Datasheet

LT6108-1/LT6108-2
16
610812fa
APPLICATIONS INFORMATION
such as a MUX or ADC. This output capacitor in parallel
with R
OUT
will create an output pole at:
f
–3dB
=
1
2• π •R
OUT
• C
L
SENSELO, SENSEHI Range
The difference between V
BATT
(see Figure 7) and V
+
, as
well as the maximum value of V
SENSE
, must be considered
to ensure that the SENSELO pin doesn’t exceed the range
listed in the Electrical Characteristics table. The SENSELO
and SENSEHI pins of the LT6108 can function from 0.2V
above the positive supply to 33V below it. These operat-
ing voltages are limited by internal diode clamps shown
in Figures 1 and 2. On supplies less than 35.5V, the lower
range is limited by V
–
+ 2.5V. This allows the monitored
supply, V
BATT
, to be separate from the LT6108 positive
supply as shown in Figure 7. Figure 8 shows the range of
operating voltages for the SENSELO and SENSEHI inputs,
for different supply voltage inputs (V
+
). The SENSELO and
SENSEHI range has been designed to allow the LT6108 to
monitor its own supply current (in addition to the load),
as long as V
SENSE
is less than 200mV. This is shown in
Figure 9.
Minimum Output Voltage
The output of the LT6108 current sense amplifier can
produce a non-zero output voltage when the sense voltage
is zero. This is a result of the sense amplifier V
OS
being
forced across R
IN
as discussed in the Output Voltage Er-
ror, ∆V
OUT(VOS)
section. Figure 10 shows the effect of the
input offset voltage on the transfer function for parts at
the V
OS
limits. With a negative offset voltage, zero input
Figure 9. LT6108 Supply Current Monitored with Load
Figure 7. V
+
Powered Separately from Load Supply (V
BATT
)
Figure 8. Allowable SENSELO, SENSEHI Voltage Range
Figure 10. Amplifier Output Voltage vs Input Sense Voltage
SENSEHI
LT6108
I
SENSE
R
SENSE
V
+
7
6
V
–
4
V
+
R
IN
V
BATT
SENSELO
8
1
OUTA
610812 F07
R
OUT
V
OUT
–
+
60
27
ALLOWABLE OPERATING VOLTAGE ON
SENSELO AND SENSHI INPUTS (V)
2.8
10
20
20.2V
40.2V
30
40
50
2.5
2.7 10 20 30 40 5035.5
V
+
(V)
60
610812 F08
VALID SENSELO/
SENSEHI RANGE
SENSEHI
LT6108
I
SENSE
R
SENSE
V
+
7
6
V
–
4
R
IN
V
BATT
SENSELO
8
1
OUTA
610812 F09
R
OUT
V
OUT
–
+
INPUT SENSE VOLTAGE (µV)
0
OUTPUT VOLTAGE (mV)
40
80
120
20
60
100
200 400 600 800
610812 F10
10001000 300 500 700 900
V
OS
= –125µV
G = 100
V
OS
= 125µV