LT1010_15 Datasheet, PDF (10/20 Pages) Linear Technology – Fast 150mA Power Buffer

LT1010
APPLICATIONS INFORMATION
This is a good example of how fast op amps can be made
quite easy to use by employing an output buffer.
Integrator
A lowpass amplifier can be formed just by using large C_F
in the inverter described earlier, as long as the increasing
closed-loop output impedance above the cutoff frequency
is not a problem and the op amp is capable of supplying
the required current at the summing junction.
C_I
I_IN
R_F
20k
–
A1
LT1012
+
C_F
500pF
A2
LT1010
V_OUT
1010 AI07
If the integrating capacitor must be driven from the buffer
output, the circuit above can be used to provide capacitive
load isolation. As before, the stability with large capacitive
loads is determined by R_FC_F .
Wideband Amplifiers
This simple circuit provides an adjustable gain video
amplifier that will drive 1V_P-P into 75Ω. The differential
pair provides gain with the LT1010 serving as an output
15V
8.2k
25Ω
+
BIAS
22µF
+
22µF
TYPICAL SPECIFICATIONS
1V_P-P INTO 75Ω
AT A = 2
0.5dB TO 10MHz
3dB DOWN AT 16MHz
AT A = 10
0.5dB TO 4MHz
–3dB = 8MHz
LT1010
OUTPUT
(75Ω)
–15V
INPUT
Q1 Q2
Q1, Q2: 2N3866
5.1k
–15V
10
PEAKING
5pF to 25pF
900Ω
1k
GAIN SET
+
0.01µF
68µF
1010 AI08
stage. Feedback is arranged in the conventional manner,
although the 68µF-0.01µF combination limits DC gain to
unity for all gain settings. For applications sensitive to
NTSC requirements, dropping the 25Ω output stage bias
value will aid performance.
R2
800Ω
–
A1
HA2625
V_IN
+
R1
100Ω
C1
15pF
A2
LT1010
V_OUT
1010 AI09
This shows the buffer being used with a wideband ampli-
fier that is not unity-gain stable. In this case, C1 cannot
be used to isolate large capacitive loads. Instead, it has an
optimum value for a limited range of load capacitances.
The buffer can cause stability problems in circuits like this.
With the TO-220 packages, behavior can be improved by
raising the quiescent current with a 20Ω resistor from the
bias terminal to V⁺. Alternately, devices in the miniDIP can
be operated in parallel.
It is possible to improve capacitive load stability by oper-
ating the buffer class A at high frequencies. This is done
by using quiescent current boost and bypassing the bias
terminal to V^– with more than 0.02µF.
R2
1.6k
INPUT
–
A1
HA2625
+
R1
400Ω
A2
LT1010
OUTPUT
1010 AI10
Putting the buffer outside the feedback loop as shown
here will give capacitive load isolation, with large output
capacitors only reducing bandwidth. Buffer offset, referred
to the op amp input, is divided by the gain. If the load re-
sistance is known, gain error is determined by the output
resistance tolerance. Distortion is low.
1010fe