Datasheet
LT1970
10
1970fe
For more information www.linear.com/LT1970
block DiagraM anD TesT circuiT
applicaTions inForMaTion
3
19
7
9
8
17
16
18
15
12
13
–
+
–
+
–
+
I
SINK
1970TC
R
FIL
1k
R
CS
1Ω
R
LOAD
1k
I
SRC
D2
D1
1×
Q1
Q2
4
5
6
2
GM1
ENABLE
COMMON
VC
SRC
VC
SRC
VC
SNK
5V
15V
VC
SNK
ISRC
ISNK
–IN
V
IN
R
G
1k
+IN
ENABLE
TSD
14
V
CC
V
+
15V
–15V
OUT
SENSE
+
FILTER
SENSE
–
V
–
V
EE
1, 10, 11, 20
10k
10k
10k
R
FB
1k
V
SRC
+
–
V
SNK
+
–
+
–
The LT1970 power op amp with precision controllable
current limit is a flexible voltage and current source
module. The drawing on the front page of this data sheet
is representative of the basic application of the circuit,
however many alternate uses are possible with proper
understanding of the sub circuit capabilities.
CIRCUIT DESCRIPTION
Main Operational Amplifier
Sub circuit block GM1, the 1X unity-gain current buffer
and output transistors Q1 and Q2 form a standard opera
-
tional amplifier. This amplifier has ± 500mA current output
capability and a 3.6MHz gain bandwidth product. Most
applications of the LT1970 will use this op amp in the main
signal path. All conventional op amp cir
cuit configurations
are supported. Inverting, noninverting, filter, summation
or nonlinear circuits may be implemented in a conven
-
tional manner. The output stage includes current limiting
at ±800mA to protect against fault conditions. The input
stage has high differential breakdown of 36V minimum
between –IN and +IN. No current will flow at the inputs
when differential input voltage is present. This feature is
important when the precision current sense amplifiers
“I
SINK
” and “I
SRC
” become active.
Current Limit Amplifiers
Amplifier stages “I
SINK
” and “I
SRC
” are very high transcon-
ductance amplifier stages with independently controlled
offset voltages. These amplifiers monitor the voltage be-
tween input pins SENSE
+
and SENSE
–
which usually sense
the voltage across a small external current sense resistor.
The transconductance amplifiers outputs connect to the
same high impedance node as the main input stage GM1
amplifier. Small voltage differences between SENSE
+
and
SENSE
–
, smaller than the user set VC
SNK
/10 and VC
SRC
/10
in magnitude, cause the current limit amplifiers to decouple
from the signal path. This is functionally indicated by diodes
D1 and D2 in the Block Diagram. When the voltage V
SENSE
increases in magnitude sufficient to equal or overcome one
of the offset voltages VC
SNK
/10 or VC
SRC
/10, the appropri-
ate current limit amplifier becomes active and because of
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