OPA548 datasheet(20/36 Pages) TI

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ENABLE AND E/D Com

THERMAL PROTECTION

OPA454

-IN

+IN

V-

V+

E/DCom

E/D

OUT

DVDD

(DigitalSupply)

5VLogic

V+

(PositiveOpAmpSupply)

(NegativeOpAmpSupply)

CURRENT LIMIT

800

200

400

1000

(ms)

-120

-20

-40

-60

-80

-100

140

120

100

-20

600

OUT

FLAG

100kW

10kW

E/DCom

-50V

+50V

FLAG

Flag

OUT

1MW

625W

+2.5V

10HzSquareWave

OUT

V+

-IN

+IN

V-

OPA454

SBOS391 – DECEMBER 2007

avoided to maximize reliability. It is always best to

provide proper heat-sinking (either by a physical plate

or by airflow) to remain considerably below the

If left disconnected, E/D Com is pulled near V–

thermal shutdown threshold. For longest operational

(negative supply) by an internal 10

µA current source.

life of the device, keep the junction temperature

When left floating, ENABLE is held approximately 2V

below +125

°C.

above E/D Com by an internal 1

µA source. Even

though active operation of the OPA454 results when

the ENABLE and E/D Com pins are not connected, a

moderately fast, negative-going signal capacitively

Figure 68 shows the thermal shutdown behavior of a

coupled to the ENABLE pin can overpower the 1

µA

socketed OPA454 that internally dissipates 1W.

pull-up current and cause device shutdown. This

Unsoldered and in a socket,

JA of the DDA package

behavior can appear

oscillation

and

is typically +128

°C/W. With the socket at +25°C, the

encountered first near extreme cold temperatures. If

output stage temperature rises to the shutdown

the enable function is not used, a conservative

temperature of +150

°C, which triggers automatic

approach is to connect ENABLE through a 30pF

thermal shutdown of the device. The device remains

capacitor to a low impedance source. Another

in thermal shutdown (output is in a high-impedance

alternative is the connection of an external current

state) until it cools to +130

°C where it again is

source from V+ (positive supply) sufficient to hold the

powered. This thermal protection hysteresis feature

enable level above the shutdown threshold. Figure 67

typically prevents the amplifier from leaving the safe

shows a circuit that connects ENABLE and E/D Com.

operating area, even with a direct short from the

Choosing RP to be 1MΩ with a +50V positive power

output to ground or either supply. The rail-to-rail

supply voltage results in IP = 50µA.

supply voltage at which catastrophic breakdown

occurs is typically 135V at +25

°C. However, the

absolute maximum specification is 120V, and the

OPA454 should not be allowed to exceed 120V under

any condition. Failure as a result of breakdown,

caused by spiking currents into inductive loads

(particularly with elevated supply voltage), is not

prevented by the thermal protection architecture.

Figure 67. ENABLE and E/D Com

Figure 24 and Figure 48 to Figure 50 show the

current limit behavior of the OPA454. Current limiting

is accomplished by internally limiting the drive to the

output transistors. The output can supply the limited

current continuously, unless the die temperature rises

to +150

°C, which initiates thermal shutdown. With

adequate heat-sinking, and use of the lowest possible

supply voltage, the OPA454 can remain in current

limit continuously without entering thermal shutdown.

Although qualification studies have shown minimal

parametric shifts induced by 400 hours of thermal

shutdown cycling, this mode of operation should be

Figure 68. Thermal Shutdown

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