MCP3422 datasheet(12/58 Pages) MICROCHIP

12 / 58 page

MCP3422/3/4

DS22088C-page 12

FIGURE 3-1:

Equivalent Analog Input Circuit.

3.3

Serial Clock Pin (SCL)

SCL is the serial clock pin of the I2C 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 VDD line

to the SCL pin. Refer to Section 5.3 “I2C Serial Com-

munications” for more details of I2C Serial Interface

communication.

3.4

Serial Data Pin (SDA)

SDA is the serial data pin of the I2C 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 VDD 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

“I2C Serial Communications” for more details of I2C

Serial Interface communication.

Typical range of the pull-up resistor value for SCL and

SDA is from 5 k

Ω to 10 kΩ for standard (100 kHz) and

fast (400 kHz) modes, and less than 1 k

Ω 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 VSS pin; they must

be connected to the same potential on the Printed

Circuit Board (PCB).

CPIN

RSS CHn

4pF

VT = 0.6V

ILEAKAGE

Sampling

Switch

CSAMPLE

(3.2 pF)

VDD

(~ ±1 nA)

LEGEND

Signal Source

ILEAKEAGE

Leakage Current at Analog Pin

RSS

Source Impedance

Sampling Switch

CHn

Analog Input Pin

Sampling Switch Resistor

CPIN

Input Pin Capacitance

CSAMPLE

Sample Capacitance

Threshold Voltage

D1, D2 =

ESD Protection Diode

VSS

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