15 FN6562.1 October 17, 2013 Powering the Input and Feedback Stages (VCC
參數(shù)資料
型號: ISL28617FVZ-T7
廠商: Intersil
文件頁數(shù): 7/19頁
文件大小: 0K
描述: IC INSTRUMENTATION AMP 24TSSOP
標準包裝: 1,000
放大器類型: 儀表
電路數(shù): 1
輸出類型: 差分,滿擺幅
轉(zhuǎn)換速率: 4 V/µs
-3db帶寬: 5.5MHz
電流 - 輸入偏壓: 200pA
電壓 - 輸入偏移: 30µV
電流 - 電源: 2.05mA
電流 - 輸出 / 通道: 45mA
電壓 - 電源,單路/雙路(±): 8 V ~ 40 V,±4 V ~ 20 V
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 24-TSSOP(0.173",4.40mm 寬)
供應(yīng)商設(shè)備封裝: 24-TSSOP
包裝: 帶卷 (TR)
ISL28617
15
FN6562.1
October 17, 2013
Powering the Input and Feedback Stages
(VCC, VEE)
The input pins IN+, IN- cannot swing rail-to-rail, but have a
maximum input voltage range given by Equation 10:
This requires the sum of the common mode input voltage and
the differential input voltage to remain within 3V of either the VCC
or VEE rail, otherwise distortion will result.
The feedback pins VFB+ and VFB- have the same input common
mode voltage constraint as the input pins IN+ and IN-. The
maximum input voltage range of the feedback pins is given by
Equation 11:
To maintain stability, it is critical to respect the ±3V requirement
in Equation 11.
Powering the Rail-to-rail Output Stage
(VCO, VEO)
The output stage (A6) is of rail-to-rail design, and is powered by the
VCO and VEO pins. The differential output pins +VOUT and -VOUT
connect to the VFB+ and VFB- pins to close the output feedback
loop. The feedback stage is powered from VCC and VEE pins. The
VFB+ and VFB- have a common mode input range 3V below the VCC
rail and 3V above the and VEE rail. If the output voltage exceeds the
feedback common mode input voltage, loop instability will result.
Therefore, the voltages at the ±VOUT pins should always be 3V
away from either rail, as shown in Equation 12:
Rail-to-rail Differential ADC Driver
The differential output stage of ISL28617 is designed to drive the
differential input stage of an ADC. In this configuration, the VCO
and VEO 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 over driving the
ADC input.
The output stage is capable of rail-to-rail operation when VCO and
VEO are powered from a single supply or from split supplies. It
has a single supply voltage range (VCO) from 3V to 15V (with VEO
at GND), and a ±1.5V to ±15V split supply voltage range. Under
all power supply conditions, VCC must be greater than VCO by 3V,
and VEE must be less than VEO by 3V to maintain the rail-to-rail
output drive capability.
The VCMO pin is an input to a very low bias current terminal, and
sets the output common mode reference voltage when driving a
differential input ADC, such that the output would have a ± input
signal span centered around an external DC reference voltage
applied to the VCMO pin.
Power Supply Voltages by Application
The ISL28617 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 VCC, VEE, VCO and VEO.
There are a common set of requirements across all power
applications:
1. A common ground connection from the input supplies, (VCC,
VEE) to the output supplies (VCO, VEO) is required for all
powering options.
2. The signal input pins IN+ and 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 ISL28617 is configured as a 5V ADC driver in a high gain
sensor bridge amplifier powered from a ±10V excitation source.
In this application, the ISL28617 must extract the low level
bipolar sensor signal and shift the level to the 0V to +5V
differential rail-to-rail signal needed by the ADC. The following
powering option is recommended:
VCC = +10V, VEE = -10V
VCO = +5V, VEO = GND
VCMO = +2.5V
VCC and VEE power supply common connects to GND
EXAMPLE 2: HIGH VOLTAGE BIPOLAR I/O BUFFER
The ISL28617 is configured as a high impedance buffer
instrumentation amplifier in a ±15V industrial sensor application. In
this application, the ISL28617 must extract and amplify the high
impedance sensor signal and send it downstream to a differential
ADC operating from ±15V supplies. The following powering options
are recommended:
1. Input and output supplies are strapped to the same supplies and
rail-to-rail input to the ADC is not required.
-VCC = VCO = +15V
-VEE = VEO = -15V
-VCMO = GND
-VCC, VEE power supply common connects to GND
and VOUT = ±12V
2. ±15V Rail-to-rail output is required, then:
-VCC = +18V, VEE = -18V
-VCO = +15V, VEO= -15V
-VCMO = GND
-VCC and VEE power supply common connects to GND
The VCO and VEO power supply pins connect to the ADC (±15V) power
supply pins. Rail-to-rail output swing requires that VCC =VCO +3V and
VEE = VEO -3V, or ±18V.
(EQ. 10)
VEE+ 3V < (VCMIRIN + VIN) < VCC - 3V;
where VIN = maximum differential voltage IN+ to IN-
(EQ. 11)
VEE+ 3V < VCMIRFB < VCC - 3V
where VCMIRFB = (+VOUT - -VOUT) +VCMO
(EQ. 12)
VEE+ 3V < VOUT < VCC - 3V;
where VOUT = |+VOUT| or |-VOUT|
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