Datasheet

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0
2
4
6
8
10
12
14
VOUT (V)
VSENSE (V)
V
CC
> 14V
V
CC
= +4.5V to +76V
C1
0.1 PF
V
OUT
To Load
+4.0V
to
+76V
R
SENSE
I
SENSE
ADC
RSN
RSP
GND
LMP8480
V
IN
+
V
IN
- V
REF
V
SENSE
V
CC
LMP8480, LMP8481
SNVS829A –JUNE 2012–REVISED AUGUST 2012 www.ti.com
UNI-DIRECTIONAL VS. BI-DIRECTIONAL OPERATION
Uni-directional operation is where the load current only flows in one direction (V
SENSE
is always positive).
Application examples would be PA monitoring, non-inductive load monitoring and laser or LED drivers. This
allows the output zero reference to be true zero volts on the output. The LMP8480 is designed for unidirectional
applications where the setting of VREF is not required. See the UNI-DIRECTIONAL OPERATION for more
details.
Bi-directional operation is where the load current can flow in both directions (V
SENSE
can be positive or
negative). Application examples would be battery charging or regenerative motor monitoring. The LMP8481 is
designed for bidirectional applications and has a pair of VREF pins to allow the setting of the output zero
reference level (V
REF
). See the BI-DIRECTIONAL OPERATION (LMP8481 ONLY) section for more details.
UNI-DIRECTIONAL OPERATION
The LMP8480 is designed for unidirectional current sense applications. The output of the amplifier will be equal
to the differential input voltage times the fixed device gain.
Figure 8. Uni-Directional Application with LMP8480
Figure 9. Uni-Directional Transfer Function for Gain-of-20 option
The output voltage can be calculated from:
VOUT = ( (V
RSP
– V
RSN
) * Av ) (1)
It should be noted that the minimum “zero” reading will be limited by the lower output swing and input offset.
The LMP8480 is functionally identical to the LMP8481, but with the V
REFA
and V
REFB
nodes grounded internally.
The LMP8481 can replace the LMP8480 if both the V
REF
inputs (pins 6 & 7) are grounded.
BI-DIRECTIONAL OPERATION (LMP8481 ONLY)
Bi-directional operation is required where the measured load current can be positive or negative. Because V
SENSE
can be positive or negative, and the output cannot swing negative, the “zero” output level must be level-shifted
above ground to a known zero reference point. The LMP8481 allows for the setting this reference point.
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