MCP651 datasheet(23/44 Pages) MICROCHIP

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DS22146A-page 23

MCP651/2/5

4.2.3

NORMAL OPERATION

The input stage of the MCP651/2/5 op amps uses a dif-

ferential PMOS input stage. It operates at low common

mode input voltage (VCM), with VCM up to VDD –1.3V

and down to VSS – 0.3V. The input offset voltage (VOS)

is measured at VCM =VSS – 0.3V and VDD –1.3V to

ensure

proper

operation.

See

Figure 2-6

and

Figure 2-7 for temperature effects.

When operating at very low non-inverting gains, the

output voltage is limited at the top by the VCM range

(< VDD –1.3V); see Figure 4-5

FIGURE 4-5:

Unity Gain Voltage

Limitations for Linear Operation.

4.3

Rail-to-Rail Output

4.3.0.1

Maximum Output Voltage

The Maximum Output Voltage (see Figure 2-16 and

Figure 2-17) describes the output range for a given

load. For instance, the output voltage swings to within

15 mV of the negative rail with a 1 k

Ω load tied to

VDD/2.

4.3.0.2

Output Current

Figure 4-6 shows the possible combinations of output

voltage (VOUT) and output current (IOUT). IOUT is

positive when it flows out of the op amp into the

external circuit.

FIGURE 4-6:

Output Current.

4.3.0.3

Power Dissipation

Since the output short circuit current (ISC) is specified

at ±100 mA (typical), these op amps are capable of

both delivering and dissipating significant power. Two

common loads, and their impact on the op amp’s power

dissipation, will be discussed.

Figure 4-7 shows a resistive load (RL) with a DC output

voltage (VOUT). VL is RL’s ground point, VSS is usually

ground (0V) and IOUT is the output current. The input

currents are assumed to be negligible.

FIGURE 4-7:

Diagram for Resistive Load

Power Calculations.

The DC currents are:

EQUATION 4-1:

The DC op amp power is:

EQUATION 4-2:

The maximum op amp power, for resistive loads at DC,

occurs when VOUT is halfway between VDD and VL or

halfway between VSS and VL:

EQUATION 4-3:

VIN

MCP65X

VDD

VOUT

VSS V

IN V

OUT

VDD 1.3V

–

≤

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

IOUT (mA)

RL = 10Ω

RL = 100Ω

RL = 1 kΩ

VOH Limited

VOL Limited

(VDD = 5.5V)

MCP65X

VDD

VOUT

IDD

ISS

IOUT

VSS

IOUT

VOUT VL

–

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

IDD IQ max 0 IOUT

()

≈

ISS

– Q min 0 IOUT

()

≈

Where:

IQ = Quiescent supply current for one

op amp (mA/amplifier)

VOUT = A DC value (V)

POA

IDD VDD VOUT

–

() I

SS VSS

VOUT

–

()

max POA

()

IDD VDD VSS

–

()

max

2 V

–

VL VSS

–

()

4RL

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