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參數(shù)資料
| 型號： | LM2830ZMFX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | High Frequency 1.0A Load - Step-Down DC-DC Regulator |
| 中文描述： | 1.75 A SWITCHING REGULATOR, 3750 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數(shù)： | 13/24頁 |
| 文件大?。?/td> | 862K |
| 代理商： | LM2830ZMFX |
Calculating Efficiency, and
Junction Temperature
The complete LM2830 DC/DC converter efficiency can be
calculated in the following manner.
Or
Calculations for determining the most significant power
losses are shown below. Other losses totaling less than 2%
are not discussed.
Power loss (P
) is the sum of two basic types of losses in
the converter: switching and conduction. Conduction losses
usually dominate at higher output loads, whereas switching
losses remain relatively fixed and dominate at lower output
loads. The first step in determining the losses is to calculate
the duty cycle (D):
V
is the voltage drop across the internal PFET when it is
on, and is equal to:
V
SW
= I
OUT
x R
DSON
V
is the forward voltage drop across the Schottky catch
diode. It can be obtained from the diode manufactures Elec-
trical Characteristics section. If the voltage drop across the
inductor (V
DCR
) is accounted for, the equation becomes:
The conduction losses in the free-wheeling Schottky diode
are calculated as follows:
P
DIODE
= V
D
x I
OUT
x (1-D)
Often this is the single most significant power loss in the
circuit. Care should be taken to choose a Schottky diode that
has a low forward voltage drop.
Another significant external power loss is the conduction
loss in the output inductor. The equation can be simplified to:
P
IND
= I
OUT2
x R
DCR
The LM2830 conduction loss is mainly associated with the
internal PFET:
If the inductor ripple current is fairly small, the conduction
losses can be simplified to:
P
COND
= I
OUT2
x R
DSON
x D
Switching losses are also associated with the internal PFET.
They occur during the switch on and off transition periods,
where voltages and currents overlap resulting in power loss.
The simplest means to determine this loss is to empirically
measuring the rise and fall times (10% to 90%) of the switch
at the switch node.
Switching Power Loss is calculated as follows:
P
SWR
= 1/2(V
IN
x I
OUT
x F
SW
x T
RISE
)
P
SWF
= 1/2(V
IN
x I
OUT
x F
SW
x T
FALL
)
P
SW
= P
SWR
+ P
SWF
Another loss is the power required for operation of the inter-
nal circuitry:
P
Q
= I
Q
x V
IN
I
Q
is the quiescent operating current, and is typically around
3.3mA for the 1.6MHz frequency option.
Typical Application power losses are:
Power Loss Tabulation
V
IN
V
OUT
I
OUT
V
D
F
SW
I
Q
T
RISE
T
FALL
R
DS(ON)
IND
DCR
D
η
5.0V
3.3V
1.0A
0.45V
1.6MHz
3.3mA
4nS
4nS
150m
70m
0.667
88%
P
OUT
3.3W
P
DIODE
150mW
P
Q
P
SWR
P
SWF
P
COND
P
IND
P
LOSS
P
INTERNAL
17mW
6mW
6mW
100mW
70mW
345mW
125mW
Σ
P
COND
+ P
SW
+ P
DIODE
+ P
IND
+ P
Q
= P
LOSS
Σ
P
COND
+ P
SWF
+ P
SWR
+ P
Q
= P
INTERNAL
P
INTERNAL
= 125mW
Thermal Definitions
T
J
= Chip junction temperature
T
A
= Ambient temperature
R
θ
JC
= Thermal resistance from chip junction to device case
R
θ
JA
= Thermal resistance from chip junction to ambient air
Heat in the LM2830 due to internal power dissipation is
removed through conduction and/or convection.
Conduction: Heat transfer occurs through cross sectional
areas of material. Depending on the material, the transfer of
heat can be considered to have poor to good thermal con-
ductivity properties (insulator vs. conductor).
Heat Transfer goes as:
Silicon
→
package
→
lead frame
→
PCB
Convection: Heat transfer is by means of airflow. This could
be from a fan or natural convection. Natural convection
occurs when air currents rise from the hot device to cooler
air.
Thermal impedance is defined as:
L
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2830ZMFX/NOPB | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| LM2830ZQMF/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2830ZQMFE/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2830ZQMFX/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM2830ZSD | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
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