PIC24FJ128GA010_12 Datasheet, PDF (22/258 Pages) Microchip Technology – 64/80/100-Pin, General Purpose, 16-Bit Flash Microcontrollers

PIC24FJ128GA010 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 F 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 tem-
perature tolerance, a 10 F 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
internal 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.
Typical DC bias voltage vs. capacitance graph for X7R
type 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 or 1.8V core voltage. Suggested
capacitors are shown in Table 2-1.
2.5 ICSP Pins
The PGECx and PGEDx pins are used for In-Circuit
Serial Programming (ICSP) and debugging purposes.
It is recommended to keep the trace length between
the ICSP connector and the ICSP pins on the device as
short as possible. If the ICSP connector is expected to
experience an ESD event, a series resistor is recom-
mended, with the value in the range of a few tens of
ohms, not to exceed 100Ω.
Pull-up resistors, series diodes and capacitors on the
PGECx and PGEDx pins are not recommended as they
will interfere with the programmer/debugger communi-
cations to the device. If such discrete components are
an application requirement, they should be removed
from the circuit during programming and debugging.
Alternatively, refer to the AC/DC characteristics and
timing requirements information in the respective
device Flash programming specification for information
on capacitive loading limits and pin input voltage high
(VIH) and input low (VIL) requirements.
For device emulation, ensure that the “Communication
Channel Select” (i.e., PGECx/PGEDx pins),
programmed into the device, matches the physical
connections for the ICSP to the Microchip
debugger/emulator tool.
For more information on available Microchip
development tools connection requirements, refer to
Section 26.0 “Development Support”.
DS39747F-page 22
 2005-2012 Microchip Technology Inc.