OPA452FASLASH500G3 datasheet(10/21 Pages) TI1

10 / 21 page

OPA452, 453

SBOS127C

www.ti.com

POWER SUPPLIES

The OPA452 and OPA453 may be operated from power

supplies of

±10V to ±40V, or a total of 80V with excellent

performance. Most behavior remains unchanged throughout

the full operating voltage range. Parameters that vary signifi-

cantly with operating voltage are shown in the Typical Char-

acteristics.

For applications that do not require symmetrical output volt-

age swing, power-supply voltages do not need to be equal.

The OPA452 and OPA453 can operate with as little as 20V

between the supplies or with up to 80V between the supplies.

For example, the positive supply could be set to 70V with the

negative supply at –10V or vice-versa.

The tabs of the DDPAK-7 and TO220 packages are electri-

cally connected to the negative supply (V–), however, these

connections should not be used to carry current. For best

thermal performance, the tab should be soldered directly to

the circuit board copper area (see Heat Sinking section).

POWER DISSIPATION

Internal power dissipation of these op amps can be quite

large. All of the specifications for the OPA452 and OPA453

may change with junction temperature. If the device is not

subjected to internal self-heating, the junction temperature

will be the same as the ambient. However, in practical

applications, the device will self-heat and the junction tem-

perature will be significantly higher than ambient. The follow-

ing calculation can be performed to establish junction tem-

perature as a function of ambient temperature and the

conditions of the application.

Consider the OPA452 in a circuit configuration where the

load is 600

Ω and the output voltage is 20V. The supplies are

±40V and the ambient temperature (T

A) is 40°C. The θJA

for the package plus heat sink is 30

°C/W.

First, the quiescent heating of the op amp is as follows:

PD(internal) = IQ • VS = 6mA • 80V = 480mW

The output current (IO) can be calculated:

IO = VO/RL = 20V/600Ω = 33.33mA

The power being dissipated (PD) in the output transistor of

the amplifier can be calculated:

PD(output stage) = IO • (VS – VO) = 33.3mA • (40 – 20) = 667mW

PD(total) = PD(internal) + PD(output stage) = 480mW + 667mW = 1147mW

The resulting junction temperature can be calculated:

TJ = TA + PD θJA

TJ = 40°C + 1147mW • 30°C/W = 74.4°C

FIGURE 3. DDPAK-7 and TO220-7 Safe Operating Area.

Where,

VO = output voltage

VS = supply voltage

IO = output current

RL = load resistance

TJ = junction temperature (°C)

TA = ambient temperature (°C)

JA = junction-to-air thermal resistance (°C/W)

To estimate the margin of safety in a complete design

(including heat sink), increase the ambient temperature until

the thermal protection is activated. Use worst-case load and

signal conditions. For good reliability, the thermal protection

should trigger more than +35

°C above the maximum ex-

pected ambient condition of your application. This ensures a

maximum junction temperature of +125

°C at the maximum

expected ambient condition.

Operation from a single power supply (or unbalanced power

supplies) can produce even larger power dissipation be-

cause a larger voltage can be impressed across the conduct-

ing output transistor. Consult Application Bulletin SBOA022

at www.ti.com for further information on how to calculate or

measure power dissipation.

Power dissipation can be minimized by using the lowest

possible supply voltage. For example, with a 50mA load, the

output will swing to within 5.0V of the power-supply rails.

Power supplies set to no more than 5.0V above the maxi-

mum output voltage swing required by the application will

minimize the power dissipation.

SAFE OPERATING AREA

The Safe Operating Area (SOA curves, Figure 3) shows the

permissible range of voltage and current. The safe output

current decreases as the voltage across the output transistor

(VS – VO) increases. For further insight on SOA, consult

Application Report SBOA022.

Output short circuits are a very demanding case for SOA. A

short-circuit to ground forces the full power-supply voltage

(V+ or V–) across the conducting transistor and produces a

100

0.1

100

| V

S | – | VO | (V)

SAFE OPERATING AREA

is total thermal

resistance including

junction-to-case.

This graph is for

+125

°C max operating

temperature.

+85

°C, = 20

+85

°C, = 40

+25

°C, = 40

+25

°C, = 3

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