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參數(shù)資料
| 型號： | SC470 |
| 廠商： | Semtech Corporation |
| 英文描述： | Synchronous Buck Controller for Dynamic Load-Voltage Applications |
| 中文描述： | 同步降壓控制器的動態(tài)負(fù)載電壓應(yīng)用 |
| 文件頁數(shù)： | 14/31頁 |
| 文件大?。?/td> | 574K |
| 代理商： | SC470 |
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14
2005 Semtech Corp.
www.semtech.com
SC470
POWER MANAGEMENT
Application Information (Cont.)
This calculation assumes the absolute worst-case
condition of a full-load to no-load step transient occurring
when the inductor current is at its highest. The
capacitance required for smaller transient steps may be
calculated by substituting the desired current for the I
OUT
term.
For our example:
C
OUT(MIN)
= 595μF.
We will select 440μF, using two 220μF, 25m
capacitors in parallel. For smaller load release overshoot,
660μF may be used.
Next we calculate the RMS input ripple current, which is
largest at the minimum battery voltage:
(
)
MIN
(
BAT
OUT
)
RMS
(
IN
V
V
I
=
)
RMS
MIN
_
BAT
OUT
I
OUT
A
V
V
For our example:
I
IN(RMS)
= 2.14A
RMS
Input capacitors should be selected with sufficient ripple
current rating for this RMS current, for example a 10μF,
1210 size, 25V ceramic capacitor can handle a little more
than 2A
RMS
(Refer to manufacturer’s data sheets).
Finally, we calculate the current limit resistor value. As
described in the current limit section, the current limit
looks at the “valley current”, which is the average output
current minus half the ripple current. We use the
maximum room temperature specification for MOSFET
R
DS(ON)
at V
GS
= 4.5V for purposes of this calculation:
I
I
I
OUT
VALLEY
=
A
2
)
MIN
(
VBAT
_
RIPPLE
The ripple at low battery voltage is used because we want
to make sure that current limit does not occur under
normal operating conditions.
(
)
2
I
R
VALLEY
ILIM
=
Ohms
10
10
4
R
6
)
ON
(
DS
For our example:
I
VALLEY
= 5.13A, R
DS(ON)
= 9m
and R
ILIM
= 7.76k
We select the next lowest 1% resistor value: 7.68k
Adding an Additional Output Voltage For Dynamic
Voltage Switching
If we design this output to be capable of dynamically
switching between 1.2V and 1.0V, then we would repeat
these calculations to determine if any components need
changing. The 1.0V output suggests a value for C
of
82pF, but the value of 56pF required by the 1.2V design
should work fine, and can always be increased if neces-
sary. Also, the current limit resistor required is slightly
higher: R
ILIM
= 7.87k
. The
higher
value should be used.
Lastly, the bottom feedback resistor, R
will need to
change to 20.0k
. The schematic in Figure 8 on Page
17 shows the complete design.
Dynamically Switching Output Voltages
It is important to note that in order for dynamic output
voltage switching to work, the SC470
must
be in
Continuous Conduction Mode (EN/PSV = floating) when
transitioning from V
to V
. Otherwise the
SC470 has no means to discharge the output voltage
and may OVP and latch off when this transition is initiated
(depending upon the difference between the two
voltages). If CCM is on, the SC470 will actively discharge
the output down to the correct voltage.
Dynamically switching output voltages is very easy,
requiring one switch to add or remove an additional
resistor in parallel to the bottom feedback resistor. Ideally,
the resistor will be switched using an open drain output
from another IC, as shown in Figure 4.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC470EVB | Synchronous Buck Controller for Dynamic Load-Voltage Applications |
| SC470IMLTRT | Synchronous Buck Controller for Dynamic Load-Voltage Applications |
| SC470ITSTRT | Synchronous Buck Controller for Dynamic Load-Voltage Applications |
| SC471EVB | Synchronous Buck Controller with Multi-Level VOUT Transition Support |
| SC471MLTRT | Synchronous Buck Controller with Multi-Level VOUT Transition Support |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC470EVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller for Dynamic Load-Voltage Applications |
| SC470IMLTRT | 功能描述:IC REG CTRLR BUCK PWM 16-MLPQ RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| SC470ITSTRT | 功能描述:IC REG CTRLR BUCK PWM 14-TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 特色產(chǎn)品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 標(biāo)準(zhǔn)包裝:1 系列:PowerWise® PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:81% 電源電壓:4.5 V ~ 18 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-5°C ~ 125°C 封裝/外殼:32-WFQFN 裸露焊盤 包裝:Digi-Reel® 產(chǎn)品目錄頁面:1303 (CN2011-ZH PDF) 其它名稱:LM3754SQDKR |
| SC471 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support |
| SC471_08 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support |
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