AD9865
currents. The gain of the secondary path, G, and the TxDAC’s
standing current, I, can be set using the following equation:
100
90
80
70
60
50
40
30
20
10
IOUTPK + 3 mA = G × I
(6)
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 AD9865 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.
IAMPN OUTPUT
TxDACs AVDD
1
2
3
4
5
6
7
8
9
10 11 12 13
I (mA)
Figure 66. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
IAMP CURRENT CONSUMPTION CONSIDERATIONS
150
140
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 IOUTPK is set to high.
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.
130
IOUTG OUTPUT
120
110
100
90
80
70
60
50
TxDAC AVDD
40
30
IOUTN OUTPUT
20
10
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
I (mA)
Figure 67. Current Consumption of TxDAC and IAMP in Current-Mode
Operation with IOUTN Only (Default IAMP Settings)
Rev. A | Page 32 of 48
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