OPA569 datasheet(15/28 Pages) TI1

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OPA569

SBOS264A

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RAIL TO RAIL INPUT RANGE

The input common-mode voltage range of the OPA569

extends 100mV beyond the supply rails. This is achieved by

a complementary input stage with an N-channel input differ-

ential pair in parallel with a P-channel differential pair. The

N-channel input pair is active for input voltages close to the

positive rail while the P-channel input pair is active for input

voltages close to the negative rail. The transition point is

typically at (V+) – 1.3V, and there is a small transition region

around the switching point where both transistors are on. It

is important to note that the two input pairs can have offsets

of different signs and magnitudes. Therefore, as the transi-

tion point is crossed, the offset of the amplifier changes. This

offset shift accounts for the reduced common-mode rejection

ratio over the full input common-mode range.

OUTPUT PROTECTION

Reactive and EMF-generating loads can return load current

to the amplifier, causing the output voltage to exceed the

power-supply voltage. This damaging condition can be

avoided with clamp diodes from the output terminal to the

power supplies, as shown in Figure 6. Schottky rectifier

diodes with a 3A or greater continuous rating are recom-

mended.

THERMAL FLAG PIN

The OPA569 has thermal sensing circuitry that provides a

warning signal when the die temperature exceeds safe limits.

Unless the Thermal Flag is connected to the Enable pin,

when this flag is triggered, the part continues to operate even

FIGURE 6. Output Protection Diode.

OPA569

Output Protection Diode

Current

Limit

Set

SET

12,

17,

–In

+In

14,

–V

Enable Pin

14,

Thermal

Flag Pin

Disable

AND

OPA569

FIGURE 7. Enable/Shutdown Control Using Thermal Flag Pin

and External Control Signal.

though the junction temperature exceeds 150

°C. This allows

maximum usable operation in very harsh conditions but

degrades reliability. The Thermal Flag pin can be used to

provide for orderly system shutdown before failure occurs. It

can be also used to evaluate the thermal environment to

determine need for and appropriate design of a shutdown

mechanism.

The thermal flag output signal is from a CMOS logic gate that

switches from V+ to V– to indicate that the amplifier is in

thermal limit. This flag output pin can source and sink up to

µA. The Thermal Flag pin is HIGH during normal opera-

tion. Power dissipated in the amplifier will cause the junction

temperature to rise. When the junction temperature exceeds

150

°C, the Thermal Flag pin will go LOW, and remain LOW

until the amplifier has cooled to 130

°C. Despite this hyster-

esis, with a method of orderly shutdown, the Thermal Flag

pin can cycle on and off, depending on load and signal

conditions. This limits the dissipation of the amplifier but may

have an undesirable effect on the load. This temperature

range exceeds the absolute maximum temperature rating

and is intended to protect the device from excessive tem-

peratures that can cause damage. Brief and infrequent

excursions in this temperature range are likely to be toler-

ated, but are not recommended.

It is possible to connect the Thermal Flag pin directly to the

Enable pin for automatic shutdown protection. When both

thermal shutdown and the amplifier enable/disable functions

are desired, the externally generated control signal and the

Thermal Flag pin outputs should be combined with an AND

gate, as shown on Figure 7. The temperature protection was

designed to protect against overload conditions. It was not

intended to replace proper heatsinking. Continuously running

the OPA569 in and out of thermal shutdown will degrade

reliability.

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