PIC18F87K90-E/PT Microchip Technology, PIC18F87K90-E/PT Datasheet - Page 384

• Manufacturer Part Number: PIC18F87K90-E/PT
• Description: 128kB Flash, 4kB RAM, 1kB EE, 16MIPS, NanoWatt XLP, LCD, 5V 80 TQFP 12x12x1mm TR
• Manufacturer: Microchip Technology
• Series: PIC® XLP™ 18Fr

Specifications of PIC18F87K90-E/PT

• Core Processor: PIC
• Core Size: 8-Bit
• Speed: 64MHz
• Connectivity: I²C, LIN, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, LCD, POR, PWM, WDT
• Number Of I /o: 69
• Program Memory Size: 128KB (64K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 24x12b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 80-TQFP
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

analog input model is shown in
PIC18F87K90 FAMILY
23.3
For the A/D Converter to meet its specified accuracy, the
charge holding capacitor (C
fully charge to the input channel voltage level. The
impedance (R
impedance directly affect the time required to charge the
capacitor C
varies over the device voltage (V
The source impedance affects the offset voltage at the
analog input (due to pin leakage current). The maxi-
mum recommended impedance for analog sources
is 2.5 k . After the analog input channel is selected or
changed, the channel must be sampled for at least the
minimum acquisition time before starting a conversion.
EQUATION 23-1:
EQUATION 23-2:
EQUATION 23-3:
DS39957D-page 384
T
V
or
T
T
T
T
Temperature coefficient is only required for temperatures > 25C. Below 25C, T
T
T
ACQ
Note:
C
ACQ
AMP
COFF
C
ACQ
HOLD
=
=
A/D Acquisition Requirements
=
=
=
=
=
=
=
HOLD
When the conversion is started, the
holding capacitor is disconnected from the
input pin.
Amplifier Settling Time + Holding Capacitor Charging Time + Temperature Coefficient
T
S
AMP
) and the internal sampling switch (R
T
0.2 s
(Temp – 25C)(0.02 s/C)
(85C – 25C)(0.02 s/C)
1.2 s
-(C
-(25 pF) (1 k + 2 k + 2.5 k) ln(0.0004883) s
1.05 s
0.2 s + 1.05 s + 1.2 s
2.45 s
. The sampling switch (R
(V
-(C
AMP
HOLD
+ T
REF
HOLD
+ T
C
– (V
ACQUISITION TIME
A/D MINIMUM CHARGING TIME
CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
+ T
)(R
C
)(R
+ T
REF
COFF
IC
IC
HOLD
+ R
COFF
/2048)) • (1 – e
+ R
Figure
DD
SS
SS
) must be allowed to
).
+ R
+ R
23-5. The source
S
S
) ln(1/2048) s
SS
) ln(1/2048)
) impedance
(-T
C
/C
HOLD
SS
(R
)
IC
+ R
SS
+ R
S
To
Equation 23-1
that 1/2 LSb error is used (1,024 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 23-3
required acquisition time, T
based
assumptions:
))
• C
• Rs
• Conversion Error 
• V
• Temperature
)
DD
HOLD
calculate
on
COFF
shows the calculation of the minimum
the
can be used. This equation assumes
= 0 ms.
the
 2009-2011 Microchip Technology Inc.
following
=
=
=
=
minimum
ACQ
25 pF
2.5 k 
1/2 LSb
3V  Rss = 2 k 
85  C
. This calculation is
application
acquisition
system
time,