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LT1211/LT1212

APPLICATI

I FOR ATIO

Supply Voltage

The LT1211/LT1212 op amps are fully functional and all

internal bias circuits are in regulation with 2.2V of supply.

The amplifiers will continue to function with as little as

1.5V, although the input common-mode range and the

phase margin are about gone. The minimum operating

supply voltage is guaranteed by the PSRR tests which are

done with the input common mode equal to 500mV and a

minimum supply voltage of 2.5V. The LT1211/LT1212 are

guaranteed over the full – 55

°C to 125°C range with a

minimum supply voltage of 2.5V.

The positive supply pin of the LT1211/LT1212 should be

bypassed with a small capacitor (about 0.01

µF) within an

inch of the pin. When driving heavy loads and for good

settling time, an additional 4.7

µF capacitor should be

used. When using split supplies, the same is true for the

negative supply pin.

Power Dissipation

The LT1211/LT1212 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 LT1211/

LT1212 are used properly, 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 LT1211/LT1212 has a positive tem-

perature coefficient. The maximum supply current of each

amplifier at 125

°C is given by the following formula:

ISMAX = 2.5 + 0.036 • (VS – 5) in mA

VS is the total supply voltage.

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, calculate the worst case power dissipation

while operating on

±15V supplies and driving a 500Ω load.

ISMAX = 2.5 + 0.036 • (30 – 5) = 3.4mA

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

PDMAX = 2 • 15V × 3.4mA + (15V – 7.5V) • 7.5V/500

= 0.102 + 0.113 = 0.215W per Amp

If this is the quad LT1212, the total power in the package

is four times that, or 0.860W. Now 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 this

example, in the SO surface mount package, the thermal

resistance is 100

°C/W junction-to-ambient in still air.

Temperature Rise = PDMAX • θJA = 0.860W • 100°C/W

= 86

°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 – 86°C = 64°C

That means the SO quad can only be operated at or below

°C on ±15V supplies with a 500Ω load.

As a guideline to help in the selection of the LT1211/

LT1212, the following table describes the maximum sup-

ply voltage that can be used with each part based on the

following assumptions:

1. The maximum ambient is 70

°C or 125°C depending

on the part rating.

2. The load is 500

Ω, includes the feedback resistors.

3. The output can be anywhere between the supplies.

PART

MAX SUPPLIES

MAX POWER AT MAX TA

LT1211MJ8

19.5V or

±16.4V

500mW

LT1211CN8

25.2V or

±18.0V

800mW

LT1211CS8

20.3V or

±17.1V

533mW

LT1212CN

21.0V or

±17.8V

1143mW

LT1212CS

17.3V or

±14.4V

800mW

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