AD8652ARZ Analog Devices Inc, AD8652ARZ Datasheet - Page 15

• Manufacturer Part Number: AD8652ARZ
• Description: IC OPAMP VF CMOS 50MHZ LN 8SOIC
• Manufacturer: Analog Devices Inc
• Series: DigiTrim®r

Specifications of AD8652ARZ

• Slew Rate: 41 V/µs
• Amplifier Type: Voltage Feedback
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Gain Bandwidth Product: 50MHz
• Current - Input Bias: 1pA
• Voltage - Input Offset: 90µV
• Current - Supply: 17.5mA
• Current - Output / Channel: 40mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Op Amp Type: Precision
• No. Of Amplifiers: 2
• Bandwidth: 50MHz
• Supply Voltage Range: 2.7V To 5.5V
• Amplifier Case Style: SOIC
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Input Protection
As with any semiconductor device, if a condition exists for the
input voltage to exceed the power supply, the device input
overvoltage characteristic must be considered. The inputs of the
AD865x family are protected with ESD diodes to either power
supply. Excess input voltage energizes internal PN junctions in
the AD865x, allowing current to flow from the input to the
supplies. This results in an input stage with picoamps of input
current that can withstand up to 4000 V ESD events (human
body model) with no degradation.
Excessive power dissipation through the protection devices
destroys or degrades the performance of any amplifier. Differential
voltages greater than 7 V result in an input current of approximately
(| V
the inputs. For input voltages beyond the positive supply, the
input current is approximately (V
voltages beyond the negative supply, the input current is about
(V
differential voltages greater than 7 V or input voltages beyond
the amplifier power supply, limit the input current to 10 mA by
using an appropriately sized input resistor (R
Figure 55.
Overdrive Recovery
Overdrive recovery is defined as the time it takes for the output
of an amplifier to come off the supply rail after an overload signal is
initiated. This is usually tested by placing the amplifier in a closed-
loop gain of 15 with an input square wave of 200 mV p-p while the
amplifier is powered from either 5 V or 3 V. The AD865x family
has excellent recovery time from overload conditions (see Figure 31
and Figure 32). The output recovers from the positive supply rail
within 200 ns at all supply voltages. Recovery from the negative rail
is within 100 ns at 5 V supply.
LAYOUT, GROUNDING, AND BYPASSING
CONSIDERATIONS
Power Supply Bypassing
Power supply pins can act as inputs for noise, so care must be
taken that a noise-free, stable dc voltage is applied. The purpose
of bypass capacitors is to create low impedances from the supply
to ground at all frequencies, thereby shunting or filtering most
of the noise.
IN
R
FOR LARGE | V
CC
I
– V
>
– V
(| V
EE
CC
EE
+ 0.7)/R
– V
– V
| – 0.7 V)/R
30mA
IN
EE
+
CC
| – 0.7V)
Figure 55. Input Protection Method
– V
I
. If the inputs of the amplifier sustain
EE
R
I
|
I
, where R
+
–
AD865x
I
IN
is the resistance in series with
– V
CC
R
R
+ V
I
I
>
>
– 0.7)/R
O
FOR V
SUPPLY VOLTAGES
(V
(V
I
IN
IN
), as shown in
– V
– V
30mA
30mA
IN
EE
EE
BEYOND
I
. For input
– 0.7V)
+ 0.7V)
Rev. C | Page 15 of 20
Bypassing schemes are designed to minimize the supply
impedance at all frequencies with a parallel combination of
capacitors of 0.1 μF and 4.7 μF. Chip capacitors of 0.1 μF (X7R
or NPO) are critical and should be as close as possible to the
amplifier package. The 4.7 μF tantalum capacitor is less critical
for high frequency bypassing, and, in most cases, only one is
needed per board at the supply inputs.
Grounding
A ground plane layer is important for densely packed PC
boards to spread the current-minimizing parasitic inductances.
However, an understanding of where the current flows in a
circuit is critical to implementing effective high speed circuit
design. The length of the current path is directly proportional to
the magnitude of parasitic inductances and, therefore, the high
frequency impedance of the path. High speed currents in an
inductive ground return create an unwanted voltage noise.
The length of the high frequency bypass capacitor leads is
critical. A parasitic inductance in the bypass grounding works
against the low impedance created by the bypass capacitor.
Place the ground leads of the bypass capacitors at the same
physical location. Because load currents also flow from the
supplies, the ground for the load impedance should be at the
same physical location as the bypass capacitor grounds. For the
larger value capacitors, intended to be effective at lower
frequencies, the current return path distance is less critical.
Leakage Currents
Poor PC board layout, contaminants, and the board insulator
material can create leakage currents that are much larger than the
input bias current of the AD865x family. Any voltage differential
between the inputs and nearby traces sets up leakage currents
through the PC board insulator, for example 1 V/100 G = 10 pA.
Similarly, any contaminants on the board can create significant
leakage (skin oils are a common problem).
To significantly reduce leakages, put a guard ring (shield)
around the inputs and the input leads that are driven to the
same voltage potential as the inputs. This ensures that there is
no voltage potential between the inputs and the surrounding
area to set up any leakage currents. To be effective, the guard
ring must be driven by a relatively low impedance source and
should completely surround the input leads on all sides, above
and below, using a multilayer board.
Another effect that can cause leakage currents is the charge
absorption of the insulator material itself. Minimizing the
amount of material between the input leads and the guard
ring helps to reduce the absorption. Also, low absorption
materials, such as Teflon® or ceramic, may be necessary in
some instances.
AD8651/AD8652