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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
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
0
No output
1
1.2288 MHz output
Internal oscillator enabled, CLKOUT enabled
(AD5700-1only)
0
No output
Crystal oscillator enabled
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
1.2288 MHz output
Crystal oscillator enabled, CLKOUT enabled
SUPPLY CURRENT CALCULATIONS
The VCC and IOVCC current consumption specifications shown
i
n Table 2 are derived using the internal reference and an
external clock source. This specification is given for a
maximum temperature of 85oC (115 A receive current and
140 A transmit current) and an extended maximum
temperature of 125oC (179 A receive current and 193 A
transmit current). Alternatively, if the external reference is
preferred, (assuming a maximum temperature of 85oC), the
receive and transmit supply current values become 118 A and
129 A respectively, including the current required by the
external reference. A similar calculation can be done for the
125oC maximum temperature case.
If the crystal oscillator or internal oscillator is used, VCC and
IOVCC current consumption figures return to the 115 A receive
current and 140 A transmit current. However, the resultant
current consumption from the crystal oscillator or internal
oscillator must now be accounted for, 60 A maximum addi-
tional current for the crystal oscillator, or 285 A maximum
additional current for the internal oscillator option. This gives
a maximum current consumption of 175 A in receive mode
and 200 A 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 A for receive current
and 425 A for transmit current.
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 A.
FULL DUPLEX OPERATION
Full duplex operation means that the modulator and demodula-
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.