AD7147 datasheet(15/73 Pages) AD

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AD7147

Data Sheet

Rev. D | Page 14 of 72

Full Power Mode

In full power mode, all sections of the AD7147 remain fully

powered and converting at all times. While a sensor is being

touched, the AD7147 processes the sensor data. If no sensor is

touched, the AD7147 measures the ambient capacitance level

and uses this data for the on-chip compensation routines. In full

power mode, the AD7147 converts at a constant rate. See the

CDC Conversion Sequence Time section for more information.

Low Power Mode

When AD7147 is in low power mode, the POWER_MODE bits

are set to 10 upon device initialization. If the external sensors

are not touched, the AD7147 reduces its conversion frequency,

thereby greatly reducing its power consumption. The part remains

in a reduced power state while the sensors are not touched. The

AD7147 performs a conversion after a delay defined by the

LP_CONV_DELAY bits, and it uses this data to update the

compensation logic and check if the sensors are active. The

LP_CONV_DELAY bits set the delay between conversions to

200 ms, 400 ms, 600 ms, or 800 ms.

In low power mode, the total current consumption of the AD7147

is an average of the current used during a conversion and the

current used while the AD7147 is waiting for the next conversion

to begin. For example, when LP_CONV_DELAY is 400 ms, the

AD7147 typically uses 0.85 mA of current for 36 ms and 14 μA

of current 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 for the AD7147 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 Ambient Compensation Control 0 (AMB_COMP_CTRL0)

AD7147 transitions to the reduced power state after the user

stops touching the sensors.

Latency from Touch to Response

In low power mode, the AD7147 remains in a low power state

until any one of the external sensors are touched. When a

sensor is touched, the AD7147 begins a conversion sequence

every 36 ms to read back data from the sensors. This means that

the latency between the user touching the sensor, and the AD7147

responding, is a maximum of LP_CONV_DELAY ms.

Low Latency from Touch to Response

In low power mode, the AD7147P model remains in a low power

state until proximity is detected on any one of the external sensors.

When proximity is detected, the AD714P begins a conversion

sequence every 36 ms, or 18 ms, or 9 ms to read back data from the

sensors. The latency between first touch and the AD7147P

responding is much reduced, compared to the AD7147, because

the part is already in a full power state by the time the user has

touched the sensor.

YES

TIMEOUT

AD7147P SETUP

AND INITIALIZATION

POWER_MODE = 10

USER IN

PROXIMITY

TO SENSOR?

CONVERSION SEQUENCE

EVERY LP_CONV_DELAY

UPDATE COMPENSATION

LOGIC DATA PATH

PROXIMITY TIMER

COUNTDOWN

CONVERSION SEQUENCE

EVERY 9/18/36ms FOR

SENSOR READBACK

USER IN

PROXIMITY

TO SENSOR?

YES

TIMEOUT

AD7147 SETUP

AND INITIALIZATION

POWER_MODE = 10

ANY

SENSOR

TOUCHED?

CONVERSION SEQUENCE

EVERY LP_CONV_DELAY

UPDATE COMPENSATION

LOGIC DATA PATH

PROXIMITY TIMER

COUNTDOWN

CONVERSION SEQUENCE

EVERY 9/18/36ms FOR

SENSOR READBACK

ANY SENSOR

TOUCHED?

Figure 23. Low Power Mode Operation, AD7147P

Figure 22. Low Power Mode Operation, AD7147

AD7147 Datasheet(PDF) 15 Page - Analog Devices

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