AD797AR-REEL7 Analog Devices Inc, AD797AR-REEL7 Datasheet - Page 13

• Manufacturer Part Number: AD797AR-REEL7
• Description: IC,Operational Amplifier,SINGLE,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD797AR-REEL7

• Rohs Status: RoHS non-compliant
• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Slew Rate: 20 V/µs
• Gain Bandwidth Product: 110MHz
• -3db Bandwidth: 8MHz
• Current - Input Bias: 250nA
• Voltage - Input Offset: 25µV
• Current - Supply: 8.2mA
• Current - Output / Channel: 50mA
• Voltage - Supply, Single/dual (±): ±5 V ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Type: -

0.1µF
BYPASSING CONSIDERATIONS
Taking full advantage of the very wide bandwidth and dynamic
range capabilities of the AD797 requires some precautions.
First, multiple bypassing is recommended in any precision
application. A 1.0 μF to 4.7 μF tantalum in parallel with 0.1 μF
ceramic bypass capacitors are sufficient in most applications.
When driving heavy loads, a larger demand is placed on the
supply bypassing. In this case, selective use of larger values of
tantalum capacitors and damping of their lead inductance with
small-value (1.1 Ω to 4.7 Ω) carbon resistors can achieve an
improvement. Figure 35 summarizes power supply bypassing
recommendations.
THE NONINVERTING CONFIGURATION
Ultralow noise requires very low values of the internal parasitic
resistance (r
very little damping of input and output reactive interactions.
With the AD797, additional input series damping is required
for stability with direct output to input feedback. A 100 Ω
resistor (R1) in the inverting input (Figure 36) is sufficient; the
100 Ω balancing resistor (R2) is recommended but is not
required for stability. The noise penalty is minimal (e
2.1 nV/√Hz), which is usually insignificant.
Best response flatness is obtained with the addition of a small
capacitor (C
(Figure 37). The input source resistance and capacitance also
affect the response slightly, and experimentation may be
necessary for best results.
USE SHORT
LEAD LENGTHS
(<5mm)
*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.
Figure 35. Recommended Power Supply Bypassing
BB
L
4.7µF
) for the input transistors (≈6 Ω). This implies
100Ω
< 33 pF) in parallel with the 100 Ω resistor
KELVIN RETURN
R2
Figure 36. Voltage Follower Connection
V
LOAD
CURRENT
S
2
3
AD797
OR
100Ω
R1
+V
–V
7
4
S
S
0.1µF
USE SHORT
LEAD LENGTHS
(<5mm)
*
*
6
R
600Ω
L
1.1Ω TO 4.7Ω
4.7µF TO 22.0µF
KELVIN RETURN
V
LOAD
CURRENT
S
N
total ≈
Rev. H | Page 13 of 20
Low noise preamplification is usually performed in the non-
inverting mode (Figure 38). For lowest noise, the equivalent
resistance of the feedback network should be as low as possible.
The 30 mA minimum drive current of the AD797 makes it easier
to achieve this. The feedback resistors can be made as low as
possible, with consideration to load drive and power consumption.
Table 6 provides some representative values for the AD797 when
used as a low noise follower. Operation on 5 V supplies allows
the use of a 100 Ω or less feedback network (R1 + R2). Because
the AD797 shows no unusual behavior when operating near its
maximum rated current, it is suitable for driving the
AD602
Optimum flatness and stability at noise gains >1 sometimes require
a small capacitor (C
Figure 38). Table 6 includes recommended values of C
gains. In general, when R2 is greater than 100 Ω and C
than 33 pF, a 100 Ω resistor should be placed in series with C
Source resistance matching is assumed, and the AD797 should not
be operated with unbalanced source resistance >200 kΩ/G.
Table 6. Values for Follower with Gain Circuit
Gain
2
2
10
20
>35
*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.
*USE THE POWER SUPPLY BYPASSING SHOWN IN FIGURE 35.
(see Figure 50) while preserving low noise performance.
R1
1 kΩ
300 Ω
33.2 Ω
16.5 Ω
10 Ω
Figure 37. Alternative Voltage Follower Connection
R1
R
S
C
S
Figure 38. Low Noise Preamplifier
L
R2
1 kΩ
300 Ω
300 Ω
316 Ω
(G − 1) × 10 Ω
) connected across the feedback resistor (R1 of
2
3
2
3
AD797
AD797
100Ω
C
R2
+V
–V
C
+V
–V
L
7
4
L
7
4
S
S
S
S
*
*
6
*
6
*
C
≈ 20 pF
≈ 10 pF
≈ 5 pF
L
R
600Ω
L
Noise
(Excluding R
3.0 nV/√Hz
1.8 nV/√Hz
1.2 nV/√Hz
1.0 nV/√Hz
0.98 nV/√Hz
L
L
for several
AD600/
is greater
AD797
L
.
S
)