
LTC6104
7
6104f
BLOCK DIAGRAM
6
–
+
–
+
5k
ROUT
VREF
5k
+INA
–INA
–INB
+INB
5k
RINB
RINA
ILOAD
VSENSE +
–
RSENSE
10V
AB
10V
VS
V–
V+
V–
V+
7
5
OUT
VOUT
1
V–
6104 F01
8
4
+ VREF
VOUT = VSENSE
ROUT
RIN
+
–
Figure 1. LTC6104 Block Diagram
When VSENSE is positive, an internal sense amplier loop
forces –INA to have the same potential as +INA. Connect-
ing an external resistor, RINA, in series with –INA causes
a current, VSENSE/RINA, to ow through RINA. The high
impedance inputs of the sense amplier will not conduct
this input current, so the current will 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 (VREF).The
output voltage is then VOUT = (VSENSE/RINA) ROUT + VREF.
Whenoperatingonadualsupply,ROUTcanbetiedtoground.
The output voltage is then VOUT = (VSENSE/RINA) ROUT.
Only one amplier is active at a time in the LTC6104. If the
load current direction (VSENSE is negative) activates the
THEORY OF OPERATION
“B” amplier, the “A” amplier 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 ows into the “OUT” pin, causing
the output voltage to change polarity. The magnitude of the
output is then VSENSE ROUT/RINB + VREF. Keep in mind
that the OUT voltage cannot swing below V–, even though
it’s sinking current. A proper VREF and ROUT need to be
chosen so that the designed OUT voltage swing does not
go beyond the specied 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 RSENSE by careful choice of connection polarity.