MAX730A Ver la hoja de datos (PDF) - Maxim Integrated

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componentes Descripción

Fabricante

MAX730A

5V, Step-Down, Current-Mode PWM DC-DC Converters

Maxim Integrated 

5V, Step-Down,

Current-Mode PWM DC-DC Converters

OUT

C5

330pF

CC

R1

510k

REF

C6

0.01µF

SS

C1

0.1µF

SHDN

BIAS

GEN

ERROR AMP

1.23V

BANDGAP

1M

±35%

SLOPE COMPENSATION

OVERCURRENT COMPARATOR

RAMP

GEN

Σ

PWM

COMPARATOR

F/F

R

Q

S

CURRENT

SENSE AMP

RSENSE

OSC

SS CLAMP

MAX730A

MAX738A

MAX744A

UNDERVOLTAGE

LOCKOUT

VIN = +6.0V TO +16.0V

V+

C2

1µF

C3*

LX

L1

D1

1N5817

VUVLO

VOUT =

+5V

C4*

GND

*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS

Figure 1. Detailed Block Diagram with External Components

single 100µH (MAX7__AC) or 33µH (MAX7__AE/AM)

inductor. The inductor’s incremental saturation current

rating should be greater than 1A, and its DC resistance

should be less than 0.8Ω. Table 2 lists inductor types

and suppliers for various applications. The surface-

mount inductors have nearly equivalent efficiencies to

the larger through-hole inductors.

Output Filter Capacitor Selection

The primary criterion for selecting the output filter

capacitor is low equivalent series resistance (ESR).

The product of the inductor current variation and the

output capacitor’s ESR determines the amplitude of the

sawtooth ripple seen on the output voltage. Also, mini-

mize the output filter capacitor’s ESR to maintain AC

stability. The capacitor’s ESR should be less than

0.25Ω to keep the output ripple less than 50mVp-p over

the entire current range (using a 100µH inductor).

Capacitor ESR rises as the temperature falls, and

excessive ESR is the most likely cause of trouble at

temperatures below 0°C. Sanyo OS-CON series

through-hole and surface-mount tantalum capacitors

exhibit low ESR at temperatures below 0°C. Refer to

Table 2 for recommended capacitor values and sug-

gested capacitor suppliers.

Other Components

The catch diode should be a Schottky or high-speed

silicon rectifier with a peak current rating of at least

1.5A for full-load (750mA) operation. The 1N5817 is a

good choice. The 330pF outer-loop compensation

capacitor provides the widest input voltage range and

best transient characteristics. For low-current applica-

tions, the 510kΩ resistor may be omitted (see the

Maximum Output Current vs. Supply Voltage graph (R1

removed) in the Typical Operating Characteristics).

10 ______________________________________________________________________________________

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