Low-Noise, 14V Input, 1A, PWM

Step-Down Converters

MAX1684

MAX1685

LX

AIN

IN

CVH

FB

L

C1

MBRS

130LT3

R1

R2

BOOT

PGND

AGND

CC

SHDN

STBY

0.1

µF

22

µF

0.1

µF

100

µF

-1.25V

TO -5.5V

(

)

1

µF

0.1

µF

CVL

SYNC/PWM

REF

ILIM/SS

0.01

µF

0.01

µF

R2

+ 1

R1

Figure 4. Inverting Output

Table 2. Inductor and Minimum Output Capacitor Selection

Table 3. Component Suppliers

22

220

MAX1684 (300kHz)

1.25 to 2.7

10

100

MAX1685 (600kHz)

L

(µH)

(µF)

L

(µH)

(µF)

(V)

22

100

10

47

2.7 to 4

47

68

22

33

4 to 6

68

47

33

22

6 to 14

capacitors have the lowest ESR of the high-value elec-

trolytic types. Use ceramic and OS-CON capacitors for

very compact, high-reliability, or wide-temperature

applications, where expense is justified. When using

very low ESR capacitors, such as ceramic or OS-CON,

check for stability while examining load-transient

response, and increase the output compensation

capacitor if needed. Table 3 lists suppliers for the vari-

ous components used with the MAX1684/MAX1685.

Ensure that the minimum capacitance value and maxi-

mum ESR values are met:

≅ 1.4%, and

Output Diode Selection

Use a 1A external Schottky diode (MBRS130LT3 or

equivalent) for the output rectifier to pass inductor cur-

rent during the start of the second half of each cycle.

This diode operates before the internal N-channel

MOSFET completely turns on and during high-current

operation. Use a Schottky diode to avoid forward bias-

ing the internal body diode of the N-channel MOSFET.

12

______________________________________________________________________________________

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847-956-0702

Sprague

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603-224-1430

Motorola

602-303-5454

602-994-6430

DIODES

TDK

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847-390-4428

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814-238-0490

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847-639-1469

INDUCTORS

Sanyo

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714-960-6492

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803-626-3123

FAX

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