ADS7863
www.ti.com
SBAS383–JUNE 2007
Power-Down
Modes and
Reset
In nap power-down mode, the ADS7863 turns off
the biasing of the comparator and the mid-voltage
buffer. In this mode, power dissipation reduces to
approximately 0.3mA within 200ns. The device goes
into nap power-down mode regardless of the
conversion state.
(Not ADS7861-Compatible)
The ADS7863 has
a
comprehensive built-in
power-down feature. There are three power-down
modes: deep power-down, nap power-down, and
auto-nap power-down. All three power-down modes
are activated with the 12th falling CLOCK edge of
the SDI access, during which the related bit asserts
(DP = '1', N = '1', or AN = '1'). All modes are
deactivated by de-asserting the respective bit in the
SDI Register. Contents of the SDI Register are not
affected by any of the power-down modes. Any
ongoing conversion aborts when deep or nap
power-down is initiated. Table 8 lists the differences
among the three power-down modes.
The auto-nap power-down mode is almost identical
to the nap mode. The only difference is the time
required to power down and the method of waking
up the device. The SDI Register bit AN is only used
to enable/disable this feature. If the auto-nap mode
is enabled, the ADS7863 turns off the biasing
automatically after finishing a conversion; thus, the
end of conversion actually activates the auto-nap
power-down. Device power dissipation reduces to
about 0.3mA within 200ns in this mode, as well.
Triggering a new conversion by applying a CONVST
pulse puts the device back into normal operation.
In deep power-down mode, all functional blocks
except the digital interface are disabled. The analog
block has its bias currents and the internal oscillator
turned off. In this mode, the power dissipation
reduces to 1μA within 2μs. The wake-up time from
deep power-down mode is 1μs.
To issue a device reset, an RD pulse must be
generated along with an SDI word containing A[2:0]
= '101'. With the 12th falling edge after generating
the RD pulse, the entire device—including the serial
interface—is forced into reset. After approximately
20ns, the serial interface becomes active again.
Table 8. Power-Down Modes
POWER-
DOWN TYPE DISSIPATION
POWER
ENABLED
BY
ACTIVATED
BY
ACTIVATION
TIME
RESUMED
BY
REACTIVATION
TIME
DISABLED
BY
Deep
Nap
1μA
DP = ‘1’
N = ‘1’
12th clock
12th clock
2μs
DP = ‘0’
N = ‘0’
1μs
DP = ‘0’
N = ‘0’
300μA
200ns
3 clocks
Each end of
conversion
Auto-nap
300μA
AN = ‘1’
200ns
CONVST pulse
3 clocks
AN = ‘0’
23
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