MCP633 datasheet(21/60 Pages) MICROCHIP

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DS20002197C-page 21

MCP631/2/3/4/5/9

4.2

Rail-to-Rail Output

4.2.1

MAXIMUM OUTPUT VOLTAGE

The maximum output voltage (see Figures 2-16

and 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

 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:

Diagram for Power

Calculations.

Figure 4-5 shows the power calculations used for a

single op amp:

•RSER is 0 in most applications and can be used

to limit IOUT.

•VOUT is the op amp’s output voltage.

•VL is the voltage at the load.

•VLG is the load’s ground point.

•VSS is usually ground (0V).

The input currents are assumed to be negligible. The

currents shown in Figure 4-5 can be approximated

using Equation 4-1:

EQUATION 4-1:

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

(

TJA) and junction temperature (TJ) can be calculated

using POAmax, the ambient temperature (TA), the

package thermal resistance (

JA, found in the

Temperature Specifications table) and the number of

op amps in the package (assuming equal power

dissipations), as shown in Equation 4-4:

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)

VDD

VLG

IDD

ISS

IOUT

RSER

VOUT

VSS

MCP63X

Where:

IQ = Quiescent supply current

OUT

–

SER

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

max 0, I

OUT





–

min 0, I

OUT





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

PRSER(t) = IOUT

SER

PL(t) = IL

OAmax

max

–





SER



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



Where:

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



OA t





OAmax JA





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