Datasheet

LM2574, LM2574HV
www.ti.com SNVS104C –JUNE 1999–REVISED APRIL 2013
Table 2. Diode Selection Guide
V
R
1 Amp Diodes
Schottky Fast Recovery
20V 1N5817
SR102
MBR120P
30V 1N5818
The following diodes are all rated to 100V
SR103
11DQ03
11DF1
MBR130P
10JF1
10JQ030
MUR110
HER102
40V 1N5819
SR104
11DQ04
11JQ04
MBR140P
50V MBR150
SR105
11DQ05
11JQ05
60V MBR160
SR106
11DQ06
11JQ06
90V 11DQ09
APPLICATION HINTS
INPUT CAPACITOR (C
IN
)
To maintain stability, the regulator input pin must be bypassed with at least a 22 μF electrolytic capacitor. The
capacitor's leads must be kept short, and located near the regulator.
If the operating temperature range includes temperatures below −25°C, the input capacitor value may need to be
larger. With most electrolytic capacitors, the capacitance value decreases and the ESR increases with lower
temperatures and age. Paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold
temperatures. For maximum capacitor operating lifetime, the capacitor's RMS ripple current rating should be
greater than
(1)
INDUCTOR SELECTION
All switching regulators have two basic modes of operation: continuous and discontinuous. The difference
between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zero for a
period of time in the normal switching cycle. Each mode has distinctively different operating characteristics,
which can affect the regulator performance and requirements.
The LM2574 (or any of the Simple Switcher family) can be used for both continuous and discontinuous modes of
operation.
In many cases the preferred mode of operation is in the continuous mode. It offers better load regulation, lower
peak switch, inductor and diode currents, and can have lower output ripple voltage. But it does require relatively
large inductor values to keep the inductor current flowing continuously, especially at low output load currents.
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