Data Sheet

ADR3625

THEORY OF OPERATION

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Rev. 0 | 14 of 21

The ADR3625 incorporates a proprietary low noise design and ad-

vanced curvature correction technology. Combined with micropower

design techniques the ADR3625 has unmatched performance.

The circuit shown in Figure 39 shows the ADR3625 simplified

schematic.

Figure 39. ADR3625 Simplified Schematic

POWER DISSIPATION

While the ADR3625 is a micropower voltage reference, it is capable

of sourcing 50 mA and sinking current up to 10 mA of load current

at room temperature across the rated input voltage range. However,

when used in applications subject to high ambient temperatures,

the input voltage and load current must be monitored carefully to

ensure that the device does not exceed its maximum allowable

power dissipation. To calculate the maximum allowable power dissi-

pation of the device, use the following equation:

PD=TJ−TAθJA

where:

PD is the device power dissipation.

TJ is the device junction temperature.

TA is the ambient temperature.

The ADR3625 has a thermal resistance of 132.5°C/W for the

8-lead MSOP. A curve that illustrates allowed power dissipation

vs. temperature for the MSOP is shown in Figure 40. The power

dissipation of the ADR3625 as a function of the input voltage is

shown in Figure 41. The top curve shows power dissipation with a

50 mA load, and the bottom curve shows power dissipation with no

load. When operated within its specified limits of VIN = 16 V and

sourcing 50 mA, the ADR3625 consumes about 800 mW at room

temperature. The power derating curve in Figure 40 shows that

the ADR3625 can only safely dissipate 120 mW at 125°C, which

is less than its maximum power output. Care must be taken when

designing the circuit so that the maximum junction temperature is

not exceeded. For best performance, keep the junction temperature

less than 150°C.

The ADR3625 includes output current-limit circuitry, as well as

thermal limit circuitry, to protect the reference from damage in the

event of excessive power dissipation. The ADR3625 is protected

from damage by a thermal shutdown circuit. However, changes

in performance can occur as a result of operating at above the

maximum rating.

Figure 40. Maximum Allowed Power Dissipation

Figure 41. Typical Power Dissipation

The safe operating area is the voltage, current, and temperature

conditions where the device can operate reliably (see Figure 42).

The safe operating area takes into account the ambient tempera-

ture and power dissipated in the 8-lead MSOP.

Figure 42. Safe Operating Area