參數(shù)資料
型號(hào)： LM2734XMK
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： Thin SOT23 1A Load Step-Down DC-DC Regulator
中文描述： 2.5 A SWITCHING REGULATOR, 1900 kHz SWITCHING FREQ-MAX, PDSO6
封裝： TSOT-23, 6 PIN
文件頁(yè)數(shù)： 8/22頁(yè)
文件大?。?/td> 459K
代理商： LM2734XMK
Application Information
(Continued)
current. Therefore, it is recommended that V
BOOST
be
greater than 2.5V above V
SW
for best efficiency. V
BOOST
–
V
SW
should not exceed the maximum operating limit of 5.5V.
5.5V
>
V
BOOST
– V
SW
>
2.5V for best performance.
When the LM2734 starts up, internal circuitry from the
BOOST pin supplies a maximum of 20mA to C
. This
current charges C
to a voltage sufficient to turn the
switch on. The BOOST pin will continue to source current to
C
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
and diode D2 supply the gate-drive current for the
NMOS switch. Capacitor C
is charged via diode D2 by
V
. During a normal switching cycle, when the internal
NMOS control switch is off (T
) (refer to
Figure 2
), V
equals V
minus the forward voltage of D2 (V
), 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
- V
SW
= V
IN
- V
FD2
+ V
FD1
When the NMOS switch turns on (T
ON
), the switch pin rises
to
V
SW
= V
IN
– (R
DSON
x I
L
),
forcing V
BOOST
to rise thus reverse biasing D2. The voltage
at V
BOOST
V
BOOST
= 2V
IN
– (R
DSON
x I
L
) – V
FD2
+ V
FD1
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 V
are greater than
5.5V, or less than 3V, C
BOOST
cannot be charged directly
from these voltages. If V
OUT
are greater than 5.5V,
C
can be charged from V
or V
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
– V
D3
)
<
5.5V
(V
INMIN
– V
D3
)
>
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
) is 1 mA.
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 (V
ZENER
– V
D2
) mA
where D is the duty cycle, V
ZENER
and V
D2
are in volts, and
I
is in milliamps. V
anode of the boost diode (D2), and V
is the average
forward voltage across D2. Note that this formula for I
gives typical current. For the worst case I
, increase the
current by 40%. In that case, the worst case boost current
will be
I
BOOST-MAX
= 1.4 x I
BOOST
R3 will then be given by
R3 = (V
IN
- V
ZENER
) / (1.4 x I
BOOST
+ I
ZENER
)
For example, let V
= 10V, V
= 5V, V
D2
= 0.7V, I
ZENER
= 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 C
BOOST
20102309
FIGURE 4. Zener Reduces Boost Voltage from V
IN
L
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8
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參數(shù)描述
LM2734XMK/NOPB 功能描述:直流/直流開關(guān)調(diào)節(jié)器 1A LOAD STEP-DOWN DC-DC REG 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
LM2734XMK/NOPB 制造商:Texas Instruments 功能描述:DC/DC Converter IC
LM2734XMKX 制造商:Texas Instruments 功能描述:CONV DC-DC SGL-OUT STEP DOWN 6PIN TSOT - Tape and Reel
LM2734XMKX/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
LM2734XQMK 制造商:Texas Instruments 功能描述:DC DC REG BUCK 1A 1.6MHZ 6TSOT 制造商:Texas Instruments 功能描述:DC DC REG, BUCK, 1A, 1.6MHZ, 6TSOT 制造商:Texas Instruments 功能描述:DC DC REG, BUCK, 1A, 1.6MHZ, 6TSOT, Primary Input Voltage:20V, No. of Outputs:1, 制造商:Texas Instruments 功能描述:DC DC REG, BUCK, 1A, 1.6MHZ, 6TSOT, Primary Input Voltage:20V, No. of Outputs:1, Output Voltage:18V, Output Current:1A, Voltage Regulator Case Style:SOT-23, No. of Pins:6, Operating Temperature Min:-40C, Operating Temperature , RoHS Compliant: Yes
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