Datasheet

MCP3301
DS21700E-page 12  2001-2011 Microchip Technology Inc.
3.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Tab le 3- 1.
TABLE 3-1: PIN FUNCTION TABLE
3.1 Voltage Reference (V
REF
)
This input pin provides the reference voltage for the
device, which determines the maximum range of the
analog input signal and the LSB size.
The LSB size is determined by the equation shown
below. As the reference input is reduced, the LSB size
is reduced accordingly.
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 accuracy of the ADC conversion
results.
3.2 Positive Analog Input (IN+)
This pin has an absolute voltage range of V
SS
-0.3V to
V
DD
+0.3V. The full scale input range is defined as the
absolute value of (IN+) - (IN-).
3.3 Negative Analog Input (IN-)
This pin has an absolute voltage range of V
SS
-0.3V to
V
DD
+0.3V. The full scale input range is defined as the
absolute value of (IN+) - (IN-).
3.4 Ground Connection (V
SS
)
If an analog ground plane is available, it is recom-
mended that this device be tied to the analog ground
plane in the circuit. See Section 5.6 “Layout Consid-
erations”, for more information regarding circuit
layout.
3.5 Chip Select/Shutdown (CS/SHDN)
The CS/SHDN pin is used to initiate communication
with the device when pulled low. This pin will end a con-
version and put the device in low power standby when
pulled high. The CS
/SHDN pin must be pulled high
between conversions and cannot be tied low for
multiple conversions. See Figure 6-2 for serial
communication protocol.
3.6 Serial Data Output (D
OUT
)
The SPI serial data output pin is used to shift out the
results of the A/D conversion. Data will always change
on the falling edge of each clock as the conversion
takes place. See Figure 6-2 for serial communication
protocol.
3.7 Serial Clock (CLK)
The SPI clock pin is used to initiate a conversion, as
well as to clock out each bit of the conversion as it takes
place. See Section 5.2 “Driving the Analog Input”
for constraints on clock speed, and Figure 6-2 for serial
communication protocol.
3.8 Power Supply (V
DD
)
The device can operate from 2.7V to 5.5V, but the per-
formance is applicable from a 4.5V to 5.5V supply
range. To ensure accuracy, a 0.1 µF ceramic bypass
capacitor should be placed as close as possible to the
pin. See Section 5.6 “Layout Considerations” for
more information regarding circuit layout.
MSOP, PDIP,
SOIC
Name Function
1V
REF
Reference Voltage Input
2 IN(+) Positive Analog Input
3 IN(-) Negative Analog Input
4V
SS
Ground
5CS
/SHDN Chip Select / Shutdown Input
6D
OUT
Serial Data Out
7 CLK Serial Clock
8V
DD
+4.5V to 5.5V Power Supply
LSB Size =
2 x V
REF
8192