AD7829-1 Analog Devices, AD7829-1 Datasheet - Page 12

• Manufacturer Part Number: AD7829-1
• Description: 3 V/5 V, 2 MSPS, 8-Bit, 8-Channel ADC
• Manufacturer: Analog Devices

Specifications of AD7829-1

• Resolution (bits): 8bit
• # Chan: 8
• Sample Rate: 2MSPS
• Interface: Par
• Analog Input Type: SE-Uni
• Ain Range: 2 V p-p,2.5V p-p,Uni 2.0V,Uni 2.5V
• Adc Architecture: Flash
• Pkg Type: SOIC,SOP

AD7829-1
V
offset to the V
to accommodate bipolar signals by applying V
circuit before V
driven by an external source, the source can be directly tied to
the level-shifting circuitry (see Figure 11); however, if the internal
V
be buffered before applying it to the level-shifting circuitry, because
the V
Figure 12).
MID
MID
3V
5V
4V
3V
2V
1V
2V
1V
, that is, the default value, is being used as an output, it must
can be used to remove offsets in a system by applying the
MID
V
MID
V
IN
V
pin has an impedance of approximately 6 kΩ (see
MID
V
V
V
MID
DD
DD
Figure 9. Analog Input Span Variation with V
= N/C (1.25V)
= 3V
= 5V
= N/C (1V)
MID
IN
Figure 10. Removing Offsets Using V
, as shown in
pin, as shown in
V
MID
V
MID
= 1.5V
V
MID
= 2.5V
Figure 11. When V
V
V
MID
IN
Figure 10; or it can be used
V
MID
= 2V
V
MID
INPUT SIGNAL RANGE
INPUT SIGNAL RANGE
FOR VARIOUS V
FOR VARIOUS V
AD7829-1
= 3.75V
MID
MID
to a level-shifting
MID
MID
is being
MID
MID
Rev. 0 | Page 12 of 20
NOTE: Although there is a V
reference of 2.5 V can be sourced, or to which an external
reference can be applied, this does not provide an option of
varying the value of the voltage reference. As stated in the
specifications for the AD7829-1, the input voltage range at this
pin is 2.5 V ± 2%.
Analog Input Structure
Figure 13 shows an equivalent circuit of the analog input
structure of the AD7829-1. The two diodes, D1 and D2, provide
ESD protection for the analog inputs. Care must be taken to
ensure that the analog input signal never exceeds the supply
rails by more than 200 mV. This causes these diodes to become
forward biased and start conducting current into the substrate.
20 mA is the maximum current these diodes can conduct
without causing irreversible damage to the part. However, it is
worth noting that a small amount of current (1 mA) conducted
into the substrate due to an overvoltage on an unselected channel
can cause inaccurate conversions on a selected channel.
0V
0V
V
V
Figure 11. Accommodating Bipolar Signals Using External V
Figure 12. Accommodating Bipolar Signals Using Internal V
V
V
2.5V
R3
R2
R3
R2
R4
R4
R1
R1
EXTERNAL
REF
V
2.5V
V
V
MID
2.5V
0V
0V
IN
IN
pin from which a voltage
V
V
V
V
V
V
IN
IN
MID
REF
MID
REF
AD7829-1
AD7829-1
MID
MID