ADA4522-2 datasheet(21/30 Pages) AD

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Data Sheet

ADA4522-2/ADA4522-4

Rev. B | Page 21 of 30

THERMAL SHUTDOWN

The ADA4522-2/ADA4522-4 have internal thermal shutdown

circuitry for each channel of the amplifier. The thermal shutdown

circuitry prevents internal devices from being damaged by an

overheat condition in the die. Overheating can occur due to a

high ambient temperature, a high supply voltage, and/or high

output currents. As specified in Table 5, take care to maintain

the junction temperature below 150°C.

Two conditions affect junction temperature (TJ): the total power

dissipation of the device (PD) and the ambient temperature

surrounding the package (TA). Use the following equation to

estimate the approximate junction temperature:

TJ = PD × θJA + TA

(1)

where θJA is the thermal resistance between the die and the

ambient environment, as shown in Table 6.

The total power dissipation is the sum of quiescent power of the

device and the power required to drive a load for all channels of

an amplifier. The power dissipation per amplifier (PD_PER_AMP)

for sourcing a load is shown in Equation 2.

PD_PER_AMP = (VSY+ − VSY−) × ISY_PER_AMP + IOUT × (VSY+ − VOUT) (2)

When sinking current, replace (VSY+ − VOUT) in Equation 2 with

(VOUT − VSY−).

Also, take note to include the power dissipation of all channels

of the amplifier when calculating the total power dissipation for

the ADA4522-2/ADA4522-4.

The thermal shutdown circuitry does not guarantee that the device

is to be free of permanent damage if the junction temperature

exceeds 150°C. However, the internal thermal shutdown function

may help avoid permanent damage or reduce the degree of damage.

Each amplifier channel has thermal shutdown circuitry, composed

of a temperature sensor with hysteresis.

As soon as the junction temperature reaches 190°C, the thermal

shutdown circuitry shuts down the amplifier. Note that either

one of the two thermal shutdown circuitries are activated; this

activation disables the channel. When the amplifier is disabled, the

output becomes open state and the quiescent current of the channel

decreases to 0.1 mA. When the junction temperature cools down to

160°C, the thermal shutdown circuitry enables the amplifier and

the quiescent current increases to its typical value.

When overheating in the die is caused by an undesirable excess

amount of output current, the thermal shutdown circuit repeats

its function. The junction temperature keeps increasing until it

reaches 190°C and one of the channels is disabled. Then, the

junction temperature cools down until it reaches 160°C, and

the channel is enabled again. The process then repeats.

INPUT PROTECTION

When either input of the ADA4522-2/ADA4522-4 exceeds

one of the supply rails by more than 300 mV, the ESD diodes

mentioned in the On-Chip Input EMI Filter and Clamp Circuit

section become forward-biased and large amounts of current

begin to flow through them. Without current limiting, this

excessive fault current causes permanent damage to the device.

If the inputs are expected to be subject to overvoltage conditions,

insert a resistor in series with each input to limit the input current

to ±10 mA maximum. However, consider the resistor thermal

noise effect on the entire circuit.

At ±15 V supply voltage, the broadband voltage noise of the

ADA4522-2/ADA4522-4 is approximately 7.3 nV/√Hz (at unity

gain), and a 1 kΩ resistor has thermal noise of 4 nV/√Hz. Adding

a 1 kΩ resistor increases the total noise to 8.3 nV/√Hz.

SINGLE-SUPPLY AND RAIL-TO-RAIL OUTPUT

The ADA4522-2/ADA4522-4 are single-supply amplifiers,

where their input voltage range includes the lower supply rail.

This feature is ideal for applications where the input common-

mode voltage is at the lower supply rail, for example, ground

sensing. On the other hand, the amplifier output is rail to rail.

Figure 72 shows the input and output waveforms of the

ADA4522-2/ADA4522-4 configured as a unity-gain buffer with

a supply voltage of ±15 V. With an input voltage of ±15 V, the

low output voltage tracks the input voltage, whereas the high

output swing clamps/distorts when the input goes out of the

input voltage range (−15 V ≤ IVR ≤ +13.5 V). However, the

device does not exhibit phase reversal.

–10

–20

–5

–15

–10

–20

–5

–15

TIME (400s/DIV)

VSY = ±15V

AV = 1

VIN

VOUT

Figure 72. No Phase Reversal

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