MSK0033 M. S Kennedy, MSK0033 Datasheet - Page 3

• Manufacturer Part Number: MSK0033
• Description: Fet Input High Speed Voltage Follower/buffer Amplifier
• Manufacturer: M. S Kennedy

HEAT SINKING
Thermal Model:
Governing Equation:
Where
Example:
output stage. This occurs when the output voltage is 1/2 the
power supply voltage. Under this condition, maximum power
transfer occurs and the output is under maximum stress.
Conditions:
as an 8 VDC output voltage.
1.) Find Driver Power Dissipation
2.) For conservative design, set T
3.) For this example, worst case T
4.) R
5.) R
6.) Rearrange governing equation to solve for R
and if so, what type, refer to the thermal model and governing
equation below.
This example demonstrates a worst case analysis for the buffer
V
V
R
T
To determine if a heat sink is necessary for your application
For a worst case analysis we will treat the ±8Vp sine wave
T
P
R
R
R
T
T
T
L
CC
O
J
D
J
C
A
S
=P
P
= 100
= ±8Vp Sine Wave, Freq. = 1KHz
JC
CS
SA
D
= Junction Temperature
= Sink Temperature
= Total Power Dissipation
= Case Temperature
= Ambient Temperature
= ±16VDC
APPLICATION NOTES
JC
CS
= (16V-8V) (8V/100 )
= 640mW
= (V
D
= Junction to Case Thermal Resistance
= Case to Heat Sink Thermal Resistance
= Heat Sink to Ambient Thermal Resistance
= 65°C/W from MSK 0033B Data Sheet
= 0.15°C/W for most thermal greases
x (R
CC
JC
-V
O
+ R
) (V
O
CS
/R
+ R
L
)
SA
) + T
J
A
=+125°C Max.
=+80°C
A
SA
3
OFFSET VOLTAGE ADJUST
CURRENT LIMITING
POWER SUPPLY BYPASSING
of no more than 5.2°C/W to maintain a junction temperature of
no more than +125°C.
200
open. If offset null is not necessary, short Pin 6 to Pin 7 and
remove the 200
Vcc.
12 and Pin 9 to Pin 10 and delete Q1 thru Q4 connections. Q1
through Q4 and the Rlim resistors form a current source current
limit scheme and current limit resistor values can be calculated
as follows:
Since current limit is directly proportional to the base-emitter
voltage drop of the 2N2222's and 2N2907's in the current
limit scheme, the current limit value will change slightly with
ambient temperature changes. The base-emitter voltage drop
will decrease as temperature increases causing the actual cur-
rent limit point to decrease.
effectively decoupled with a high and low frequency bypass
circuit to avoid power supply induced oscillation. An effective
decoupling scheme consists of a 0.1 microfarad ceramic ca-
pacitor in parallel with a 4.7 microfarad tantalum capacitor from
each power supply pin to ground.
The heat sink in this example must have a thermal resistance
See Figure 1. To externally null the offset voltage, connect a
See Figure 1. If no current limit is required, short Pin 1 to Pin
Both the negative and the positive power supplies must be
R
potentiometer between Pins 7 and 10 and leave Pin 6
SA
+Rlim
= ((125°C - 80°C) / .64W) - 65°C/W - .15°C/W
= 70.3 - 65.15
= 5.2°C/W
= ((T
J
Vbe
Isc
- T
potentiometer. Do not connect Pin 7 to -
A
)/P
D
) - (R
JC
) - (R
-Rlim
CS
)
Vbe
Isc
Rev. D 9/06