ADS7279_14 Datasheet, PDF (28/51 Pages) Texas Instruments – LOW-POWER, 14-BIT, 1MHz, SINGLE/DUAL UNIPOLAR INPUT, ANALOG-TO-DIGITAL CONVERTERS WITH SERIAL INTERFACE

ADS7279
ADS7280
SBAS436A – MAY 2008 – REVISED JUNE 2009 ............................................................................................................................................................... www.ti.com
Auto Nap Mode
Auto nap mode is almost identical to nap mode. The only difference is the time when the device is actually
powered down and the method used to wake up the device. Configuration register bit D4 is only used to
enable/disable Auto nap mode. If Auto nap mode is enabled, the device turns off the biasing after the conversion
has finished; that is, the end of conversion activates Auto nap power-down mode. Supply current falls from
5.7mA in normal mode to about 0.3mA within 200ns. A CONVST command resumes the device and turns on the
biasing on again in 3 CCLKs (143ns with a 21MHz conversion clock). The device can also be woken up by
disabling auto nap mode when bit D4 of the configuration register is set to '1'. Any channel select command
0XXXb, a wake-up command, or the set default mode command 1111b can also wake up the device from Auto
nap power-down. Table 2 compares the various power-down modes.
NOTE:
1. This wake-up command is the word 1011b in the command word. This command sets bits
D2 and D3 to '1' in the configuration register, but not D4. A wake-up command removes
the device from any of these power-down states, Deep/Nap/Auto nap power-down.
2. Wake-up time is defined as the time between when the host processor tries to wake up the
converter and when a conversion start can occur.
TYPE OF
POWER-DOWN
Normal operation
Deep power-down
Nap power-down
Auto nap
power-down
SUPPLY
CURRENT
AT 5V/3V
5.7mA/4.5mA
4nA/1nA
0.3mA/0.25mA
0.3mA/0.25mA
Table 2. Power-Down Mode Comparisons
POWER-DOWN BY
—
Setting CFR
Setting CFR
EOC (end of
conversion)
TIME TO
POWER-DOWN
(ns)
—
100
200
200
WAKE-UP BY
—
Woken up by command 1011b
Woken up by command 1011b
Woken up by CONVST, any channel
select command, default command
1111b, or wake up command 1011b.
WAKE-UP
TIME
—
1µs
3 CCLKs
ENABLE
—
Set CFR
Set CFR
3 CCLKs Set CFR
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