參數(shù)資料
型號(hào)： LM2574
廠商： ON SEMICONDUCTOR
英文描述： 0.5 A, Adjustable Output Voltage, Step-Down Switching Regulator(0.5A,可調(diào)輸出電壓,降壓型開關(guān)穩(wěn)壓器)
中文描述： 0.5甲，可調(diào)輸出電壓，降壓型開關(guān)穩(wěn)壓器（0.5A的，可調(diào)輸出電壓，降壓型開關(guān)穩(wěn)壓器）
文件頁(yè)數(shù)： 19/26頁(yè)
文件大?。?/td> 295K
代理商： LM2574
LM2574, NCV2574
http://onsemi.com
19
The high input current needed for startup is now partially
supplied by the input capacitor C
in
.
Design Recommendations:
The inverting regulator operates in a different manner
than the buck converter and so a different design procedure
has to be used to select the inductor L1 or the output
capacitor C
out
.
The output capacitor values must be larger than what is
normally required for buck converter designs. Low input
voltages or high output currents require a large value output
capacitor (in the range of thousands of F).
The recommended range of inductor values for the
inverting converter design is between 68 H and 220 H. To
select an inductor with an appropriate current rating, the
inductor peak current has to be calculated.
D1
MBR150
L1
68 H
Output
7
1
Feedback
12 to 25 V
Unregulated
DC Input
C
in
22 F
/50 V
5
4
3
ON/OFF
(5)
Pwr
Gnd
(6)
+V
in
12 V @ 100 mA
Regulated
Output
C
out
680 F
/16 V
LM257412
C1
0.1 F
R1
47 k
R2
47 k
2
Sig
Gnd
(4)
Figure 28. Inverting BuckBoost Regulator with
Delayed Startup
(3)
(12)
(14)
The following formula is used to obtain the peak inductor
current:
Ipeak
ILoadVin
|VO|
Vin
Vinx ton
2L1
where
ton
|VO|
Vin
|VO|xfosc
, and f
osc
= 52 kHz.
Under normal continuous inductor current operating
conditions, the worst case occurs when V
in
is minimal.
It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
features could be very useful. A delayed startup circuit
applied to a buckboost converter is shown in Figure 28.
Figure 34 in the “Undervoltage Lockout” section describes
an undervoltage lockout feature for the same converter
topology.
With the inverting configuration, the use of the ON/OFF
pin requires some level shifting techniques. This is caused
by the fact, that the ground pin of the converter IC is no
longer at ground. Now, the ON/OFF pin threshold voltage
(1.3 V approximately) has to be related to the negative
output voltage level. There are many different possible
shutdown methods, two of them are shown in Figures 29
and 30.
LM2574XX
(12)
5
2
and
4
3
Gnds
Pins
(4)
and
(6)
ON/OFF
(5)
+V
in
R2
47 k
C
in
22 F
NOTE
: This picture does not show the complete circuit.
R1
47 k
R3
470
Shutdown
Input
MOC8101
V
out
Off
On
5.0 V
0
+V
in
Figure 29. Inverting BuckBoost Regulator Shutdown
Circuit Using an Optocoupler
NOTE
: This picture does not show the complete circuit.
Figure 30. Inverting BuckBoost Regulator Shutdown
Circuit Using a PNP Transistor
R2
5.6 k
Q1
2N3906
LM2574XX
5
2
and
4
3
Gnds
Pins
ON/OFF
(5)
R1
12 k
V
out
+V
in
Shutdown
Input
Off
On
+V
0
+V
in
C
in
22 F
(12)
(4)
and
(6)
Negative Boost Regulator
This example is a variation of the buckboost topology
and it is called negative boost regulator. This regulator
experiences relatively high switch current, especially at low
input voltages. The internal switch current limiting results in
lower output load current capability.
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LM2574-12 制造商:Texas Instruments 功能描述:
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