Datasheet

AD5700/AD5700-1 Data Sheet
Rev. F | Page 16 of 24
Table 7. Clock Configuration Options
XTAL_EN
CLK_CFG1 CLK_CFG0 CLKOUT Description
1 0 0 No output 3.6864 MHz CMOS clock connected at XTAL1 pin
1 0 1 No output 1.2288 MHz CMOS clock connected at XTAL1 pin
1 1 0 No output Internal oscillator enabled (AD5700-1 only)
1 1 1 1.2288 MHz output Internal oscillator enabled, CLKOUT enabled (AD5700-1only)
0 0 0 No output Crystal oscillator enabled
0 0 1 3.6864 MHz output Crystal oscillator enabled, CLKOUT enabled
0 1 0 1.8432 MHz output Crystal oscillator enabled, CLKOUT enabled
0 1 1 1.2288 MHz output Crystal oscillator enabled, CLKOUT enabled
SUPPLY CURRENT CALCULATIONS
The V
CC
and IOV
CC
current consumption specifications shown
in Table 2 are derived using the internal reference and an
external clock source. This specification is given for a
maximum temperature of 85
o
C (115 µA receive current and
140 µA transmit current) and an extended maximum
temperature of 125
o
C (179 µA receive current and 193 µA
transmit current). Alternatively, if the external reference is
preferred, (assuming a maximum temperature of 85
o
C), the
receive and transmit supply current values become 118 µA and
129 µA respectively, including the current required by the
external reference. A similar calculation can be done for the
125
o
C maximum temperature case.
If the crystal oscillator or internal oscillator is used, V
CC
and
IOV
CC
current consumption figures return to the 115 µA receive
current and 140 µA transmit current. However, the resultant
current consumption from the crystal oscillator or internal
oscillator must now be accounted for, 60 µA maximum addi-
tional current for the crystal oscillator, or 285 µA maximum
additional current for the internal oscillator option. This gives
a maximum current consumption of 175 µA in receive mode
and 200 µA in transmit mode, when using the internal reference
and the crystal oscillator. Utilizing the internal reference
and the internal oscillator (AD5700-1 only) results in a total
maximum current consumption of 400 µA for receive current
and 425 µA for transmit current.
POWER-DOWN MODE
The AD5700/AD5700-1 can be placed into power-down mode
by holding the
RESET
pin low. If using the internal reference, it
is recommended to tie the REF_EN pin to the
RESET
pin so
that it is also powered down. If the reference is not powered
down while
RESET
is low, the output voltage on the REF pin is
approximately 1.7 V until
RESET
is brought high again.
In this mode, the receive, transmit, and oscillator circuits are all
switched off, and the device consumes a typical current of 16 µA.
FULL DUPLEX OPERATION
Full duplex operation means that the modulator and demodula-
tor of the AD5700/AD5700-1 are enabled at the same time. This
is a powerful feature, enabling a self-test procedure of not only
the HART device but also the complete signal path between the
HART device and the host controller. This provides verification
that the local communications loop is functional. This increased
level of system diagnostics is useful in production self-test and
is advantageous in improving the application’s safety integrity
level (SIL) rating. The full duplex mode of operation is enabled by
connecting the DUPLEX pin to logic high.