Datasheet
LT1970
10
1970fc
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
1
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 fl exible 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 subcircuit capabilities.
CIRCUIT DESCRIPTION
Main Operational Amplifi er
Subcircuit block GM1, the 1X unity-gain current buffer
and output transistors Q1 and Q2 form a standard op-
erational amplifi er. This amplifi er 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 circuit con-
fi gurations are supported. Inverting, noninverting, fi lter,
summation or nonlinear circuits may be implemented in
a conventional 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 fl ow at
the inputs when differential input voltage is present. This
feature is important when the precision current sense
amplifi ers “I
SINK
” and “I
SRC
” become active.
Current Limit Amplifi ers
Amplifi er stages “I
SINK
” and “I
SRC
” are very high transcon-
ductance amplifi er stages with independently controlled
offset voltages. These amplifi ers monitor the voltage be-
tween input pins SENSE
+
and SENSE
–
which usually sense
the voltage across a small external current sense resistor.
The transconductance amplifi ers outputs connect to the
same high impedance node as the main input stage GM1
amplifi er. 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 amplifi ers 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 suffi cient to equal or overcome one
of the offset voltages VC
SNK
/10 or VC
SRC
/10, the appropri-
ate current limit amplifi er becomes active and because of