Datasheet

ADA4522-1/ADA4522-2/ADA4522-4 Data Sheet
Rev. F | Page 22 of 33
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
(R
S1
and R
S2
), two common-mode capacitors (C
CM1
and C
CM2
),
and a differential capacitor (C
DM
). 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–
R
S1
200
R
S2
200
D1
D2 D5 D6
D4
D3
C
CM1
C
DM
C
CM2
13168-069
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 (T
J
): the total power
dissipation of the device (P
D
) and the ambient temperature
surrounding the package (T
A
). Use the following equation to
estimate the approximate junction temperature:
T
J
= P
D
× θ
JA
+ T
A
(1)
where θ
JA
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 (P
D_PER_AMP
)
for sourcing a load is shown in Equation 2.
P
D_PER_AMP
= (V
SY+
− V
SY−
) × I
SY_PER_AMP
+ I
OUT
× (V
SY+
− V
OUT
) (2)
When sinking current, replace (V
SY+
− V
OUT
) in Equation 2 with
(V
OUT
− V
SY−
).
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.
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