PIC16F877-20/P Microchip Technology, PIC16F877-20/P Datasheet - Page 428

• Manufacturer Part Number: PIC16F877-20/P
• Description: IC MCU FLASH 8KX14 EE 40DIP
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F877-20/P

• Core Size: 8-Bit
• Program Memory Size: 14KB (8K x 14)
• Core Processor: PIC
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 33
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 368 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Controller Family/series: PIC16F
• No. Of I/o's: 33
• Eeprom Memory Size: 256Byte
• Ram Memory Size: 368Byte
• Cpu Speed: 20MHz
• No. Of Timers: 3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 444-1001 - DEMO BOARD FOR PICMICRO MCU
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

PICmicro MID-RANGE MCU FAMILY
23.4
DS31023A-page 23-6
A/D Acquisition Requirements
For the A/D converter to meet its specified accuracy, the charge holding capacitor (C
be allowed to fully charge to the input channel voltage level. The analog input model is shown in
Figure
directly affect the time required to charge the capacitor C
ance varies over the device voltage (V
ance for analog sources is 10 k . As the impedance is decreased, the acquisition time may be
decreased. 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,
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.
Equation 23-1:
Equation 23-2:
Example 23-1
This calculation is based on the following application system assumptions.
C
Rs
Conversion Error
V
Temperature
V
Example 23-1:
T
T
Temperature coefficient is only required for temperatures > 25 C.
T
T
T
DD
HOLD
HOLD
V
or
Tc
ACQ
ACQ
ACQ
C
ACQ
HOLD
=
=
23-3. The source impedance (R
=
=
=
=
Amplifier Settling Time +
Holding Capacitor Charging Time +
Temperature Coefficient
T
=
=
T
2 s + Tc + [(Temp - 25 C)(0.05 s/ C)]
-C
-120 pF (1 k + 7 k + 10 k ) ln(0.0004885)
-120 pF (18 k ) ln(0.0004885)
-2.16 s (-7.6241)
16.47 s
2 s + 16.47 s + [(50 C - 25 C)(0.05 s/ C)]
18.47 s + 1.25 s
19.72 s
shows the calculation of the minimum required acquisition time T
AMP
AMP
HOLD
Acquisition Time
A/D Minimum Charging Time
(V
-(120 pF)(1 k + R
Calculating the Minimum Required Acquisition Time (Case 1)
+ T
+ T
REF
(R
=
=
=
=
=
C
C
- (V
IC
+ T
+ T
+ R
Preliminary
120 pF
10 k
1/2 LSb
5V
50 C (system max.)
0V @ time = 0
REF
COFF
COFF
SS
/2048)) • (1 - e
+ R
Rss = 7 k
SS
S
DD
) ln(1/2047)
S
+ R
),
) and the internal sampling switch (R
Equation 23-1
Figure
S
) ln(1/2047)
(-Tc/C
23-3. The maximum recommended imped-
(see graph in
HOLD
HOLD
may be used. This equation assumes
(R
IC
. The sampling switch (R
+ R
SS
Figure
1997 Microchip Technology Inc.
+ R
S
))
)
23-3)
ACQ
SS
) impedance
.
HOLD
SS
) imped-
) must