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參數(shù)資料
| 型號： | RT9238 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | VRM 8.5 PWM AND TRIPLE LINEAR POWER SYSTEM CONTROLLER |
| 中文描述： | VRM電源8.5脈寬調(diào)制和三線性電源系統(tǒng)控制器 |
| 文件頁數(shù)： | 18/24頁 |
| 文件大?。?/td> | 434K |
| 代理商： | RT9238 |
RT9238
Preliminary
www.richtek-ic.com.tw
18
DS9238-01 July 2001
Fig.13, 14 shown the I
SENSE
and VCORE wave
forms.
Fig.13 I
SENSE
Current
Fig.14 V
CORE
Wave Form at Load Transient
Component Selection Guidelines
Output Capacitor Selection
The output capacitors for each output have unique
requirements. In general the output capacitors should
be selected to meet the dynamic regulation
requirements. Additionally, the PWM converter
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.
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
rather
than
requirements.
actual
capacitance
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
applications
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
sizes.
However,
inductance (ESL) of these capacitors increases with
case size and can reduce the usefulness of the
capacitor to high slew-rate transient loading.
Unfortunately, ESL is not a specified parameter.
Work with your capacitor supplier and measure the
capacitor’s impedance with frequency to select a
suitable component. In most cases, multiple
electrolytic capacitors of small case size perform
better than a single large case capacitor.
for
the
bulk
the
equivalent
series
Linear Output Capacitors
The output capacitors for the linear regulators provide
dynamic load current. Thus capacitors C
OUT2
, C
OUT3
,
and C
OUT4
should be selected for transient load
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
Time
1.6ms 1.8ms 2.0ms
0
μ
A
-20
μ
A
-40
μ
A
-60
μ
A
-80
μ
A
I
S
Time
1.6ms 1.8ms 2.0ms 2.2ms
1.3V
1.2V
1.4V
V
C
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