LT1055_15 Datasheet, PDF (11/16 Pages) Linear Technology – Precision, High Speed, JFET Input Operational Amplifiers

LT1055/LT1056
APPLICATIONS INFORMATION
Phase Reversal Protection
Most industry standard JFET input op amps (e.g., LF155/
LF156, LF351, LF411, OP15/16) exhibit phase reversal at
the output when the negitive common mode limit at the
input is exceeded (i.e., from –12V to –15V with ±15V
supplies). This can cause lock-up in servo systems. As
shown below, the LT1055/LT1056 does not have this
problem due to unique phase reversal protection circuitry
(Q1 on simplified schematic).
Voltage Follower with Input Exceeding the Negative
Common Mode Range
INPUT
±15V
SINE WAVE
15V
2_– 7
LT1055/56
3₊
4
–15V
6 _OUTPUT
2k
LT1055/56 AI05
Output
Output
Input
(LF155/LF56, LF441, OP-15/OP-16)
LT1055/LT1056
0.5ms/DIV
LT1055/56 AI06
0.5ms/DIV
LT1055/56 AI07
0.5ms/DIV
LT1055/56 AI08
TYPICAL APPLICATIONS ^†
Exponential Voltage-to-Frequency Converter for Music Synthesizers
INPUT
0V TO 10V
EXPONENT
TRIM
2500Ω*
3.57k*
ZERO TRIM
11.3k*
6
500k
4.7k
500pF
POLYSTYRENE
5
15V
4 2_–
7
6
LT1055
3₊
1.1k
–15V
2N3906
2N3904
500Ω*
SAWTOOTH
OUTPUT
1k*
562Ω*
15V
LM329
10k*
1k*
1
2
10k*
15V
2_–
7
LM301A
6 ^3k
3₊
8
1N148
1
3
4 _0.01µF
SCALE FACTOR
1V IN OCTAVE OUT
*1% METAL FILM RESISTOR
PIN NUMBERED TRANSISTORS = CA3096 ARRAY
–15V
TEMPERATURE CONTROL LOOP
4.7k
13
14
15V
9
8
7
15 _2.2k
33Ω
LT1055/56 TA03
†_{For ten additional applications utilizing the}
LT1055 and LT1056, please see the LTC1043
data sheet and Application Note 3.
10556fc
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