ADA4522-4ARZ-R7 datasheet(23/33 Pages) AD

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Data Sheet

ADA4522-1/ADA4522-2/ADA4522-4

THEORY OF OPERATION

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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 sur-

rounding 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

ADA4522-1/ADA4522-2/ADA4522-4.

The thermal shutdown circuitry does not guarantee the device 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 is 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 ADA4522-1/ADA4522-2/ADA4522-4 ex-

ceeds 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 a ±15 V supply voltage, the broadband voltage noise of the

ADA4522-1/ADA4522-2/ADA4522-4 is approximately 5.8 nV/√Hz

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

Adding a 1 kΩ resistor increases the total noise to 7 nV/√Hz.

SINGLE-SUPPLY AND RAIL-TO-RAIL OUTPUT

The ADA4522-1/ADA4522-2/ADA4522-4 are single-supply amplifi-

ers, 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.

Conversely, the amplifier output is rail to rail. Figure 73 shows

the input and output waveforms of the ADA4522-1/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.

Figure 73. Input and Output Waveforms, No Phase Reversal

LARGE SIGNAL TRANSIENT RESPONSE

When the ADA4522-1/ADA4522-2/ADA4522-4 are configured in a

closed-loop configuration with a large input transient (for example,

a step input voltage), the internal back to back diodes may turn on.

Consider a case where the amplifier is in unity-gain configuration

with a step input waveform. This case is shown in Figure 74.

The noninverting input is driven by an input signal source and the

inverting input is driven by the output of the amplifier. The maximum

amplifier output current depends on the input step function and the

external source resistance at the input terminals of the amplifier.

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