LT1253C 查看數據表（PDF） - Linear Technology

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LT1253C

Low Cost Dual and Quad Video Amplifiers

Linear Technology 

LT1253/LT1254

TYPICAL PERFOR A CE CHARACTERISTICS

Transient Response

Transient Response

VS = ±5V

AV = 1

RL = 150Ω

RF = 787Ω

VO = 1V

LT1253/54 • TPC16

RF = 562Ω VS = ±5V

RG = 61.9Ω AV = 10

VO = 1.5V RL = 150Ω

LT1253/54 • TPC17

UU W U

APPLICATIO S I FOR ATIO

Power Dissipation

The LT1253/LT1254 amplifiers combine high speed and

large output current drive into very small packages. Be-

cause these amplifiers work over a very wide supply range,

it is possible to exceed the maximum junction temperature

under certain conditions. To insure that the LT1253/

LT1254 are used properly, we must calculate the worst

case power dissipation, define the maximum ambient

temperature, select the appropriate package and then

calculate the maximum junction temperature.

The worst case amplifier power dissipation is the total of

the quiescent current times the total power supply voltage

plus the power in the IC due to the load. The quiescent

supply current of the LT1253/LT1254 has a strong nega-

tive temperature coefficient. The supply current of each

amplifier at 150°C is less than 7mA and typically is only

4.5mA. The power in the IC due to the load is a function of

the output voltage, the supply voltage and load resistance.

The worst case occurs when the output voltage is at half

supply, if it can go that far, or its maximum value if it

cannot reach half supply.

For example, let’s calculate the worst case power dissipa-

tion in a video cable driver operating on a ±12V supply that

delivers a maximum of 2V into 150Ω.

PDMAX = 2 × VS × ISMAX + (VS – VOMAX) × VOMAX/RL

PDMAX = 2 × 12V × 7mA + (12V – 2V) × 2V/150

= 0.168 + 0.133 = 0.301 Watt per Amp

Now if that is the dual LT1253, the total power in the

package is twice that, or 0.602W. We now must calculate

how much the die temperature will rise above the ambient.

The total power dissipation times the thermal resistance of

the package gives the amount of temperature rise. For the

above example, if we use the S8 surface mount package,

the thermal resistance is 150°C/W junction to ambient in

still air.

Temperature Rise = PDMAX × RθJA = 0.602W

× 150°C/W = 90.3°C

The maximum junction temperature allowed in the plastic

package is 150°C. Therefore the maximum ambient al-

lowed is the maximum junction temperature less the

temperature rise.

Maximum Ambient = 150°C – 90.3°C = 59.7°C

Note that this is less than the maximum of 70°C that is

specified in the absolute maximum data listing. In order to

use this package at the maximum ambient we must lower

the supply voltage or reduce the output swing.

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