AD7880

–12–

REV. 0

as a function of time for such operation. The total conversion

time for each cycle is 11

× 15 µs (where 15 µs is the time taken

for a single conversion) corresponding to 1.65

Hence:

Average Power

= {20 mW

+ {2 mW

× (9.9998)/(10)}

= 2.029 mW

AD7880 DATA ACQUISITION LAYOUT

Figure 24 shows the AD7880 in a data acquisition circuit. The

corresponding printed circuit board (PCB) layout and

silkscreen are shown in Figures 25 to 27.

The only additional component required for a full data acquisi-

tion system is an antialiasing filter. There is a component grid

provided near the analog input on the PCB which may be used

for such a filter or any other input conditioning circuitry. To fa-

cilitate this option there is a shorting link (labeled LK1 on the

PCB) on the analog input track. With LK1 in place, the analog

input connects to the buffer amplifier driving the AD7880.

With LK1 removed, a wire link is needed to connect the analog

input to the PCB component grid.

INTERFACE CONNECTIONS

The data acquisition board contains a parallel connection port

labeled SKT4. This is a 26-contact IDC Connector and pro-

vides for direct microprocessor connection to the board. This

connector, the pinout of which is shown in Figure 23, contains

all data, control and status signals of the AD7880 (with the ex-

ception of the CONVST and the CLKIN inputs both of which

are provided via SKT2 and SKT3 respectively). It also contains

decoded R/W and STRB inputs which are necessary for inter-

facing to many microprocessors including the TMS320C25 and

the Motorola 68000 series. Link LK7 selects RD directly or al-

ternatively, the decoded version. Note that the AD7880 CS in-

put must be decoded prior to the AD7880 evaluation board.

SKT1, SKT2 and SKT3 are three sub-miniature connectors

(SMC) which provide input connections for the analog input,

the CONVST input and the CLKIN input. Three different in-

put ranges can be accepted by the AD7880 each of which is

configured by selecting shorting plug options A, B or C of LK4.

Position A corresponds to the 0 V to 5 V unipolar configuration

of Figure 5, position B corresponds to the bipolar

±5 V configu-

ration of Figure 7 and position C allows for a 0 V to +10 V uni-

polar range as shown in Figure 6.

POWER SUPPLY CONNECTIONS

supply. In circumstances where bipolar

±5 V or a unipolar 0 V

to 10 V input ranges are required, provision has been allowed

for the connection of separate op amp power supplies (

±15 V,

±12 V, ±5 V, etc.) to V+ and V–. LK2 and LK3 shorting links

allow for the selection of user defined op amp power supplies or

the on-board single +5 V supply.

LINK OPTIONS

There are seven link options which must be set before using the

board. These are outlined below:

LK1

Connects the analog input to a buffer amplifier. The

analog input may also be connected to a component

grid for signal conditioning.

LK2, LK3 Allows for various op amp power supplies to be

used to drive the input buffer of the AD7880. Ex-

ternal supplies may be connected to V+ and V–.

Alternatively, the AD7880’s +5 V system supply

and AGND can be selected to drive a single supply

op amp.

LK4

Configures the various analog input ranges, 0 V to

5 V, 0 V to 10 V or

±5 V.

LK5

could also be wired in.

LK6

Selects power-down or sleep mode. The shorting

LK7

Connects the AD7880 RD input directly to the RD

input of SKT4 or to a decoded STRB and R/W

input. This shorting plug setting depends on the

microprocessor, e.g., the TMS320C25 requires a

decoded RD signal.

DB10

DB8

DB6

DB4

DB2

DB0

GND

R/W

RD

CS

1

3

5

7

9

13

15

17

19

25

23

21

11

N/C

2

4

6

8

10

14

16

18

20

26

24

22

12

DB11

DB9

DB7

DB5

DB3

DB1

GND

STRB

BUSY

N/C

N/C

N/C

5V

+

5V

+

BUSY

Figure 23. SKT4, IDC Connector Pinout

COMPONENT LIST

IC1

Op Amp*

IC2

AD7880 Analog-to-Digital Converter

IC3

74HC00 Quad NAND Gate

C1, C3, C5

10

µF Capacitors

C2, C4, C6, C7

0.1

µF Capacitors

R1, R2

10 k

Ω Pull-up Resistors

LK1, LK2, LK3

Shorting Links

LK4, LK5, LK6

LK7

SKT1, SKT2, SKT3 Sub-Miniature Connectors

Vendor No: Sealectro 50-051-0000 (Socket)

SKT4

26-Contact (2 Row) IDC Connector

NOTE

*See ANALOG INPUT BUFFERING section.

.