AD7607 Analog Devices, AD7607 Datasheet - Page 19

• Manufacturer Part Number: AD7607
• Description: 8-Channel DAS with 14-Bit, Bipolar, Simultaneous Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7607

• Resolution (bits): 14bit
• # Chan: 8
• Sample Rate: 200kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: SE-Bip
• Ain Range: Bip 10V,Bip 5.0V
• Adc Architecture: SAR
• Pkg Type: QFP

Data Sheet
THEORY OF OPERATION
CONVERTER DETAILS
The AD7607 is a data acquisition system that employs a high
speed, low power, charge redistribution, successive approxi-
mation analog-to-digital converter (ADC) and allows the
simultaneous sampling of eight analog input channels. The analog
inputs on the AD7607 can accept true bipolar input signals. The
RANGE pin is used to select either ±10 V or ±5 V as the input
range. The AD7607 operates from a single 5 V supply.
The AD7607 contains input clamp protection, input signal scaling
amplifiers, a second-order antialiasing filter, track-and-hold
amplifiers, an on-chip reference, reference buffers, a high speed
ADC, a digital filter, and high speed parallel and serial interfaces.
Sampling on the AD7607 is controlled using the CONVST signals.
ANALOG INPUT
Analog Input Ranges
The AD7607 can handle true bipolar input voltages. The logic
level on the RANGE pin determines the analog input range of
all analog input channels. If this pin is tied to a logic high, the
analog input range is ±10 V for all channels. If this pin is tied
to a logic low, the analog input range is ±5 V for all channels.
A logic change on this pin has an immediate effect on the analog
input range; however, there is a typical settling time of ~80 µs,
in addition to the normal acquisition time requirement.
Recommended practice is to hardwire the RANGE pin
according to the desired input range for the system signals.
During normal operation, the applied analog input voltage should
remain within the analog input range selected via the range pin.
A RESET pulse must be applied after power-up to ensure the
analog input channels are configured for the range selected.
When in a power-down mode, it is recommended to tie the
analog inputs to GND. As per the input clamp protection section,
the overvoltage clamp protection is recommended for use in
transient overvoltage conditions and should not remain active
for extended periods. Stressing the analog inputs outside of the
conditions mentioned here may degrade the Bipolar Zero Code
error and THD performance of the AD7607.
Analog Input Impedance
The analog input impedance of the AD7607 is 1 MΩ. This is
a fixed input impedance that does not vary with the AD7607
sampling frequency. This high analog input impedance elimi-
nates the need for a driver amplifier in front of the AD7607,
allowing for direct connection to the source or sensor. With the
need for a driver amplifier eliminated, bipolar supplies (which
are often a source of noise in a system) can be removed from
the signal chain.
Rev. B | Page 19 of 32
Analog Input Clamp Protection
Figure 30 shows the analog input structure of the AD7607.
Each AD7607 analog input contains clamp protection circuitry.
Despite single 5 V supply operation, this analog input clamp
protection allows for an input overvoltage of up to ±16.5 V.
Figure 31 shows the voltage vs. current characteristic of the
clamp circuit. For input voltages of up to ±16.5 V, no current
flows in the clamp circuit. For input voltages that are above ±16.5 V,
the AD7607 clamp circuitry turns on and clamps the analog
input to ±16.5 V.
A series resistor should be placed on the analog input channels
to limit the current to ±10 mA for input voltages above ±16.5 V.
In an application where there is a series resistance on an analog
input channel, Vx, a corresponding resistance is required on the
analog input GND channel, VxGND (see Figure 32). If there is
no corresponding resistor on the VxGND channel, an offset
error occurs on that channel.
VxGND
ANALOG
SIGNAL
–10
–20
–30
–40
–50
INPUT
30
20
10
Figure 32. Input Resistance Matching on the Analog Input
Vx
0
–20
AV
T
A
CC
= 25°C
–15
, V
Figure 31. Input Protection Clamp Profile
CLAMP
CLAMP
R
R
DRIVE
C
Figure 30. Analog Input Circuitry
–10
= 5V
VxGND
1MΩ
1MΩ
VINx
SOURCE VOLTAGE (V)
–5
R
R
AD7607
FB
FB
CLAMP
CLAMP
0
SECOND-
ORDER
5
LPF
1MΩ
1MΩ
10
R
R
FB
FB
15
AD7607
20