ACT8942
Rev 2, 15-Nov-12
1. To disable the regulator, set ON[ ] to 1 first then
clear it to 0.
I2C interface. If an output voltage is lower than the
power-OK threshold, typically 7% below the
programmed regulation voltage, that regulator's
OK[ ] bit will be 0.
REG1, REG2, REG3 Turn-on Delay
Each of REG1, REG2 and REG3 features a
programmable Turn-on Delay which help ensure a
reliable qualification. This delay is programmed by
DELAY[2:0], as shown in Table 8.
If a DC/DC's nFLTMSK[-] bit is set to 1, the
ACT8942 will interrupt the processor if that DC/DC's
output voltage falls below the power-OK threshold.
In this case, nIRQ will assert low and remain
asserted until either the regulator is turned off or
back in regulation, and the OK[ ] bit has been read
via I2C.
Table 8:
REGx/DELAY[ ] Turn-On Delay
DELAY[2] DELAY[1] DELAY[0] TURN-ON DELAY
PCB Layout Considerations
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0 ms
2 ms
High switching frequencies and large peak currents
make PC board layout an important part of step-
down DC/DC converter design. A good design
minimizes excessive EMI on the feedback paths
and voltage gradients in the ground plane, both of
which can result in instability or regulation errors.
4 ms
8 ms
16 ms
32 ms
64 ms
128 ms
Step-down DC/DCs exhibit discontinuous input
current, so the input capacitors should be placed as
close as possible to the IC, and avoiding the use of
via if possible. The inductor, input filter capacitor,
and output filter capacitor should be connected as
close together as possible, with short, direct, and
wide traces. The ground nodes for each regulator's
power loop should be connected at a single point in
a star-ground configuration, and this point should
be connected to the backside ground plane with
multiple via. The output node for each regulator
should be connected to its corresponding OUTx pin
through the shortest possible route, while keeping
sufficient distance from switching nodes to prevent
noise injection. Finally, the exposed pad should be
directly connected to the backside ground plane
using multiple via to achieve low electrical and
thermal resistance.
Operating Mode
By default, REG1, REG2, and REG3 each operate
in fixed-frequency PWM mode at medium to heavy
loads, while automatically transitioning to
a
proprietary power-saving mode at light loads in
order to maximize standby battery life. In
applications where low noise is critical, force fixed-
frequency PWM operation across the entire load
current range, at the expense of light-load
efficiency, by setting the MODE[ ] bit to 1.
OK[ ] and Output Fault Interrupt
Each DC/DC features a power-OK status bit that
can be read by the system microprocessor via the
Table 7:
REGx/VSET[ ] Output Voltage Setting
REGx/VSET[5:3]
REGx/VSET[2:0]
000
001
010
011
100
101
110
111
000
001
010
011
100
101
110
111
0.600
0.625
0.650
0.675
0.700
0.725
0.750
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000
1.025
1.050
1.075
1.100
1.125
1.150
1.175
1.200
1.250
1.300
1.350
1.400
1.450
1.500
1.550
1.600
1.650
1.700
1.750
1.800
1.850
1.900
1.950
2.000
2.050
2.100
2.150
2.200
2.250
2.300
2.350
2.400
2.500
2.600
2.700
2.800
2.900
3.000
3.100
3.200
3.300
3.400
3.500
3.600
3.700
3.800
3.900
Innovative PowerTM
Active-Semi Proprietary―For Authorized Recipients and Customers
ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of NXP.
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