PIC12F1822 MICROCHIP [Microchip Technology], PIC12F1822 Datasheet - Page 143

• Manufacturer Part Number: PIC12F1822
• Description: 8/14-Pin Flash Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

15.3
For the ADC to meet its specified accuracy, the charge
holding capacitor (C
charge to the input channel voltage level. The Analog
Input model is shown in Figure 15-4. The source
impedance (R
impedance directly affect the time required to charge
the capacitor C
impedance varies over the device voltage (V
to
impedance for analog sources is 10 k. As the
EQUATION 15-1:
 2010 Microchip Technology Inc.
The value for T
Solving for T
Therefore:
Assumptions:
Note 1: The reference voltage (V
Figure 15-4.
V
V
V
Note: Where n = number of bits of the ADC.
2: The charge holding capacitor (C
3: The maximum recommended impedance for analog sources is 10 k. This is required to meet the pin
A/D Acquisition Requirements
AP P LI ED
AP P LI ED
AP P LI ED
leakage specification.
S
T
) and the internal sampling switch (R
T
C
ACQ
T
ACQ
:
HOLD
C
C
The








Temperature
can be approximated with the following equations:
=
=
=
=
1
1 e
1 e
HOLD
= 2µs + 1.12µs + [(50°C - 25°C) (0.05µs/°C)]
=
=
=
. The sampling switch (R
ACQUISITION TIME EXAMPLE
–
–
–
1.12
4.42µs
–
–
Amplifier Settling Time
T
2µs
C
10pF 1k
--------------------------

maximum
AMP
) must be allowed to fully
2
–
--------- -
–
-------- -
HOLD
RC
RC
µs
T
Tc
n
+
C
+







+
T
1
1

C
 1
=
R
=
T

+
–
IC
C
=
V
V
+
+

REF
+

A PP LIE D
CHOLD
recommended


7k
50°C and external impedance of 10k
Temperature - 25°C
T
R
COFF
) has no effect on the equation, since it cancels itself out.

=
SS
+
+
HOLD
DD
V
10k
PIC12F/LF1822/16F/LF1823
R
CHOLD
), refer


S
+
1
) is not discharged after each conversion.
 ln(1/511)

Preliminary
SS
SS
–
Hold Capacitor Charging Time

)
)
--------------------------

ln(0.001957)
2
n
+
 0.05µs/°C
1
1

 1
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 15-1 may be
used. This equation assumes that 1/2 LSb error is used
(1,024 steps for the ADC). The 1/2 LSb error is the
maximum error allowed for the ADC to meet its
specified resolution.
–


;[1] V
;[2] V
;combining [1] and [2]



CHOLD
CHOLD
5.0V V
+
charged to within 1/2 lsb
charge response to V
DD
Temperature Coefficient
DS41413A-page 143
APPLIED