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| 型號(hào)： | PIC18F4553 |
| 廠商： | Microchip Technology Inc. |
| 英文描述： | 28/40/44-Pin High-Performance, Enhanced Flash, USB Microcontrollers with 12-Bit A/D and nanoWatt Technology |
| 中文描述： | 28/40/44-Pin高性能，增強(qiáng)型閃存，USB微控制器與12位A / D和納瓦技術(shù) |
| 文件頁(yè)數(shù)： | 26/46頁(yè) |
| 文件大?。?/td> | 607K |
| 代理商： | PIC18F4553 |
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PIC18F2458/2553/4458/4553
DS39887B-page 24
Preliminary
2007 Microchip Technology Inc.
2.1
A/D Acquisition Requirements
For the A/D Converter to meet its specified accuracy,
the charge holding capacitor (C
HOLD
) must be allowed
to fully charge to the input channel voltage level. The
analog input model is shown in Figure 2-3. The source
impedance (R
S
) and the internal sampling switch (R
SS
)
impedance directly affect the time required to charge
the capacitor C
HOLD
. The sampling switch (R
SS
)
impedance varies over the device voltage (V
DD
). The
source impedance affects the offset voltage at the ana-
log input (due to pin leakage current).
The maximum
recommended impedance for analog sources is
2.5 k
Ω
. After the analog input channel is selected
(changed), the channel must be sampled for at least
the minimum acquisition time before starting a
conversion.
To calculate the minimum acquisition time, Equation 2-1
may be used. This equation assumes that 1/2 LSb error
is used (4096 steps for the 12-bit A/D). The 1/2 LSb error
is the maximum error allowed for the A/D to meet its
specified resolution.
Example 2-3 shows the calculation of the minimum
required acquisition time, T
ACQ
. This calculation is
based
on
the
following
assumptions:
application
system
C
HOLD
Rs
Conversion Error
V
DD
Temperature
=
=
≤
=
=
25 pF
2.5 k
Ω
1/2 LSb
3V
→
Rss = 4 k
Ω
85
°
C (system max.)
EQUATION 2-1:
T
ACQ
=
ACQUISITION TIME
Amplifier Settling Time + Holding Capacitor Charging Time + Temperature Coefficient
EQUATION 2-2:
A/D MINIMUM CHARGING TIME
EQUATION 2-3:
T
ACQ
CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
T
AMP
+ T
C
+ T
COFF
Note:
When the conversion is started, the
holding capacitor is disconnected from the
input pin.
=
T
AMP
+ T
C
+ T
COFF
V
HOLD
or
T
C
=
(V
REF
– (V
REF
/4096)) (1 – e
(-T
C
/C
HOLD
(R
IC
+ R
SS
+ R
S
))
)
=
-(C
HOLD
)(R
IC
+ R
SS
+ R
S
) ln(1/4096)
=
T
AMP
=
0.2 μs
(Temp – 25
°
C)(0.02 μs/
°
C)
(85
°
C – 25
°
C)(0.02 μs/
°
C)
1.2 μs
T
COFF
=
Temperature coefficient is only required for temperatures > 25
°
C. Below 25
°
C, T
COFF
= 0 μs.
T
C
=
-(C
HOLD
)(R
IC
+ R
SS
+ R
S
) ln(1/4096) μs
-(25 pF) (1 k
Ω
+ 4 k
Ω
+ 2.5 k
Ω
) ln(0.0002441) μs
1.56 μs
0.2 μs + 1.56
μ
s + 1.2 μs
2.96 μs
T
ACQ
=
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| PIC18F4553-I/ML | 功能描述:8位微控制器 -MCU 32KB FLSH 2048 RAM FSUSB 2.0 12B ADC RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時(shí)鐘頻率:50 MHz 程序存儲(chǔ)器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC18F4553-I/P | 功能描述:8位微控制器 -MCU 32KB FLSH 2048 RAM FSUSB 2.0 12B ADC RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時(shí)鐘頻率:50 MHz 程序存儲(chǔ)器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC18F4553-I/P | 制造商:Microchip Technology Inc 功能描述:8-Bit Microcontroller IC |
| PIC18F4553-I/PT | 功能描述:8位微控制器 -MCU 32KB FLSH 2048 RAM FSUSB 2.0 12B ADC RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時(shí)鐘頻率:50 MHz 程序存儲(chǔ)器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
| PIC18F4553T-I/ML | 功能描述:8位微控制器 -MCU 32KB FLSH 2048 RAM FSUSB 2.0 12B ADC RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時(shí)鐘頻率:50 MHz 程序存儲(chǔ)器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT |
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