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AD9866
transistors remain in the active region during peak load
currents. The gain of the secondary path, G, and the TxDAC's
standing current, I, can be set using the following equation:
IOUT
+ 3 mA = G × I
PK
The voltage output driver exhibits a high output impedance if
the bias currents for the npn transistors are removed. This
feature is advantageous in half-duplex applications (for
example, power lines) in which the Tx output driver must go
into a high impedance state while in Rx mode. If the AD9866 is
configured for the half-duplex mode (MODE = 0), the IAMP,
TxDAC, and interpolation filter are automatically powered
down after a Tx burst (via TXEN), thus placing the Tx driver
into a high impedance state while reducing its power
consumption.
IAMP CURRENT CONSUMPTION CONSIDERATIONS
The Tx path's analog current consumption is an important
consideration when determining its contribution to the overall
on-chip power dissipation. This is especially the case in full-
duplex applications, where the power dissipation can exceed the
maximum limit of 1.66 W, if the IAMP's IOUT
The analog current consumption includes the TxDAC's analog
supply (Pin 43) along with the standing current from the
IAMP's outputs. Equation 2 and Equation 5 can be used to
calculate the power dissipated in the IAMP for the current and
voltage-mode configuration. Figure 66 shows the current
consumption for the TxDAC and IAMP as a function of the
TxDAC's standing current, I, when only the IOUTN outputs are
used. Figure 67 shows the current consumption for the TxDAC
and IAMP as a function of the TxDAC's standing current, I,
when the IOUTN and IOUTG outputs are used. Both figures
are with the default current mirror gain settings of N = 4 and
G = 12.
(6)
is set to high.
PK
Rev. A | Page 32 of 48
100
90
80
70
60
IAMPN OUTPUT
50
40
30
20
10
1
2
3
4
5
6
Figure 66. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
150
140
130
120
110
100
90
80
70
60
50
TxDAC AVDD
40
30
20
10
1.0
1.5
2.0
2.5
3.0
3.5
Figure 67. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
TxDACs AVDD
7
8
9
10
11
12
13
I (mA)
IOUTG OUTPUT
IOUTN OUTPUT
4.0
4.5
5.0
5.5
6.0
6.5
7.0
I (mA)
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