EVAL-AD7472CB Datasheet, PDF (2/14 Pages) Analog Devices – Evaluation Board for 12-bit high speed, low power, successive-approximation ADC

EVAL-AD7472CB
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
LK4
LK5
LK6
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".
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.
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.
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
LK10
This link selects the source of the V_DD supply.
When this link is in position "A" V_DD must be supplied from an external source via J2.
When this link is in position "B" V_DD is supplied from the EVAL-CONTROL BOARD.
This link selects the source of the V_SS supply.
When this link is in position "A" V_SS must be supplied from an external source via J2.
When this link is in position "B" V_SS is supplied from the EVAL-CONTROL BOARD.
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
Continued on next page
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REV. A