LM2574N-ADJ/NOPB National Semiconductor, LM2574N-ADJ/NOPB Datasheet - Page 20
![IC REG SIMPLE SWITCHER 8-DIP](/photos/7/60/76056/lm2574n-adj_nopb_sml.jpg)
LM2574N-ADJ/NOPB
Manufacturer Part Number
LM2574N-ADJ/NOPB
Description
IC REG SIMPLE SWITCHER 8-DIP
Manufacturer
National Semiconductor
Series
SIMPLE SWITCHER®r
Type
Step-Down (Buck)r
Specifications of LM2574N-ADJ/NOPB
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
1.23 ~ 37 V
Current - Output
500mA
Frequency - Switching
52kHz
Voltage - Input
4 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Through Hole
Package / Case
8-DIP (0.300", 7.62mm)
Power - Output
750mW
Current, Input Bias
50 nA
Current, Output
0.5 A
Current, Supply
5 mA
Frequency, Oscillator
52 kHz
Package Type
MDIP-8
Regulator Type
Buck (Step-Down)
Temperature, Operating, Range
-40 to +125 °C
Voltage, Input
40 V
Voltage, Output
1.23 to 37 V
Primary Input Voltage
40V
No. Of Outputs
1
Output Voltage
37V
Output Current
500mA
No. Of Pins
8
Operating Temperature Range
-40°C To +125°C
Msl
MSL 1 - Unlimited
Input Voltage Primary Max
40V
Rohs Compliant
Yes
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
*LM2574N-ADJ
*LM2574N-ADJ/NOPB
LM2574N-ADJ
*LM2574N-ADJ/NOPB
LM2574N-ADJ
www.national.com
Additional Applications
Note: Pin numbers are for 8-pin DIP package.
Because of the boosting function of this type of regulator, the
switch current is relatively high, especially at low input volt-
ages. Output load current limitations are a result of the maxi-
mum current rating of the switch. Also, boost regulators can
not provide current limiting load protection in the event of a
shorted load, so some other means (such as a fuse) may be
necessary.
UNDERVOLTAGE LOCKOUT
In some applications it is desirable to keep the regulator off
until the input voltage reaches a certain threshold. An under-
voltage lockout circuit which accomplishes this task is shown
in Figure 13 while Figure 14 shows the same circuit applied
to a buck-boost configuration. These circuits keep the regu-
lator off until the input voltage reaches a predetermined
level.
V
TH
V
Z1
+ 2V
FIGURE 12. Negative Boost
BE
(Q1)
(Continued)
DS011394-20
20
Note: Complete circuit not shown.
Note: Pin numbers are for 8-pin DIP package.
Note: Complete circuit not shown (see Figure 11 ).
Note: Pin numbers are for 8-pin DIP package.
DELAYED STARTUP
The ON /OFF pin can be used to provide a delayed startup
feature as shown in Figure 15 . With an input voltage of 20V
and for the part values shown, the circuit provides approxi-
mately 10 ms of delay time before the circuit begins switch-
ing. Increasing the RC time constant can provide longer de-
lay times. But excessively large RC time constants can
cause problems with input voltages that are high in 60 Hz or
120 Hz ripple, by coupling the ripple into the ON /OFF pin.
ADJUSTABLE OUTPUT, LOW-RIPPLE POWER SUPPLY
A 500 mA power supply that features an adjustable output
voltage is shown in Figure 16 . An additional L-C filter that re-
duces the output ripple by a factor of 10 or more is included
in this circuit.
Note: Complete circuit not shown.
Note: Pin numbers are for 8-pin DIP package.
FIGURE 13. Undervoltage Lockout for Buck Circuit
FIGURE 14. Undervoltage Lockout
FIGURE 15. Delayed Startup
for Buck-Boost Circuit
DS011394-23
DS011394-21
DS011394-22