CAT3200HU2_14 Datasheet, PDF (8/9 Pages) ON Semiconductor – Low Noise Regulated Charge Pump DC-DC Converter

CAT3200HU2
Application Information
Ceramic Capacitors
Ceramic capacitors of different dielectric materials lose
their capacitance with higher temperature and voltage at
different rates. For example, a capacitor made of X5R or
X7R material will retain most of its capacitance from −40°C
to 85°C whereas a Z5U or Y5V style capacitor will lose
considerable capacitance over that range.
Z5U and Y5V capacitors may also have voltage
coefficient causing them to lose 60% or more of their
capacitance when the rated voltage is applied. When
comparing different capacitors it is often useful to consider
the amount of achievable capacitance for a given case size
rather than discussing the specified capacitance value. For
example, over rated voltage and temperature conditions, a
1 mF, 10 V, Y5V ceramic capacitor in an 0603 case may not
provide any more capacitance than a 0.22 mF, 10 V, X7R
available in the same 0603 case. For many CAT3200HU2
applications these capacitors can be considered roughly
equivalent.
Output Ripple
The output ripple voltage is related to the output capacitor
size C_OUT and ESR (equivalent series resistance) and can be
calculated using the formula below:
V_R + I_LOAD ń (2 @ F_OSC @ C_OUT) ) 2 @ ESR_COUT @ I_LOAD
where F_OSC is the switching frequency.
Efficiency
The efficiency is basically set by the ratio between the
input voltage V_IN and the output voltage V_OUT, and can be
calculated using the formula below:
Efficiency [%] + 100 @ P_OUT ń P_IN
+ 100 @ V_OUT @ I_LOAD ń (V_IN @ I_IN)
where F_OSC is the switching frequency, and
I_IN + I_GND ) 2 @ I_LOAD
If we neglect the Ground current (I_GND), then the
efficiency is basically equal to:
Efficiency [%] ^ 100 @ V_OUT ń (2 @ V_IN)
Layout Guidance
The CAT3200HU2 2 MHz switching frequency requires
minimum trace length and impedance for C_IN, C_OUT, and
C_FLY capacitors. This can be accomplished by placing these
components close to the IC. The C_IN capacitor ground
connection can connect directly to PGND and a wide, single
trace should connect PGND and SGND. C_OUT should be
star-connected to SGND, along with FB resistor network, if
used.
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