參數(shù)資料
型號(hào)： ISL88550A
廠商： Intersil Corporation
英文描述： Synchronous Step Down Controller with Sourcing and Sinking LDO Regulator
中文描述： 同步降壓控制器，具有采購(gòu)和下沉LDO穩(wěn)壓器
文件頁(yè)數(shù)： 21/25頁(yè)
文件大小： 928K
代理商： ISL88550A
21
FN6168.0
October 12, 2005
ILIM connected to the center tap. The external 250mV to 2V
adjustment range corresponds to a 25mV to 200mV valley
current-limit threshold. When adjusting the current limit, use
1% tolerance resistors and a divider current of approximately
10μA to prevent significant inaccuracy in the valley current-
limit tolerance.
Setting the Foldback Current Limit (Buck)
Alternately, foldback current limit can be implemented if UVP
is disabled. Foldback current limit reduces the power
dissipation of external components so they can withstand
indefinite output overload or short circuit. With automatic
recovery after the fault condition is removed. To implement
foldback current limit, connect a resistor from V
OUT
to ILIM
(R1 in the typical application circuit), in addition to the
resistor-divider network (R4 and R5) used for setting the
adjustable current limit.
The following is a procedure for calculating the values of R1,
R4, and R5:
1. Calculate the voltage, V
ILIM
:
2. Pick a percentage of foldback, P
FB
, from 15% to 40%.
3. Calculate the voltage,V
VILIM(0V)
, when the output is
shorted (0V).
FIGURE 27. FOLDBACK CURRENT LIMIT
4. The value of R4 can be calculated as:
5. The parallel combination of R1 and R5 is calculated as:
6. Then R5 can be calculated as:
7. Then R1 is calculated as:
Boost-Supply Capacitor Selection (Buck)
The boost capacitor should be 0.1μF to 4.7μF, depending on
the input and output voltages, external components, and PC
board layout. The boost capacitance should be as large as
possible to prevent it from charging to excessive voltage, but
small enough to adequately charge during the minimum low-
side MOSFET conduction time, which happens at maximum
operating duty cycle (this occurs at minimum input voltage).
In addition, ensure that the boost capacitor does not
discharge to below the minimum gate-to-source voltage
required to keep the high-side MOSFET fully enhanced for
lowest on-resistance. This minimum gate to source voltage
(V
GS(MIN)
) is determined by:
where V
DD
is 5V, Q
G
is the total gate charge of the high-side
MOSFET, and C
BOOST
is the boost capacitor value where
C
BOOST
is C7 in the typical application circuit.
Transient Response (Buck)
The inductor ripple current also affects transient response
performance, especially at low V
IN
- V
OUT
differentials. Low
inductor values allow the inductor current to slew faster,
replenishing charge removed from the output filter capacitors
by a sudden load step. The output sag is also a function of
the maximum duty factor, which can be calculated from the
on-time and minimum off-time:
where t
OFF(MIN)
is the minimum off-time (see the Electrical
Characteristics) and K is from Table 1.
The overshoot during a full-load to no-load transient due to
stored inductor energy can be calculated as:
)
2
Q
(
DSON
)
MAX
(
LOAD
I
ILIM
V
R
2
LIR
1
10
×
×
×
=
VDDQ
REF
ILIM
ISL88551A
R4
R5
C
REF
GND
R1
ISL88550A/
ILIM
V
FB
)
V
0
(
ILIM
V
P
×
=
A
10
V
V
2
4
R
)
V
0
(
ILIM
μ
=
4
R
A
10
V
μ
2
R
5
R
//
1
R
=
(
)
(
)
(
)
[
]
5
R
//
1
R
)
V
0
(
ILIM
V
ILIM
V
)
V
0
(
ILIM
V
ILIM
V
5
R
//
1
R
R
4
R
VDDQ
R
4
R
VDDQ
5
R
×
×
×
×
=
[
]
5
R
//
1
R
5
R
//
1
R
R
5
R
R
5
R
1
R
×
=
(
)
BOOST
G
DD
MIN
GS
C
Q
V
V
×
=
(
)
(
)
(
)
(
)
+
×
×
+
×
×
=
MIN
OFF
IN
OUT
V
IN
OUT
V
OUT
MIN
OFF
IN
OUT
V
2
MAX
LOAD
I
SAG
V
t
K
V
V
C
2
t
K
V
L
(
)
V
OUT
OUT
2
MAX
LOAD
C
×
SOAR
V
2
L
I
×
×
=
ISL88550A
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ISL88550AEVAL1Z 功能描述:EVALUATION BOARD 1 ISL88550A RoHS:是 類(lèi)別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)估板 - DC/DC 與 AC/DC（離線）SMPS 系列:- 產(chǎn)品培訓(xùn)模塊:Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類(lèi)型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓?fù)浣Y(jié)構(gòu):升壓 頻率 - 開(kāi)關(guān):3MHz 板類(lèi)型:完全填充 已供物品:板 已用 IC / 零件:MAX8969
ISL88550AIRZ 功能描述:電壓模式 PWM 控制器 INTEGRTD DDR PWR CNT RLR 2 8LD 5X5 TQFN RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開(kāi)關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
ISL88550AIRZ-T 功能描述:DC/DC 開(kāi)關(guān)控制器 INTEGRTD DDR PWR CNT RLR 2 8LD 5X5 TQFN RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK
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