rt9238 ETC-unknow, rt9238 Datasheet - Page 18

• Manufacturer Part Number: rt9238
• Description: Vrm 8.5 Pwm And Triple Linear Power System Controller
• Manufacturer: ETC-unknow

RT9238
Fig.13, 14 shown the I
forms.
Component Selection Guidelines
Output Capacitor Selection
The output capacitors for each output have unique
requirements. In general the output capacitors should
be
requirements.
requires an output capacitor to filter the current ripple.
The load transient for the microprocessor core
requires high quality capacitors to supply the high
slew rate (di/dt) current demands.
www.richtek-ic.com.tw
18
-20µA
-40µA
-60µA
-80µA
1.4V
1.3V
1.2V
Fig.14 V
selected
0µA
1.6ms
CORE
1.6ms
to
Fig.13 I
Additionally,
Wave Form at Load Transient
meet
SENSE
1.8ms
1.8ms
Time
SENSE
Time
Time
the
Time
Current
the
dynamic
and VCORE wave
2.0ms
PWM
2.0ms
regulation
converter
2.2ms
Preliminary
PWM Output Capacitors
Modern microprocessors produce transient load rates
above 1A/ns. High frequency capacitors initially
supply the transient current and slow the load rate-of-
change seen by the bulk capacitors. The bulk filter
capacitor values are generally determined by the
ESR (effective series resistance) and voltage rating
requirements
requirements.
High frequency decoupling capacitors should be
placed as close to the power pins of the load as
physically possible. Be careful not to add inductance
in the circuit board wiring that could cancel the
usefulness of these low inductance components.
Consult with the manufacturer of the load on specific
decoupling requirements.
Use only specialized low-ESR capacitors intended for
switching-regulator
capacitors. The bulk capacitor’s ESR determines the
output ripple voltage and the initial voltage drop
following a high slew-rate transient’s edge. An
aluminum electrolytic capacitor’s ESR value is related
to the case size with lower ESR available in larger
case
inductance (ESL) of these capacitors increases with
case size and can reduce the usefulness of the
capacitor
Unfortunately, ESL is not a specified parameter.
Work with your capacitor supplier and measure the
capacitor’s impedance with frequency to select a
suitable
electrolytic capacitors of small case size perform
better than a single large case capacitor.
Linear Output Capacitors
The output capacitors for the linear regulators provide
dynamic load current. Thus capacitors C
and C
regulation.
PWM Output Inductor Selection
The PWM converter requires an output inductor. The
output inductor is selected to meet the output voltage
ripple requirements and sets the converter’s
OUT4
sizes.
component.
to
should be selected for transient load
high
rather
However,
applications
slew-rate
In
than
the
most
actual
DS9238-01 July 2001
equivalent
transient
cases,
for
OUT2
capacitance
the
, C
loading.
multiple
series
OUT3
bulk
,