LTC3203_15 Datasheet, PDF (13/16 Pages) Linear Technology – 500mA Output Current Low Noise Dual Mode Step-Up Charge Pumps

LTC3203/LTC3203-1
LTC3203B/LTC3203B-1
APPLICATIO S I FOR ATIO
10nH
7
V_IN
V_IN
0.1µF
2.2µF LTC3203*
9, 11 _GND
3203 F05
Figure 5. 10nH Inductor Used for Input Noise Reduction
A 10nH inductor will reject the fast current notches,
thereby presenting a nearly constant current load to the
input power supply. For economy the 10nH inductor can
be fabricated on the PC board with about 1cm (0.4") of PC
board trace.
Flying Capacitor Selection
Warning: Polarized capacitors such as tantalum or
aluminum should never be used for the flying capacitors
since their voltage can reverse upon start-up of the
LTC3203/LTC3203-1/LTC3203B/LTC3203B-1. Low ESR
ceramic capacitors should always be used for the flying
capacitors.
The flying capacitors control the strength of the charge
pump. In order to achieve the rated output current, it is
necessary to have at least 2.2µF of capacitance for each of
the flying capacitors.
Ceramic capacitors of different materials lose their ca-
pacitance with higher temperature and voltage at different
rates. For example, a capacitor made of X7R material will
retain most of its capacitance from –40°C to 85°C whereas
Z5U or Y5V style capacitors will lose considerable capaci-
tance over that range. Z5U and Y5V capacitors may also
have a poor voltage coefficient causing them to lose 60%
or more of their capacitance when the rated voltage is
applied. Therefore, when comparing different capacitors,
it is often more appropriate to compare the amount of
achievable capacitance for a given case size rather than
comparing the specified capacitance value. For example,
over rated voltage and temperature conditions, a 4.7µF,
10V, Y5V ceramic capacitor in a 0805 case may not
provide any more capacitance than a 1µF, 10V, X5R or
X7R capacitor available in the same 0805 case. In fact,
over bias and temperature range the 1µF, 10V, X5R or X7R
will provide more capacitance than the 4.7µF, 10V, Y5V
capacitor. The capacitor manufacturer’s data sheet should
be consulted to determine what value of capacitor is
needed to ensure minimum capacitance values are met
over operating temperature and bias voltage.
Below is a list of ceramic capacitor manufacturers and
how to contact them:
AVX
Kemet
Murata
Taiyo Yuden
Vishay
TDK
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.component.tdk.com
32031fa
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