AD5749 datasheet(24/28 Pages) AD

24 / 28 page

AD5749

Rev. 0 | Page 24 of 28

APPLICATIONS INFORMATION

TRANSIENT VOLTAGE PROTECTION

The AD5749 contains ESD protection diodes that prevent damage

from normal handling. The industrial control environment can,

however, subject I/O circuits to much higher transients. To protect

the AD5749 from excessively high voltage transients, external

power diodes and a surge current limiting resistor may be

required, as shown in Figure 35. The constraint on the resistor

value is that during normal operation the output level at IOUT

must remain within its voltage compliance limit of AVDD −

2.75 V and the two protection diodes and resistor must have

appropriate power ratings. Further protection can be added

with transient voltage suppressors if needed.

AD5749

AVDD

IOUT

RLOAD

Figure 35. Output Transient Voltage Protection

THERMAL CONSIDERATIONS

It is important to understand the effects of power dissipation

on the package and how it affects junction temperature. The

internal junction temperature should not exceed 125°C. The

AD5749 is packaged in a 32-lead, 5 mm × 5 mm LFCSP pack-

age. The thermal impedance, θJA, is 28°C/W. It is important that

the devices not be operated under conditions that cause the

junction temperature to exceed its limit. Worst-case conditions

occur when the AD5749 is operated from the maximum AVDD

(55 V) and driving the maximum current (24 mA) directly to

ground. The quiescent current of the AD5749 should also be

taken into account, nominally ~4 mA.

The calculations in Table 12 estimate maximum power

dissipation under these worst-case conditions, and determine

maximum ambient temperature based on this. These figures

assume that proper layout and grounding techniques are

followed to minimize power dissipation, as outlined in the

Layout Guidelines section.

Table 12. Thermal and Supply Considerations

Considerations

32-Lead LFCSP Package

Maximum allowed power dissipation when operating at an ambient

temperature of 85°C

125

−

JMAX

Maximum allowed ambient temperature when operating from a supply of

55 V and driving 24 mA directly to ground (include 4 mA for internal AD5749

current)

TJMAX − (PD × θJA) = 125 − ((55 × 0.028) × 28) = 81.8°C

Maximum allowed supply voltage when operating at an ambient

temperature of 85°C and driving 24 mA directly to ground

()

028

125

−

JMAX

AD5749 Datasheet(PDF) 24 Page - Analog Devices

AD5749 Datasheet(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL