LT1499 LINER [Linear Technology], LT1499 Datasheet - Page 13

• Manufacturer Part Number: LT1499
• Description: 10MHz, 6V/us, Dual/Quad Rail-to-Rail Input and Output Precision C-Load Op Amps
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
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
amplifier. 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 amplifier has a
2.5MHz crossing frequency and a 60 phase margin at 6dB
of gain. The feedback resistors and the total input capaci-
tance 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
+
U
INFORMATION
I
t
U
OUT
r
< 1 s
=
V
+
0.5
500pF
– V
U
IN
W
100
0.5
1k
N
I
OUT
Si9430DY
U
R
1498/99 TA03
L
C
C
L
C
L
C
C
L
= 500pF
C
L
V
= 500pF
L
= 10nF
L
IN
= 10nF
= 0pF
= 0pF
1k
Figure 2a. LT1498 Small-Signal Response
Figure 2b. LT1498 Large-Signal Response
V
A
V
A
S
V
S
V
= 5V
= 1
= 5V
= 1
1A Voltage Controlled Current Sink
+
–
1/2 LT1498
V
+
I
t
OUT
r
< 1 s
=
0.5
V
LT1498/LT1499
IN
500pF
100
1k
I
1498/99 F02a
1498/99 F02b
OUT
V
+
Si9410DY
R
0.5
1498/99 TA04
L
13