16F876 Microchip Technology, 16F876 Datasheet - Page 115

• Manufacturer Part Number: 16F876
• Description: 28/40-pin 8-Bit CMOS FLASH Microcontrollers
• Manufacturer: Microchip Technology

EQUATION 11-1:
FIGURE 11-2: ANALOG INPUT MODEL
T
T
T
1999 Microchip Technology Inc.
ACQ
C
ACQ
Note 1: The reference voltage (V
2: The charge holding capacitor (C
3: The maximum recommended impedance for analog sources is 10 k . This is required to meet the pin leak-
4: After a conversion has completed, a 2.0T
=
=
=
=
=
=
=
=
age specification.
During this time, the holding capacitor is not connected to the selected A/D input channel.
Amplifier Settling Time +
Hold Capacitor Charging Time +
Temperature Coefficient
T
2 S + T
C
- 120pF (1k + 7k + 10k ) In(0.0004885)
16.47 S
2 S + 16.47 S + [(50°C -25×C)(0.05 S/×C)
19.72 S
AMP
HOLD
Legend C
+ T
(R
C
VA
C
ACQUISITION TIME
IC
+ [(Temperature -25°C)(0.05 S/°C)]
V
I
R
SS
C
+ T
R
LEAKAGE
T
+ R
PIN
IC
HOLD
S
COFF
SS
ANx
C
5 pF
+ R
PIN
= input capacitance
= threshold voltage
= leakage current at the pin due to
= interconnect resistance
= sampling switch
= sample/hold capacitance (from DAC)
various junctions
S
REF
) In(1/2047)
) has no effect on the equation, since it cancels itself out.
HOLD
V
DD
V
V
) is not discharged after each conversion.
T
T
= 0.6V
= 0.6V
AD
delay must complete before acquisition can begin again.
I
± 500 nA
LEAKAGE
R
IC
1k
V
SS R
DD
Sampling
Switch
6V
5V
4V
3V
2V
SS
Sampling Switch
5 6 7 8 9 10 11
V
C
= DAC capacitance
= 120 pF
SS
( k
PIC16F87X
HOLD
)
DS30292B-page 115