ISL70517SEH Datasheet, PDF (20/27 Pages) Intersil Corporation – Precision test and measurement

ISL70517SEH
common-mode input voltage, loop instability will result.
Therefore, the voltages at the ±V_OUT pins should always be 3V
away from either rail, as shown in Equation 12.
V_EE + 3V≤V_OUT≤ V_CC – 3V;
(EQ. 12)
where V_OUT = +V_OUT or -V_OUT
Rail-to-Rail ADC Driver
The single-ended output stage of the ISL70517SEH is designed
to drive the single-ended input stage of an ADC. In this
configuration, the V_CO, V_EO power supply pins connect directly to
the ADC power supply pins. This output swing arrangement is
ideal for driving rail-to-rail ADC drive without the possibility of
overdriving the ADC input.
The output stage is capable of rail-to-rail operation when V_CO, V_EO
are powered from a single supply or from split supplies. It has a
single supply voltage range (V_CO) from 3V to 15V (with V_EO at
GND) and a ±1.5V to ±15V split supply voltage range. Under all
power supply conditions, V_CC must be greater than V_CO by 3V and
V_EE must be less than V_EO by 3V to maintain the rail-to-rail output
drive capability.
The V_REF pin is an input to a very low bias current terminal and
sets the output reference voltage such that the output would
have a ± input signal span centered around an external DC
reference voltage applied to the V_REF pin.
Power Supply Voltages by Application
The ISL70517SEH can be adapted to a wide variety of
instrumentation amplifier applications where the signal source is
powered from supply voltages that are different from the supply
voltages powering downstream circuits. The following examples
are included as a guide to the proper connection and voltages
applied to the supply pins V_CC, V_EE, V_CO, and V_EO.
There are a common set of requirements across all power
applications:
1. A common ground connection from the input supplies (V_CC,
V_EE) to the output supplies (V_CO, V_EO) is required for all
powering options.
2. The signal input pins IN+, IN- cannot float and must have a DC
return path to ground.
3. The input and output supplies cannot both be operated in
single supply mode due to the 3V feedback amplifier
common-mode headroom requirement in Equation 11.
The following are typical power examples:
EXAMPLE 1: BIPOLAR INPUT TO SINGLE SUPPLY
OUTPUT
The ISL70517SEH is configured as a 5V ADC driver in a high gain
sensor bridge amplifier powered from a ±10V excitation source.
In this application, the ISL70517SEH must extract the low level
bipolar sensor signal and shift the level to the 0V to +5V
rail-to-rail signal needed by the ADC.
The following powering option is recommended:
• V_CC = +10V, V_EE = -10V
• V_CO = +5V, V_EO = GND
• V_REF = +2.5V
• V_CC, V_EE power supply common connects to GND
EXAMPLE 2: HIGH VOLTAGE BIPOLAR I/O BUFFER
The ISL70517SEH is configured as a high impedance buffer
instrumentation amplifier in a ±15V industrial sensor
application. In this application, the ISL70517SEH must extract
and amplify the high impedance sensor signal and send it
downstream to an ADC operating from ±15V supplies. The
following powering options are recommended:
• Input and output supplies are strapped to the same supplies
and rail-to-rail input to the ADC is not required.
- V_CC = V_CO = +15V
- V_EE = V_EO = -15V
- V_REF = GND
- V_CC, V_EE power supply common connects to GND and
V_OUT = ±12V.
• ±15V rail-to-rail output is required, then:
- V_CC = +18V, V_EE = -18V
- V_CO = +15V, V_EO = -15V
- V_REF = GND
- V_CC, V_EE power supply common connects to GND
The V_CO and V_EO power supply pins connect to the ADC ±15V
power supply pins. Rail-to-rail output swing requires that
V_CC = V_CO +3V and V_EE = V_EO -3V, or ±18V.
EXAMPLE 3: GAINS LESS THAN 1
The ISL70517SEH is configured to a gain of 0.2V/V driving a
rail-to-rail 3V ADC. In this application, the maximum input
dynamic range is ±15V.
• V_CC = +18V, V_EE = -18V
• V_CO = +3V, V_EO = GND
• V_REF = +1.5V
• V_CC, V_EE power supply common connects to GND
In this attenuator configuration, the input signal range is ±15V,
which requires an additional ±3V of input overhead from the
input supplies. Thus, V_CC and V_EE = ±18V.
AC Performance Considerations
The ISL70517SEH closed loop frequency response is formed by
the feedback G_M amplifier and gain resistor R_FB and has the
characteristics of a current feedback amplifier. Therefore, the
-3dB gain does not significantly decrease at high gains as is the
case with the constant gain-bandwidth response of the classic
voltage feedback amplifier.
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FN8699.4
December 15, 2016