LT1010(RevC) View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LT1010
(Rev.:RevC)

Fast ±150mA Power Buffer

Linear Technology 

LT1010

APPLICATIO S I FOR ATIO

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.

15pF

10k

15V

+

68pF 22µF

33Ω

Q3

2N3906

0.18Ω

1k

10k

INPUT

–

LT1056

+

Q1

MJE2955

LT1010

100Ω

100Ω

Q2

MJE3055

OUTPUT

33Ω

–15V

HEAT SINK OUTPUT TRANSISTORS

Q4

2N3904

22µF

1k

1010 AI17

0.18Ω

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

functions 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 con-

figuration 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 similarly filtered version of the input

5V

INPUT

Q1

2N5486

Q2

2N2222

10M 100Ω

–5V

10k

0.01µF

A A2

LT1010

–5V

4

B

OUTPUT

10M

0.1µF

3

6

A1

LTC1050

2

7

2000pF

5V

0.1µF

1k

1010 AI18

signal. The amplified difference between these signals is

used to set Q2’s bias, and hence, Q1’s channel current.

This forces Q1’s VGS 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 junc-

tion. A2’s output is also fed back to the shield around Q1’s

gate lead, bootstrapping the circuit’s effective input ca-

pacitance 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 (1VP-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 (1VP-P) is 18MHz. – 3dB band-

width is 58MHz. At A = 10, full power is available to

10MHz, with the – 3dB point at 36MHz.

1010fc

13

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