Datasheet

ADP1649 Data Sheet
Rev. 0 | Page 26 of 28
The worst-case capacitance accounting for capacitor variation
over temperature, component tolerance, and voltage is calcu-
lated using the following equation:
C
EFF
= C
OUT
× (1 − TEMPCO) × (1 − TOL)
where:
C
EFF
is the effective capacitance at the operating voltage.
TEMPCO is the worst-case capacitor temperature coefficient.
TOL is the worst-case component tolerance.
In this example, the 10 μF X5R capacitor has the following
characteristics:
• TEMPCO from −40°C to +85°C is 15%.
• TOL is 10%.
• C
OUT
at VOUT (max) = 5 V, is 3 μF, as shown in Figure 41.
Figure 41. DC Bias Characteristic of a 6.3 V, 10 μF Ceramic Capacitor
Substituting these values in the equation yields
C
EFF
= 3 μF × (1 − 0.15) × (1 − 0.1) = 2.3 μF
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is 3.0 μF.
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
6.305.043.782.52
DC BIAS VOLTAGE (V)
CAPACITANCE CHANGE (%)
1.260
10779-041