V

LOGIC

V

OUT

CMOS

OPA551

Logic

Ground

47kΩ

HP5082-2835

Flag

80 µA to

160 µA

HCT

OPA551

Logic

Ground

V

OUT

+5V

27kΩ

OPA551, OPA552

SBOS100B – JULY 1999 – REVISED JANUARY 2016

www.ti.com

Feature Description (continued)

7.3.4 Thermal Protection

The OPA55x has thermal shutdown circuitry that protects the amplifier from damage caused by overload

conditions. The thermal protection circuitry disables the output when the junction temperature reaches

approximately 160°C, allowing the device to cool. When the junction temperature cools to approximately 140°C,

the output circuitry is automatically re-enabled.

The thermal shutdown function is not intended to replace proper heat sinking. Activation of the thermal shutdown

circuitry is an indication of excessive power dissipation or an inadequate heat sink. Continuously running the

amplifier into thermal shutdown can degrade reliability.

The thermal shutdown indicator (flag) pin can be monitored to determine if shutdown is occurring. During normal

operation, the current output from the flag pin is typically 50 nA. During shutdown, the current output from the

flag pin increases to 120

μA (typical). This current output allows for easy interfacing to external logic. Refer to

Figure 25 and Figure 26 for two examples that implement this function.

HCT logic has relatively well-controlled logic level. A properly chosen resistor value can ensure proper logic high level

throughout the full range of flag output current.

Figure 25. Interfacing With HCT Logic

Interface to virtually any CMOS logic gate by choosing resistor value that provides a guaranteed logic high voltage

with the minimum (80 µA) flag current. A diode clamp to the logic supply voltage assures that the CMOS is not

damaged by overdrive.

Figure 26. Interfacing With CMOS Logic

7.4 Device Functional Modes

The OPA551 and OPA552 have a single functional mode. The device is operational when the power supply is

above 8 V and the junction temperature is below 160°C.

12

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