ANALOG DEVICES EVAL-AD7476, EVAL-AD7477CB Service Manual

EVAL-AD7476

a	EvaluationBoardfor1MSPS,
	12-/ 10-Bit ADCs
	EVAL-AD7476/77CB

FEATURES

Full-Featured Evaluation Board for the AD7476/ AD7477

EVAL-CONTROL BOARD Compatible Stand Alone Capability

On-Board Analog Buffering and Reference Various Linking Options

PC Software for Control and Data Analysis when used with EVAL-CONTROL BOARD

INTRODUCTION

This Technical Note describes the evaluation board for the AD7476/77. The AD7476/77 are, respectively, 12 bit and 10 bit, high speed, low power, successive-approxima- tion ADC's. The parts operate from a single 2.35 V to 5.25 V power supply and feature throughtput rates up to 1MSPS. The parts contain a low-noise, wide bandwidth track/hold amplifier which can handle input frequencies in excess of 1MHz. Full data on the AD7476/77 is available in the AD7476/77 data sheet available from Analog Devices and should be consulted in conjunction with this Technical Note when using the Evaluation Board.

On-board components include an AD780 which is a pin programmable +2.5 V or +3 V ultra high precision bandgap reference, an OP467 quad op-amp used to buffer the analog inputs and the REF195 precision bandgap, voltage reference, providing a 5 V reference voltage. There are various link options which are explained in detail on page 2.

Interfacing to this board is through a 96-way connector. This 96-way connector is compatible with the EVALCONTROL BOARD which is also available from Analog

Devices. External sockets are provided for the AIN input, the VIN input and the VBIASED input.

OPERATING THE AD7476/77 EVALUATION BOARD

Power Supplies

When using this evaluation board with the EVAL-CON- TROL BOARD all supplies are provided from the EVALCONTROL BOARD through the 96 way connector.

When using the board as a stand alone unit external supplies must be provided. This evaluation board has seven

power supply inputs: AVDD, AGND, +12 V, -12 V, AGND, DVDD and DGND. +5 V must be connected to the AVDD input to supply the AD780 and the Ref195 voltage refer-

ence. The VDD for the AD7476/77 can be supplied from either the AVDD external supply or from the selected voltage reference chip. +12 V and -12 V are used to supply the OP467 quad op-amp. 0V is connected to one or

both of the AGND inputs. The DVDD input can be used to supply a separate +5V for the 74LS04 DVDD pin. The

DGND input must be tied to 0V. The supplies are decoupled to the relevant ground plane with 10µF tantalum

and 0.1µF multilayer ceramic capacitors at the point where they enter the board. The supply pins of the quad op-amp and references are also decoupled to AGND with 10µF tantalum and a 0.1µF ceramic capacitors. The AD7476/77 AVDD supply pin is decoupled to AGND with 10uF tantalum and 0.1µF multilayer ceramic capacitors.

Extensive ground planes are used on this board to minimize the effect of high frequency noise interference. There

are two ground planes, AGND and DGND. These are connected at one location close to the AD7476/77.

Figure 1. FUNCTIONAL BLOCK DIAGRAM

External

Voltage

Power Supplies

Reference

Vdd

CS

Input Buffer

AD7476/77

ADC

SCLK

96 Pin

VIN

SDATA

DIN

Connector

Power

Bias-up

Supply

Circuit

Circuit

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EVAL-AD7476/77CB

LINK AND SWITCH OPTIONS

There are 12 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 option is used to select	a 50W termination on the analog input buffer circuit.
	When this link is “inserted” the	50W termination is applied.
	When this link is “removed” the	50W termination is removed.
LK2	This link option controls the program pin of the AD780 voltage reference.
	When this link is “inserted” the AD780 output voltage is set to +3.0 V.
	When this link is “removed” the AD780 output voltage is set to +2.5 V.
LK3	This link is used to select a 50W	termination on the input of the bias-up circuit.
	When this link is “inserted” the	50W termination is applied.

