Data Sheet

ADR3625

THEORY OF OPERATION

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Rev. 0 | 15 of 21

INTERNAL PROTECTION

The ADR3625 has two internal protection circuits for monitoring the

output current and internal junction temperature.

The ADR3625 has a current-limit circuit that limits the output source

current in the event of a short circuit from the VOUT FORCE pin to

ground. The limit is set to 90 mA (typical) and does not vary much

over temperature or input voltage.

An overtemperature shutdown circuit disables the output source

current when the internal junction temperature reaches 178°C.

There is 3°C of hysteresis. Once the junction temperature reduces

beyond the hysteresis, the output drive circuit reenables. Degrada-

tion can occur or reliability can be affected when the junction

temperature of the device exceeds 150°C.

LONG-TERM DRIFT

The stability of a precision signal path over its lifetime, or between

calibration procedures, is dependent on the long-term stability of

the analog components in its path, such as op amps, references,

and data converters. To help system designers predict the long-

term drift of the circuits that use the ADR3625, Analog Devices

measured the output voltage of multiple units for more than

4500 hours (more than 6 months) using a high precision measure-

ment system, including an ultrastable oil bath. To replicate the

real-world system performance, the devices under test (DUTs) were

soldered onto an FR4 PCB using a standard reflow profile (as

defined in the JEDEC J-STD-020D standard), rather than testing

them in sockets. This manner of testing is important because

expansion and contraction of the PCB can apply stress to the IC

package and contribute to shifts in the offset voltage.

Note that early life drift (0 hours to 250 hours) accounts for 50%

of the total drift observed over 4500 hours, as shown in Figure 43.

The first 1000 hours account for the 80% of the total drift, and the

remaining 3500 hours account for the remaining 20% of the drift.

Thus, the early life drift is the dominant contributor, whereas the

drift after 1000 hours is significantly lower.

Figure 43. Long-Term Drift

THERMAL HYSTERESIS

In addition to stability over time, as described in the Long-Term

Drift section, it is useful to know the thermal hysteresis, that is, the

stability vs. cycling of temperature. Thermal hysteresis is an impor-

tant parameter because it tells the system designer how closely the

signal returns to its starting amplitude after the ambient temperature

changes and the subsequent return to room temperature. Figure 44

shows the change in output voltage as the temperature cycles four

times from room temperature to +125°C to −40°C and back to room

temperature.

Other than the first full cycle, the output hysteresis is typically

−7 ppm. The histogram in Figure 45 shows that the hysteresis

is larger when the device cycles through only a half cycle, from

room temperature to 125°C and back to room temperature, typically

15 ppm.

Figure 44. Change in Output Voltage over Four Full Temperature Cycle

Figure 45. Output Voltage Hysteresis Histogram (−40°C to +125°C)