9
LT1787/LT1787HV
1787fc
PIN FUNCTIONS
UUU
FIL
–
, FIL
+
(Pins 1, 8): Negative and Positive Filter Termi-
nals. Differential mode noise can be filtered by connecting
a capacitor across FIL
–
and FIL
+
. Pole frequency
f
–3dB
= 1/(2πRC), R = 1.25kΩ.
V
S
–
(Pin 2): Negative Input Sense Terminal. Negative
sense voltage will result in an output sinking current
proportional to the sense current. V
S
–
is connected to an
internal gain-setting resistor R
G1A
and supplies bias cur-
rent to the internal amplifier.
DNC (Pin 3): Do Not Connect. Connected internally. Do not
connect external circuitry to this pin.
V
EE
(Pin 4): Negative Supply or Ground for Single Supply
Operation.
V
OUT
(Pin 5): Voltage Output or Current Output propor-
tional to the magnitude of the sense current flowing
through R
SENSE
. For bidirectional current sensing opera-
tion, V
OUT
= A
V
• V
SENSE
+ V
OUT(O)
+ V
BIAS
,
where:
V
OUT
> V
BIAS
for V
S
+
> V
S
–
V
OUT
< V
BIAS
for V
S
+
< V
S
–
V
OUT(O)
is the no load output voltage at V
SENSE
= 0V.
V
BIAS
(Pin 6): Output Bias Pin. For single supply, bidirec-
tional current sensing operation, V
BIAS
is connected to an
external bias voltage, so that at V
SENSE
= 0V, V
OUT
=
V
OUT(O)
+ V
BIAS
. For dual supply, bidirectional current
sensing operation, V
BIAS
is connected to ground. Thus,
V
OUT
= V
OUT(O)
at V
SENSE
= 0V.
V
S
+
(Pin 7): Positive Input Sense Terminal. Positive sense
voltage will result in an output sourcing current propor-
tional to the sense current. V
S
+
is connected to an internal
gain-setting resistor R
G2A
. Connecting a supply to V
S
+
and
a load to V
S
–
will allow the LT1787 to measure its own
supply current.
BLOCK DIAGRAM
W
R
SENSE
1787 F 01
R
G2A
1.25k
R
G2B
1.25k
R
G1A
1.25k
R
G1B
1.25k
V
OUT
I
OUT
V
BIAS
R
OUT
20k
V
S
–
–
+
A1
Q1
Q2
CURRENT MIRROR
V
EE
FIL
–
V
S
+
FIL
+
I
SENSE
Figure 1. LT1787 Functional Diagram
