Reading a Conversion

Digitized data from up to four channels are stored in

memory to be read out through the parallel interface.

After receiving an INT signal, the user can access up to

four conversion results by performing up to four read

operations.

With CS low, the conversion result from CH_1 is

accessed, and INT is reset high on the first RD falling

edge. On the RD rising edge, the internal address

pointer is advanced. If a single conversion is pro-

grammed, only one RD pulse is required, and the

address pointer is reset to CH_1. For multichannel con-

versions, up to four RD falling edges sequentially

access the data for channels 1 through 4. For

n chan-

nels converted (1 <

n

≤ 4), the address pointer is reset

to CH_1 after

n RD pulses. Do not perform a read oper-

ation during conversion, as it will corrupt the conver-

sion’s accuracy.

__________Applications Information

External Clock

The MAX125/MAX126 require a TTL-compatible clock

up to 16MHz for proper operation. The clock duty

cycle’s range is between 30% and 70%.

Internal and External Reference

The MAX125/MAX126 can be used with an internal or

external reference voltage. An external reference can

be connected directly at REFIN. An internal buffer with

a gain of +1 provides 2.5V at REFOUT.

Internal Reference

The full-scale range with the internal reference is ±5V

for the MAX125 and ±2.5V for the MAX126. Bypass

REFIN with a 0.1µF capacitor to AGND and bypass the

REFOUT pin with a 4.7µF (min) capacitor to AGND

(Figure 6). The maximum value to compensate the ref-

erence buffer is 22µF. Larger values are acceptable if

low-ESR capacitors are used.

External Reference

For operation over a wide temperature range, an exter-

nal 2.5V reference with tighter specifications improves

accuracy. The MAX6325 is an excellent choice

to match the MAX125/MAX126 accuracy over the

commercial and extended temperature ranges with a

2x4-Channel, Simultaneous-Sampling

14-Bit DAS

10

______________________________________________________________________________________

X = Don’t care

Table 1. Modes of Operation

A3

A2

A1

0

0

0

0

0

0

0

0

1

0

0

1

A0

0

1

0

1

CONVERSION

TIME (µs)

3

6

9

12

MODE

Input Mux A/Two-Channel Conversion

Input Mux A/Three-Channel Conversion

Input Mux A/Four-Channel Conversion

0

1

0

0

3

Input Mux B/Single-Channel Conversion

0

1

0

1

6

Input Mux B/Two-Channel Conversion

0

1

1

0

9

Input Mux B/Three-Channel Conversion

0

1

1

1

12

Input Mux B/Four-Channel Conversion

1

X

X

X

—

Power-Down

TO DAC

REFIN

10k

0.1

µF

4.7

µF

2.5V

REFOUT

7

6

(2.5V)

(2.5V)

MAX125

MAX126

Figure 6. Internal Reference

Input Mux A/Single-Channel Conversion (default at power-up)