參數(shù)資料
型號: PIC16LF721T-I/SO
廠商: Microchip Technology
文件頁數(shù): 118/135頁
文件大?。?/td> 0K
描述: MCU PIC 3.5KB FLASH 20SOIC
標準包裝: 1,600
系列: PIC® XLP™ 16F
核心處理器: PIC
芯體尺寸: 8-位
速度: 16MHz
連通性: I²C,SPI,UART/USART
外圍設備: 欠壓檢測/復位,POR,PWM,WDT
輸入/輸出數(shù): 17
程序存儲器容量: 7KB(4K x 14)
程序存儲器類型: 閃存
RAM 容量: 256 x 8
電壓 - 電源 (Vcc/Vdd): 1.8 V ~ 3.6 V
數(shù)據(jù)轉換器: A/D 12x8b
振蕩器型: 內部
工作溫度: -40°C ~ 85°C
封裝/外殼: 20-SOIC(0.295",7.50mm 寬)
包裝: 帶卷 (TR)
2010-2011 Microchip Technology Inc.
Preliminary
DS41430C-page 83
PIC16(L)F720/721
9.3
A/D Acquisition Requirements
For the ADC to meet its specified accuracy, the charge
holding capacitor (CHOLD) must be allowed to fully
charge to the input channel voltage level. The Analog
Input model is shown in Figure 9-3. The source
impedance (RS) and the internal sampling switch (RSS)
impedance directly affect the time required to charge
the capacitor CHOLD. The sampling switch (RSS)
impedance varies over the device voltage (VDD), refer
to
The
maximum
recommended
impedance for analog sources is 10 k
. As the
source impedance is decreased, the acquisition time
may be decreased. After the analog input channel is
selected (or changed), an A/D acquisition must be
done before the conversion can be started. To
calculate the minimum acquisition time, Equation 9-1
may be used. This equation assumes that 1/2 LSb error
is used (256 steps for the ADC). The 1/2 LSb error is
the maximum error allowed for the ADC to meet its
specified resolution. It is noted that if the device is
operated at or below 2.0V VDD with the FRC clock
selected for the ADC and if the analog input changes
by more than 1 or 2 LSBs from the previous
conversion, then the use of at least 16
s TACQ time is
recommended.
EQUATION 9-1:
ACQUISITION TIME EXAMPLE
TACQ
Amplifier Settling Time
Hold Capacitor Charging Time
Temperature Coefficient
++
=
TAMP
TC
TCOFF
++
=
2s
TC
Temperature - 25°C
0.05s/°C
++
=
TC
CHOLD RIC
RSS
RS
++
ln(1/511)
=
20pF 1k
7k 10k
++
ln(0.001957)
=
2.25
=
s
TACQ
2s
2.25s
50°C- 25°C
0.05s/°C
++
=
5.5s
=
VAPPLIED 1e
Tc
RC
---------
VAPPLIED 1
1
2
n1
+
1
--------------------------
=
VAPPLIED 1
1
2
n1
+
1
--------------------------
VCHOLD
=
VAPPLIED 1e
TC
RC
----------
VCHOLD
=
;[1] VCHOLD charged to within 1/2 lsb
;[2] VCHOLD charge response to VAPPLIED
;combining [1] and [2]
The value for TC can be approximated with the following equations:
Solving for TC:
Therefore:
Temperature
50°C and external impedance of 10k
5.0V VDD
=
Assumptions:
Note: Where n = number of bits of the ADC.
Note: TCOFF is zero for temperatures below 25 degrees C.
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