AD7148 datasheet(12/56 Pages) AD

12 / 56 page

AD7148

Rev. 0 | Page 12 of 56

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.

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

TIMEOUT

USER IN

PROXIMITY

TO SENSOR?

PROXIMITY TIMER

COUNT DOWN

CONVERSION SEQUENCE

EVERY 36ms FOR

SENSOR READBACK

USER IN

PROXIMITY

TO SENSOR?

CONVERSION SEQUENCE

EVERY LP_CONV_DELAY

UPDATE COMPENSATION

LOGIC DATA PATH

AD7148 SETUP

AND INITIALIZATION

POWER_MODE = 10

Figure 19. Low Power Mode Operation

AD7148 Datasheet(PDF) 12 Page - Analog Devices

AD7148 Datasheet(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

Datasheet Download

Link URL