전자부품 데이터시트 검색엔진
  Korean  ▼
ALLDATASHEET.CO.KR

X  

LM2734XMKX 데이터시트(PDF) 8 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
부품명 LM2734XMKX
상세설명  Thin SOT23 1A Load Step-Down DC-DC Regulator
Download  22 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
제조업체  NSC [National Semiconductor (TI)]
홈페이지  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM2734XMKX 데이터시트(HTML) 8 Page - National Semiconductor (TI)

Back Button LM2734XMKX Datasheet HTML 4Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 5Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 6Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 7Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 8Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 9Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 10Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 11Page - National Semiconductor (TI) LM2734XMKX Datasheet HTML 12Page - National Semiconductor (TI) Next Button
Zoom Inzoom in Zoom Outzoom out
 8 / 22 page
background image
Application Information (Continued)
current. Therefore, it is recommended that V
BOOST
be
greater than 2.5V above V
SW for best efficiency. VBOOST
V
SW should not exceed the maximum operating limit of 5.5V.
5.5V > V
BOOST –VSW > 2.5V for best performance.
When the LM2734 starts up, internal circuitry from the
BOOST pin supplies a maximum of 20mA to C
BOOST. This
current charges C
BOOST to a voltage sufficient to turn the
switch on. The BOOST pin will continue to source current to
C
BOOST until the voltage at the feedback pin is greater than
0.76V.
There are various methods to derive V
BOOST:
1.
From the input voltage (V
IN)
2.
From the output voltage (V
OUT)
3.
From an external distributed voltage rail (V
EXT)
4.
From a shunt or series zener diode
In the Simplifed Block Diagram of Figure 1, capacitor
C
BOOST and diode D2 supply the gate-drive current for the
NMOS switch. Capacitor C
BOOST is charged via diode D2 by
V
IN. During a normal switching cycle, when the internal
NMOS control switch is off (T
OFF) (refer to Figure 2), VBOOST
equals V
IN minus the forward voltage of D2 (VFD2), during
which the current in the inductor (L) forward biases the
Schottky diode D1 (V
FD1). Therefore
the voltage stored
across C
BOOST is
V
BOOST -VSW =VIN -VFD2 +VFD1
When the NMOS switch turns on (T
ON), the switch pin rises
to
V
SW =VIN –(RDSON xIL),
forcing V
BOOST to rise thus reverse biasing D2. The voltage
at V
BOOST is then
V
BOOST =2VIN –(RDSON xIL)– VFD2 +VFD1
which is approximately
2V
IN - 0.4V
for many applications. Thus the gate-drive voltage of the
NMOS switch is approximately
V
IN - 0.2V
An alternate method for charging C
BOOST is to connect D2 to
the output as shown in Figure 3. The output voltage should
be between 2.5V and 5.5V, so that proper gate voltage will
be applied to the internal switch. In this circuit, C
BOOST
provides a gate drive voltage that is slightly less than V
OUT.
In applications where both V
IN and VOUT are greater than
5.5V, or less than 3V, C
BOOST cannot be charged directly
from these voltages. If V
IN and VOUT are greater than 5.5V,
C
BOOST can be charged from VIN or VOUT minus a zener
voltage by placing a zener diode D3 in series with D2, as
shown in Figure 4. When using a series zener diode from the
input, ensure that the regulation of the input supply doesn’t
create a voltage that falls outside the recommended V
BOOST
voltage.
(V
INMAX –VD3) < 5.5V
(V
INMIN –VD3) > 1.6V
An alternative method is to place the zener diode D3 in a
shunt configuration as shown in Figure 5. A small 350mW to
500mW 5.1V zener in a SOT-23 or SOD package can be
used for this purpose. A small ceramic capacitor such as a
6.3V, 0.1µF capacitor (C4) should be placed in parallel with
the zener diode. When the internal NMOS switch turns on, a
pulse of current is drawn to charge the internal NMOS gate
capacitance. The 0.1 µF parallel shunt capacitor ensures
that the V
BOOST voltage is maintained during this time.
Resistor R3 should be chosen to provide enough RMS cur-
rent to the zener diode (D3) and to the BOOST pin. A
recommended choice for the zener current (I
ZENER)is1mA.
The current I
BOOST into the BOOST pin supplies the gate
current of the NMOS control switch and varies typically
according to the following formula:
I
BOOST = 0.56 x (D + 0.54) x (VZENER –VD2)mA
where D is the duty cycle, V
ZENER and VD2 are in volts, and
I
BOOST is in milliamps. VZENER is the voltage applied to the
anode of the boost diode (D2), and V
D2 is the average
forward voltage across D2. Note that this formula for I
BOOST
gives typical current. For the worst case I
BOOST, increase the
current by 40%. In that case, the worst case boost current
will be
I
BOOST-MAX =1.4xIBOOST
R3 will then be given by
R3=(V
IN -VZENER)/(1.4xIBOOST +IZENER)
For example, let V
IN = 10V, VZENER =5V, VD2 = 0.7V, IZENER
= 1mA, and duty cycle D = 50%. Then
I
BOOST = 0.56 x (0.5 + 0.54) x (5 - 0.7) mA = 2.5mA
R3 = (10V - 5V) / (1.4 x 2.5mA + 1mA) = 1.11k
20102308
FIGURE 3. V
OUT Charges CBOOST
20102309
FIGURE 4. Zener Reduces Boost Voltage from V
IN
www.national.com
8


