Data Sheet

MCP3422/3/4
DS22088C-page 12 © 2009 Microchip Technology Inc.
FIGURE 3-1: Equivalent Analog Input Circuit.
3.3 Serial Clock Pin (SCL)
SCL is the serial clock pin of the I
2
C interface. The
device act only as a slave and the SCL pin accepts
only external serial clocks. The input data from the
Master device is shifted into the SDA pin on the rising
edges of the SCL clock and output from the slave
device occurs at the falling edges of the SCL clock.
The SCL pin is an open-drain N-channel driver.
Therefore, it needs a pull-up resistor from the V
DD
line
to the SCL pin. Refer to Section 5.3 “I
2
C Serial Com-
munications” for more details of I
2
C Serial Interface
communication.
3.4 Serial Data Pin (SDA)
SDA is the serial data pin of the I
2
C interface. The SDA
pin is used for input and output data. In read mode, the
conversion result is read from the SDA pin (output). In
write mode, the device configuration bits are written
(input) though the SDA pin. The SDA pin is an open-
drain N-channel driver. Therefore, it needs a pull-up
resistor from the V
DD
line to the SDA pin. Except for
start and stop conditions, the data on the SDA pin must
be stable during the high period of the clock. The high
or low state of the SDA pin can only change when the
clock signal on the SCL pin is low. Refer to Section 5.3
“I
2
C Serial Communications” for more details of I
2
C
Serial Interface communication.
Typical range of the pull-up resistor value for SCL and
SDA is from 5 kΩ to 10 kΩ for standard (100 kHz) and
fast (400 kHz) modes, and less than 1 kΩ for high
speed mode (3.4 MHz).
3.5 Exposed Thermal Pad (EP)
There is an internal electrical connection between the
Exposed Thermal Pad (EP) and the V
SS
pin; they must
be connected to the same potential on the Printed
Circuit Board (PCB).
C
PIN
V
R
SS
CHn
4pF
V
T
= 0.6V
V
T
= 0.6V
I
LEAKAGE
Sampling
Switch
SS
R
S
C
SAMPLE
(3.2 pF)
V
DD
(~ ±1 nA)
LEGEND
V = Signal Source I
LEAKEAGE
= Leakage Current at Analog Pin
R
SS
= Source Impedance SS = Sampling Switch
CHn = Analog Input Pin R
S
= Sampling Switch Resistor
C
PIN
= Input Pin Capacitance C
SAMPLE
= Sample Capacitance
V
T
= Threshold Voltage
D
1
, D
2
= ESD Protection Diode
D
1
D
2
V
SS