Datasheet

LTC6104
7
6104f
BLOCK DIAGRAM
6
–
+
–
+
5k
R
OUT
V
REF
5k5k
+INA –INA –INB +INB
5k
R
INB
R
INA
I
LOAD
V
SENSE
+–
R
SENSE
10V
AB
10V 10V
V
S
V
–
V
+
V
–
V
+
7 5
OUT
V
OUT
1
V
–
6104 F01
8
4
+ V
REF
V
OUT
= V
SENSE
•
R
OUT
R
IN
+
–
Figure 1. LTC6104 Block Diagram
When V
SENSE
is positive, an internal sense amplifi er loop
forces –INA to have the same potential as +INA. Connect-
ing an external resistor, R
INA
, in series with –INA causes
a current, V
SENSE
/R
INA
, to fl ow through R
INA
. The high
impedance inputs of the sense amplifi er will not conduct
this input current, so the current will fl ow through an
internal MOSFET to the OUT pin.
The output current can be transformed into a voltage by
adding a resistor from OUT to a reference voltage (V
REF
). The
output voltage is then V
OUT
= (V
SENSE
/R
INA
) • R
OUT
+ V
REF
.
When operating on a dual supply, R
OUT
can be tied to ground.
The output voltage is then V
OUT
= (V
SENSE
/R
INA
) • R
OUT
.
Only one amplifi er is active at a time in the LTC6104. If the
load current direction (V
SENSE
is negative) activates the
THEORY OF OPERATION
“B” amplifi er, the “A” amplifi er will be inactive. The signal
current goes into the –INB pin, through the MOSFET, and
into the current mirror. The mirror reverses the polarity of
the signal so that current fl ows into the “OUT” pin, causing
the output voltage to change polarity. The magnitude of the
output is then V
SENSE
• R
OUT
/R
INB
+ V
REF
. Keep in mind
that the OUT voltage cannot swing below V
–
, even though
it’s sinking current. A proper V
REF
and R
OUT
need to be
chosen so that the designed OUT voltage swing does not
go beyond the specifi ed voltage range of the output.
Supply current is drawn from +INB pin. The user may
choose to include this current in the monitored current
through R
SENSE
by careful choice of connection polarity.