PIC24FJ256GA110 Datasheet, PDF (13/22 Pages) Microchip Technology – 64/80/100-Pin, 16-Bit General Purpose Flash Microcontrollers with Peripheral Pin Select

PIC24FJ256GA110 FAMILY
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 satisfac-
tory temperature stability (ex: ±15% over a wide
temperature range, but consult the manufacturer's data
sheets for exact specifications). However, Y5V capaci-
tors typically have extreme temperature tolerance
specifications of +22%/-82%. Due to the extreme
temperature tolerance, a 10 µF nominal rated Y5V type
capacitor may not deliver enough total capacitance to
meet minimum internal voltage regulator stability and
transient response requirements. Therefore, Y5V
capacitors are not recommended for use with the inter-
nal 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
10
0
-10
-20
-30
-40
-50
-60
-70 _{6.3V Capacitor}
-80
01234 5
16V Capacitor
10V Capacitor
6 7 8 9 10 11 12 13 14 15 16 17
DC Bias Voltage (VDC)
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 2.5V core voltage. Suggested capacitors
are shown in Table 2-1.
 2008-2013 Microchip Technology Inc.
DS80368N-page 13