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CN5815 Datasheet(PDF) 9 Page - Shanghai Consonance Electronics Incorporated
CONSONANCE [Shanghai Consonance Electronics Incorporated]
CN5815 Datasheet(HTML) 9 Page - Shanghai Consonance Electronics Incorporated
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where the first term is due to the bulk capacitance and second term due to the ESR of output capacitor.
For many designs it is possible to choose a single capacitor type that satisfies both the ESR and
bulk C requirements. In certain demanding applications, however, the ripple voltage can be
improved significantly by connecting two or more types of capacitors in parallel. For example,
using a low ESR ceramic capacitor can minimize the ESR step, while an electrolytic capacitor can
be used to supply the required bulk C.
The output capacitor in a boost LED driver experiences high RMS ripple currents. The RMS output capacitor
ripple current is:
Note that the ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life. This
makes it advisable to further derate the capacitor or to choose a capacitor rated at a higher temperature than
required. Several capacitors may also be placed in parallel to meet size or height requirements in the design.
Input Capacitor Selection
The input voltage source impedance and cable length determines the size of the input capacitor,
which is typically in the range of 10?F to 100?F. A low ESR capacitor or two type of capacitors in
parallel is recommended.
The RMS input capacitor ripple current for a boost LED driver is:
Please note that the input capacitor can see a very high surge current when a battery is suddenly
connected to the input of the converter and solid tantalum capacitors can fail catastrophically
under these conditions.
Frequency Compensation Network Design
Figure 2 shows the AC response-related circuit of a boost LED driver using the CN5815.
Figure 2 AC Response-Related Circuit
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