AD1940/AD1941
Rev. B | Page 34 of 36
There are two specifications that should be taken into
consideration when choosing a regulator transistor. First, the
transistor’s current amplification factor (h
FE
or beta) should be
at least 100. Second, the transistor’s collector needs to be able to
dissipate the heat generated when regulating from 3.3 V or 5 V
to 2.5 V. The maximum current draw of the AD1940/AD1941 is
163 mA (maximum digital current + maximum PLL current).
The equations for the minimum power dissipation specs for
both 3.3 V and 5 V follow:
(5 V – 2.5 V) × 163 mA = 480 mW
(3.3 V – 2.5 V) × 163 mA = 130 mW
If the regulator is not used in the design, VREF, VDRIVE, and
VSENSE can be tied to ground. VSUPPLY should be connected
to the same or higher potential as the VDD pin.
