AD7329 Analog Devices, AD7329 Datasheet - Page 31

• Manufacturer Part Number: AD7329
• Description: 1 MSPS , 8-Channel, Software Selectable True Bipolar Input, 12-Bit Plus Sign A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7329

• Resolution (bits): 13bit
• # Chan: 8
• Sample Rate: 1MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni,SE-Uni
• Ain Range: Bip (Vref),Bip (Vref) x 2,Bip (Vref) x 4,Bip 10V,Bip 2.5V,Bip 5.0V,Uni (Vref),Uni 10V
• Adc Architecture: SAR
• Pkg Type: SOP

REFERENCE
The AD7329 can operate with either the internal 2.5 V on-chip
reference or an externally applied reference. The internal reference
is selected by setting the REF bit in the control register to 1. On
power-up, the REF bit is 0, which selects the external reference for
the AD7329 conversion. Suitable reference sources for the AD7329
include AD780, AD1582, ADR431, REF193, and ADR391.
The internal reference circuitry consists of a 2.5 V band gap
reference and a reference buffer. When operating the AD7329 in
internal reference mode, the 2.5 V internal reference is available
at the REF
using a 680 nF capacitor. It is recommended that the internal
reference be buffered before applying it elsewhere in the system.
The internal reference is capable of sourcing up to 90 μA.
On power-up, if the internal reference operation is required for
the ADC conversion, a write to the control register is necessary
to set the REF bit to 1. During the control register write, the
conversion result from the first initial conversion is invalid. The
reference buffer requires 500 μs to power up and charge the
680 nF decoupling capacitor during the power-up time.
The AD7329 is specified for a 2.5 V to 3 V reference range.
When a 3 V reference is selected, the ranges are ±12 V, ±6 V,
±3 V, and 0 V to +12 V. For these ranges, the V
must be equal to or greater than the maximum analog input
range selected.
V
The AD7329 has a V
the serial interface operates. V
interface to both 3 V and 5 V processors. For example, if the
AD7329 is operated with a V
powered from a 3 V supply. This allows the AD7329 to accept
large bipolar input signals with low voltage digital processing.
DRIVE
IN
/REF
OUT
pin, which should be decoupled to AGND
DRIVE
feature to control the voltage at which
CC
DRIVE
of 5 V, the V
allows the ADC to easily
DRIVE
DD
pin can be
and V
SS
supply
Rev. A | Page 31 of 40
TEMPERATURE INDICATOR
The AD7329 has an on-chip temperature indicator. The tem-
perature indicator can be used to provide local temperature
measurements on the AD7329. To access the temperature indicator,
the ADC should be configured in pseudo differential mode,
Mode 1 = Mode 0 = 1, which sets Channel Bits ADD2, ADD1,
and ADD0 to 1. V
voltage within the specified pseudo differential input range for
the selected analog input range. When a conversion is initiated in
this configuration, the output code represents the temperature
(see Figure 50 and Figure 51). When using the temperature
indicator on the AD7329, the part should be operated at low
throughput rates, such as approximately 30 kSPS for the ±2.5 V
range. The throughput rate is reduced for the temperature indicator
mode because the AD7329 requires more acquisition time for
this mode.
Figure 50. ADC Output Code vs. Temperature for ±2.5 V Range
5450
5400
5350
5300
5250
5200
5150
5100
5050
4420
4410
4400
4390
4380
4370
4360
4350
4340
Figure 51. ADC Output Code vs. Temperature for ±10 V Range
–40
–40
–20
–20
IN
7 must be tied to AGND or to a small dc
0
0
TEMPERATURE (°C)
TEMPERATURE (°C)
±10V RANGE, INT REF
20
20
40
V
V
±2.5V RANGE
INTERNAL REFERENCE
30kSPS
CC
DD
40
= V
= 12V, V
V
V
50kSPS
60
CC
DD
DRIVE
/V
= V
SS
DRIVE
SS
60
= ±12V
= 5V
80
= –12V
AD7329
= 5V
100
80