MCP6031_08 datasheet(17/34 Pages) MICROCHIP

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DS22041B-page 17

MCP6031/2/3/4

4.9

Application Circuits

4.9.1

BATTERY CURRENT SENSING

The MCP6031/2/3/4 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 ultra low quiescent

current (0.9 µA, 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, which is within its Maximum Output

Voltage Swing specification.

FIGURE 4-7:

High Side Battery Current

Sensor.

4.9.2

PRECISION COMPARATOR

Use high gain before a comparator to improve the lat-

ter’s input offset performance. Figure 4-8 shows a gain

of 11 V/V placed before a comparator. The reference

voltage VREF can be any value between the supply

rails.

FIGURE 4-8:

Precision, Non-inverting

Comparator.

4.9.3

DRIVING MCP3421

ΔΣ A/D

CONVERTER

A RSH and CSH snubber reduces the output impedance

of MCP6031 op amp, which reduces the gain error

caused by switching transients, which occur at the

MCP3421 ADC's sampling rate. The snubber also

maintains feedback stability and avoids AC response

peaking and step response overshoot and ringing

(caused by the op amp’s inductive output impedance

resonating with the ADC’s input capacitance). The cost

for this improvement is low. Best of all, using an op amp

with higher supply current is avoided. See Figure 4-9.

This figure also includes a resistor to balance the

impedance at the ADC's inputs (RBAL) at the sampling

frequency; it may not be needed in all designs.

FIGURE 4-9:

Driving the MCP3421 using

an R-C Snubber.

VDD

IDD

MCP6031

100 k

1.4V

VOUT

5.5V

OUT

–

10 V/V

() 10

()

⋅

------------------------------------------

VIN

VOUT

MCP6031

100 k

MCP6541

VREF

VIN

MCP6031

RSH

CSH

1.00 k

2.2 µF

RBAL

1.00 k

MCP3421

ΔΣ

1.00 k

ZIND

2.25 M

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