PIC18F4580-I/P Microchip Technology Inc., PIC18F4580-I/P Datasheet - Page 247

• Manufacturer Part Number: PIC18F4580-I/P
• Description: 40 PIN, 32 KB FLASH, 1536 RAM, 36 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC18F4580-I/P

• A/d Inputs: 11-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 10 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 36
• Interface: CAN/I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 40-pin PDIP
• Programmable Memory: 32K Bytes
• Ram Size: 1.5K Bytes
• Speed: 40 MHz
• Timers: 1-8 bit, 3-16 bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

To
Equation 20-1 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 20-1 shows the calculation of the minimum
required acquisition time T
based on the following application system assumptions:
• C
• Rs
• Conversion Error
• V
• Temperature
• V
EQUATION 20-1:
EQUATION 20-2:
EXAMPLE 20-1:
 2004 Microchip Technology Inc.
T
V
or
Tc
T
Temperature coefficient is only required for temperatures > 25 C.
T
T
T
ACQ
ACQ
ACQ
C
ACQ
Note:
HOLD
DD
HOLD
HOLD
calculate
=
=
=
=
=
=
=
=
When using external voltage references with the A/D converter, the source impedance of the external
voltage references must be less than 20 to obtain the specified A/D resolution. Higher reference source
impedances will increase both offset and gain errors. Resistive voltage dividers will not provide a sufficiently
low source impedance.
To maintain the best possible performance in A/D conversions, external V
an operational amplifier or other low output impedance circuit.
Amplifier Settling Time + Holding Capacitor Charging Time + Temperature Coefficient
T
T
2 s + T
-C
-120 pF (1 k + 7 k + 2.5 k ) ln(0.0004885)
-120 pF (10.5 k ) ln(0.0004885)
-1.26 s (-7.6241)
9.61 s
2 s + 9.61 s + [(50 C – 25 C)(0.05 s/ C)]
11.61 s + 1.25 s
12.86 s
AMP
AMP
HOLD
(V
-(120 pF)(1 k + R
the
REF
+ T
+ T
=
=
=
=
=
C
(R
C
ACQUISITION TIME
A/D MINIMUM CHARGING TIME
CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
– (V
C
minimum
+ [(Temp – 25 C)(0.05 s/ C)]
+ T
IC
+ T
120 pF
2.5 k
1/2 LSb
5V
50 C (system max.)
0V @ time = 0
+ R
REF
COFF
COFF
ACQ
/2048)) • (1 – e
SS
Rss = 7 k
. This calculation is
+ R
SS
acquisition
S
) ln(1/2047)
+ R
S
) ln(1/2047)
(-Tc/C
HOLD
time,
(R
IC
+ R
SS
+ R
S
))
)
REF
inputs should be buffered with
PIC18FXX8
DS41159D-page 245