Datasheet

LT6109-1/LT6109-2
15
610912fa
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 LT6109 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 LT6109 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 LT6109 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
sense voltage produces an output voltage. With a positive
offset voltage, the output voltage is zero until the input
sense voltage exceeds the input offset voltage. Neglect-
ing V
OS
, the output circuit is not limited by saturation of
pull-down circuitry and can reach 0V.
Response Time
The LT6109 amplifier is designed to exhibit fast response
to inputs for the purpose of circuit protection or current
monitoring. This response time will be affected by the
external components in two ways, delay and speed.
APPLICATIONS INFORMATION
Figure 9. LT6109 Supply Current Monitored with Load
Figure 7. V
+
Powered Separately from Load Supply (V
BATT
)
Figure 8. Allowable SENSELO, SENSEHI Voltage Range
SENSEHI
LT6109
I
SENSE
R
SENSE
V
+
9
V
–
5
V
+
R
IN
V
BATT
SENSELO
10
1
OUTA 8
610912 F07
R
OUT
V
OUT
–
+
60
50
40
30
20
20.2V
40.2V
10
27
ALLOWABLE OPERATING VOLTAGES ON
SENSELO AND SENSEHI INPUTS (V)
2.8V
2.5V
2.7 10 20 30 35.5 40 50
V
+
(V)
60
610912 F08
VALID SENSELO/
SENSEHI RANGE
SENSEHI
LT6109
I
SENSE
R
SENSE
V
+
9
V
–
5
R
IN
V
BATT
SENSELO
10
1
OUTA 8
610912 F09
R
OUT
V
OUT
–
+
Figure 10. Amplifier Output Voltage vs Input Sense Voltage
INPUT SENSE VOLTAGE (µV)
0
OUTPUT VOLTAGE (mV)
40
80
120
20
60
100
200 400 600 800
610912 F10
10001000 300 500 700 900
V
OS
= –125µV
V
OS
= 125µV
G = 100