MCP3421 datasheet(10/42 Pages) MICROCHIP

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MCP3421

DS22003E-page 10

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). The High-Speed mode is not

recommended for VDD less than 2.7V.

FIGURE 3-1:

Equivalent Analog Input Circuit.

CPIN

RSS

VIN+,VIN-

4pF

VT = 0.6V

ILEAKAGE

Sampling

Switch

CSAMPLE

(3.2 pF)

VDD

(~ ±1 nA)

Legend:

Signal Source

ILEAKAGE = Leakage Current at Analog Pin

RSS = Source Impedance

Sampling Switch

VIN+, VIN- = Analog Input Pin

RS = Sampling Switch Resistor

CPIN = Input Pin Capacitance

CSAMPLE = Sample Capacitance

VT = Threshold Voltage

D1, D2 =

ESD Protection Diode

VSS

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