Datasheet

MCP6401/1R/1U/2/4/6/7/9
DS22229D-page 20 © 2009-2011 Microchip Technology Inc.
4.7.2 BATTERY CURRENT SENSING
The MCP6401/1R/1U/2/4/6/7/9 op amps’ Common
Mode Input Range, which goes 0.3V beyond both
supply rails, supports their use in high-side and low-
side battery current sensing applications. The low
quiescent current (45 µA, typical) helps prolong battery
life, and the rail-to-rail output supports detection of low
currents.
Figure 4-9 shows a high-side battery current sensor
circuit. The 10Ω resistor is sized to minimize power
losses. The battery current (I
DD
) through the 10Ω
resistor causes its top terminal to be more negative
than the bottom terminal. This keeps the Common
Mode input voltage of the op amp below V
DD
, which is
within its allowed range. The output of the op amp will
also be below V
DD
, which is within its Maximum Output
Voltage Swing specification.
FIGURE 4-9: Supply Current Sensing.
4.7.3 INSTRUMENTATION AMPLIFIER
The MCP6401/1R/1U/2/4/6/7/9 op amps are well
suited for conditioning sensor signals in battery-
powered applications. Figure 4-10 shows a two op amp
instrumentation amplifier, using the MCP6402, that
works well for applications requiring rejection of
Common Mode noise at higher gains. The reference
voltage (V
REF
) is supplied by a low impedance source.
In single supply applications, V
REF
is typically V
DD
/2.
FIGURE 4-10: Two Op Amp
Instrumentation Amplifier.
V
DD
I
DD
100 kΩ
1MΩ
1.8V
V
OUT
10Ω
to
6.0V
I
DD
V
DD
V
OUT
–
10 V/V()10
Ω () ⋅
----------------------------------------- -=
To load
MCP6401
V
OUT
V
1
V
2
–()1
R
1
R
2
------
2R
1
R
G
---------++
⎝⎠
⎛⎞
V
REF
+=
V
REF
R
1
R
2
R
2
R
1
V
OUT
R
G
V
2
V
1
½ MCP6402 ½ MCP6402