AD8027AR Analog Devices Inc, AD8027AR Datasheet - Page 20

• Manufacturer Part Number: AD8027AR
• Description: IC OPAMP R-R LDIST LN LP 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of AD8027AR

• Rohs Status: RoHS non-compliant
• Amplifier Type: Voltage Feedback
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 100 V/µs
• -3db Bandwidth: 190MHz
• Current - Input Bias: 4µA
• Voltage - Input Offset: 200µV
• Current - Supply: 6.5mA
• Current - Output / Channel: 120mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Gain Bandwidth Product: -

AD8027/AD8028
PCB Layout
As with all high speed op amps, achieving optimum perform-
ance from the AD8027/AD8028 requires careful attention to
PCB layout. Particular care must be exercised to minimize lead
lengths of the bypass capacitors. Excess lead inductance can
influence the frequency response and even cause high
frequency oscillations. The use of a multilayer board with an
internal ground plane can reduce ground noise and enable a
tighter layout.
To achieve the shortest possible lead length at the inverting
input, the feedback resistor, R
board and span the distance from the output, Pin 6, to the
input, Pin 2. The return node of the resistor, R
situated as closely as possible to the return node of the negative
supply bypass capacitor connected to Pin 4.
On multilayer boards, all layers underneath the op amp should
be cleared of metal to avoid creating parasitic capacitive
elements. This is especially true at the summing junction
(the −input). Extra capacitance at the summing junction can
cause increased peaking in the frequency response and lower
phase margin.
Grounding
To minimize parasitic inductances and ground loops in high
speed, densely populated boards, a ground plane layer is critical.
Understanding where the current flows in a circuit is critical in
the implementation of high speed circuit design. The length of
the current path is directly proportional to the magnitude of the
parasitic inductances and, therefore, the high frequency
impedance of the path. Fast current changes in an inductive
ground return can create unwanted noise and ringing.
F
, should be located beneath the
G
, should be
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The length of the high frequency bypass capacitor pads and
traces is critical. A parasitic inductance in the bypass grounding
works against the low impedance created by the bypass
capacitor. Because load currents flow from supplies as well as
ground, the load should be placed at the same physical location
as the bypass capacitor ground. For large values of capacitors,
which are intended to be effective at lower frequencies, the
current return path length is less critical.
Power-Supply Bypassing
Power-supply pins are actually inputs, and care must be taken to
provide a clean, low noise, dc voltage source to these inputs.
The bypass capacitors have two functions:
•
•
Decoupling methods are designed to minimize the bypassing
impedance at all frequencies. This can be accomplished with a
combination of capacitors in parallel to ground.
Good-quality ceramic chip capacitors should be used and
always kept as close as possible to the amplifier package . A
parallel combination of a 0.01 μF ceramic and a 10 μF electro-
lytic covers a wide range of rejection for unwanted noise. The
10 μF capacitor is less critical for high frequency bypassing, and,
in most cases, one per supply line is sufficient.
Provide a low impedance path for unwanted frequencies
from the supply inputs to ground, thereby reducing the
effect of noise on the supply lines.
Provide sufficient localized charge storage, for fast switching
conditions and minimizing the voltage drop at the supply
pins and the output of the amplifier. This is usually accom-
plished with larger electrolytic capacitors.