MP8110 – PRECISION HIGH-SIDE CURRENT-SENSE AMPLIFIER
MP8110 Rev. 0.9 www.MonolithicPower.com 4
9/21/2007 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2007 MPS. All Rights Reserved.
OPERATION
The MP8110 is a current-sense amplifier with a
wide operating input voltage range of 2.5V to
40V.It has 1.4V to 40V Common-Mode range.
This feature allows the monitoring of current
flow out of a battery in deep discharge, and also
enables high-side current sensing up to the
supply voltage, V
CC
. Current flows through the
sense resistor, R
S
, which generates a sense
voltage V
RS
. The high precision sense amplifier
built into the MP8110 monitors the differential
voltage across R
S
and dynamically adjusts the
gate voltage of the internal P-channel MOSFET
to maintain a equal passing current as I
RG1
. The
current amplifier gain is therefore set as: R
GS
/
R
G1
.
Choosing Sensing Resistor
Given the gain and maximum load current,
select R
S
such that V
RS
does not exceed
+0.25V and V
OUT1
does not exceed 5V. To
measure lower currents more accurately, use a
high value for Rs. A higher value develops a
higher sense voltage, which overcomes offset
voltage errors of the internal current amplifier.
In applications of monitoring very high current,
ensure R
S
is able to dissipate its own I
2
R
losses. If the resistor rating power is exceeded,
its value may drift or it may fail altogether,
causing a differential voltage across the
terminals in excess of the absolute maximum
range (0.25V).
