PIC16F690-E/P Microchip Technology Inc., PIC16F690-E/P Datasheet - Page 118

• Manufacturer Part Number: PIC16F690-E/P
• Description: 20 PIN, 7 KB FLASH, 256 RAM, 18 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F690-E/P

• A/d Inputs: 12-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 7 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 18
• Interface: USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 20-pin PDIP
• Programmable Memory: 7K Bytes
• Ram Size: 256 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

PIC16F631/677/685/687/689/690
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 k . As the source impedance is
decreased, the acquisition time may be decreased.
After the analog input channel is selected (or changed),
EQUATION 9-1:
DS41262C-page 116
Note 1: The reference voltage (V
The value for T
Solving for T
Therefore:
Assumptions:
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
HOLD
leakage specification.
T
V
S
V
V
ACQ
T
) and the internal sampling switch (R
AP PLIE D
T
. The sampling switch (R
AP P LI ED
ACQ
AP P LIED
C
C
=
=
=
=
:
=
HOLD
C
=
=
=
ACQUISITION TIME EXAMPLE
Temperature
–
–
5µ
7.67µ
can be approximated with the following equations:
1.37
10pF 1k
⎛
⎝
C
Amplifier Settling Time
T
5µs
⎛
⎜
⎝
⎛
⎜
⎝
S
1
) must be allowed to fully
AMP
HOLD
1 e
1 e
+
µs
–
S
+
–
–
1.37µ
----------- -
2047
+
T
1
–
--------- -
R
C
–
-------- -
RC
RC
T
T
DD
Tc
IC
+
C
C
S
+
⎞
⎠
⎞
⎟
⎠
⎞
⎟
⎠
), see Figure 9-4.
+
+
+
REF
7k
=
Temperature - 25°C 0.05µs/°C
T
=
=
=
R
SS
COFF
) has no effect on the equation, since it cancels itself out.
SS
50°C- 25°C 0.05µ
) impedance
50°C and external impedance of 10k
V
V
V
+
+
CHOLD
A P PLIE D
HOLD
CHOLD
10k
R
S
+
) is not discharged after each conversion.
Preliminary
ln(1/2047)
SS
Hold Capacitor Charging Time
ln(0.0004885)
)
⎛
⎝
1
–
----------- -
2047
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
5.0V V
+
charge response to V
charged to within 1/2 lsb
Temperature Coefficient
© 2006 Microchip Technology Inc.
DD
APPLIED