MSK707H Datasheet, PDF (3/6 Pages) M.S. Kennedy Corporation – ULTRA-ACCURATE/HIGH SLEW RATE INVERTING OPERATIONAL AMPLIFIER

APPLICATION NOTES
HEAT SINKING
To determine if a heat sink is necessary for your application and
if so, what type, refer to the thermal model and governing equation
below.
Thermal Model:
Governing Equation:
TJ=PD x (RθJC + RθCS + RθJC) + TA
Where
TJ=Junction Temperature
PD=Total Power Dissipation
RθJC=Junction to Case Thermal Resistance
RθCS=Case to Heat Sink Thermal Resistance
RθSA=Heat Sink to Ambient Thermal Resistance
TC=Case Temperature
TA=Ambient Temperature
TS=Sink Temperature
Example:
This example demonstrates a worst case analysis for the op-amp
output stage. This occurs when the output voltage is 1/2 the power
supply voltage. Under this condition, maximum power transfer oc-
curs and the output is under maximum stress.
Conditions:
VCC=±16VDC
VO=±8Vp Sine Wave, Freq.=1KHz
RL=100Ω
For a worst case analysis we will treat the +8Vp sine wave
as an 8VDC output voltage.
1.) Find Driver Power Dissapation
PD=(VCC-VO) (VO/RL)
=(16V-8V) (8V/100Ω)
=0.64W
2.) For conservative design, set TJ=+125°C
3.) For this example, worst case TA=+90°C
4.) RθJC=45°C/W from MSK 707 Data Sheet
5.) RθCS=0.15°C/W for most thermal greases
6.) Rearrange governing equation to solve for RθSA
RθSA=((TJ-TA)/PD) - (RθJC) - (RθCS)
=((125°C -90°C)/0.64W) - 45°C/W - 0.15°C/W
=54.7 - 46.15
=9.5°C/W
OUTPUT SHORT CIRCUIT PROTECTION
The output section of the MSK 707 can be protected from direct
shorts to ground by placing current limit resistors between pins 1
and 12 and pins 9 and 10 as shown in Figure 1.
The value of the short circuit current limit resistors (±RSC) can
be calculated as follows.
+RSC=VCC-0.7/+ISC
-RSC=VCC+0.7/-ISC
Short circuit current limit should be set at least 2X above the
highest normal operating output current to keep the value of RSC low
enough to ensure that the voltage dropped accross the short circuit
current limit resistor doesn't adversely affect normal operation.
INTERNAL FEEDBACK RESISTOR
The MSK 707 is equipped with an internal 2KΩ feedback resistor.
Bandwidth and slew rate can be optimized by connecting the MSK
707 as shown in Figure 2. Placing the feedback resistor inside the
hybrid reduces printed circuit board trace length and its' asscociated
capacitance which acts as a capacitive load to the op-amp output.
Reducing the capacitive load allows the output to slew faster and
greater bandwidths will be realized. Refer to Table 1 for recom-
mended RIN values for various gains.
TABLE 1
APPROXIMATE
DESIRED GAIN
-1
-2
-10
RIN
VALUE
1.5KΩ
750Ω
150Ω
Whenever the internal resistor is not being used it is good practice
to short pin 4 and 5 to avoid inadvertently picking up spurious sig-
nals.
Recommended External Component Selection
Guide Using External Rf
TABLE 2
APPROXIMATE
DESIRED GAIN
1
-1
1
-2
1
-5
1
-8
1
-10
1
-20
RI(+)
249Ω
160Ω
169Ω
100Ω
90.9Ω
100Ω
RI(-) Rf(Ext) Cf
499Ω 499Ω 2
249Ω 499Ω 2
200Ω 1KΩ
2
124Ω 1KΩ
2
100Ω 1KΩ
2
100Ω 2KΩ 2
1 The positive input resistor is selected to minimize any bias current induced offset
voltage.
2 The feedback capacitor will help compensate for stray input capacitance. The value of
this capacitor can be dependent on individual applications. A 0.5 to 5pF capacitor is
usually optimum for most applications.
3 Effective load is RL in parallel with Rf.
3
PRELIMINARY Rev. - 2/04