유사한 부품 번호 - LM2734XMKX

제조업체부품명데이터시트상세설명
logo
Texas Instruments
LM2734XMKX/NOPB TI1-LM2734XMKX/NOPB Datasheet
1Mb / 31P
[Old version datasheet]   LM2734 Thin SOT 1A Load Step-Down DC-DC Regulator
LM2734XMKX/NOPB TI1-LM2734XMKX/NOPB Datasheet
1Mb / 36P
[Old version datasheet]   Thin SOT 1-A Load Step-Down DC-DC Regulator
More results

유사한 설명 - LM2734XMKX

제조업체부품명데이터시트상세설명
logo
National Semiconductor ...
LM2734Z NSC-LM2734Z Datasheet
775Kb / 9P
   Thin SOT23 1A Load Step-Down DC-DC Regulator
logo
Texas Instruments
LM2734Z TI1-LM2734Z_14 Datasheet
1Mb / 29P
[Old version datasheet]   Thin SOT23 1A Load Step-Down DC-DC Regulator
logo
National Semiconductor ...
LM2736 NSC-LM2736 Datasheet
444Kb / 22P
   Thin SOT23 750mA Load Step-Down DC-DC Regulator
logo
Texas Instruments
LM2736 TI1-LM2736_14 Datasheet
1Mb / 27P
[Old version datasheet]   Thin SOT23 750mA Load Step-Down DC-DC Regulator
LMR12007 TI1-LMR12007 Datasheet
1Mb / 30P
[Old version datasheet]   LMR12007 Thin SOT23 750mA Load Step-Down DC-DC Regulator
LMR12007 TI1-LMR12007 Datasheet
1Mb / 30P
[Old version datasheet]   LMR12007 Thin SOT23 750mA Load Step-Down DC-DC Regulator
LM2734 TI1-LM2734 Datasheet
1Mb / 31P
[Old version datasheet]   LM2734 Thin SOT 1A Load Step-Down DC-DC Regulator
LM2734Z TI-LM2734Z_15 Datasheet
1Mb / 32P
[Old version datasheet]   LM2734Z/LM2734ZQ Thin SOT 1A Load Step-Down DC-DC Regulator
LM2736YMKX TI-LM2736YMKX Datasheet
1Mb / 31P
[Old version datasheet]   LM2736 Thin SOT 750mA Load Step-Down DC-DC Regulator
LM2736XMK TI-LM2736XMK Datasheet
1Mb / 31P
[Old version datasheet]   LM2736 Thin SOT 750mA Load Step-Down DC-DC Regulator
More results


Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22


데이터시트 다운로드

Go To PDF Page


링크 URL




개인정보취급방침
ALLDATASHEET.CO.KR
ALLDATASHEET 가 귀하에 도움이 되셨나요?  [ DONATE ] 

Alldatasheet는?   |   광고문의   |   운영자에게 연락하기   |   개인정보취급방침   |   링크교환   |   제조사별 검색
All Rights Reserved©Alldatasheet.com


Mirror Sites
English : Alldatasheet.com  |   English : Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp
Russian : Alldatasheetru.com  |   Korean : Alldatasheet.co.kr  |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com
Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl  |   Vietnamese : Alldatasheet.vn
Indian : Alldatasheet.in  |   Mexican : Alldatasheet.com.mx  |   British : Alldatasheet.co.uk  |   New Zealand : Alldatasheet.co.nz
Family Site : ic2ic.com  |   icmetro.com