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LT1630/LT1631

16301fa

applicaTions inForMaTion

VBIAS

+IN

–IN

OUT

V–

V+

Q12

Q14

1630/31 F01

225

V–

Q11

Q13

Q15

BUFFER

AND

OUTPUT BIAS

Figure 1. LT1630 Simplified Schematic Diagram

Power Dissipation

The LT1630/LT1631 amplifiers combine high speed and

large output current drive in a small package. Because

the amplifiers operate over a very wide supply range, it

is possible to exceed the maximum junction temperature

of 150°C in plastic packages under certain conditions.

Junction temperature, TJ, is calculated from the ambient

temperature, TA, and power dissipation, PD, as follows:

LT1630CN8: TJ = TA + (PD • 130°C/W)

LT1630CS8: TJ = TA + (PD • 190°C/W)

LT1631CS: TJ = TA + (PD • 150°C/W)

The power dissipation in the IC is the function of the

supply voltage, output voltage and load resistance. For

a given supply voltage, the worst-case power dissipation

PDMAX occurs at the maximum supply current and when

the output voltage is at half of either supply voltage (or the

maximumswingiflessthan1/2supplyvoltage).Therefore

PDMAX is given by:

PDMAX = (VS • ISMAX) + (VS/2)2/RL

To ensure that the LT1630/LT1631 are used properly,

calculate the worst-case power dissipation, get the ther-

mal resistance for a chosen package and its maximum

junction temperature to derive the maximum ambient

temperature.

Example: An LT1630CS8 operating on ±15V supplies and

driving a 500Ω, the worst-case power dissipation per

amplifier is given by:

PDMAX = (30V • 4.75mA) + (15V – 7.5V)(7.5/500)

= 0.143 + 0.113 = 0.256W

If both amplifiers are loaded simultaneously, then the

total power dissipation is 0.512W. The SO-8 package has

a junction-to-ambient thermal resistance of 190°C/W in

still air. Therefore, the maximum ambient temperature that

the part is allowed to operate is:

TA = TJ – (PDMAX • 190°C/W)

TA = 150°C – (0.512W • 190°C/W) = 53°C

For a higher operating temperature, lower the supply

voltage or use the DIP package part.

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