______________ Typical Applications

Unipolar Operation

Figure 16a shows the analog circuit connections for

unipolar operation, and Figure 16b shows the nominal

transfer characteristic for unipolar operation. Since the

offset and full-scale errors of the MX7575/MX7576 are

very small, it is not necessary to null these errors in

most cases. If calibration is required, follow the steps in

the sections below.

Offset Adjust

The offset error can be adjusted by using the offset trim

capability of an op amp (when it is used as a voltage fol-

lower) to drive the analog input, AIN. The op amp should

have a common-mode input range that includes 0V. Set

its initial input to 4.8mV (1/2LSB), while varying its offset

until the ADC output code flickers between 0000 0000

and 0000 0001.

Full-Scale Adjustment

Make the full-scale adjustment by forcing the analog

input, AIN, to 2.445V (FS - 3/2LSB). Then vary the refer-

ence input voltage until the ADC output code flickers

between 1111 1110 and 1111 1111.

Bipolar Operation

Figure 18a shows an example of the circuit connection

for bipolar operation, and Figure 18b shows the nominal

transfer characteristic for bipolar operation. The output

code provided by the MX7575 is offset binary. The ana-

log input range for this circuit is ±2.46V (1LSB =

19.22mV), even though the voltage appearing at AIN is

in the 0V to 2.46V range. In most cases, the MX7575 is

accurate enough that calibration will not be necessary. If

calibration is not needed, resistors R1–R7 should have a

0.1% tolerance, with R4 and R5 replaced by one 10k

Ω

resistor, and R2 and R3 with one 1k

Ω resistor. If calibra-

tion is required, follow the steps in the sections below.

Offset Adjust

Adjust the offset error by applying an analog input volt-

age of 2.43V (+FS - 3/2LSB). Then adjust resistor R5

until the output code flickers between 1111 1110 and

1111 1111.

Full-Scale Adjust

Null the full-scale error by applying an analog input

voltage of -2.45V (-FS + 1/2LSB). Then adjust resistor

R3 until the output code flickers between 0000 0000

and 0000 0001.

CMOS, µP-Compatible, 5µs/10µs, 8-Bit ADCs

10

______________________________________________________________________________________

16

17

15

5

4

1

2

3

9

18

+5V

+5V

47

µF

47

µF

0.1

µF

3.3k

+1.23V

0.1

µF

+5V

2.46V(max)

+

-

D7–D0

DATA OUT

CONTROL INPUTS

100pF, 1%

100k, 2%

AIN

REF

AGND

CLK

BUSY

CS

RD

TP/

MODE

MX7575

MX7576

0000 0011

0000 0010

0000 0001

0000 0000

1111 1111

1111 1110

1111 1101

1LSB

2LSBs

3LSBs

0

AIN, INPUT VOLTAGE (IN TERMS OF LSBs)

FS - 1LSB

FULL-SCALE

TRANSITION

(FS - 3/2LSB)

OUTPUT

CODE

1LSB = –––

2FS

256

11

12

13

14

7

-55

-25

25

75

8

10

AMBIENT TEMPERATURE (°C)

0

125

100

50

9

MX7576

MX7575

Figure 16a. Unipolar Configuration

Figure 16b. Nominal Transfer Characteristic for Unipolar

Operation

Figure 17. Typical Conversion Times vs. Temperature Using

Internal Clock