PIC12F609-H/MD MICROCHIP [Microchip Technology], PIC12F609-H/MD Datasheet - Page 86

• Manufacturer Part Number: PIC12F609-H/MD
• Description: 8-Pin, Flash-Based 8-Bit CMOS Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

PIC12F609/615/617/12HV609/615
10.3
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 10-4. The source
impedance (R
impedance directly affect the time required to charge the
capacitor C
varies over the device voltage (V
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),
EQUATION 10-1:
DS41302D-page 86
Note 1: The reference voltage (V
Assumptions:
The value for T
Solving for T
Therefore:
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
HOLD
leakage specification.
T
V
S
V
V
ACQ
T
) and the internal sampling switch (R
AP PLIE D
T
. The sampling switch (R
ACQ
AP P LI ED
AP P LIED
C
C
=
=
=
=
=
:
C
HOLD
=
=
=
ACQUISITION TIME EXAMPLE
Temperature
–
2µs
–
4.67µs
can be approximated with the following equations:
1.37


C
10pF 1k
Amplifier Settling Time
T
2µs






1
) must be allowed to fully
AMP
HOLD
1 e
1 e
+
µs
–
+
–
–
1.37µs

----------- -
2047
+
T

R
1
–
--------- -
C
–
-------- -
RC
DD
RC

T
T
Tc
IC
+
C
C
), see Figure 10-4.
+








+
+
+

REF

7k
=
Temperature - 25°C
T

=
=
=
R
SS


) has no effect on the equation, since it cancels itself out.
COFF
SS
50°C- 25°C
50°C and external impedance of 10k
) impedance
V
V
V
+
+
CHOLD
CHOLD
A P PLIE D
HOLD
10k
R
S
 ln(1/2047)
+

) is not discharged after each conversion.
SS

Hold Capacitor Charging Time
ln(0.0004885)
 0.05µs/°C
)



1
–
 0.05µs/°C
----------- -
2047

1
an A/D acquisition must be done before the conversion
can be started. To calculate the minimum acquisition
time, Equation 10-1 may be used. This equation
assumes that 1/2 LSb error is used (1024 steps for the
ADC). The 1/2 LSb error is the maximum error allowed
for the ADC to meet its specified resolution.




;[2] V
;combining [1] and [2]
;[1] V


CHOLD
CHOLD

5.0V V
+
charge response to V
charged to within 1/2 lsb
Temperature Coefficient
 2010 Microchip Technology Inc.
DD
APPLIED