AD8227ARMZ Analog Devices Inc, AD8227ARMZ Datasheet - Page 23

• Manufacturer Part Number: AD8227ARMZ
• Description: IC AMP INSTR R-R 250KHZ 8MSOP
• Manufacturer: Analog Devices Inc

Specifications of AD8227ARMZ

• Slew Rate: 0.8 V/µs
• Amplifier Type: Instrumentation
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• -3db Bandwidth: 250kHz
• Current - Input Bias: 20nA
• Voltage - Input Offset: 200µV
• Current - Supply: 350µA
• Current - Output / Channel: 13mA
• Voltage - Supply, Single/dual (±): 2.2 V ~ 36 V, ±1.5 V ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• No. Of Amplifiers: 1
• Input Offset Voltage: 200µV
• Bandwidth: 250kHz
• Amplifier Output: Rail To Rail
• Cmrr: 90dB
• Supply Voltage Range: ± 1.5V To ± 18V
• Supply Current: 350µA
• Amplifier: RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DRIVING AN ADC
Figure 66 shows several different methods for driving an ADC.
The ADC in the
this example because it has an unbuffered charge sampling
architecture that is typical of most modern ADCs. This type of
architecture typically requires an RC buffer stage between the
ADC and the amplifier to work correctly.
Option 1 shows the minimum configuration required to drive
a charge sampling ADC. The capacitor provides charge to the
ADC sampling capacitor, and the resistor shields the AD8227
from the capacitance. To keep the AD8227 stable, the RC time
constant of the resistor and capacitor needs to stay above 5 μs.
This circuit is mainly useful for lower frequency signals.
ADuC7026
microcontroller was chosen for
AD8227
AD8227
AD8227
+15V
–15V
3.3V
3.3V
OPTION 1: DRIVING LOW FREQUENCY SIGNALS
OPTION 2: DRIVING HIGH FREQUENCY SIGNALS
OPTION 3: PROTECTING ADC FROM LARGE VOLTAGES
REF
REF
REF
100Ω
10kΩ
AD8616
AD8616
100nF
3.3V
3.3V
Figure 66. Driving an ADC
Rev. 0 | Page 23 of 24
10Ω
10Ω
Option 2 shows a circuit for driving higher frequency signals.
It uses a precision op amp (AD8616) with relatively high band-
width and output drive. This amplifier can drive a resistor and
capacitor with a much higher time constant and is, therefore,
suited for higher frequency applications.
Option 3 is useful for applications where the AD8227 needs to
run off a large voltage supply but drives a single-supply ADC.
In normal operation, the AD8227 output stays within the ADC
range, and the AD8616 simply buffers it. However, in a fault
condition, the output of the AD8227 may go outside the supply
range of both the AD8616 and the ADC. This is not an issue in
the circuit, because the 10 kΩ resistor between the two amplifiers
limits the current into the AD8616 to a safe level.
10nF
10nF
ADC0
ADC1
ADC2
ADuC7026
AGND
AV
3.3V
DD
AD8227