AD7875LP datasheet(16/20 Pages) AD

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REV. B

AD7870/AD7875/AD7876

–16–

SKT5 is a 9-way D-type connector that is meant for serial inter-

facing only. An inverted DB9/SCLK output is also provided on

this connector for systems that accept data on a rising clock

edge. The SKT5 pinout is shown in Figure 27.

Figure 27. SKT5, D-Type Connector Pinout

SKT1, SKT2 and SKT3 are three BNC connectors which pro-

vide input connections for the analog input, the

CONVST input

and an external clock input. The use of an external clock source

is optional; there is a shorting plug (LK2) on the ADC CLK in-

put that must be connected to either –5 V (for the ADCs own

internal clock) or to SKT3.

POWER SUPPLY CONNECTIONS

The PCB requires two analog power supplies and one 5 V digi-

tal supply . The analog supplies are labelled V+ and V–, and the

range for both supplies is 12 V to 15 V (see silkscreen in Figure

29). Connection to the 5 V digital supply is made through any

of the connectors (SKT4 to SKT6). The –5 V supply required

by the ADC is generated from a voltage regulator on the V–

power supply input (IC3 in Figure 27).

SHORTING PLUG OPTIONS

There are seven shorting plug options that 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 Selects either the ADC internal clock or an external

clock source.

LK3 Configures the ADC 12/

8/CLK input for the appropri-

ate serial or parallel interface.

LK4 Connects the ADC

RD input directly to the two parallel

connectors or to a decoded

STRB and R/W input. This

shorting plug setting depends on the microprocessor e.g.,

the TMS32010 has a separate

RD output while the

TMS32020 has

STRB and R/W outputs.

LK5– Connect the pull-up resistors R3, R4 and R5 to

SSTRB,

LK7 SCLK and SDATA. These shorting plugs should be

removed for parallel interfacing.

COMPONENT LIST

IC1

AD711 Op Amp

IC2

AD7870/AD7875/AD7876 Analog-to-

Digital Converter

IC3

MC79L05 –5 V Regulator

IC4

74HC00 Quad NAND Gate

IC5

74HC74 Dual D-Type Flip Flop

C1, C3, C5, C7,

µF Capacitors

C9, C11

C2, C4, C6, C8,

0.1

µF Capacitors

C10, C12

R1, R2

10 k

Ω Pull-Up Resistors

R3*, R5*

4.7 k

Ω Pull-Up Resistors

R4*

2 k

Ω Pull-Up Resistor

LK1, LK2

Shorting Plugs

LK3, LK4

LK5, LK6, LK7

SKT1, SKT2, SKT3 BNC Sockets

SKT4

26-Contact (2-Row) IDC Connector

SKT5

9-Contact D-Type Connector

SKT6

96-Contact (3-Row) Eurocard Connector

*Required for Serial Communication only.

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