AD7656BSTZ-1 Analog Devices Inc, AD7656BSTZ-1 Datasheet - Page 21

• Manufacturer Part Number: AD7656BSTZ-1
• Description: 6-CHANNEL 16-BIT SE BIPOLAR I.C.
• Manufacturer: Analog Devices Inc

Specifications of AD7656BSTZ-1

• Number Of Bits: 16
• Sampling Rate (per Second): 250k
• Data Interface: Serial, Parallel
• Number Of Converters: 6
• Power Dissipation (max): 143mW
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7656-1EDZ - BOARD EVAL CONTROL AD7656-1EVAL-AD7656-1CBZ - BOARD EVAL FOR AD7656-1EVAL-AD7656CBZ - BOARD EVAL FOR AD7656
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADC TRANSFER FUNCTION
The output coding of the AD7656-1/AD7657-1/AD7658-1 is
twos complement. The designed code transitions occur midway
between successive integer LSB values, that is, 1/2 LSB, 3/2 LSB.
The LSB size is FSR/65,536 for the AD7656-1, FSR/16,384 for
the AD7657-1, and FSR/4096 for the AD7658-1. The ideal
transfer characteristic is shown in Figure 26.
The LSB size is dependent on the analog input range selected
(see Table 9).
INTERNAL/EXTERNAL REFERENCE
The REFIN/REFOUT pin allows access to the 2.5 V reference of
the AD7656-1/AD7657-1/AD7658-1, or it allows an external
reference to be connected to provide the reference source for
conversions.
The AD7656-1/AD7657-1/AD7658-1 can each accommodate a
2.5 V external reference range. When using an external reference,
the internal reference must be disabled. After a reset, the AD7656-1/
AD7657-1/AD7658-1 default to operating in external reference
mode with the internal reference buffers enabled.
The internal reference can be enabled in either hardware or
software mode. To enable the internal reference in hardware mode,
set the H /S SEL pin to 0 and the REF
internal reference in software mode, set H /S SEL to 1 and write to
Table 9. LSB Size for Each Analog Input Range
Parameter
LSB Size
FS Range
Figure 26. AD7656-1/AD7657-1/AD7658-1 Transfer Characteristic
000 ... 001
000 ... 000
100 ... 010
100 ... 001
100 ... 000
011 ... 111
011 ... 110
111 ... 111
–FSR/2 + 1/2LSB
±10 V
0.305 mV
20 V/65,536
AGND – 1LSB
Input Range for AD7656-1
ANALOG INPUT
EN/ DIS
+FSR/2 – 3/2LSB
pin to 1. To enable the
±5 V
0.152 mV
10 V/65,536
Rev. 0 | Page 21 of 32
±10 V
1.22 mV
20 V/16,384
Input Range for AD7657-1
the control register to set DB9 of the register to 1. For the internal
reference mode, the REFIN/REFOUT pin should be decoupled
using a 1 μF capacitor.
The AD7656-1/AD7657-1/AD7658-1 each contain three on-
chip reference buffers. Each of the three ADC pairs has an
associated reference buffer. These reference buffers require
external decoupling capacitors, using 1 μF capacitors, on the
REFCAPA, REFCAPB, and REFCAPC pins. The internal
reference buffers can be disabled in software mode by writing
to Bit DB8 in the internal control register. If serial interface is
selected, the internal reference buffers can be disabled in hardware
mode by setting the DB14/REFBUF
reference and its buffers are disabled, an external buffered
reference should be applied to the REFCAPx pins.
TYPICAL CONNECTION DIAGRAM
Figure 27 shows the typical connection diagram for the AD7656-1/
AD7657-1/AD7658-1, illustrating the reduction in the number
and value of decoupling capacitors required. There are eight
AV
used for the AD7656-1/AD7657-1/AD7658-1 conversion process;
therefore, they should be well decoupled. The AV
is applied to eight AV
capacitor The AD7656-1/AD7657-1/AD7658-1 can operate with
the internal reference or an externally applied reference. In this
configuration, the parts are configured to operate with the
external reference. The REFIN/REFOUT pin is decoupled with
a 1 μF capacitor. The three internal reference buffers are enabled.
Each of the REFCAPx pins is decoupled with a 1 μF capacitor.
If the same supply is being used for the AV
ferrite or small RC filter should be placed between the supply pins.
AGND pins are connected to the AGND plane of the system.
The DGND pins are connected to the digital ground plane in
the system. The AGND and DGND planes should be connected
together at one place in the system. This connection should be
as close as possible to the AD7656-1/AD7657-1/AD7658-1 in
the system.
CC
supply pins on each part. The AV
±5 V
0.610 mV
10 V/16,384
AD7656-1/AD7657-1/AD7658-1
CC
pins can be decoupled using just one 1 μF
±10 V
4.88 mV
20 V/4096
Input Range for AD7658-1
EN /DIS
CC
pin high. If the internal
CC
supplies are the supplies
and DV
±5 V
2.44 mV
10 V/4096
CC
supply which
CC
supplies, a