AD7656YSTZ Analog Devices Inc, AD7656YSTZ Datasheet - Page 21

• Manufacturer Part Number: AD7656YSTZ
• Description: IC ADC 16BIT 6CH 250KSPS 64LQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7656YSTZ

• Data Interface: Serial, Parallel
• Number Of Bits: 16
• Sampling Rate (per Second): 250k
• Number Of Converters: 6
• Power Dissipation (max): 143mW
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Resolution (bits): 16bit
• Sampling Rate: 250kSPS
• Input Channel Type: Single Ended
• Supply Voltage Range - Digital: 4.75V To 5.25V
• Supply Current: 26mA
• 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, Lead free / RoHS Compliant

ADC TRANSFER FUNCTION
The output coding of the AD7656/AD7657/AD7658 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/65536 for the AD7656, FSR/16384 for the
AD7657, and FSR/4096 for the AD7658. The ideal transfer
characteristic is shown in Figure 25.
The LSB size is dependent on the analog input range selected
(see Table 9).
REFERENCE SECTION
The RFIN/REFOUT pin either allows access to the AD7656/
AD7657/AD7658’s 2.5 V reference or it allows an external
reference to be connected, providing the reference source for
each part’s conversions. The AD7656/AD7657/AD7658 can
accommodate a 2.5 V to 3 V external reference range. When
using an external reference, the internal reference needs to be
disabled. After a reset, the AD7656/AD7657/AD7658 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, the H /S SEL pin = 0 and the REF
enable the internal reference in software mode, H /S SEL = 1 and
a write to the control register is necessary to make DB9 of the
register = 1. For the internal reference mode, the REFIN/REFOUT
pin should be decoupled using 10 μF and 100 nF capacitors.
The AD7656/AD7657/AD7658 contain three on-chip reference
buffers. Each of the three ADC pairs has an associated reference
buffer. These reference buffers require external decoupling
capacitors on REFCAPA, REFCAPB, and REFCAPC pins,
and 10 μF and 100 nF decoupling capacitors should be placed
on these REFCAP pins. The internal reference buffers can be
disabled in software mode by writing to Bit DB8 in the internal
control register. If operating the devices in serial mode,
Table 9. LSB Size for Each Analog Input Range
Range
Input Range
LSB Size
FS Range
Figure 25. AD7656/AD7657/AD7658 Transfer Characteristic
–FSR/2 + 1/2LSB
000...001
000...000
100...010
100...001
100...000
011...111
011...110
111...111
±10 V
0.305 mV
20 V/65536
AGND – 1LSB
ANALOG INPUT
AD7656
+FSR/2 – 3/2LSB
±5 V
0.152 mV
10 V/65536
EN/DIS
pin = 1. To
Rev. A | Page 21 of 32
±10 V
1.22 mV
20 V/16384
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 REFCAP pins.
TYPICAL CONNECTION DIAGRAM
Figure 26 shows the typical connection diagram for the
AD7656/AD7657/AD7658. There are eight AV
the parts. The AV
AD7656/AD7657/AD7658 conversion process; therefore, it
should be well decoupled. Each AV
individually decoupled with a 10 μF tantalum capacitor and a
100 nF ceramic capacitor. The AD7656/AD7657/AD7658 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 10 μF and 100 nF capacitor pair. The three
internal reference buffers are enabled. Each of the REFCAP pins
are decoupled with the 10 μF and 100 nF capacitor pair.
Six of the AV
ADC cores on the AD7656/AD7657/AD7658 and, as a result,
are used for the conversion process. Each analog input pin is
surrounded by an AV
AV
individual ADC cores. For example, Pin 33 is V1, Pin 34 is the
AV
Core 1. An alternative reduced decoupling solution is to group
these six AV
Pin 40 and Pin 41, and Pin 46 and Pin 47.
For the AD7656, a 100 μF decoupling capacitor can be placed
on each of the pin pairs. All of the other supply and reference
pins should be decoupled with a 10 μF decoupling capacitor.
When the AD7657 is configured in this reduced decoupling
configuration, each of the three AV
decoupled with a 33 μF capacitor. When the AD7658 is configured
in this same configuration, each of the three AV
should be decoupled with a 22 μF capacitor.
If the same supply is being used for the AV
supply, a ferrite or small RC filter should be placed between the
supply pins.
The 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 made as close as possible to the
AD7656/AD7657/AD7658 in the system.
CC
CC
AD7657
and AGND pins are the supply and ground for the
supply for ADC Core 1, and Pin 32 is the AGND for ADC
0.610 mV
10 V/16384
±5 V
CC
CC
supply pins into three pairs, Pin 34 and Pin 35,
supply pins are used as the supply to the six
CC
supply is the supply that is used for the
CC
supply pin and an AGND pin. These
AD7656/AD7657/AD7658
±10 V
4.88 mV
20 V/4096
EN/DIS
pin high. If the internal
CC
CC
supply pin should be
pin pairs should be
AD7658
CC
supply and DV
CC
±5 V
2.44mV
10 V/4096
CC
supply pins on
pin pairs
CC