideal choice for this
application.
Generally an input capacitor is not required, but a sm all
ceram ic capacitor m ay be added to aid EMC, typically
1F to 4.7F.
Inductor Selection
Th e in d u cto r va lu e m u s t b e ch o s e n to s a tis fy
perform ance, cost and size requirem ents of the overall
solution.
Schottky diode selection
As with the switching transistor, the Schottky rectifier
diode has a m ajor im pact on the converter efficiency. A
Schottky diode with a low forward voltage and fast
recovery tim e should be used for this application.
Inductor selection has a significant im pact on the
co n ve rte r p e rfo rm a n ce . Fo r a p p lica tio n s w h e re
efficiency is critical, an inductor with a series resistance
of 250m ⍀ or less should be used.
The diode should be selected so that the m axim um
forward current rating is greater or equal to the
m axim um peak current in the inductor, and the
m axim um reverse voltage is greater or equal to the
output voltage. The Zetex ZHCS Series m eet these
needs.
A list of recom m ended inductors is listed in the table
below:
Com bination devices
To m inim ise the external com ponent count Zetex
recom m ends the ZX3CDBS1M832 com bination of
NPN transistor and Schottky diode in a 3m m x 2m m
MLP package. This device is recom m ended for use in
applications using 1 to 4 white LEDs.
The IC is also capable of driving MOSFETs. Zetex
recom m ends the ZXMNS3BM832 com bination of low
threshold voltage N-Channel MOSFET and Schottky
diode in a 3m m x 2m m MLP package. This device is
recom m ended for use in applications using 1 to 8 white
LEDs.
Pa rt No .
Ma n u fa ct u re
S u m id a
L
IP K (A)
0.5
RDC( )
CMD4D11-100MC
CMD4D11-220MC
LPO2506OB-103
S T2006103
10H
22H
10H
10H
0.457
0.676
0.24
0.1
S u m id a
0.4
Co ilcra ft
1.0
S ta n d e x Ele ctro n ics In c
0.6
ISSUE 1 - J ANUARY 2003
5
DIODES [ DIODES INCORPORATED ]
