LT1498IS8 Linear Technology, LT1498IS8 Datasheet - Page 15

• Manufacturer Part Number: LT1498IS8
• Description: IC,Operational Amplifier,DUAL,BIPOLAR,SOP,8PIN,PLASTIC
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
without oscillation at unity gain. When driving a heavy
capacitive load, the bandwidth is reduced to maintain
stability. Figures 2a and 2b illustrate the stability of the
device for small-signal and large-signal conditions with
capacitive loads. Both the small-signal and large-signal
transient response with a 10nF capacitive load are well
behaved.
Feedback Components
To minimize the loading effect of feedback, it is possible
to use the high value feedback resistors to set the gain.
However, care must be taken to insure that the pole formed
by the feedback resistors and the total input capacitance
at the inverting input does not degrade the stability of the
amplifi er. For instance, the LT1498/LT1499 in a noninvert-
ing gain of 2, set with two 30k resistors, will probably
oscillate with 10pF total input capacitance (5pF input
capacitance + 5pF board capacitance). The amplifi er has
a 2.5MHz crossing frequency and a 60° phase margin at
6dB of gain. The feedback resistors and the total input
capacitance create a pole at 1.06MHz that induces 67° of
phase shift at 2.5MHz! The solution is simple, either lower
the value of the resistors or add a feedback capacitor of
10pF of more.
TYPICAL APPLICATIONS
V
IN
1k
1A Voltage Controlled Current Source
V
–
+
1/2 LT1498
+
I
t
OUT
r
< 1μs
=
V
+
0.5Ω
500pF
– V
IN
100Ω
0.5Ω
1k
I
OUT
Si9430DY
R
14989 TA03
L
C
C
V
C
C
L
L
IN
C
C
L
L
= 500pF
= 500pF
L
L
= 10nF
= 10nF
= 0pF
= 0pF
1k
Figure 2a. LT1498 Small-Signal Response
Figure 2b. LT1498 Large-Signal Response
V
A
V
A
S
V
S
V
1A Voltage Controlled Current Sink
= 5V
= 1
= 5V
= 1
–
+
1/2 LT1498
V
+
I
t
OUT
r
< 1μs
LT1498/LT1499
=
0.5Ω
V
IN
500pF
100Ω
1k
I
OUT
14989 F02b
14989 F02a
V
+
Si9410DY
R
0.5Ω
14989 TA04
L
15
14989fe