MCP6441 datasheet(15/30 Pages) MICROCHIP

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DS22257A-page 15

MCP6441

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 4-6.

FIGURE 4-6:

Example Guard Ring Layout

for Inverting Gain.

Non-inverting Gain and Unity-Gain Buffer:

Connect the non-inverting pin (VIN+) to the

input with a wire that does not touch the

PCB surface.

Connect the guard ring to the inverting input

pin (VIN–). This biases the guard ring to the

Common Mode input voltage.

Inverting

Gain

and

Transimpedance

Gain

Amplifiers (convert current to voltage, such as

photo detectors):

Connect the guard ring to the non-inverting

input pin (VIN+). This biases the guard ring

to the same reference voltage as the op

amp (e.g., VDD/2 or ground).

Connect the inverting pin (VIN–) to the input

with a wire that does not touch the PCB

surface.

4.6

Application Circuits

4.6.1

BATTERY CURRENT SENSING

The MCP6441 op amp’s 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

(450 nA, typical) helps prolong battery life, and the

rail-to-rail output supports detection of low currents.

Figure 4-7 shows a high side battery current sensor

circuit. The 10

Ω resistor is sized to minimize power

losses. The battery current (IDD) 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 VDD, which is

within its allowed range. The output of the op amp will

also be below VDD, within its Maximum Output Voltage

Swing specification.

FIGURE 4-7:

Battery Current Sensing.

Guard Ring

VIN–VIN+

VSS

VDD

IDD

100 k

1.4V

VOUT

6.0V

OUT

–

10 V/V

() 10

()

⋅

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