LT1055/LT1056
U
W U U
APPLICATIONS INFORMATION
Phase Reversal Protection
Voltage Follower with Input Exceeding the Negative
Common-Mode Range
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).
15V
7
2
3
–
6
LT1055/56
OUTPUT
2k
INPUT
±15V
SINE WAVE
+
4
–15V
LT1055/56 AI05
Output
LT1055/LT1056
Output
Input
(LF155/LF56, LF441, OP-15/OP-16)
0.5ms/DIV
0.5ms/DIV
0.5ms/DIV
LT1055/56 AI06
LT1055/56 AI07
LT1055/56 AI08
U
TYPICAL APPLICATIONS †
Exponential Voltage-to-Frequency Converter for Music Synthesizers
INPUT
0V TO 10V
EXPONENT
11.3k*
TRIM
500pF
2N3906
2500Ω*
POLYSTYRENE
15V
5
2N3904
2
6
4
7
–
500Ω*
6
LT1055
3.57k*
ZERO TRIM
500k
3
+
SAWTOOTH
OUTPUT
–15V
1.1k
4.7k
1k*
562Ω*
15V
LM329
4.7k
15V
10k*
10k*
1k*
15V
7
2
–
+
9
3k
6
8
LM301A
13
14
8
3
7
1N148
1
1
4
2
33Ω
3
15
0.01µF
2.2k
SCALE FACTOR
†For ten additional applications utilizing the
LT1055 and LT1056, please see the LTC1043
data sheet and Application Note 3.
–15V
TEMPERATURE CONTROL LOOP
1V IN OCTAVE OUT
*1% METAL FILM RESISTOR
PIN NUMBERED TRANSISTORS = CA3096 ARRAY
LT1055/56 TA03
9
Linear [ Linear ]
