2.7V to 3.6V and 4.5V to 5.5V, Low-Power,

4-/12-Channel, 2-Wire Serial, 12-Bit ADCs

20

______________________________________________________________________________________

Effective Number of Bits

Effective number of bits (ENOB) indicates the global

accuracy of an ADC at a specific input frequency and

sampling rate. An ideal ADC’s error consists of quanti-

zation noise only. With an input range equal to the

ADC’s full-scale range, calculate the ENOB as follows:

ENOB = (SINAD - 1.76) / 6.02

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the RMS

sum of the input signal’s first five harmonics to the fun-

damental itself. This is expressed as:

harmonics.

Spurious-Free Dynamic Range

Spurious-free dynamic range (SFDR) is the ratio of the

RMS amplitude of the fundamental (maximum signal

component) to the RMS value of the next largest distor-

tion component.

THD

VVV

V

V

log

=×

++

+

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎜

⎞

⎠

⎟

⎟

20

2

2

3

2

4

2

5

2

1

SINAD dB

SignalRMS

NoiseRMS THDRMS

(

)

log

=×

+

⎡

⎣⎢

⎤

⎦⎥

20

*RC NETWORK IS OPTIONAL

**AIN11/REF (MAX1238/MAX1239)

ANALOG

INPUTS

μC

SDA

SCL

GND

RC NETWORK*

SDA

SCL

2k

Ω

AIN0

AIN1

AIN3**/REF

3.3V or 5V

5V

5V

MAX1236

MAX1237

MAX1238

MAX1239

0.1

μF

0.1

μF

Typical Operating Circuit

SDA

SCL

AIN3/REF

1

2

8

7

GND

AIN1

AIN2

AIN0

μMAX

TOP VIEW

3

4

6

5

MAX1236

MAX1237

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

AIN0

AIN8

AIN9

AIN10

AIN11/REF

GND

SDA

SCL

MAX1238

MAX1239

QSOP

AIN1

AIN2

AIN5

AIN3

AIN4

AIN6

AIN7

Pin Configurations