参数资料
型号: 5962-9050001HX
厂商: MS KENNEDY CORP
元件分类: 运算放大器
英文描述: OP-AMP, 5000 uV OFFSET-MAX, 1200 MHz BAND WIDTH, DFM14
文件页数: 3/5页
文件大小: 305K
代理商: 5962-9050001HX
1.) Find Driver Power Dissipation
PD = [(quiescent current) x (+VS - (-VS))] +
[(+VS-VO) x IOUT]
= [(50mA) x (80V)] + [(20V) x (0.05A)]
= 4W + 1.0W
= 5Watts
2.) For conservative design, set TJ=+125°C.
3.) For this example, TA=+25°C
4.) RθJC = 16°C/W from MSK 1461B 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 - 25°C) / 5W) - (16°C/W) - (0.15°C/W)
3.85°C/W
The heat sink in this example must have a thermal
resistance of no more than 3.85°C/W to maintain a junction
temperature of no more than +125°C.
APPLICATION NOTES
HEAT SINKING
To select the correct heat sink for your application,
refer to the thermal model and governing equation below.
Thermal Model:
Governing Equation:
CURRENT LIMIT
The output current of the MSK 1461 is internally lim-
ited to approximately ±750mA by two 0.8 internal cur-
rent limit resistors. Additional current limit can be achieved
through the use of two external current limit resistors.
One resistor (+RSC) limits the positive output current and
the other (-RSC) limits the negative output current. The
value of the current limit resistors can be determined as
follows:
Since the 0.65V term is obtained from the base to
emitter voltage drop of a bipolar transistor, the equation
only holds true for +25°C operation. As case tempera-
ture increases, the 0.65V term will decrease making the
actual current limit set point decrease slightly.
±RSC = [(0.65V/±ILIM) - 0.8]
TJ=PD x (RθJC + RθCS + RθSA) + 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:
In our example the amplifier application requires the
output to drive a 20 volt peak sine wave across a 400
load for 50mA of peak output current. For a worst case
analysis we will treat the 50mA peak output current as a
D.C. output current. The power supplies shall be set to
±40VDC.
The following schematic illustrates how to connect
each current limit resistor:
IN
Any designer who has worked with power operational
amplifiers is familiar with Safe Operating Area (S.O.A.)
curves. S.O.A. curves are a graphical representation of
the following three power limiting factors of any bipolar
transistor output op-amp.
1. Wire Bond Current Carrying Capability
2. Transistor Junction Temperature
3. Secondary Breakdown Limitations
Since the MSK 1461 utilizes a MOSFET output, there
are no secondary breakdown limitations and therefore no
need for S.O.A. curves. The only limitation on output
power is the junction temperature of the output drive tran-
sistors.
Whenever possible, junction temperature should be kept
below 150°C to ensure high reliability. See "Heat Sink-
ing" for more information involving junction temperature
calculations.
SAFE OPERATING AREA
Both the negative and the positive power supplies must
be effectively decoupled with a high and low frequency
bypass circuit to avoid power supply induced oscillation.
An effective decoupling scheme consists of a 0.1F ce-
ramic capacitor in parallel with a 4.7F tantalum capaci-
tor from each power supply pin to ground.
POWER SUPPLY BYPASSING
INPUT OFFSET ADJUST CONNECTION
Rev. C 6/02
3
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