Internal Reference
The +1.23V bandgap reference supplies up to 100µA
at REF. Connect a 0.01µF bypass capacitor from REF
to GND.
Oscillator
The internal oscillator of the MAX730A typically oper-
ates at 170kHz (160kHz for the MAX738A and 185kHz
for the MAX744A). The MAX744A is guaranteed to
operate at a minimum of 159kHz and a maximum of
212.5kHz over the operating voltage and temperature
range, making it ideal for use in portable communica-
tions systems. The
Typical Operating Characteristics
graphs indicate oscillator frequency stability over tem-
perature and supply voltage.
____________Applications Information
Figure 3 shows the standard 5V step-down application
circuits. Table 3 lists the components for the desired
operating temperature range. These circuits are useful
in systems that require high current at high efficiency
and are powered by an unregulated supply, such as a
battery or wall-plug AC-DC transformer. These circuits
operate over the entire line, load, and temperature
ranges using the single set of component values shown
in Figure 3 and listed in Table 3.
Inductor Selection
The MAX730A/MAX738A/MAX744A require no inductor
design because they are tested in-circuit, and are
guaranteed to deliver the power specified in the
Electrical Characteristics with high efficiency using a
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 9
Table 1. Typical Soft-Start Times
MAX730A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ) V+ (V) I
OUT
(mA) C4 (µF) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
510 6 0 100 2 6 11 28
510 9 0 100 1 4 6 15
510 11 0 100 1 2 4 11
510 9 150 100 1 4 8 21
510 9 300 100 1 5 9 27
510 9 150 390 3 6 9 23
510 9 150 680 4 6 9 24
None 6 0 100 16 34 51 125
None 9 0 100 10 22 34 82
None 11 0 100 8 18 28 66
None 9 150 100 34 134 270 1263
None 9 150 390 39 147 280 1275
None 9 150 680 40 152 285 1280
MAX738A/MAX744A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ) V+ (V) I
OUT
(mA) C4 (µF) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
510 7 0 100 1 4 6 18
510 12 0 100 1 2 3 8
510 16 0 100 1 1 2 6
510 12 300 100 1 3 5 3
510 12 750 100 1 5 8 21
None 7 0 100 12 27 40 100
None 12 0 100 7 16 25 54
None 16 0 100 6 13 20 68
None 12 300 100 27 112 215 1114
(14 paginas)
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