X
X
R
R
P
P
7
7
7
7
0
0
8
8
a
a
n
n
d
d
X
X
R
R
P
P
7
7
7
7
4
4
0
0
Q
Q
u
u
a
a
d
d
C
C
h
h
a
a
n
n
n
n
e
e
l
l
D
D
i
i
g
g
i
i
t
t
a
a
l
l
P
P
W
W
M
M
S
S
t
t
e
e
p
p
D
D
o
o
w
w
n
n
C
C
o
o
n
n
t
t
r
r
o
o
l
l
l
l
e
e
r
r
s
s
?2012 Exar Corporation
13/28
Rev. 1.2.2
power up. However, most users will want the part to automatically power up when power is
applied to the system. To that end there are a number of recommended solutions.
The most ideal sequencing method is to provide an RC time constant delay from DVDD to the
Enable pin. A 10kohm resistor and a 0.1uF are all that is required. If the system needs to
externally control the Enable pin as well, it is recommended that the Enable pin be pulled to ground
using an open drain I/O. Using 3.3V active logic would back feed DVDD and exceed the maximum
rated voltage of the pin.
For those using active 3.3V or 5V logic on the Enable pin an RC delay from VCCA to the Enable pin
may be used. When using an RC delay from VCCA, attention must be paid to the amount of
bypass capacitance loading AVDD since it will delay the time it takes for AVDD to power up and
regulate. The AVDD and DVDD pins do not require more than 2.2uF for proper bypassing. See
Figure 21 for the recommended components for sequencing the Enable pin through an RC delay
from VCCA. If more capacitance is added to AVDD and DVDD, the time constant must be
increased. Once Enable is asserted, an internal CHIP_READY flag goes high and enables the I
2
C to
acknowledge the Hosts serial commands. Channels that are configured as always-on channels are
enabled. Channels that are configured to be enabled by GPIOs are also enabled if the respective
GPIO is asserted.
Enable Pin
VCCA
10K
.1uF
Fig. 19: RC Delay for Enable taken from VCCA
In almost all cases, a simple check will ensure proper sequencing has been achieved. VCCA
regulates at approximately 4.6V when the Enable pin is logic level low and at 5.1V when Enable is
asserted. VCCA will typically power up and regulate before AVDD and because the internal logic is
not yet powered up there is no internal shutdown signal, it will regulate at 5.1V. Once AVDD has
reached sufficient voltage (and Enable is low) it will assert the internal shutdown signal and VCCA
will reduce its regulated voltage to 4.6V. When the Enable is asserted, the chip will power up and
VCCA will regulate at 5.1V. If our device is sequenced properly, VCCA will achieve 5.1V then drop
down to 4.6V and toggle back to 5.1V. See Figure 22 for an example.
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