參數(shù)資料
型號: PIC18F87J90-I/PT
廠商: Microchip Technology
文件頁數(shù): 26/59頁
文件大?。?/td> 0K
描述: IC PIC MCU FLASH 128KB 80-TQFP
產(chǎn)品培訓(xùn)模塊: PIC18 J Series MCU Overview
8-bit PIC® Microcontroller Portfolio
標(biāo)準(zhǔn)包裝: 119
系列: PIC® 18F
核心處理器: PIC
芯體尺寸: 8-位
速度: 48MHz
連通性: I²C,SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,LCD,LVD,POR,PWM,WDT
輸入/輸出數(shù): 67
程序存儲器容量: 128KB(64K x 16)
程序存儲器類型: 閃存
RAM 容量: 3.8K x 8
電壓 - 電源 (Vcc/Vdd): 2 V ~ 3.6 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 12x10b
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 80-TQFP
包裝: 托盤
產(chǎn)品目錄頁面: 644 (CN2011-ZH PDF)
配用: AC162079-ND - HEADER MPLAB ICD2 18F85J90 64/80
AC164323-ND - MODULE SKT FOR 100TQFP
PIC18F87J90 FAMILY
DS39933D-page 32
2010 Microchip Technology Inc.
2.2
Power Supply Pins
2.2.1
DECOUPLING CAPACITORS
The use of decoupling capacitors on every pair of
power supply pins, such as VDD, VSS, AVDD and
AVSS, is required.
Consider the following criteria when using decoupling
capacitors:
Value and type of capacitor: A 0.1
F (100 nF),
10-20V capacitor is recommended. The capacitor
should be a low-ESR device, with a resonance
frequency in the range of 200 MHz and higher.
Ceramic capacitors are recommended.
Placement on the printed circuit board: The
decoupling capacitors should be placed as close
to the pins as possible. It is recommended to
place the capacitors on the same side of the
board as the device. If space is constricted, the
capacitor can be placed on another layer on the
PCB using a via; however, ensure that the trace
length from the pin to the capacitor is no greater
than 0.25 inch (6 mm).
Handling high-frequency noise: If the board is
experiencing high-frequency noise (upward of
tens of MHz), add a second ceramic type capaci-
tor in parallel to the above described decoupling
capacitor. The value of the second capacitor can
be in the range of 0.01
F to 0.001 F. Place this
second capacitor next to each primary decoupling
capacitor. In high-speed circuit designs, consider
implementing a decade pair of capacitances as
close to the power and ground pins as possible
(e.g., 0.1
F in parallel with 0.001 F).
Maximizing performance: On the board layout
from the power supply circuit, run the power and
return traces to the decoupling capacitors first,
and then to the device pins. This ensures that the
decoupling capacitors are first in the power chain.
Equally important is to keep the trace length
between the capacitor and the power pins to a
minimum, thereby reducing PCB trace
inductance.
2.2.2
TANK CAPACITORS
On boards with power traces running longer than
six inches in length, it is suggested to use a tank capac-
itor for integrated circuits, including microcontrollers, to
supply a local power source. The value of the tank
capacitor should be determined based on the trace
resistance that connects the power supply source to
the device, and the maximum current drawn by the
device in the application. In other words, select the tank
capacitor so that it meets the acceptable voltage sag at
the device. Typical values range from 4.7
F to 47 F.
2.3
Master Clear (MCLR) Pin
The MCLR pin provides two specific device
functions: Device Reset, and Device Programming
and Debugging. If programming and debugging are
not required in the end application, a direct
connection to VDD may be all that is required. The
addition of other components, to help increase the
application’s resistance to spurious Resets from
voltage
sags,
may
be
beneficial.
A
typical
configuration is shown in Figure 2-1. Other circuit
designs may be implemented, depending on the
application’s requirements.
During programming and debugging, the resistance
and capacitance that can be added to the pin must
be considered. Device programmers and debuggers
drive the MCLR pin. Consequently, specific voltage
levels (VIH and VIL) and fast signal transitions must
not be adversely affected. Therefore, specific values
of R1 and C1 will need to be adjusted based on the
application and PCB requirements. For example, it is
recommended that the capacitor, C1, be isolated
from the MCLR pin during programming and
debugging operations by using a jumper (Figure 2-2).
The
jumper
is
replaced
for
normal
run-time
operations.
Any components associated with the MCLR pin
should be placed within 0.25 inch (6 mm) of the pin.
FIGURE 2-2:
EXAMPLE OF MCLR PIN
CONNECTIONS
Note 1: R1
10 k is recommended. A suggested
starting value is 10 k
. Ensure that the
MCLR pin VIH and VIL specifications are met.
2: R2
470 will limit any current flowing into
MCLR from the external capacitor, C, in the
event of MCLR pin breakdown, due to
Electrostatic Discharge (ESD) or Electrical
Overstress (EOS). Ensure that the MCLR pin
VIH and VIL specifications are met.
C1
R2
R1
VDD
MCLR
PIC18FXXJXX
JP
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