MCP621 datasheet(25/68 Pages) MICROCHIP

25 / 68 page

 2009-2021 Microchip Technology Inc. and its subsidiaries

DS20002188E-page 25

MCP621/1S/2/3/4/5/9

Figure 4-7 shows a capacitive load (CL), which is

driven by a sine wave with DC offset. The capacitive

load causes the op amp to output higher currents at

higher frequencies. Because the output rectifies IOUT,

the op amp’s dissipated power increases (even though

the capacitor does not dissipate power).

FIGURE 4-8:

Diagram for Capacitive Load

Power Calculations.

The output voltage is assumed to be:

EQUATION 4-4:

The op amp’s currents are:

EQUATION 4-5:

The op amp’s instantaneous power, average power

and peak power are:

EQUATION 4-6:

The power dissipated in a package depends on the

powers dissipated by each op amp in that package:

EQUATION 4-7:

The maximum ambient-to-junction temperature rise

(

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

using the maximum expected package power (PPKG),

ambient temperature (TA) and the package thermal

resistance (

JA) found in Table 1-4:

EQUATION 4-8:

The worst-case power derating for the op amps in a

particular package can be easily calculated:

EQUATION 4-9:

Several techniques are available to reduce

TJA for a

given package:

• Reduce

JA

- Use another package

- Improve the PCB layout (ground plane, etc.)

- Add heat sinks and air flow

• Reduce max (PPKG)

- Increase RL

- Decrease CL

- Limit IOUT using RISO (see Figure 4-9)

- Decrease VDD

VDD

VOUT

IDD

ISS

IOUT

VSS

MCP62X

VOUT

VDC VAC

t



sin

Where:

VDC =DC offset (V)

VAC = Peak output swing (VPK)

 = Radian frequency (2 f) (rad/s)

IOUT

dVOUT

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



VACCL

t



cos

IDD IQ max 0 IOUT





ISS

– Q min 0 IOUT





Where:

IQ = Quiescent supply current for one op

amp (mA/amplifier)

POA

IDD VDD VOUT

–

 I

SS VSS

VOUT

–



ave POA



VDD VSS

–

 I

4VAC fCL



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





max POA



VDD VSS

–

 I

2VAC fCL



PPKG

POA



Where:

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

T

PPKGJA

TA TJA

PPKG

TJmax TA

–



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



Where:

TJmax = Absolute maximum junction

temperature (°C)

TA = Ambient temperature (°C)

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