參數(shù)資料
型號(hào)： LM3477MM
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： High Efficiency High-Side N-Channel Controller for Switching Regulator
中文描述： 1 A SWITCHING CONTROLLER, 575 kHz SWITCHING FREQ-MAX, PDSO8
封裝： MSOP-8
文件頁(yè)數(shù)： 14/23頁(yè)
文件大?。?/td> 815K
代理商： LM3477MM
Design Section
(Continued)
This is the fraction of the switching period that the switch is
on. The switch is off for the remainder of the period. This
fraction is expressed as:
D’ = 1 D
The LM3477/A has limits for the maximum and minimum
duty cycle (see
ELECTRICAL CHARACHTERISTICS
). The
maximum duty cycle of 93% (typical) will limit how low the
input voltage may drop while maintaining a regulated output
voltage (the dropout voltage). In situations where a very low
dropout voltage is required, it is necessary to include V
, V
Q
and V
losses in the maximum duty cycle calculation.
Voltage drops in the inductor will lower the dropout voltage
as well.
The minimum duty cycle of the LM3477/Acorresponds to the
minimum on time, or blank out time (see
ELECTRICAL
CHARACHTERISTICS
).
D
MIN
= T
MIN
*
f
s
This will not limit how high the input voltage can rise, how-
ever the LM3477/A will operate in hysteretic mode once the
operating duty cycle decreases to the minimum duty cycle.
Programming the Current Limit/Hysteretic Threshold
DEFINITIONS:
Current Limit: The current limit is the point at which the
LM3477/A begins to limit the peak switch current. The cur-
rent limit in the LM3477/A varies with duty cycle, which is a
function of the V
IN
V
OUT
differential.
Hysteric Threshold: Hysteretic threshold is the current at
which the LM3477/A enters the hysteretic mode of operation
(see
OVER VOLTAGE PROTECTION
section). The hyster-
etic threshold is with respect to the peak switch current.
Setting Current Limit and Hysteretic Threshold
The adjustable current limit of the LM3477/A is set by the
sense resistor R
SN
. The voltage across R
SN
is compared to
an internal control voltage V
C
. The onset of current limiting is
when V
equals V
, or V
. V
SEN
is defined
here as the differential voltage from the V
pin. V
decreases as the duty cycle increases, as shown in
Figure 7
. Therefore, it is important to know both V
and V
at the maximum operating duty cycle, or lowest
V
IN
condition.
V
CL(MIN)
= V
CL(0)(MIN)
D
(MAX)
(V
CL(0)(MIN)
V
CL(100)(MIN)
)
where D
MAX
is the duty cycle at the lowest V
IN
condition.
To avoid current limit,
V
SEN(peak)
<
V
CL(MIN)
Therefore,
200033K3
FIGURE 7. Current Limit and Hysteretic Threshold vs
Duty Cycle
L
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM3477MM 制造商:Texas Instruments 功能描述:SWITCH CONTROLLER SMD 3477 MSOP8
LM3477MM/NOPB 功能描述:DC/DC 開(kāi)關(guān)控制器 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
LM3477MMX 功能描述:DC/DC 開(kāi)關(guān)控制器 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
LM3477MMX/NOPB 功能描述:DC/DC 開(kāi)關(guān)控制器 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
LM3478 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Efficiency Low-Side N-Channel Controller for Switching Regulator
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