MSK1461 Ver la hoja de datos (PDF) - M.S. Kennedy

Número de pieza

componentes Descripción

Fabricante

MSK1461

HIGH SPEED/VOLTAGE OP AMP

M.S. Kennedy 

APPLICATION NOTES

HEAT SINKING

To select the correct heat sink for your application,

refer to the thermal model and governing equation below.

Thermal Model:

CURRENT LIMIT

The output current of the MSK 1461 is internally lim-

ited to approximately ±750mA by two 0.8Ω 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:

±RSC = [(0.65V/±ILIM) - 0.8Ω]

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.

Governing Equation:

The following schematic illustrates how to connect

each current limit resistor:

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

INPUT OFFSET ADJUST CONNECTION

IN

POWER SUPPLY BYPASSING

Example:

In our example the amplifier application requires the

output to drive a 20 volt peak sine wave across a 400Ω

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.

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 0.1µF ce-

ramic capacitor in parallel with a 4.7µF tantalum capaci-

tor from each power supply pin to ground.

SAFE OPERATING AREA

Any designer who has worked with power operational

1.) Find Driver Power Dissipation

amplifiers is familiar with Safe Operating Area (S.O.A.)

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, worst case TA=+50°C

4.) RθJC = 12°C/W from MSK 1461B Data Sheet

5.) RθCS = 0.15°C/W for most thermal greases

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

6.) Rearrange governing equation to solve for RθSA

need for S.O.A. curves. The only limitation on output

RθSA = ((TJ - TA)/PD) - (RθJC) - (RθCS)

= ((125°C - 50°C) / 5W) - (12°C/W) - (.15°C/W)

≅ 2.85°C/W

power is the junction temperature of the output drive tran-

sistors.

Whenever possible, junction temperature should be

The heat sink in this example must have a thermal

resistance of no more than 2.85°C/W to maintain a junc-

tion temperature of no more than +125°C.

kept below 150°C to ensure

Sinking" for more information

ture calculations.

3

high reliability. See "Heat

involving junction tempera-

Rev. B 8/00

Share Link: