ACT5830
Rev PrB, 05-Mar-08
LOW-DROPOUT LINEAR REGULATORS
FUNCTIONAL DESCRIPTIONS
Capacitor Selection
The input capacitor reduces peak currents and
noise at the voltage source. Connect a low ESR
bulk capacitor (>1µF suggested) to the input. Select
this bulk capacitor to meet the input ripple require-
ments and voltage rating, rather than capacitor size.
General Description
The ACT5830 features eight high performance, low-
dropout, low-noise and low quiescent current LDOs
with high PSRR.
Programming Output Voltages (VSET)
All LDOs feature independently-programmable out-
put voltages that are set via the I2C serial interface,
increasing the ACT5830 flexibility while reducing
total solution size and cost.
PCB Layout Considerations
The ACT5830’s LDOs provide good DC, AC, and
noise performance over a wide range of operating
conditions, and are relatively insensitive to layout
considerations. When designing a PCB, however,
careful layout is necessary to prevent other circuitry
from degrading LDO performance.
Set the output voltage by writing to the
LDOx/VSET[_] register. See Table 7:
LDO1234568/VSET[4:0]
and
Table
8:
LDO7/VSET[_] Output Voltage Settings for a de-
tailed description of voltage programming options.
A good design places input and output capacitors
as close to the LDO inputs and output as possible,
and utilizes a star-ground configuration for all regu-
lators to prevent noise-coupling through ground.
Output traces should be routed to avoid close prox-
imity to noisy nodes, particularly the SW nodes of
the DC/DC.
Enabling and Disabling LDOs
For information regarding enabling and disabling
the LDOs during the startup and shutdown se-
quence section. Once the startup routine is com-
pleted the remaining LDOs can be enabled/disabled
via either the I2C interface or the TCXO_EN
(LDO4), RX_EN (LDO5), TX_EN (LDO6), and
PWR_HOLD (LDO1, LDO2, LDO3, LDO7, and
LDO8).
REFBP is a filtered reference noise, and internally
has a direct connection to the linear regulator con-
troller. Any noise injected onto REFBP will directly
affect the outputs of the linear regulators, and there-
fore special care should be taken to ensure that no
noise is injected to the outputs via REFBP. As with
the LDO output capacitors, the REFBP by pass ca-
pacitor should be placed as close to the IC as pos-
sible, with short, direct connections to the star-
ground. Avoid the use of vias whenever possible.
Noisy nodes, such as from the DC/DC, should be
routed as far away from REFBP as possible.
Reference Bypass Pin
The ACT5830 contains a conference bypass pin
which filters noise from the reference, providing a
low-noise voltage reference to the LDOs. Bypass
REF to G with a 0.01µF ceramic capacitor.
Compensation and Stability
The LDOs need an output capacitor for stability.
This capacitor should be connected as close to the
OUT and G pins as possible to maximize device’s
performance. To ensure best performance for the
device, the output capacitor should have a mini-
mum capacitance of 1µF, and ESR value between
10mꢀ and 500mꢀ. High quality ceramic capacitors
such as X7R and X5R dielectric types are strongly
recommended.
See the Capacitor Selection sections for more infor-
mation.
Innovative PowerTM
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Copyright © 2008 Active-Semi, Inc.
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