11
LT1055/LT1056
10556fc
APPLICATIONS INFORMATION
WU
U
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).
0.5ms/DIV
10V/DIV
LT1055/56 AI06
LT1055/56 AI07
LT1055/56 AI08
TYPICAL APPLICATIONS
U
Exponential Voltage-to-Frequency Converter for Music Synthesizers
INPUT
0V TO 10V
LT1055/56 TA03
–
+
11.3k*
EXPONENT
TRIM
2500
*
562
*
3.57k*
ZERO TRIM
15V
500k
500
*
4.7k
1.1k
10k*
3k
10k*
1k*
4.7k
2
3
4
5
6
–15V
7
LT1055
15V
500pF
POLYSTYRENE
6
2
3
15V
7
LM301A
15V
6
8
2N3906
2N3904
SAWTOOTH
OUTPUT
LM329
0.01
F
1
4
2
3
1
1N148
13
14
15 2.2k
9
7
8
33
TEMPERATURE CONTROL LOOP
SCALE FACTOR
1V IN OCTAVE OUT
*1% METAL FILM RESISTOR
PIN NUMBERED TRANSISTORS = CA3096 ARRAY
–
+
For ten additional applications utilizing the
LT1055 and LT1056, please see the LTC1043
data sheet and Application Note 3.
Voltage Follower with Input Exceeding the Negative
Common Mode Range
–
+
2k
–15V
15V
OUTPUT
2
3
4
INPUT
±15V
SINE WAVE
7
6
LT1055/56
LT1055/56 AI05
Output
LT1055/LT1056
Output
(LF155/LF56, LF441, OP-15/OP-16)
Input