MSK-0021FP Datasheet, PDF (3/8 Pages) M.S. Kennedy Corporation – HIGH POWER OP-AMP

APPLICATION NOTES
HEAT SINKING
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CURRENT LIMIT
To select the correct heat sink for your application, refer to the
thermal model and governing equation below.
Thermal Model:
The MSK 0021 has an on-board current limit scheme de-
signed to limit the output drivers anytime output current
exceeds a predetermined limit. The following formula may
be used to determine the value of the current limit resistance
necessary to establish the desired current limit.
RSC=
_0_.7_
ISC
Current Limit Connection
Governing Equation:
TJ = PD X (RθJC + RθCS + RθSA) + TA
Where
TJ
PD
RθJC
RθCS
RθSA
TC
TA
TS
= Junction Temperature
= Total Power Dissipation
= Junction to Case Thermal Resistance
= Case to Heat Sink Thermal Resistance
= Heat Sink to Ambient Thermal Resistance
= Case Temperature
= Ambient Temperature
= Sink Temperature
Example: (TO-3 PACKAGE)
In our example the amplifier application requires the output to drive
a 10 volt peak sine wave across a 10 ohm load for 1 amp of output
current. For a worst case analysis we will treat the 1 amp peak
output current as a D.C. output current. The power supplies are
±15 VDC.
1.) Find Power Dissipation
PD=[(quiescent current) X (+VCC - (VCC))] + [(VS - VO) X IOUT]
=(3.5 mA) X (30V) + (5V) X (1A)
=0.1W + 6W
=6.1W
2.) For conservative design, set TJ = +150°C.
3.) For this example, worst case TA = +25°C.
4.) RθJC = 2.0°C/W typically for the TO-3 package.
5.) Rearrange governing equation to solve for RθSA:
RθSA = (TJ - TA) / PD - (RθJC) - (RθCS)
= (150°C - 25°C) / 6.1W - (2.0°C/W) - (0.15°C/W)
= 18.5°C/W
The heat sink in this example must have a thermal resistance of no
more than 18.5°C/W to maintain a junction temperature of less than
+150°C.
3
See "Application Circuits" in this data sheet for additional
information on current limit connections.
POWER SUPPLY BYPASSING
Both the negative and the positive power supplies must
be effectively decoupled with a high and low frequency by-
pass circuit to avoid power supply induced oscillation. An
effective decoupling scheme consists of a 0.1 microfarad
ceramic capacitor in parallel with a 4.7 microfarad tantalum
capacitor from each power supply pin to ground. It is also a
good practice with high power op-amps, such as the MSK
0021, to place a 30-50 microfarad capacitor with a low
effective series resistance, in parallel with the other two power
supply decoupling capacitors. This capacitor will eliminate
any peak output voltage clipping which may occur due to
poor power supply load regulation. All power supply
decoupling capacitors should be placed as close to the pack-
age power supply pins as possible.
SAFE OPERATING AREA
The safe operating area curve is a graphical representation
of the power handling capability of the amplifier under vari-
ous conditions. The wire bond current carrying capability,
transistor junction temperature and secondary breakdown
limitations are all incorporated into the safe operating area
curves. All applications should be checked against the S.O.A.
curves to ensure high M.T.B.F.
Rev. A 6/03