9
LT1010
1010fc
be unrealistic to use these worst-case numbers above
because paralleled units are operating under identical
conditions. The offset voltage specified for V
S
=
±
15V,
V
IN
= 0V and T
A
= 25
°
C will suffice for a worst-case
condition.
APPLICATIO S I FOR ATIO
W
U
U
U
At lower frequencies, the buffer is within the feedback loop
so that its offset voltage and gain errors are negligible. At
higher frequencies, feedback is through C
F
, so that phase
shift from the load capacitance acting against the buffer
output resistance does not cause loop instability.
Stability depends upon the R
F
C
F
time constant or the
closed-loop bandwidth. With an 80kHz bandwidth, ring-
ing is negligible for C
L
= 0.068
µ
F and damps rapidly for
C
L
= 0.33
µ
F. The pulse response is shown in the graph.
A1
LT1010
V
IN
V
–
A2
LT1010
V
+
I
S
∆
I
OUT
I
S
+
∆
I
OUT
I
S
–
∆
I
OUT
V
OUT
1010 AI03
I
S
A2
LT1010
R
S
R
F
20k
V
IN
C
F
100pF
C
L
1010 AI04
V
OUT
–
+
A1
LT1007
Output load current will be divided based on the output
resistance of the individual buffers. Therefore, the avail-
able output current will not quite be doubled unless output
resistances are matched. As for offset voltage, the 25
°
C
limits should be used for worst-case calculations.
Parallel operation is not thermally unstable. Should one
unit get hotter than its mates, its share of the output and
its standby dissipation will decrease.
As a practical matter, parallel connection needs only some
increased attention to heat sinking. In some applications,
a few ohms equalization resistance in each output may be
wise. Only the most demanding applications should re-
quire matching, and then just of output resistance at 25
°
C.
Isolating Capacitive Loads
The inverting amplifier below shows the recommended
method of isolating capacitive loads. Noninverting ampli-
fiers are handled similarly.
TIME (
µ
s)
0
OUTPUT VOLTAGE (V)
0
200
1010 AI05
0
50
100
150
5
–5
–5
5
C
L
= 0.068
µ
F
C
L
= 0.33
µ
F
Pulse Response
Small-signal bandwidth is reduced by C
F
, but consider-
able isolation can be obtained without reducing it below
the power bandwidth. Often, a bandwidth reduction is
desirable to filter high frequency noise or unwanted
signals.
A2
LT1010
R
F
2k
R
S
2k
V
IN
C
F
1nF
C
L
1010 AI06
V
OUT
–
+
A1
LT118A
The follower configuration is unique in that capacitive
load isolation is obtained without a reduction in small-
signal bandwidth, although the output impedance of the
buffer comes into play at high frequencies. The precision
unity-gain buffer above has a 10MHz bandwidth without
capacitive loading, yet it is stable for all load capacitance
to over 0.3
µ
F, again determined by R
F
C
F
.
