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MCP3421

18-Bit Analog-to-Digital Converter with I2C Interface and On-Board Reference

Microchip Technology 

MCP3421

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 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). The High-Speed mode is not

recommended for VDD less than 2.7V.

RSS VIN+,VIN-

VDD

D1 VT = 0.6V

Sampling

Switch

SS RS

V

CPIN

4 pF

D2

VT = 0.6V

ILEAKAGE

(~ ±1 nA)

CSAMPLE

(3.2 pF)

Legend:

V = Signal Source

RSS = Source Impedance

VIN+, VIN- = Analog Input Pin

CPIN = Input Pin Capacitance

VT = Threshold Voltage

VSS

ILEAKAGE = Leakage Current at Analog Pin

SS = Sampling Switch

RS = Sampling Switch Resistor

CSAMPLE = Sample Capacitance

D1, D2 = ESD Protection Diode

FIGURE 3-1:

Equivalent Analog Input Circuit.

DS22003E-page 10

© 2009 Microchip Technology Inc.

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