mcp3208t-ci-sl Microchip Technology Inc., mcp3208t-ci-sl Datasheet - Page 14

• Manufacturer Part Number: mcp3208t-ci-sl
• Description: 2.7v 4-channel/8-channel 12-bit A/d Converters With Spi Serial Interface
• Manufacturer: Microchip Technology Inc.

MCP3204/3208
This diagram illustrates that the source impedance (R
adds to the internal sampling switch (R
directly effecting the time that is required to charge the
capacitor (Csample). Consequently, larger source
impedances increase the offset, gain and integral
linearity errors of the conversion (see Figure 4-2).
4.2
For each device in the family, the reference input
(V
the reference input is reduced, the LSB size is reduced
accordingly. The theoretical digital output code pro-
duced by the A/D converter is a function of the analog
input signal and the reference input, as shown below.
FIGURE 4-1:
FIGURE 4-2:
vs. Input resistance (R
0.1 LSB deviation in INL from nominal
conditions.
DS21298D-page 14
REF
Legend
2.5
2.0
1.5
1.0
0.5
0.0
VA
) determines the analog input voltage range. As
CHx
C
R
100
VA
V
pin
ss
t
Reference Input
R
SS
=
=
=
=
=
CHx
Input Resistance (Ohms)
Signal Source
Source Impedance
Input Channel Pad
Input Pin Capacitance
Threshold Voltage
V
Analog Input Model.
Maximum Clock Frequency
DD
V
S
= 2.7 V
DD
) to maintain less than a
1000
= 5 V
7 pF
C
PIN
V
SS
DD
) impedance,
V
V
T
T
C
I
leakage
= 0.6V
= 0.6V
sample
SS
R
10000
s
S
)
=
=
=
=
Leakage Current At The Pin
Due To Various Junctions
Sampling switch
Sampling switch resistor
Sample/hold capacitance
I
±1 nA
LEAKAGE
EQUATION
When using an external voltage reference device, the
system designer should always refer to the manufac-
turer’s recommendations for circuit layout. Any instabil-
ity in the operation of the reference device will have a
direct effect on the operation of the A/D converter.
V
V
Digital Output Code
IN
REF
= analog input voltage
SS
Sampling
Switch
= reference voltage
R
S
= 1 kΩ
© 2007 Microchip Technology Inc.
=
V
SS
4096 V
-------------------------- -
C
= DAC capacitance
= 20 pF
SAMPLE
V
REF
×
IN