PIC16F887-E/P Microchip Technology Inc., PIC16F887-E/P Datasheet - Page 109

• Manufacturer Part Number: PIC16F887-E/P
• Description: 40 PIN, 14KB FLASH, 368 RAM, 36 I/O, PDIP
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F887-E/P

• A/d Inputs: 14-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 5 MIPS
• Eeprom Memory: 256 Bytes
• Frequency: 20 MHz
• Input Output: 35
• Interface: I2C/SPI/USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 40-pin PDIP
• Programmable Memory: 14K Bytes
• Ram Size: 368 Bytes
• Resistance, Drain To Source On: Bytes
• Serial Interface: MSSP or EUSART
• 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

9.3
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 9-4. 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 kΩ. As the source impedance is
decreased, the acquisition time may be decreased.
After the analog input channel is selected (or changed),
EQUATION 9-1:
© 2008 Microchip Technology Inc.
Note 1: The reference voltage (V
The value for T
Solving for T
Therefore:
Assumptions:
V
V
V
2: The charge holding capacitor (C
3: The maximum recommended impedance for analog sources is 10 kΩ. This is required to meet the pin
A/D Acquisition Requirements
AP PLIE D
AP P LI ED
AP P LIED
HOLD
leakage specification.
T
S
ACQ
T
) and the internal sampling switch (R
T
. The sampling switch (R
ACQ
C
⎛
⎝
C
⎛
⎜
⎝
⎛
⎜
⎝
=
1
=
=
=
=
:
1 e
1 e
C
HOLD
=
=
=
–
ACQUISITION TIME EXAMPLE
Temperature
–
–
2µ
4.67µ
–
can be approximated with the following equations:
–
1.37
10pF 1k
--------------------------
(
C
Amplifier Settling Time
T
2µs
S
2
) must be allowed to fully
AMP
HOLD
–
--------- -
–
-------- -
RC
n
RC
+
µs
T
Tc
+
S
+
C
1.37µ
(
1
⎞
⎟
⎠
⎞
⎟
⎠
1
+
T
(
) 1
R
C
=
=
Ω
T
DD
–
IC
+
C
S
+
), see Figure 9-4.
V
V
+
+
+
[
REF
⎞
⎠
(
7k
=
CHOLD
A P PLIE D
Temperature - 25°C
T
[
R
SS
(
Ω
COFF
=
) has no effect on the equation, since it cancels itself out.
SS
50°C- 25°C
) impedance
50°C and external impedance of 10k
+
+
V
HOLD
10k
CHOLD
R
PIC16F882/883/884/886/887
S
⎛
⎝
) ln(1/2047)
+
1
Ω
) is not discharged after each conversion.
SS
)
Hold Capacitor Charging Time
–
ln(0.0004885)
)
) 0.05µ
--------------------------
(
(
2
n
+
) 0.05µs/°C
1
1
(
S
) 1
/°C
an A/D 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
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
Ω
5.0V V
+
charge response to V
charged to within 1/2 lsb
Temperature Coefficient
DD
DS41291E-page 107
APPLIED