PIC16F684-I/SLG Microchip, PIC16F684-I/SLG Datasheet - Page 70

• Manufacturer Part Number: PIC16F684-I/SLG
• Description: pic, flash, Microcontrollers, Microprocessors, Semiconductors and Actives, ic, mcu
• Manufacturer: Microchip

PIC16F684
9.2
For the A/D converter to meet its specified accuracy, the
charge holding capacitor (C
fully charge to the input channel voltage level. The ana-
log input model is shown in Figure 9-4. The source
impedance (R
impedance directly affect the time required to charge
the capacitor C
ance varies over the device voltage (V
Figure 9-4. The maximum recommended impedance
for analog sources is 10 k . As the impedance is
decreased, the acquisition time may be decreased.
EQUATION 9-1:
FIGURE 9-4:
DS41202C-page 68
T
T
ACQ
Note 1: The reference voltage (V
ACQ
T
Legend: C
C
= T
= 2 s + T
= -120 pF (1 k
= 16.47 s
= Amplifier Settling Time + Hold Capacitor Charging Time + Temperature Coefficient
= C
= 19.72 s
= 2 s + 16.47 s + [(50°C-25°C)(0.05 s/°C)]
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
AMP
HOLD
leakage specification.
V
I
R
SS
C
S
LEAKAGE
T
HOLD
PIN
IC
HOLD
) and the internal sampling switch (R
+ T
(R
C
C
IC
+ [(Temperature -25°C)(0.05 s/°C)]
. The sampling switch (R
+ T
+ R
VA
ACQUISITION TIME
ANALOG INPUT MODEL
COFF
= Input Capacitance
= Threshold Voltage
= Leakage Current at the pin due to
= Interconnect Resistance
= Sampling Switch
= Sample/Hold Capacitance (from DAC)
R
SS
various junctions
S
k
HOLD
+ R
ANx
C
5 pF
S
PIN
) In(1/2047)
) must be allowed to
k ) In(0.0004885)
REF
) has no effect on the equation, since it cancels itself out.
SS
HOLD
DD
V
) imped-
DD
), see
V
V
) is not discharged after each conversion.
T
T
Preliminary
SS
= 0.6V
= 0.6V
)
I
± 500 nA
LEAKAGE
After the analog input channel is selected (changed),
this acquisition must be done before the conversion can
be started.
To calculate the minimum acquisition time, Equation 9-1
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.
To calculate the minimum acquisition time, T
the “PICmicro
Manual” (DS33023).
R
IC
1k
V
SS R
DD
Sampling
Switch
6V
5V
4V
3V
2V
®
SS
Mid-Range MCU Family Reference
Sampling Switch
5 6 7 8 9 10 11
V
 2004 Microchip Technology Inc.
C
= DAC capacitance
= 120 pF
SS
(k )
HOLD
ACQ
, see