LT1010_15 Datasheet, PDF (11/20 Pages) Linear Technology – Fast 150mA Power Buffer

LT1010
APPLICATIONS INFORMATION
R3
800Ω
INPUT
C1
–
20pF
A1
HA2625
+
A2
LT1010
R4
39Ω
OUTPUT 1
R1 R2
50Ω 200Ω
A3
LT1010
R5
39Ω
OUTPUT 2
1010 AI11
OTHER
SLAVES
The 50Ω video line splitter here puts feedback on one
buffer with the others slaved. Offset and gain accuracy of
slaves depend on their matching with master.
When driving long cables, including a resistor in series
with the output should be considered. Although it reduces
gain, it does isolate the feedback amplifier from the effects
of unterminated lines which present a resonant load.
When working with wideband amplifiers, special attention
should always be paid to supply bypassing, stray capaci-
tance and keeping leads short. Direct grounding of test
probes, rather than the usual ground lead, is absolutely
necessary for reasonable results.
The LT1010 has slew limitations that are not obvious
from standard specifications. Negative slew is subject
to glitching, but this can be minimized with quiescent
current boost. The appearance is always worse with fast
rise signal generators than in practical applications.
Track and Hold
The 5MHz track and hold shown here has a 400kHz power
bandwidth driving ±10V. A buffered input follower drives
the hold capacitor, C4, through Q1, a low resistance FET
switch. The positive hold command is supplied by TTL
logic with Q3 level shifting to the switch driver, Q2. The
output is buffered by A3.
When the gate is driven to V^– for HOLD, it pulls charge
out of the hold capacitor. A compensating charge is put
into the hold capacitor through C3. The step into hold is
made independent of the input level with R7 and adjusted
to zero with R10.
Since internal dissipation can be quite high when driving
fast signals into a capacitive load, using a buffer in a power
package is recommended. Raising buffer quiescent current
to 40mA with R3 improves frequency response.
This circuit is equally useful as a fast acquisition sample
and hold. An LT1056 might be used for A3 to reduce drift
in hold because its lower slew rate is not usually a problem
in this application.
Current Sources
A standard op amp voltage to current converter with a
buffer to increase output current is shown here. As usual,
V⁺
R1
INPUT ^2k +
A1
LT118A
–
HOLD
C1
50pF
C2
150pF
R3
20Ω
A2
LT1010
Q1
2N5432
SD
R2
2k
D1
R4
C4
HP2810 _2k
1nF
R5
Q3
1k _2N2907
R6
1k
Q2
2N2222
C3
100pF
C5
10pF
R7
200k
–
A3
LT118A
+
A4
LT118A
R8
5k
V^–
*2N2369 EMITTER BASE JUNCTION
OUTPUT
D2*
6V
R9
10k
R10 _R11
50k _6.2k
1010 AI12
1010fe
11