PIC16F785-E/SS Microchip Technology, PIC16F785-E/SS Datasheet - Page 88

• Manufacturer Part Number: PIC16F785-E/SS
• Description: 20 PIN, 3.5 KB STD FLASH, 128 RAM, 18 I/O PB FREE,
• Manufacturer: Microchip Technology
• Series: PIC® 16Fr

Specifications of PIC16F785-E/SS

• Rohs Compliant: YES
• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 20MHz
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 17
• Program Memory Size: 3.5KB (2K x 14)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 128 x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 5.5 V
• Data Converters: A/D 14x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 20-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT20SS1-1 - SOCKET TRANSITION 20DIP 20SSOPAC162060 - HEADER INTRFC MPLAB ICD2 20PIN
• Connectivity: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PIC16F785/HV785
12.2
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 12-4. The
source impedance (R
switch (R
required to charge the capacitor C
switch (R
(V
mended impedance for analog sources is 10 kΩ. 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.
EQUATION 12-1:
DS41249E-page 86
DD
Note 1: The reference voltage (V
), see Figure 12-4. The maximum recom-
The value for Tc can be approximated with the following equations:
Solving for Tc:
Therefore:
Assumptions:
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
SS
SS
) impedance varies over the device voltage
V
Tacq
leakage specification.
) impedance directly affect the time
V
V
T
AP P LIED
T
A PP LIED
ACQ
A PP LIE D
c
=
=
=
=
=
=
=
=
5µs
Temperature
–
–
7.62
ACQUISITION TIME EXAMPLE
1.37
S
10pF 1k
⎛
⎝
C
Amplifier Settling Time
T
5µs
) and the internal sampling
⎛
⎜
⎝
⎛
⎜
⎝
1
AMP
HOLD
1 e
1 e
+
µs
µs
–
–
+
–
1.37µs
(
----------- -
2047
+
Tc
(
HOLD
1
Ric
–
--------- -
–
-------- -
RC
RC
Ω
Tc
T
Tc
+
HOLD
C
+
⎞
⎠
⎞
⎟
⎠
⎞
⎟
⎠
+
+
+
) must be allowed
[
REF
(
7k
=
Temperature - 25°C
T
Rss
[
=
=
=
. The sampling
(
COFF
Ω
50°C- 25°C
) has no effect on the equation, since it cancels itself out.
50°C and external impedance of 10k
V
V
V
+
+
C HOLD
CHOLD
AP P LI ED
HOLD
10k
Rs
) ln(1/2047)
+
Ω
) is not discharged after each conversion.
)
Hold Capacitor Charging Time
ln(0.0004885)
) 0.05µs/°C
⎛
⎝
(
1
–
) 0.05µs/°C
----------- -
2047
(
1
To
Equation 12-1 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.
)
⎞
⎠
]
calculate
;[2] Vchold charge response to Vapplied
;Combining [1] and [2]
;[1] Vchold charged to within 1/2 lsb
)
]
Ω
the
5.0V V
+
Temperature Coefficient
minimum
© 2008 Microchip Technology Inc.
DD
acquisition
time,