MCP6V86 datasheet(21/52 Pages) MICROCHIP

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DS20006398A-page 21

MCP6V86/6U/7/9

4.2.1.3

Input Current Limits

In order to prevent damage and/or improper operation

of these amplifiers, the circuit must limit the currents

into the input pins (see Section 1.1 “Absolute Maxi-

mum Ratings†”). This requirement is independent of

the voltage limits discussed previously.

Figure 4-6 shows one approach to protecting these

inputs. The R1 and R2 resistors limit the possible cur-

rent in or out of the input pins (and into D1 and D2). The

diode currents will dump onto VDD.

FIGURE 4-6:

Protecting the Analog Inputs

Against High Currents.

It is also possible to connect the diodes to the left of the

R1 and R2 resistors. In this case, the currents through

the D1 and D2 diodes need to be limited by some other

mechanism. The resistors then serve as inrush current

limiters; the DC current into the input pins (VIN+ and

VIN-) should be very small.

A significant amount of current can flow out of the

inputs (through the ESD diodes) when the Common-

mode Input Voltage (VCM) is below ground (VSS); see

Figure 2-15.

4.2.2

RAIL-TO-RAIL OUTPUT

The output voltage range of the MCP6V86/6U/7/9

devices’ zero-drift op amps is VDD – 5 mV (typical), and

VSS + 5 mV (typical) when RL = 10 kΩ is connected to

VDD/2 and VDD = 5.5V. Refer to Figures 2-17 and 2-18

for more information.

This op amp is designed to drive light loads; use

another amplifier to buffer the output from heavy loads.

4.3

Application Tips

4.3.1

INPUT OFFSET VOLTAGE OVER

TEMPERATURE

Table 1-1 gives both the linear and quadratic

Temperature Coefficients (TC1 and TC2) of the input

offset voltage. The input offset voltage, at any tempera-

ture in the specified range, can be calculated as fol-

lows:

EQUATION 4-1:

4.3.2

OFFSET AT POWER-UP

When these parts power up, the Input Offset (VOS)

starts at its uncorrected value. Circuits with high DC

gain can cause the output to reach one of the two rails.

In this case, the time to a valid output is delayed by an

Output Overdrive Time (like tODR) in addition to the

Start-up Time (like tSTR).

It can be simple to avoid this extra start-up time. Reduc-

ing the gain is one method; adding a capacitor across

the Feedback Resistor (RF) is another method.

VDD

min(R1,R2)>

VSS –min(V1,V2)

2mA

VOUT

min(R1,R2)>

max(V1,V2)– VDD

2mA

MCP6V8X

–

VOS TA



VOS TC1TTC2T

Where:

T =TA –+25°C

VOS(TA) = Input offset voltage at TA

VOS = Input offset voltage at +25°C

TC1 = Linear temperature coefficient

TC2 = Quadratic temperature coefficient

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