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參數(shù)資料
| 型號： | LM2647MTC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual Synchronous Buck Regulator Controller |
| 中文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數(shù)： | 20/25頁 |
| 文件大?。?/td> | 763K |
| 代理商： | LM2647MTC |
Application Information
(Continued)
The V-I crossover losses (exist only in upper FET) are:
Pswon_u = 1/2
VIN
Io
f
ton_u
Pswon_u = 464mW
Pswoff_u = 1/2
VIN
Io
f
toff_u
Pswoff_u = 232mW
There is another loss term associated with charging C
every cycle, then dumping it into the FET before the next
charge cycle. This applies to both upper and lower FETs.
Pcoss_u = 1/2
C
OSS_u
VIN
2
f
Pcoss_l = 1/2
C
OSS_l
VIN
2
f
From the datasheets of the chosen FETs, ’Coss’ are respec-
tively about:
C
OSS_u
= 250pF
C
OSS_l
= 500pF
So
Pcoss_u = 15mW
Pcoss_I = 30mW
Summing up,
Psw_u = 464+132+15=611mW
Psw_I = 30mW
Controller Losses
In addition to the losses in the FETs, there is another loss
term associated with the switching, and this is dissipated in
the controller. The LM2647 has to pump in current pulses at
each transition to turn-ON or turn-OFF the FETs. Several
simplified or more complicated equations exist for calculat-
ing this, but this is most easily deduced by simply turning to
the measured consumption (see Electrical Characteristics
table). The current into the V5 pin is I
and reflects the
driver consumption. This can be as high as 1.5mA (mea-
sured at 300kHz). Let us also include the current into the
control sections (VDD pin), which can be as high as 4mA.
The total controller consumption is therefore
P
IC
= (I
Q_V5
+ I
Q_VDD
) x 5
P
IC
= 28mW
Inductor Losses
The DC resistance (‘DCR’) of the chosen inductor is typically
is 26m
. The DC loss is therefore DCR*Io
2
. The core losses
typically add 10% more to this. Therefore our estimate of
total inductor loss is
Pind=1.1 x (DCR x Io
2
)
Pind = 257mW
Capacitor Losses
The output capacitor of a typical buck regulator has very low
ripple current going through it. So its loss term can be
ignored. The input capacitor however provides the sharp
pulses of current for the Switch, and therefore the RMS
current through it can be fairly high. But the dissipation can
still be negligible if the ESR is very low. This is the situation
if the input capacitors are monolithic ceramic capacitors as in
the Evaluation board (if Tantalum or Aluminum electrolytic
capacitors are used at the input, their dissipation must be
accounted for here). The final efficiency/loss terms are pro-
vided in
Table 1
.
20056323
FIGURE 13. Crossover (turn-on or turn-off)
L
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| LM2647MTC/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(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 |
| LM2647MTCX | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(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 |
| LM2647MTCX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(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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| LM26480 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Externally Programmable Dual High-Current Step-Down DC/DC and Dual Linear Regulators |
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