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Advance Information
FS8308
Page 15
April 2003
Single Voltage Operation
This IC requires two separate power supplies to operate. If only one voltage source is
available, ex. use battery to serve as power source, the user can apply the configuration as
shown in the following which is referred to as single voltage operation.
Since there is only one voltage source provided in the so-called single voltage configura-
tion, which is directly connected to V
dd2, one needs to choose a reasonable R value to set
V
dd1 to operate within the safe region, whose requirement is Vdd1 > 0.95V. Keep in mind
that the lower V
dd1 is, the less current this IC will consume, but the poorer crystal buffer
output it drives. In order to balance the trade-off between the current consumption and
crystal buffer driving capability, V
dd1 is suggested to be about 1.1V. Vdd1 vs. Vdd2 for vari-
ous R at fin=470MHz is plotted in the following figure. Note that although smaller resistor
R makes this IC consume more current, the reward is with wider power supply input
range. Typical value of R is recommended to be around 1.6K
Ω..
Single Voltage Characteristic: Vdd1 vs. Vdd2 for Various R
VDD2
VDD1
R
POWER SUPPLY
1.5
2.0
2.5
3.0
3.5
4.0
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
Safe Operation Region
fin=470MHz, Pfin=-10dBm
xin=24MHz, N=4032, R=5
Vdd2 (V)
R=1.2K
R=1.6K
R=1.8K
R=2.0K
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