Information

PIC24FJ64GA104
DS80000486H-page 8  2009-2013 Microchip Technology Inc.
2.4.1 CONSIDERATIONS FOR CERAMIC
CAPACITORS
In recent years, large value, low-voltage, surface
mount ceramic capacitors have become very cost
effective in sizes up to a few tens of microfarad. The
low-ESR, small physical size and other properties
make ceramic capacitors very attractive in many types
of applications.
Ceramic capacitors are suitable for use with the inter-
nal voltage regulator of this microcontroller. However,
some care is needed in selecting the capacitor to
ensure that it maintains sufficient capacitance over the
intended operating range of the application.
Typical low-cost, 10 µF ceramic capacitors are available
in X5R, X7R and Y5V dielectric ratings (other types are
also available, but are less common). The initial toler-
ance specifications for these types of capacitors are
often specified as ±10% to ±20% (X5R and X7R), or
-20%/+80% (Y5V). However, the effective capacitance
that these capacitors provide in an application circuit will
also vary based on additional factors, such as the
applied DC bias voltage and the temperature. The total
in-circuit tolerance is, therefore, much wider than the
initial tolerance specification.
The X5R and X7R capacitors typically exhibit satisfactory
temperature stability (ex: ±15% over a wide temperature
range, but consult the manufacturer's data sheets for
exact specifications). However, Y5V capacitors typically
have extreme temperature tolerance specifications of
+22%/-82%. Due to the extreme temperature tolerance,
a 10µF nominal rated Y5V type capacitor may not deliver
enough total capacitance to meet minimum internal
voltage regulator stability and transient response require-
ments. Therefore, Y5V capacitors are not recommended
for use with the internal voltage regulator if the application
must operate over a wide temperature range.
In addition to temperature tolerance, the effective
capacitance of large value ceramic capacitors can vary
substantially, based on the amount of DC voltage
applied to the capacitor. This effect can be very signifi-
cant, but is often overlooked or is not always
documented.
A typical DC bias voltage vs. capacitance graph for
16V, 10V and 6.3V rated capacitors is shown in
Figure 2-4.
FIGURE 2-4 DC BIAS VOLTAGE vs.
CAPACITANCE
CHARACTERISTICS
When selecting a ceramic capacitor to be used with the
internal voltage regulator, it is suggested to select a
high-voltage rating, so that the operating voltage is a
small percentage of the maximum rated capacitor volt-
age. For example, choose a ceramic capacitor rated at
16V for the 2.5C core voltage. Suggested capacitors
are shown in Table 2-1.
-80
-70
-60
-50
-40
-30
-20
-10
0
10
5 1011121314151617
DC Bias Voltage (VDC)
Capacitance Change (%)
01234 6789
16V Capacitor
10V Capacitor
6.3V Capacitor