ADA4522-4ARUZ-R7 datasheet(22/32 Pages) AD

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ADA4522-1/ADA4522-2/ADA4522-4

Data Sheet

Rev. E | Page 22 of 32

ON-CHIP INPUT EMI FILTER AND CLAMP CIRCUIT

Figure 72 shows the input EMI filter and clamp circuit. The

ADA4522-1/ADA4522-2/ADA4522-4 have internal ESD

protection diodes (D1, D2, D3, and D4) that are connected

between the inputs and each supply rail. These diodes protect

the input transistors in the event of electrostatic discharge and

are reverse biased during normal operation. This protection

scheme allows voltages as high as approximately 300 mV

beyond the rails to be applied at the input of either terminal

without causing permanent damage. See Table 5 in the Absolute

Maximum Ratings section for more information.

The EMI filter is composed of two 200 Ω input series resistors

(RS1 and RS2), two common-mode capacitors (CCM1 and CCM2),

and a differential capacitor (CDM). These RC networks set the

−3 dB low-pass cutoff frequencies at 50 MHz for common-

mode signals, and at 33 MHz for differential signals. After the

EMI filter, back to back diodes (D5 and D6) are added to protect

internal circuit devices from high voltage input transients. Each

diode has about 1 V of forward turn on voltage. See the Large

Signal Transient Response section for more information on the

effect of high voltage input transient on the ADA4522-1/

ADA4522-2/ADA4522-4.

As specified in the Absolute Maximum Ratings section (see

Table 5), the maximum input differential voltage is limited to

±5 V. If more than ±5 V is applied, a continuous current larger

than ±10 mA flows through one of the back to back diodes.

This current compromises long-term reliability and can cause

permanent damage to the device.

V+

+IN x

–IN x

V–

RS1

200Ω

RS2

200Ω

CCM1

CDM

CCM2

NOTES

1. THE INPUTS ARE +IN x/–IN x ON THE ADA4522-2

AND ADA4522-4, AND +IN/–IN ON THE ADA4522-1.

Figure 72. Input EMI Filter and Clamp Circuit

THERMAL SHUTDOWN

The ADA4522-1/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 ADA4522-1/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

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 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.

ADA4522-4ARUZ-R7 Datasheet(PDF) 22 Page - Analog Devices

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