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( )
CC CC DD
boost CC
I V V
C = 2
V f V
´ -
´
D ´ ´
(4)
( )
CC CC DD
boost CC
I V V
C =
V f V
´ -
D ´ ´
(5)
TPA2013D1
SLOS520 – AUGUST 2007
TPA2013D1 CAPACITOR EQUATIONS
The value of the boost capacitor is determined by the minimum value of working capacitance required for stability
and the maximum voltage ripple allowed on V
CC
in the application. The minimum value of working capacitance is
10 μ F. Do not use any component with a working capacitance less than 10 μ F.
For X5R or X7R ceramic capacitors, Equation 4 shows the relationship between the boost capacitance, C, to
load current, load voltage, ripple voltage, input voltage, and switching frequency (I
CC
, V
CC
, Δ V, V
DD
, f
boost
respectively). Insert the maximum allowed ripple voltage into Equation 4 to solve for C. A factor of 2 is included
to implement the rules and specifications listed earlier.
For aluminum or tantalum capacitors, Equation 5 shows the relationship between he boost capacitance, C, to
load current, load voltage, ripple voltage, input voltage, and switching frequency (I
CC
, V
CC
, Δ V, V
DD
, f
boost
respectively). Insert the maximum allowed ripple voltage into Equation 5 to solve for C. Solve this equation
assuming ESR is zero.
Capacitance of aluminum and tantalum capacitors is normally not sensitive to applied voltage so there is no
factor of 2 included in Equation 5 . However, the ESR in aluminum and tantalum capacitors can be significant.
Choose an aluminum or tantalum capacitor with ESR around 30 m Ω . For best perfornamce using of tantalum
capacitor, use at least a 10 V rating. Note that tantalum capacitors must generally be used at voltages of half
their ratings or less.
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