EVAL-AD7472CB

–2–

REV. A

Analog Input Section

The analog input section of this evaluation board accommodates unipolar and bipolar signals. Unipolar signals within the

AD7472 analog input signal range of 0 V - 2.5 V are connected via SK5. They are then buffered by the on-board buffer before

being applied to the VIN pin of the AD7472. Bipolar signals are connected via SK3 and are biased up by the on-board bias-

up buffer circuit before being applied to the VIN pin of the AD7472. The input impedence of the bias-up circuit is 50W which

is determined by the value of R7. The input impedence may be modified by removing/changing the value of R7. To obtain

optimum performance from this evaluation board the use of an impedence matched,

passive filter is recommended before the

analog signal is applied to the evaluation board.

For example, when using a 100KHz input tone, a 100KHz 50W filter from

TTE (part number KC5-100K-15K-50/50-720B) is suitable.

R8 Potentiometer (50Kohm)

This variable resistor is used to trim the DC bias voltage applied to the optional analog input bias-up circuit. This bias voltage

is factory preset to 1.25 V which biases a bipolar signal to swing around the midpoint of the analog input range (0 - 2.5 V).

If any adjustment is required, the user can use the histogram window in the eval-board software to analyze the DC voltage

variation while adjusting the trim pot. To view this properly, an analog input signal should not be applied to the board. Under

normal operation this pot should not be adjusted as it is preset for optimum performance.

LINK AND SWITCH OPTIONS

There are 11 link options which must be set for the required operating setup before using the evaluation board. The functions

of these options are outlined below.

Link No.

Function.

LK1

This link is used to select the DC bias voltage to be applied to the optional Vin bias-up circuit.

If the user is using the bias-up circuit, this link must be inserted which will apply the 2.7 V reference voltage

to the bias-up circuit. This causes a bipolar signal (applied to the bipolar vin input socket) to be biased up

around +1.25 V before it is applied to the AD7472 VIN pin. - see also LK10 (below)

If the bias up circuit is not being used this link should be removed.

LK2

This link must be in position "A" if external power supplies are being used. In this position the control logic

is being powered by the voltage applied to the VDD input.

When power is being supplied from the EVAL-CONTROL BOARD, this link can be moved to position "B"

if the user wants to drive the control logic from a separate +5 V which is generated on the EVAL-CONTROL

BOARD.

LK3

This link option selects the source of the CLKIN input.

When this link is in position "A" the CLKIN input is provided by the

EVAL-CONTROL BOARD.

When this link is in position "B" the CLKIN input is provided via the on-board 25MHz oscillator.

When this link is in position "C", an external CLKIN signal must be provided via SK1.

When using the on-board generated burst clock, this link must be in position "D".

LK4

This link option selects the source of the

CONVST input.

When this link is in position "A" the

CONVST input is provided by the EVAL-CONTROL BOARD.

When this link is in position "B" the

CONVST input is provided via the external socket, SK2.

LK5

This link option selects the source of the

RD input.

When this link is in position "A" the

RD input is provided by the EVAL-CONTROL BOARD.

When this link is in position "B" the

RD input is tied to GND. This option must be selected while using the

High Speed Converter Interface Board.

LK6

This link option selects the source of the

CS input.

When this link is in position "A" the

CS input is provided by the EVAL-CONTROL BOARD.

When this link is in position "B" the

CS input is tied to GND. This option must be selected while using the

High Speed Converter Interface Board.

LK7

This link option sets the voltage applied to the VDRIVE pin on the AD7472.

When this link is in position "A", VDRIVE is connected directly to the DVDD pin.

When this link is in position "B", an external voltage must be applied to the VDRIVE pin Via J3.

LK8

LK9

When this link is in position "A"

When this link is in position "B"

LK10

This link must be

in position "A" if a bipolar AIN signal is being applied to the bipolar Vin socket, SK3.

This link must be in position "B" if a unipolar AIN signal is being applied to the unipolar Vin socket, SK5

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