MCP6H02 MICROCHIP [Microchip Technology], MCP6H02 Datasheet - Page 19

• Manufacturer Part Number: MCP6H02
• Manufacturer: MICROCHIP [Microchip Technology]

4.6
In applications where low input bias current is critical,
PCB surface leakage effects need to be considered.
Surface leakage is caused by humidity, dust or other
contamination on the board. Under low-humidity condi-
tions, a typical resistance between nearby traces is
10
to flow; which is greater than the MCP6H01/2/4 family’s
bias current at +25°C (10 pA, typical).
The easiest way to reduce surface leakage is to use a
guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin.
An example of this type of layout is shown in
Figure
FIGURE 4-7:
for Inverting Gain.
1.
2.
© 2011 Microchip Technology Inc.
12
Ω. A 15V difference would cause 15 pA of current
Non-inverting Gain and Unity-Gain Buffer:
a.
b.
Inverting Gain and Trans-impedance Gain
Amplifiers (convert current to voltage, such as
photo detectors):
a.
b.
4-7.
Guard Ring
PCB Surface Leakage
Connect the non-inverting pin (V
input with a wire that does not touch the
PCB surface.
Connect the guard ring to the inverting input
pin (V
common mode input voltage.
Connect the guard ring to the non-inverting
input pin (V
to the same reference voltage as the op
amp (e.g., V
Connect the inverting pin (V
with a wire that does not touch the PCB
surface.
IN
–). This biases the guard ring to the
IN
DD
+). This biases the guard ring
Example Guard Ring Layout
/2 or ground).
V
IN
– V
IN
+
IN
–) to the input
V
IN
SS
+) to the
4.7
4.7.1
The MCP6H01/2/4 op amps can be used in current
sensing applications.
(R
voltage, as well as a difference amplifier that amplifies
the voltage across the resistor while rejecting common
mode noise. R
an acceptable Common Mode Rejection Ratio
(CMRR). Moreover, R
R
the source.
To ensure proper operation, the op amp common mode
input voltage must be kept within the allowed range.
The reference voltage (V
low-impedance source. In single-supply applications,
V
.
FIGURE 4-8:
Using Difference Amplifier.
REF
1
SEN
and R
R
SEN
is typically V
) that converts the sensor current (I
Application Circuits
2
in order to minimize the resistive loading of
DIFFERENCE AMPLIFIER
V
1
I
OUT
SEN
and R
R
R
DD
1
1
R
MCP6H01/2/4
=
/2.
SEN
SEN
2
(
High Side Current Sensing
must be well matched to obtain
V
Figure 4-8
1
<< R
should be much smaller than
–
MCP6H01
V
REF
2
1
)
, R
⎛
⎝
V
) is supplied by a
R
R
----- -
R
R
DD
2
2
1
2
2
⎞
⎠
shows a resistor
DS22243C-page 19
+
V
REF
V
V
REF
SEN
OUT
) to