PIC18F8722-I/PT Microchip Technology Inc., PIC18F8722-I/PT Datasheet - Page 278

• Manufacturer Part Number: PIC18F8722-I/PT
• Description: 80 PIN, 128 KB FLASH, 4K RAM, 70 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F8722-I/PT

• A/d Inputs: 16-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 10 MIPS
• Eeprom Memory: 1024 Bytes
• Input Output: 70
• Interface: SPI/I2C/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 80-pin TQFP
• Programmable Memory: 128K Bytes
• Ram Size: 3.9K Bytes
• Speed: 40 MHz
• Timers: 2-8 bit, 3-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

PIC18F8722 FAMILY
21.1
For the A/D converter to meet its specified accuracy,
the charge holding capacitor (C
to fully charge to the input channel voltage level. The
analog input model is shown in Figure 21-3. The
source impedance (R
switch (R
required to charge the capacitor C
switch (R
(V
at the analog input (due to pin leakage current). The
maximum recommended impedance for analog
sources is 2.5 kΩ. After the analog input channel is
selected (changed), the channel must be sampled for
at least the minimum acquisition time before starting a
conversion.
EQUATION 21-1:
EQUATION 21-2:
EQUATION 21-3:
DS39646B-page 276
T
V
or
T
T
T
T
Temperature coefficient is only required for temperatures > 25°C. Below 25°C, T
T
T
ACQ
C
ACQ
AMP
COFF
C
ACQ
DD
Note:
HOLD
). The source impedance affects the offset voltage
=
=
A/D Acquisition Requirements
SS
=
=
=
=
=
SS
=
=
) impedance varies over the device voltage
When the conversion is started, the
holding capacitor is disconnected from the
input pin.
Amplifier Settling Time + Holding Capacitor Charging Time + Temperature Coefficient
T
) impedance directly affect the time
AMP
T
0.2 µs
(Temp – 25°C)(0.02 µs/°C)
(85°C – 25°C)(0.02 µs/°C)
1.2 µs
-(C
-(25 pF) (1 kΩ + 2 kΩ + 2.5 kΩ) ln(0.0004883) µs
1.05 µs
0.2 µs + 1 µs + 1.2 µs
2.4 µs
(V
-(C
AMP
+ T
REF
HOLD
HOLD
+ T
C
– (V
ACQUISITION TIME
A/D MINIMUM CHARGING TIME
CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
S
+ T
)(R
C
)(R
) and the internal sampling
+ T
COFF
REF
IC
IC
+ R
COFF
/2048)) • (1 – e
+ R
HOLD
SS
SS
HOLD
+ R
+ R
) must be allowed
S
S
) ln(1/2047) µs
. The sampling
) ln(1/2048)
(-T
C
/C
HOLD
Preliminary
(R
IC
+ R
SS
+ R
S
To
Equation 21-1 may be used. This equation assumes
that 1/2 LSb error is used (1024 steps for the A/D). The
1/2 LSb error is the maximum error allowed for the A/D
to meet its specified resolution.
Example 21-3 shows the calculation of the minimum
required acquisition time T
based
assumptions:
C
Rs
Conversion Error
V
Temperature
))
DD
HOLD
)
calculate
on
COFF
the
= 0 ms.
the
=
=
≤
=
=
following
minimum
 2004 Microchip Technology Inc.
25 pF
2.5 kΩ
1/2 LSb
5V → Rss = 2 kΩ
85°C (system max.)
ACQ
. This calculation is
application
acquisition
system
time,