BQ2022A_17 Datasheet, PDF (22/37 Pages) Texas Instruments – 1K-Bit Serial EPROM with SDQ Interface

bq2022A
SLUS724E – SEPTEMBER 2006 – REVISED MARCH 2016
www.ti.com
9 Power Supply Recommendations
The bq2022A is a low-power device that only needs to be turned on when communicating. The device power
comes from the voltage supply that is used for digital I/O in the system. A dedicated VCC pin does not exist in
the device for which there is not a requirement of a supply input bypass capacitor. The device obtains its power
from the SDQ communication input which can be sustained during normal communication activity.
The ramp time of the SDQ voltage when power is initially applied may be slow due to current limiting from the
source. Ramp times greater than 200 µs might cause undesired bouncing of the POR circuit and result in the
device not generating a presence pulse. To account for this undesired effect on the device a best practice for the
communication master would be to issue a “hard” reset to the device by pulling down the SDQ line for >5 ms and
then releasing the SDQ bus before issuing the reset pulse that is approximately 480 µs long.
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2
3
4
5
Figure 21. Power Up Best Practice
Figure 21 illustrates the best practice for dealing with initial power on ramps, shown as (1) in the figure, that may
be long in duration. The host should issue a “hard” reset, (2), of > 5 ms, which resets the device and generate a
presence delay and presence pulse, (3). After that, a “soft” reset of approximately 480 µs can be applied, (4),
which also generates a high presence delay and low presence pulse, (5).
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