LT1212 Linear Technology Corporation, LT1212 Datasheet - Page 13

• Manufacturer Part Number: LT1212
• Description: 14mhz, 7v/?s, Single Supply Dual And Quad Precision Op Amps
• Manufacturer: Linear Technology Corporation

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 F) within an
inch of the pin. When driving heavy loads and for good
settling time, an additional 4.7 F 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:
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.
A
PPLICATI
I
V
SMAX
S
is the total supply voltage.
= 2.5 + 0.036 • (V
O
U
S
I FOR ATIO
U
S
– 5) in mA
W
U
For example, calculate the worst case power dissipation
while operating on 15V supplies and driving a 500 load.
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.
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.
That means the SO quad can only be operated at or below
64 C on 15V supplies with a 500 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:
PART
LT1211MJ8
LT1211CN8
LT1211CS8
LT1212CN
LT1212CS
I
P
P
Temperature Rise = P
Maximum Ambient = 150 C – 86 C = 64 C
1. The maximum ambient is 70 C or 125 C depending
2. The load is 500 , includes the feedback resistors.
3. The output can be anywhere between the supplies.
SMAX
DMAX
DMAX
on the part rating.
= 2.5 + 0.036 • (30 – 5) = 3.4mA
= 2 • V
= 2 • 15V 3.4mA + (15V – 7.5V) • 7.5V/500
= 0.102 + 0.113 = 0.215W per Amp
MAX SUPPLIES
25.2V or 18.0V
20.3V or 17.1V
21.0V or 17.8V
17.3V or 14.4V
19.5V or 16.4V
S
• I
SMAX
= 86 C
DMAX
+ (V
LT1211/LT1212
•
S
– V
JA
= 0.860W • 100 C/W
OMAX
MAX POWER AT MAX T
1143mW
) • V
500mW
800mW
533mW
800mW
OMAX
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A