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參數資料
| 型號： | ISL6550AIR-T |
| 英文描述： | Analog IC |
| 中文描述： | 模擬IC |
| 文件頁數： | 10/14頁 |
| 文件大小： | 415K |
| 代理商： | ISL6550AIR-T |
10
capacitor. A conservative approach is presented in the
following equation.
Output Capacitor Selection
An output capacitor is required to filter the output and supply
the load transient current. The filtering requirements are a
function of the switching frequency and the ripple current.
The load transient requirements are a function of the slew
rate (di/dt) and the magnitude of the transient load current.
These requirements are generally met with a mix of
capacitors and careful layout.
Modern digital ICs can produce high transient load slew
rates. High frequency capacitors initially supply the transient
and slow the current load rate 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 actual capacitance 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 applications for the bulk capacitors. The
bulk capacitor’s ESR will determine the output ripple voltage
and the initial voltage drop after a high slew-rate transient. An
aluminum electrolytic capacitor’s ESR value is related to the
case size with lower ESR available in larger case sizes.
However, the Equivalent Series 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.
Output Inductor Selection
The output inductor is selected to meet the output voltage
ripple requirements and minimize the converter’s response
time to the load transient. The inductor value determines the
converter’s ripple current and the ripple voltage is a function
of the ripple current. The ripple voltage and current are
approximated by the following equations:
Increasing the value of inductance reduces the ripple current
and voltage. However, the large inductance values reduce
the converter’s response time to a load transient.
One of the parameters limiting the converter’s response to
a load transient is the time required to change the inductor
current. Given a sufficiently fast control loop design, the
ISL6527 will provide either 0% or 100% duty cycle in
response to a load transient. The response time is the time
required to slew the inductor current from an initial current
value to the transient current level. During this interval the
difference between the inductor current and the transient
current level must be supplied by the output capacitor.
Minimizing the response time can minimize the output
capacitance required.
The response time to a transient is different for the application
of load and the removal of load. The following equations give
the approximate response time interval for application and
removal of a transient load:
where: I
TRAN
is the transient load current step, t
RISE
is the
response time to the application of load, and t
FALL
is the
response time to the removal of load. The worst case
response time can be either at the application or removal of
load. Be sure to check both of these equations at the
minimum and maximum output levels for the worst case
response time.
Input Capacitor Selection
Use a mix of input bypass capacitors to control the voltage
overshoot across the MOSFETs. Use small ceramic
capacitors for high frequency decoupling and bulk capacitors
to supply the current needed each time Q
1
turns on. Place the
small ceramic capacitors physically close to the MOSFETs
and between the drain of Q
1
and the source of Q
2
.
The important parameters for the bulk input capacitor are the
voltage rating and the RMS current rating. For reliable
operation, select the bulk capacitor with voltage and current
ratings above the maximum input voltage and largest RMS
current required by the circuit. The capacitor voltage rating
should be at least 1.25 times greater than the maximum input
voltage and a voltage rating of 1.5 times is a conservative
guideline. The RMS current rating requirement for the input
capacitor of a buck regulator is approximately 1/2 the DC load
current.
The maximum RMS current required by the regulator may be
closely approximated through the following equation:
For a through hole design, several electrolytic capacitors may
be needed. For surface mount designs, solid tantalum
capacitors can be used, but caution must be exercised with
regard to the capacitor surge current rating. These capacitors
must be capable of handling the surge-current at power-up.
C
PUMP
I
V
CC
f
s
------------------------------------
1.5
×
=
I =
V
IN
- V
OUT
f
s
x L
V
OUT
V
IN
V
OUT
=
I x ESR
x
t
RISE
=
L x I
TRAN
V
IN
- V
OUT
t
FALL
=
L x I
TRAN
V
OUT
I
RMSMAX
V
IN
---------------
I
OUTMAX
2
1
12
------
V
-------------------------------
V
s
–
V
IN
---------------
×
2
×
+
×
=
ISL6527
相關PDF資料 |
PDF描述 |
|---|---|
| ISL6550BIB-T | Analog IC |
| ISL6550BIR-T | Analog IC |
| ISL6550CIB-T | Analog IC |
| ISL6550CIR-T | Analog IC |
| ISL6522EVAL1 | Buck and Synchronous Rectifier Pulse-Width Modulator (PWM) Controller |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ISL6550CIR | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ISL6551AB | 制造商:Rochester Electronics LLC 功能描述:FULL BRIDGE CONTROLLER - Bulk |
| ISL6551AB-T | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ISL6551ABZ | 功能描述:IC REG CTRLR FLYBACK PWM 28-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩壓器 - DC DC 切換控制器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:275kHz 占空比:50% 電源電壓:18 V ~ 110 V 降壓:無 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:-40°C ~ 85°C 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) |
| ISL6551ABZ-T | 功能描述:IC REG CTRLR FLYBACK PWM 28-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩壓器 - DC DC 切換控制器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:275kHz 占空比:50% 電源電壓:18 V ~ 110 V 降壓:無 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:-40°C ~ 85°C 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) |
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