LM1937 datasheet(4/6 Pages) HTC

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WHITE LED STEP-UP CONVERTER

LM1937

HTC

- 4 -

APPLICATIONS INFORMATION

Inductor Selection

A 22mH inductor is recommended for most LM1937

applications. Although small size and high efficiency are

major concerns, the inductor should have low core

losses at 1.2MHz and low DCR (copper wire resistance).

Some inductors in this category with small size are listed

in Table 1. The efficiency comparison of different

inductors is shown in Figure 3.

Table 1. Recommended Inductors

Figure 3. Efficiency Comparison of Different Inductors

Capacitor Selection

The small size of ceramic capacitors makes them

ideal for LM1937 applications. X5R and X7R types are

recommended because they retain their capacitance

over wider voltage and temperature ranges than other

types such as Y5V or Z5U. A 1µF input capacitor and

a 0.22µF output capacitor are sufficient for most

LM1937 applications.

Table 2. Recommended Ceramic Capacitor

Manufacturers

Diode Selection

Schottky diodes, with their low forward voltage drop

and fast reverse recovery, are the ideal choices for

LM1937 applications. The forward voltage drop of a

Schottky diode represents the conduction losses in the

diode, while the diode capacitance (CT or CD)

represents the switching losses. For diode selection,

both forward voltage drop and diode capacitance need

to be considered. Schottky diodes with higher current

ratings usually have lower forward voltage drop and

larger diode capacitance, which can cause significant

switching losses at the 1.2MHz switching frequency of

the LM1937. A Schottky diode rated at 100mA to

200mA is sufficient for most LM1937 applications.

Some recommended Schottky diodes are listed in

Table 3.

Table 3. Recommended Schottky Diodes

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