Datasheet
LT1970
18
1970fe
For more information www.linear.com/LT1970
applicaTions inForMaTion
In some applications it may be necessary to know what
the current into the load is at any time. Figure 10 shows an
LT1787 high side current sense amplifier monitoring the
current through sense resistor R
S
. The LT1787 is biased
from the V
EE
supply to accommodate the common mode
input range of ±10V. The sense resistor is scaled down
to provide a 100mV maximum differential signal to the
current sense amplifier to preserve linearity. The LT1880
amplifier provides gain and level shifting to produce a 0V
to 5V output signal (2.5V DC ±5mV/mA) with up to 1kHz
full-scale bandwidth. An A/D converter could then digi
-
tize this instantaneous current reading to provide digital
feedback from the circuit.
The
LT1970 is just as easy to use as a standard operational
amplifier. Basic amplification of a precision reference
voltage creates a very simple bench DC power supply as
shown in Figure 11. The built-in power stage produces an
adjustable 0V to 25V at 4mA to 100mA of output current.
Voltage and current adjustments are derived from the
LT1634-5 5V reference. The output current capability is
500mA, but this supply is restricted to 100mA for power
dissipation reasons. The worst-case output voltage for
maximum power dissipated in the LT1970 output stage
occurs if the output is shorted to ground or set to a voltage
near zero. Limiting the output current to 100mA sets the
maximum power dissipation to 3W. To allow the output to
Figure 9. Digitally Controlled Analog Pin Driver
VC
SRC
COMMON
V
EE
VC
SNK
V
–
FILTER
V
+
18V
R6
3k
10µF 0.1µF
EN
V
CC
ISNK
ISRC
SENSE
–
SENSE
+
TSD
OUT
+IN
R2
10.2k
R1
3.4k
0V
5V
APPLY LOAD
DRIVE
OPTIONAL TEST PIN
ON/OFF CONTROL
Hi-Z
LT1970
–18V
10µF 0.1µF
SENSE
–IN
R
S
1Ω
FORCE
TEST PIN
LOAD
1970 F09
R4
10.2k
V
CC
V
REF
5V
CLR
DAC A
DAC B
CS/LD
SCK
DI
DAC C
DAC D
R3
3.4k
LTC1664
QUAD 10-BIT DAC
DECODER
3-WIRE
SERIAL
INTERFACE
+
R5
3k
+
V
OUT
= 15V
I
SOURCE(MAX)
= ≈ –4mA TO –500mA
≈ ±15V
CODE C – CODE D
1024
( )
0.5 • CODE B
1024 • R
S
I
SINK(MAX)
= ≈ 4mA TO 500mA
0.5 • CODE A
1024 • R
S
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