LM308AD Просмотр технического описания (PDF) - Motorola => Freescale
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LM308AD Datasheet PDF : 8 Pages
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LM308A
SUGGESTED DESIGN APPLICATIONS
INPUT GUARDING
Special care must be taken in the assembly of printed
circuit boards to take full advantage of the low input currents
of the LM308A amplifier. Boards must be thoroughly cleaned
with alcohol and blown dry with compressed air. After
cleaning, the boards should be coated with epoxy or silicone
rubber to prevent contamination.
Figure 7. Fast (1) Summing Amplifier with
Low Input Current
Even with properly cleaned and coated boards, leakage
currents may cause trouble at +125°C, particularly since the
input pins are adjacent to pins that are at supply potentials.
This leakage can be significantly reduced by using guarding
to lower the voltage difference between the inputs and
adjacent metal runs. The guard, which is a conductive ring
surrounding the inputs, is connected to a low–impedance
point that is at approximately the same voltage as the inputs.
Leakage currents from high voltage pins are then absorbed
by the guard.
Figure 8. Sample and Hold
RS
Input
R1
150 k 0.002 µF
C5 (2)
R4
R2
1M
LM308A
Compen B
300 pF
0.002
µF
2
3
1.0 M
150 pF
1
6
Output
LM101A (3)
or equiv
(1) Power Bandwidth: 250 kHz
Small Signal Bandwidth:
3.5 MHz
Slew Rate: 10 V/µs
(2) C5 =
6 X 10–8
R1
(3) In addition to increasing speed,
the LM101A raises high and low
frequency gain, increases output
drive capability and eliminates
thermal feedback.
VCC
Input
1.0 M
Q1
Sample
Q2
1.0 µF (1)
Output
30 pF
(1) Teflon, Polyethylene or Polycarbonate
Dielectric Capacitor
Figure 9. Connection of Input Guards
Inverting Amplifier
Follower
Noninverting Amplifier
R1
R2
Input
R3 (1)
C1
Output
(1) Used to compensate for large source resistances.
R3 (1)
Input
C1
Output
R2
R3 (1)
Output
R1
C1
Input
R1 R2
Note:
must be an impedance.
R1 +R2
4
MOTOROLA ANALOG IC DEVICE DATA
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