RT9641AGS RICHTEK [Richtek Technology Corporation], RT9641AGS Datasheet - Page 9

• Manufacturer Part Number: RT9641AGS
• Description: Triple Linear Regulator Controller Support ACPI Control Interface
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Placement of the decoupling and bulk capacitors should
follow a placement reflecting their purpose. As such, the
high-frequency decoupling capacitors (C
placed as close as possible to the load they are decoupling;
the ones decoupling the controller (C
the controller pins, the one decoupling the load close to
the load connector or the load itself (if embedded). The
bulk capacitance (aluminum electrolytic or tantalum
capacitors) placement is not as critical as the high-
frequency capacitor placement, but having these capacitors
close to the load they serve is preferable.
The only critical small signal component is the soft-start
capacitor, C
the control IC and connect to ground though a vias placed
close to the capacitor's ground pad. Minimize any leakage
current paths from SS node, since the internal current
source is only 5μA.
A multi-layer printed circuit board is recommended. Figure1
shows the connections of most of the components to the
converter. Note that each individual capacitor could
represent numerous physical capacitors. Dedicate one
solid layer for a ground plane and make all critical
component ground connections through vias placed as
close to the component as possible. Dedicate another
DS9641A/B-11 March 2007
+12V
+5V
+3.3V
C
HF1
SB
IN
Figure 1 . Printed Circuit Board Islands
IN
Q2
Q3
SS
C
ISLAND ON POWAR PLANE LAYER
ISLAND ON CIRCUIT/POWER PLANE LAYER
C
VIA CONNECTION TO GROUND PLANE
V
SS
. Locate the component close to SS pin of
BULK1
OUT1
C
12V
SS
3V3DLSB
3V3DL
RT9641A/B
12V
GND
5VDLSB
VSEN2
5VSB
DRV2
5VDL
DLA
C
5VSB
C
V
V
BULK2
OUT3
OUT2
Q5
Q1
12V
, C
HF
C
C
5VSB
C
HF3
BULK2
) should be
IN
) close to
Q4
C
HF2
solid layer as a power plane and break this plane into
smaller islands of common voltage levels. Ideally, the power
plane should support both the input power and output
power nodes. Use copper filled polygons on the top and
bottom circuit layers to create power islands connecting
the filtering components (output capacitors) and the loads.
Use the remaining printed circuit layers for small signal
wiring.
Component Selection Guidelines
Output Capacitors Selection
The output capacitors for all outputs should be selected
to allow the output voltage to meet the dynamic regulation
requirements of active state operation (S0, S1). The load
transient for the various microprocessor system's
components may require high quality capacitors to supply
the high slew rate (di/dt) current demands. Thus, it is
recommended that capacitors C
selected for transient load regulation.
Also, during the transition between active and sleep
states, there is a short interval of time during which none
of the power pass elements are conducting-during this
time the output capacitors have to supply all the output
current. The output voltage drop during this brief period of
time can be approximated with the following formula:
ESR
I
C
t
typical)
Since the output voltage drop is heavily dependent on the
ESR (equivalent series resistance) of the output capacitor
bank, the capacitors should be chosen to maintain the
output voltage above the lowest allowable regulation level.
Input Capacitors Selection
The input capacitors for an RT9641A/B application must
have sufficiently low ESR so that the input voltage does
not dip excessively when energy is transferred to the output
capacitors.
Δ
Δ
OUT
t
: active-to-sleep or sleep-to-active transition time (5μs
OUT
V
V
OUT
OUT
: output current during transition
OUT
: output capacitor bank capacitance
:output voltage drop
= I
: output capacitor bank ESR
OUT
x (ESR
OUT
+ t
t
/ C
RT9641A/B
OUT1
OUT
and C
), where
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OUT2
should be
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