Full Scale

Analog Input Range and Input Protection

Internal protection diodes, which clamp the analog

However, for accurate conversions near full scale, the

If the analog input exceeds 50mV beyond the sup-

plies, do not forward bias the protection diodes of

off-channels over two milliamperes, as excessive

current will degrade the conversion accuracy of the

on-channel.

The full-scale input voltage depends on the voltage at

VREF. See Tables 1a and 1b.

Quick Look

To evaluate the analog performance of the

MAX186/MAX188 quickly, use the circuit of Figure 5.

The MAX186/MAX188 require a control byte to be writ-

ten to DIN before each conversion. Tying DIN to +5V

feeds in control bytes of $FF (HEX), which trigger

Low-Power, 8-Channel,

Serial 12-Bit ADCs

_______________________________________________________________________________________

9

Reference

Zero

Scale

Full Scale

Internal Reference

(MAX186 only)

0V

+4.096V

0V

at VREF

0V

VREF

External Reference

at REFADJ

Reference

Negative

Full Scale

Zero

Scale

Internal Reference

(MAX186 only)

-4.096V/2

0V

External Reference

at REFADJ

x A*

0V

at VREF

-1/2 VREF

0V

+4.096V/2

x A*

+1/2 VREF

0.1µF

DGND

AGND

CS

SCLK

DIN

DOUT

SSTRB

SHDN

+5V

N.C.

0.01µF

CH7

REFADJ

VREF

C2

0.01µF

+2.5V

REFERENCE

C1

4.7µF

D1

1N4148

+5V

0V TO

4.096V

ANALOG

INPUT

+2.5V

**

OSCILLOSCOPE

CH1

CH2

CH3

CH4

* FULL-SCALE ANALOG INPUT, CONVERSION RESULT = $FFF (HEX)

**REQUIRED FOR MAX188 ONLY. A POTENTIOMETER MAY BE USED IN PLACE OF THE REFERENCE FOR TEST PURPOSES.

MAX186

MAX188

+5V

2MHz

OSCILLATOR

SCLK

SSTRB

DOUT*

Figure 5. Quick-Look Circuit

* A = 1.678 for the MAX186, 1.638 for the MAX188

Table 1b. Bipolar Full Scale, Zero Scale, and

Negative Full Scale

Table 1a. Unipolar Full Scale and Zero Scale

* A = 1.678 for the MAX186, 1.638 for the MAX188