	When this link is “removed” the 50W termination is removed.
LK4	This link option is used to connect the output of either the REF195 or the AD780 to the VDD	pin of the
	AD7476/77 ( if link 12 is in position C).
	When this link is in position A the AD780 supplies the VDD voltage for the AD7476/77.
	When this link is in position B the REF195 supplies the VDD voltage for the AD7476/77.
LK5	This link option sets the DC bias voltage that is applied to the optional bias-up/filter circuit.
	When this link is in position “A”, the bias voltage is set to the same level as the voltage that is applied
	to the AD7476/77 VDD pin. In this configuration a bipolar analog input applied to the Vin SMB socket is
	biased up by the bias circuit and is presented at the Vbiased SMB as a uni-polar signal biased	around
	VDD/2.
	When this link option is placed in position “B”, the bias voltage is set to AGND. In this configuration the bias-
	up circuit is not used.
LK6	This link option is used to select the source of the +12 V supply.
	In position A, the +12 V is supplied from the EVAL-CONTROL BOARD through the 96 way connector.
	In position B, the +12 V is supplied from an external source through the power connector, J6.
LK7	This link option is used to select the source of the -12 V supply.
	In position A, the -12 V is supplied from the EVAL-CONTROL BOARD through the 96 way connector.
	In position B, the -12 V is supplied from an external source through the power connector, J6.
LK8-9	These links control the transfer of data from the AD7476/77 during a conversion for various frequencies of
	SCLK.
	Link 8 and 9 should be in position "A" for slower SCLK frequencies, giving valid data on the rising edge.
	Link 8 and 9 should be in position "B" for fast SCLK frequencies, giving valid data on the following edge.
LK10	This link selects the source of the Vcc +5 V supply for the 74LS04.
	When this link is in position "A", Vcc power is supplied from the same power source supplying the AD7476/
	77 VDD pin.
	When this link is in position "B", VCC power must be must be supplied from an external source via the power
	connector, J5.
LK11	This link option is used to connect the input of the VIN analog buffer to the AIN input socket or to AGND.
	When this link is in position “A” the AIN socket is tied to the input of the VIN buffer. In this configuration,
	an analog signal applied to the Ain input socket is buffered and presented at the AD7476/77 VIN input.
	When this link is in position “B” the VIN buffer input is tied to AGND.
LK12	This link selects the source of the VDD supplied to the AD7476/77.
	When this link is in position “A” the VDD must be supplied from an external source via J5.
	When this link is in position “B” the VDD is supplied from the EVAL-CONTROL BOARD.
	When this link is in position “C” the VDD is supplied from either the AD780 or the REF195	references.

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EVAL-AD7476/77CB

SET-UP CONDITIONS

Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are as per the required operating mode. Table I shows the position in which all the links are set when the evaluation

board	is sent out.
			Table I. Initial Link and Switch Positions
Link	No.	Position	Function.
LK1		Removed	50W termination resistor is not applied to the	input	of	the	VIN circuit.
LK2		Removed	AD780 is set to provide a +2.5V reference.
LK3		Removed	50W termination resistor is not applied to the	input	of	the	bias-up circuit.
LK4		Removed	This is not relevant due to the position of LK12.
LK5		A	EVAL-CONTROL BOARD is selected as the DC bias voltage for the optional
			bias-up/filter circuit.
LK6		A	+12V supplied from EVAL-CONTROL BOARD via J4.
LK7		A	-12V supplied from EVAL-CONTROL BOARD via J4.
LK8		B	SCLK signal from EVAL-CONTROL BOARD is not inverted, (for faster values
			of SCLK).
LK9		B	SCLK signal from EVAL-CONTROL BOARD is not inverted, (for faster values
			of SCLK).
LK10		Removed	This is not relevant due to the position of LK8 and LK9, (As 74LS04 is not in
			use).
LK11		A	Ain SMB is connected to the input of the analog input buffer.
LK12		B	VDD for the AD7476/77 is supplied from the EVAL-CONTROL BOARD via J4.

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EVAL-AD7476/77CB

EVALUATION BOARD INTERFACING

Interfacing to the evaluation board is via a 96-way connector, J4. J4 is used to connect the evaluation board to the EVAL-CONTROL BOARD or other system. The pinout for the J4 connector is shown in Figure 2 and its pin designations are given in Table II.

1

32

A

B

C

1

32

Figure 2. Pin Configuration for the 96-Way

Connector, J1

96-Way Connector Pin Description

DR0

Data Receive Zero. This input is connected to the

SDATA pin of the AD7476/77.

TFS0/RFS0 Transmit/Receive Frame Sync Zero. These two outputs are connected to the CS pin of the AD7476/77.

SCLK0	Serial Clock Zero. This serial clock is connected
	to the SCLK pin of the AD7476/77 with the
	option of an inverting buffer.
DGND	Digital Ground. These lines	are connected to
	the digital ground plane on	the evaluation
	board. It allows the user to provide the digital
	supply via the connector along with the other
	digital signals.
AGND	Analog Ground. These lines are connected to
	the analog ground plane on the evaluation board.
AVDD	Analog +5 V Supply. These lines are connected
	to the AVDD supply line on the board.
+12V	+12 V Supply. This line is connected to the +12
	V supply line on the board via LK6.
-12V	-12 V Supply. This line is connected to the -12
	V supply line on the board via LK7.

Table II. 96-Way Connector Pin Functions.

	Row A	RowB	RowC
1
2
3
4	DGND	DGND	DGND
5			DR0
6	TFS0		RFS0
7	SCLK0		SCLK0
8
9
10
11
12	DGND	DGND	DGND
13
14
15
16	DGND	DGND	DGND
17
18
19
20	DGND	DGND	DGND
21	AGND	AGND	AGND
22	AGND	AGND	AGND
23	AGND	AGND	AGND
24	AGND	AGND	AGND
25	AGND	AGND	AGND
26	AGND	AGND	AGND
27		AGND
28		AGND
29	AGND	AGND	AGND
30	-12 V	AGND	+12 V
31
32	AVDD	AVDD	AVDD

Note : The unused pins of the 96-way connector are not shown.

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