Applications information, Table 1. typical soft-start times – Rainbow Electronics MAX744A User Manual
Page 9
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 (k
Ω
)
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 (k
Ω
)
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