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ADC-228MM

8-Bit, 20MHz, Complete Flash A/D Converter

Unspecified 

®

®

ADC-228

TECHNICAL NOTES

1. Rated performance requires using good high-frequency

techniques. The analog and digital ground pins are

connected to each other internally. Avoid ground related

problems by connecting the grounds to one point, the

ground plane beneath the converter. Due to the inductance

and resistance of the power supply return paths, return the

analog and digital ground separately to the power supplies.

2. Bypass all the analog and digital supplies and the +5V

REFERENCE (pin 3) to ground with a 4.7µF, 25V tantalum

electrolytic capacitor in parallel with a 0.1µF ceramic

capacitor.

3. DATEL uses conservative definitions when specifying

integral linearity (end-point) and differential linearity (code

transition). The specifications using the less conservative

definitions have also been provided as a comparative

specification for products specified this way.

4. Single conversions (one-shot mode) would require another

clock edge to read out data. Users desiring to provide just

a single clock pulse could use the circuit shown in Figure 2

to obtain the data.

CLOCK

IN

74HC86

250Ω

100pF

CLOCK

OUT

50ns

DATA N

SAMPLED

25ns

PULSES

DATA N

VALID

40ns

Figure 2. ADC-228 Single Clock Pulse

Circuit and Operation

ANALOG

INPUT

51Ω

+5V

0.1µF

–15V

0.1µF

4.7µF +

NLINV 8

NMINV 9

CS1 11

CS1 12

CLOCK 18

VIN 5

9kΩ

*Optional

1

10

ADC-228

19

0.1µF

2, 4, 6, 7

4.7µF +

14

15

16

17

21

22

23

24

13, 20

3

B1 (MSB)

B2

B3

B4

B5

B6

B7

B8 (LSB)

NO CONNECTION

+5V REFERENCE OUT

+

4.7µF

0.1µF

* Use optional resistor only if

amp is not used to drive input.

R = VEE /1.667mA

+

4.7µF

+15V

Figure 3. ADC-228 Typical Connections

Table 1. ADC-228 Unipolar Output Coding

ANALOG

INPUT

+4.96V

+3.75V

+2.50V

+1.25V

+0.02V

0.00V

CODE

+FS – 1 LSB

+ 3/4 FS

+ 1/2 FS

+ 1/4 FS

+ 1 LSB

ZERO

STRAIGHT BIN.

NMINV = 0

NLINV = 0

1111 1110

1100 0000

1000 0000

0100 0000

0000 0001

0000 0000

COMP. BIN.

NMINV = 1

NLINV = 1

0000 0001

0011 1111

0111 1111

1011 1111

1111 1110

1111 1111

Table 2. ADC-228 Bipolar Output Coding

(Assumes analog input is externally offset)

ANALOG

INPUT

+2.480V

+1.250V

+0.020V

+0.000V

–1.250V

–2.480V

–2.500V

CODE

+FS – 1 LSB

+1/2 FS

+1 LSB

ZERO

–1/2 FS

–FS + 1 LSB

–FS

TWO’S

COMP.

NMINV = 1

NLINV = 0

0111 1111

0100 0000

0000 0001

0000 0000

1100 0000

1000 0001

1000 0000

COMP.

TWO’S COMP.

NMINV = 0

NLINV = 1

1000 0000

1011 1111

1111 1110

1111 1111

0011 1111

0111 1110

0111 1111

3

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