AD7148 Analog Devices, AD7148 Datasheet - Page 12

• Manufacturer Part Number: AD7148
• Manufacturer: Analog Devices

Specifications of AD7148

• Resolution (bits): 16bit
• # Chan: 8
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser
• Analog Input Type: SE-Uni
• Ain Range: ± 8 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

AD7148
Low Power Mode
When in low power mode, the POWER_MODE bits are set
to 10 upon device initialization. If the external sensors are not
touched, the AD7148 reduces its conversion frequency, thereby
greatly reducing its power consumption. The part remains in
a reduced power state while the sensors are not touched. After a
delay defined by the LP_CONV_DELAY bits (200 ms, 400 ms,
600 ms or 800 ms), the AD7148 performs a conversion and uses
this data to update the compensation logic.
When an external sensor is touched, the AD7148 begins a conver-
sion sequence every 25 ms to read back data from the sensors.
In low power mode, total current consumption is an average of the
current used during a conversion and the current used while the
AD7148 is waiting for the next conversion to begin. For example,
when LP_CONV_DELAY is 400 ms, the AD7148 typically uses
0.85 mA current for 25 ms and 14 μA for 400 ms during the
conversion interval. Note that these conversion timings can be
altered through the register settings. See the CDC Conversion
Sequence Time section for more information.
CONVERSION SEQUENCE
UPDATE COMPENSATION
EVERY LP_CONV_DELAY
LOGIC DATA PATH
Figure 19. Low Power Mode Operation
NO
AND INITIALIZATION
POWER_MODE = 10
AD7148 SETUP
Rev. A | Page 12 of 56
TO SENSOR?
PROXIMITY
USER IN
YES
The time required for the AD7148 to transition from a full power
state to a reduced power state after the user stops touching the
external sensors is configurable. The PWR_DOWN_TIMEOUT
bits in the AMB_COMP_CTRL0 register (Address 0x002[13:12])
control the time delay before the AD7148 transitions to the reduced
power state after the user stops touching the sensors.
Low Latency from Touch to Response
In low power mode, the AD7148 remains in a low power state until
proximity is detected on any one of the external sensors. When
proximity is detected, the AD718 is automatically configured into
the full power mode operation, thus converting each sequence
every 36 ms. Using this method, the latency delay is minimized
because the AD7148 is operating in full power mode by the time
the user physically makes contact with a sensor.
YES
CONVERSION SEQUENCE
SENSOR READBACK
EVERY 36ms FOR
PROXIMITY TIMER
COUNT DOWN
TO SENSOR?
PROXIMITY
USER IN
NO
TIMEOUT