PIC16F877A-I/PT Microchip Technology Inc., PIC16F877A-I/PT Datasheet - Page 116

• Manufacturer Part Number: PIC16F877A-I/PT
• Description: 44 PIN, 7 KB FLASH, 368 RAM, 33 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F877A-I/PT

• A/d Inputs: 8-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 5 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 33
• Interface: I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 44-pin TQFP
• Programmable Memory: 14K Bytes
• Ram Size: 368 Bytes
• Speed: 20 MHz
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

PIC16F87X
11.1
For the A/D converter to meet its specified accuracy,
the charge holding capacitor (C
to fully charge to the input channel voltage level. The
analog input model is shown in Figure 11-2. The source
impedance (R
impedance directly affect the time required to charge
the capacitor C
impedance varies over the device voltage (V
Figure 11-2. The maximum recommended imped-
ance for analog sources is 10 k . As the impedance
is decreased, the acquisition time may be decreased.
EQUATION 11-1:
FIGURE 11-2:
DS30292C-page 114
T
T
T
ACQ
C
ACQ
Note 1: The reference voltage (V
A/D Acquisition Requirements
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
S
AMP
HOLD
) and the internal sampling switch (R
Legend C
HOLD
+ T
C
(R
VA
C
+ [(Temperature -25°C)(0.05 s/°C)]
. The sampling switch (R
ACQUISITION TIME
ANALOG INPUT MODEL
IC
+ T
V
I
R
SS
C
R
+ R
LEAKAGE
PIN
T
IC
HOLD
S
COFF
SS
ANx
+ R
C
5 pF
HOLD
PIN
= input capacitance
= threshold voltage
= leakage current at the pin due to
= interconnect resistance
= sampling switch
= sample/hold capacitance (from DAC)
S
) In(1/2047)
various junctions
) must be allowed
REF
) has no effect on the equation, since it cancels itself out.
HOLD
V
DD
DD
), see
V
V
) is not discharged after each conversion.
T
T
SS
SS
= 0.6V
= 0.6V
)
)
AD
delay must complete before acquisition can begin again.
I
± 500 nA
LEAKAGE
After the analog input channel is selected (changed),
this acquisition must be done before the conversion
can be started.
To
Equation 11-1 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
(DS33023).
R
IC
calculate
PICmicro™
1k
V
SS R
DD
Sampling
Switch
6V
5V
4V
3V
2V
SS
the
Mid-Range
Sampling Switch
5 6 7 8 9 10 11
V
minimum
C
= DAC capacitance
= 120 pF
SS
(k )
HOLD
2001 Microchip Technology Inc.
Reference
acquisition
ACQ
Manual
, see
time,