MCP631 datasheet(22/42 Pages) MICROCHIP

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MCP631/2/3/5

DS22197A-page 22

4.2

Rail-to-Rail Output

4.2.1

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

50 mV of the negative rail with a 1 k

Ω load tied to

VDD/2.

4.2.2

OUTPUT CURRENT

Figure 4-4 shows the possible combinations of output

voltage (VOUT) and output current (IOUT), when

VDD =5.5V. IOUT is positive when it flows out of the op

amp into the external circuit.

FIGURE 4-4:

Output Current.

4.2.3

POWER DISSIPATION

Since the output short circuit current (ISC) is specified

at ±70 mA (typical), these op amps are capable of both

delivering and dissipating significant power.

Figure 4-5 show the quantities used in the following

power calculations for a single op amp. RSER is 0 Ω in

most applications; it can be used to limit IOUT. VOUT is

the op amp’s output voltage, VL is the voltage at the

load, and VLG is the load’s ground point. VSS is usually

ground (0V). The input currents are assumed to be

negligible. The currents shown are approximately:

EQUATION 4-1:

FIGURE 4-5:

Diagram for Power

Calculations.

The instantaneous op amp power (POA(t)), RSER power

(PRSER(t)) and load power (PL(t)) are:

EQUATION 4-2:

The maximum op amp power, for resistive loads,

occurs when VOUT is halfway between VDD and VLG or

halfway between VSS and VLG:

EQUATION 4-3:

The maximum ambient to junction temperature rise

(

ΔTJA) and junction temperature (TJ) can be calculated

using POAmax, ambient temperature (TA), the package

thermal resistance (

θJA) found in Table 1-4, and the

number of op amps in the package (assuming equal

power dissipations):

EQUATION 4-4:

-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)

VOUT –VLG

IOUT =IL =

RSER +RL

IDD ≈ IQ +max(0,IOUT)

ISS ≈ –IQ +min(0,IOUT)

Where:

IQ = quiescent supply current

VDD

VLG

IDD

ISS

IOUT

RSER

VOUT

VSS

MCP63X

POA(t) = IDD (VDD –VOUT)+ISS (VSS –VOUT)

PRSER(t) = IOUT

SER

PL(t) = IL

POAmax ≤

max2(VDD –VLG ,VLG –VSS)

4(RSER +RL)

ΔT

JA =POA(t) θJA ≤ nPOAmaxθJA

TJ =TA + ΔTJA

Where:

n = number of op amps in package (1, 2)

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