HI7190EVAL Intersil, HI7190EVAL Datasheet - Page 11

• Manufacturer Part Number: HI7190EVAL
• Description: EVALUATION PLATFORM HI7190
• Manufacturer: Intersil

Specifications of HI7190EVAL

• Number Of Adc's: 1
• Number Of Bits: 24
• Sampling Rate (per Second): 200k
• Data Interface: Serial
• Inputs Per Adc: 1 Differential
• Input Range: ±2.5 V
• Power (typ) @ Conditions: 15mW @ 200kSPS
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: HI7190
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

junction. The feedback loop forces the average of the fed
back signal to be equal to the input signal V
Analog Inputs
The analog input on the HI7190 is a fully differential input
with programmable gain capabilities. The input accepts both
unipolar and bipolar input signals and gains range from 1 to
128. The common mode range of this input is from AV
AV
voltage lies within the power supplies. The input impedance
of the HI7190 is dependent upon the modulator input
sampling rate and the sampling rate varies with the selected
PGIA gain. Table 3 shows the sampling rates and input
impedances for the different gain settings of the HI7190.
Note that this table is valid only for a 10MHz master clock. If
the input clock frequency is changed, then the input
impedance will change accordingly. The equation used to
calculate the input impedance is:
Z
where C
the modulator sampling rate.
Bipolar/Unipolar Input Ranges
The input on the HI7190 can accept either unipolar or bipolar
input voltages. Bipolar or unipolar options are chosen by
programming the B/U bit of the Control Register.
Programming the part for either unipolar or bipolar operation
does not change the input signal conditioning.
The inputs are differential, and as a result are referenced to the
voltage on the V
and the HI7190 is configured for unipolar operation with a gain
of 1 and a V
input is +1.25V to +3.75V. If V
configured for bipolar mode with gain of 1 and a V
the analog input range on the V
IN
8, 16, 32, 64, 128
DD
= 1/(C
V
FIGURE 6. SIMPLE MODULATOR BLOCK DIAGRAM
IN
TABLE 3. EFFECTIVE INPUT IMPEDANCE vs GAIN
provided that the absolute value of the analog input
GAIN
in
IN
1
2
4
is the nominal input capacitance (8pF) and f
x f
REF
+
-
S
),
∑
INLO
of +2.5V, the input voltage range on the V
input. For example, if V
PGIA
SAMPLING RATE
78.125
156.25
(kHz)
312.5
DAC
INLO
625
11
V
INTEGRATOR
V
INHI
RLO
RHI
is +1.25V and the HI7190 is
∫
input is -1.25V to +3.75V.
INPUT IMPEDANCE
INLO
IN
COMPARATOR
.
REF
(MΩ)
is +1.25V
1.6
0.8
0.4
0.2
+
-
of +2.5V,
SS
S
INHI
is
to
HI7190
Programmable Gain Instrumentation Amplifier
The Programmable Gain Instrumentation Amplifier allows the
user to directly interface low level sensors and bridges directly
to the HI7190. The PGIA has 4 selectable gain options of 1, 2,
4, 8 which are implemented by multiple sampling of the input
signal. Input signals can be gained up further to 16, 32, 64 or
128. These higher gains are implemented in the digital section
of the design to maintain a high signal to noise ratio through
the front end amplifiers. The gain is digitally programmable in
the Control Register via the serial interface. For optimum
PGIA performance the V
of the analog supplies.
Differential Reference Input
The reference inputs of the of the HI7190, V
provide a differential reference input capability. The nominal
differential voltage (V
common mode voltage cab be anywhere between AV
AV
degradation in performance with the maximum reference
voltage being V
be used but performance will be degraded since the LSB
size is reduced.
The full scale range of the HI7190 is defined as:
FSR
FSR
and V
operation of the device.
The reference inputs provide a high impedance dynamic
load similar to the analog inputs and the effective input
impedance for the reference inputs can be calculated in the
same manner as it is for the analog input impedance. The
only difference in the calculation is that C
inputs is 10.67pF. Therefore, the input impedance range for
the reference inputs is from 149kΩ in a gain of 8 or higher
mode to 833kΩ in the gain of 1 mode.
V
The voltage at the V
analog circuitry is referenced to and should always be tied to
the midpoint of the AV
provides a common mode input voltage for the internal
operational amplifiers and must be driven from a low noise,
low impedance source if it is not tied to analog ground.
Failure to do so will result in degraded HI7190 performance.
It is recommended that V
operating off of AV
V
ends of the power supplies which is limited by the common
mode input range where the internal operational amplifiers
remain in the linear, high gain region of operation. The
HI7190 is designed to have a range of AV
CM
CM
DD
BIPOLAR
UNIPOLAR
also determines the headroom at the upper and lower
. Larger values of V
RHI
Input
must always be greater than V
= 2 x V
= V
REF
REF
DD
REF
= +5V. Smaller values of V
CM
/GAIN
REF
DD
= +5V and AV
/GAIN
CM
input is the voltage that the internal
CM
REF
and AV
= V
pin should be tied to the mid point
be tied to analog ground when
RHI
can be used without
SS
- V
SS
supplies. This point
RLO
= -5V supplies.
) is +2.5V and the
RLO
IN
SS
for the reference
RHI
+1.8V < V
for proper
REF
and V
June 27, 2006
can also
FN3612.10
SS
RLO
CM
and
,
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