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

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)

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)

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