LT1787 データシートの表示（PDF） - Linear Technology
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LT1787 Datasheet PDF : 16 Pages
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LT1787/LT1787HV
APPLICATIONS INFORMATION
with absolute minimum swing at 30mV above VEE. VOUT
may swing positive to within 0.75V of VS+ or a maximum
of 35V, a limit set by internal junction breakdown. Within
these contraints, an amplified, level shifted representation
of the RSENSE voltage is developed across ROUT.
Split Supply Bipolar Output Swing
Figure 2 shows the LT1787 used with split power supplies.
The VBIAS pin is connected to ground, and the output
signal appears at the VOUT pin. Bidirectional input currents
can be monitored with the output swinging positive for
current flow from VS+ and VS–. Input currents in the
opposite direction cause VOUT to swing below ground.
Figure 2 shows an optional output capacitor connected
from VOUT to ground. This capacitor may be used to filter
the output signal before it is processed by other
circuitry.Figure 3 shows the voltage transfer function of
the LT1787 used in this configuration.
Single Supply with Shifted VBIAS
Figure 4 shows the LT1787 used in a single supply mode
with the VBIAS pin shifted positive using an external
LT1634 voltage reference. The VOUT output signal can
swing above and below VBIAS to allow monitoring of
positive or negative currents through the sense resistor,
as shown in Figure 5. The choice of reference voltage is not
critical except for the precaution that adequate headroom
must be provided for VOUT to swing without saturating the
internal circuitry. The component values shown in Figure 4
allow operation with VS supplies as low as 3.1V.
TO
CHARGER/
LOAD
–5V
RSENSE
1 FIL–
2 VS–
FIL+ 8
LT1787 VS+ 7
3
DNC
4
VEE
C2
1µF
VBIAS 6
ROUT
5
VOUT
C1
1µF
15V
C3*
1000pF
OUTPUT
*OPTIONAL
1787 F02
Figure 2. Split Supply Operation
1.5
VS = 3.3V TO 60V
TA = – 40°C TO 85°C
1.0
0.5
0
–0.5
–1.0
–1.5
–128 –96 –64 –32 0 32 64 96 128
SENSE VOLTAGE (VS+ – VS–) (mV)
1787 F03
Figure 3. Split Supply Output Voltage
TO
CHARGER/
LOAD
RSENSE
1 FIL–
FIL+ 8
2 VS– LT1787HV VS+ 7
3
DNC
4
VEE
VBIAS 6
ROUT
5
VOUT
3.3V
C1
TO
1µF
60V
3.3V
20k
5%
C2
1µF
C3*
1000pF
LT1634-1.25
*OPTIONAL
OUTPUT
1787 F04
Figure 4. Charge/Discharge Current Monitor on
Single Supply with VBIAS = 1.25V
1.5
VS = 3.3V TO 60V
TA = – 40°C TO 85°C
1.0
0.5
0
–0.5
–1.0
–1.5
–128 –96 –64 –32 0 32 64 96 128
SENSE VOLTAGE (VS+ – VS–) (mV)
1787 F05
Figure 5. Single Supply Output Voltage
with VBIAS = 1.25V
1787fc
11
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