Datasheet AD8614, AD8644 (Analog Devices) - 10

link to page 9 link to page 10 link to page 10
AD8614/AD8644 INPUT OVERVOLTAGE PROTECTION
To calculate the internal junction temperature of the AD8614/AD8644, the following formula can be used: As with any semiconductor device, whenever the condition exists for the input to exceed either supply voltage, attention TJ = PDISS × θJA + TA needs to be paid to the input overvoltage characteristic. As an where: overvoltage occurs, the amplifier can be damaged, depending TJ is the AD8614/AD8644 junction temperature. on the voltage level and the magnitude of the fault current. PDISS is the AD8614/AD8644 power dissipation. When the input voltage exceeds either supply by more than θJA is the AD8614/AD8644 junction-to-ambient package thermal 0.6 V, internal pin junctions energize, allowing current to flow resistance. from the input to the supplies. Observing Figure 26, the TA is the ambient temperature of the circuit. AD8614/AD8644 have 1.5 kΩ resistors in series with each input, which helps to limit the current. This input current is not The power dissipated by the device can be calculated as: inherently damaging to the device as long as it is limited to PDISS = ILOAD × (VS – VOUT) 5 mA or less. If the voltage is large enough to cause more than where: 5 mA of current to flow, an external series resistor should be added. The size of this resistor is calculated by dividing the ILOAD is the AD8614/AD8644 output load current. maximum overvoltage by 5 mA and subtracting the internal VS is the AD8614/AD8644 supply voltage. 1.5 kΩ resistor. For example, if the input voltage could reach 100 V, VOUT is the AD8614/AD8644 output voltage. the external resistor should be (100 V ÷ 5 mA) – 1.5 kΩ = 18.5 kΩ. Figure 27 provides a convenient way to determine if the device This resistance should be placed in series with either or both is being overheated. The maximum safe power dissipation can inputs if they are subjected to the overvoltages. be found graphically, based on the package type and the ambient
OUTPUT PHASE REVERSAL
temperature around the package. By using the previous equation, it is a simple matter to see if PDISS exceeds the device’s power derating The AD8614/AD8644 are immune to phase reversal as long as curve. To ensure proper operation, it is important to observe the the input voltage is limited to within the supply rails. Although recommended derating curves shown in Figure 27. the device’s output does not change phase, large currents due to
1.5
input overvoltage can result, damaging the device. In applica- tions where the possibility of an input voltage exceeding the
) W ( 14-LEAD SOIC PACKAGE
supply voltage exists, overvoltage protection should be used, as
N θJA = 120°C/W IO
described in the previous section.
T A 1.0 IP POWER DISSIPATION ISS 14-LEAD TSSOP PACKAGE D θJA = 180°C/W R
The maximum power that can be safely dissipated by the
E W
AD8614/AD8644 is limited by the associated rise in junction
PO 0.5
temperature. The maximum safe junction temperature is 150°C,
M 5-LEAD SOT-23 PACKAGE IMU θJA = 230°C/W
and should not be exceeded or device performance could suffer.
X
If this maximum is momentarily exceeded, proper circuit
MA
27 0 5- operation is restored as soon as the die temperature is reduced. 48
0
06
–35 –15 5 25 45 65 85
Leaving the device in an overheated condition for an extended
AMBIENT TEMPERATURE (°C)
period can result in permanent damage to the device. Figure 27. Maximum Power Dissipation vs. Temperature (5-Lead and 14-Lead Package Types)
UNUSED AMPLIFIERS
It is recommended that any unused amplifiers in the quad package be configured as a unity-gain follower with a 1 kΩ feedback resistor connected from the inverting input to the output, and the noninverting input tied to the ground plane. Rev. B | Page 10 of 16 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONFIGURATIONS TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ELECTRICAL CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION OUTPUT SHORT-CIRCUIT PROTECTION INPUT OVERVOLTAGE PROTECTION OUTPUT PHASE REVERSAL POWER DISSIPATION UNUSED AMPLIFIERS CAPACITIVE LOAD DRIVE DIRECT ACCESS ARRANGEMENT A ONE-CHIP HEADPHONE/MICROPHONE PREAMPLIFIER SOLUTION OUTLINE DIMENSIONS ORDERING GUIDE