Datasheet

LT1010
13
1010fe
APPLICATIONS INFORMATION
High Current Booster
The circuit below uses a discrete stage to get 3A output
capacity. The configuration shown provides a clean, quick
way to increase LT1010 output power. It is useful for high
current loads such as linear actuator coils in disk drives.
The 33Ω resistors sense the LT1010’s supply current
with the grounded 100Ω resistor supplying a load for
the LT1010. The voltage drop across the 33Ω resistors
biases Q1 and Q2. Another 100Ω value closes a local
feedback loop, stabilizing the output stage. Feedback
to the LT1056 control amplifier is via the 10k value. Q3
and Q4, sensing across the 0.18Ω units, furnish current
limiting at about 3.3A.
similarly filtered version of the input signal. The amplified
difference between these signals is used to set Q2’s bias,
and hence, Q1’s channel current. This forces Q1’s V
GS
to
whatever voltage is required to match the circuit’s input
and output potentials. The 2000pF capacitor at A1 provides
stable loop compensation. The RC network in A1’s output
prevents it from seeing high speed edges coupled through
Q2’s collector-base junction. A2’s output is also fed back to
the shield around Q1’s gate lead, bootstrapping the circuit’s
effective input capacitance down to less than 1pF.
Gain-Trimmable Wideband FET Amplifier
A potential difficulty with the previous circuit is that the
gain is not quite unity. The figure labeled A on the next
page maintains high speed and low bias while achieving
a true unity-gain transfer function.
This circuit is somewhat similar except that the Q2-Q3
stage takes gain. A2 DC stabilizes the input-output path and
A1 provides drive capability. Feedback is to Q2’s emitter
from A1’s output. The 1k adjustment allows the gain to be
precisely set to unity. With the LT1010, output stage slew
and full power bandwidth (1V
P-P
) are 100V/µs and 10MHz
respectively. –3dB bandwidth exceeds 35MHz. At A = 10
(e.g., 1k adjustment set at 50Ω), full power bandwidth
stays at 10MHz while the –3dB point falls to 22MHz.
With the optional discrete stage, slew exceeds 1000V/µs
and full power bandwidth (1V
P-P
) is 18MHz. –3dB band-
width is 58MHz. At A = 10, full power is available to 10MHz,
with the –3dB point at 36MHz.
LT1010
100Ω
33Ω
–15V
33Ω
10k
22µF
15V
100Ω
1k
0.18Ω
1k
0.18Ω
Q1
MJE2955
Q2
MJE3055
OUTPUT
1010 AI17
Q4
2N3904
Q3
2N3906
–
+
LT1056
10k
68pF
INPUT
+
22µF
HEAT SINK OUTPUT TRANSISTORS
+
15pF
Wideband FET Input Stabilized Buffer
The figure below shows a highly stable unity-gain buffer
with good speed and high input impedance. Q1 and Q2
constitute a simple, high speed FET input buffer. Q1 func-
tions as a source follower with the Q2 current source load
setting the drain-source channel current. The LT1010 buffer
provides output drive capability for cables or whatever
load is required. Normally, this open-loop configuration
would be quite drifty because there is no DC feedback. The
LTC
®
1050 contributes this function to stabilize the circuit.
It does this by comparing the filtered circuit output to a
A2
LT1010
1k
10k
–5V
5V
3
BA
OUTPUT
6
4
–5V
5V
7
0.1µF
2
Q2
2N2222
INPUT
Q1
2N5486
–
+
2000pF 0.1µF
1010 AI18
0.01µF
10M
100Ω
A1
LTC1050
10M