MCP607-I/PG Microchip Technology, MCP607-I/PG Datasheet - Page 14

• Manufacturer Part Number: MCP607-I/PG
• Description: DUAL 25 UA, 2.5V OP AMP, -40C to +85C, 8-PDIP, TUBE
• Manufacturer: Microchip Technology

MCP606/7/8/9
FIGURE 4-6:
4.7
In applications where low input bias current is critical,
Printed Circuit Board (PCB) surface-leakage effects
need to be considered. Surface leakage is caused by
humidity, dust or other contamination on the board.
Under low humidity conditions, a typical resistance
between nearby traces is 10
cause 5 pA of current to flow, which is greater than the
MCP606/7/8/9 family’s bias current at 25°C (1 pA, typi-
cal).
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 4-7:
for Inverting Gain.
DS11177E-page 14
V
DD
¼ MCP604 (A)
R
R
V
REF
1
2
PCB Surface Leakage
=
V
V
DD
DD
⋅
V
------------------
R
IN
1
Guard Ring
R
Unused Op Amps.
Example Guard Ring Layout
+
-
2
V
R
2
REF
12
Ω. A 5V difference would
V
IN
+
¼ MCP604 (B)
V
V
Figure
SS
DD
4-7.
1.
2.
4.8
4.8.1
The MCP606/7/8/9 op amps can be used to sense the
load current on the low-side of a battery using the
circuit in
power supply (minus the current required to power the
MCP606) flows through a sense resistor (R
converts it to voltage. This is gained by the the amplifier
and resistors, R
of the amplifier is at the load’s negative supply (V
the gain from R
FIGURE 4-8:
Sensor.
Since the input bias current and input offset voltage of
the MCP606 are low, and the input is capable of swing-
ing below ground, there is very little error generated by
the amplifier. The quiescent current is very low, which
helps conserve battery power. The rail-to-rail output
makes it possible to read very low currents.
Non-inverting Gain and Unity-gain Buffer:
a)
b)
Inverting Gain and Transimpedance Gain
(convert current to voltage, such as photo
detectors) amplifiers:
a)
b)
2.5V
6.0V
to
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.
Application Circuits
Figure
V
LOW-SIDE BATTERY CURRENT
SENSOR
OUT
IN
SEN
G
4-8. In this circuit, the current from the
R
5 kΩ
10Ω
–). This biases the guard ring to the
R
SEN
and R
=
G
to V
V
IN
DD
LM
+). This biases the guard ring
Low Side Battery Current
F
OUT
© 2008 Microchip Technology Inc.
/2 or ground).
50 kΩ
+
. Since the non-inverting input
R
I
MCP606
L
F
is R
R
SEN
F
/R
(
R F
G
IN
.
⁄
–) to the input
R
G
IN
)
SEN
+) to the
To Load
To Load
(V
(V
I
), which
V
L
LM
LP
OUT
)
)
LM
),