MSK3554 Просмотр технического описания (PDF) - M.S. Kennedy

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MSK3554

HIGH SPEED, WIDEBAND OPERATIONAL AMPLIFIER

M.S. Kennedy 

APPLICATION NOTES

HEAT SINKING

Refer to the following thermal model and governing equa-

tions to determine appropriate heat sinking for your application.

Thermal Model:

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

= ((125°C - 90°C) / .64W) - 37°C/W - .15°C/W

= 54.7 - 37.15

= 17.54°C/W

The heat sink in this example must have a thermal resistance

of no more than 17.54°C/W to maintain a junction temperature

of no more than +125°C.

OFFSET NULL

Typically, the MSK 3554(B) has an input offset voltage of

less than ±0.5mV. If it is desirable to adjust the offset closer

to "zero", or to a value other than "zero", the circuit below is

recommended. Rp should be a ten-turn 20KΩ potentiometer.

Typical offset adjust is ±20mV.

Governing Equation:

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:

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 occurs 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 8 VDC output voltage.

COMPENSATION

The compensation capacitor is connected between pins 1

and 3 and is used to optimize bandwidth and slew rate while

maintaining circuit stability. The effect of compensation ca-

pacitance can be seen in the Bode Plot under the Typical Perfor-

mance Curves. As closed loop gain increases, compensation

capacitance can decrease and higher slew rates and wider band-

widths will be realized. See the component selection table for

recommended values of input and feedback resistance as well

as feedback capacitance and compensation capacitance.

1.) Find Driver Power Dissipation

PD = (VCC-VO) (VO/RL)

= (16V-8V) (8V/100Ω)

= .64W

2.) For conservative design, set TJ=+125°C

3.) For this example, worst case TA=+90°C

4.) RθJC = 37°C/W from MSK 3554B Data Sheet

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

6.) Rearrange governing equation to solve for RθSA

GAIN

-1

-10

-100

follower

COMPONENT SELECTION TABLE

Rin

Rfb

Cfb

5.6KΩ

5.6KΩ

2.0pF

560Ω

5.6KΩ

1.2pF

100Ω

10KΩ

0.0pF

0Ω

0Ω

0pF

Ccomp

10pF

10pF

0.0pF

12pF

3

Rev. B 7/00

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