MAX886ECJ Просмотр технического описания (PDF) - Maxim Integrated

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MAX886ECJ

Wireless and Satellite Handset Power-Management ICs

Maxim Integrated 

Wireless and Satellite Handset

Power-Management ICs

high-speed rectifiers with reverse recovery times

around 50ns or faster, such as the MUR series, are

acceptable. Ensure that the diode’s peak current rating

exceeds the peak current (1A), and that its breakdown

voltage exceeds VBATT. Schottky diodes are preferred

for heavy loads due to their low forward voltage, espe-

cially in low-voltage applications.

Capacitor Selection

Choose filter capacitors to service input and output

peak currents with acceptable voltage ripple. The

capacitor’s equivalent series resistance (ESR) is a

major contributor to ripple; therefore, low-ESR capaci-

tors are recommended for OUT1–OUT5. A tantalum

capacitor is recommended for OUT0 (see Figures 2a

and 2b, and Table 6).

The input filter capacitor reduces peak currents drawn

from the power source, and reduces noise and voltage

ripple on the input, which are caused by the circuit’s

switching action. Since the current from the battery is

interrupted each time the PMOS switch opens, pay spe-

cial attention to the ripple current rating of the input filter

capacitor and use a low-ESR capacitor. Choose input

capacitors with working voltage ratings higher than the

maximum input voltage. Input capacitors prevent spikes

and ringing on the power source from obscuring the

current-feedback signal and causing jitter.

Bypass REF with 0.22µF to GND. The capacitor should

be placed within 0.2 inches of the IC, next to REF, with

a direct trace to GND.

Table 6. OUT0 and OUT4 Regulator

Component Recommendations

fOSC

C11

L1

C6

C12

(kHz)

(µF)

(µH)

(µF)

(µF)

925

10

10

0.22

10

670

15

15

0.33

15

535

22

22

0.47

22

375

33

33

1

33

Table 7. Component Suppliers

COMPANY

AVX

Coilcraft

Coiltronics

Dale

Internal Rectifier

Motorola

Sanyo

Sprague

Sumida

PHONE

803-946-0690

847-639-6400

516-241-7876

605-668-4131

310-322-3331

602-303-5454

619-661-6835

408-988-8000

847-956-0666

FAX

803-626-3123

847-639-1469

516-241-9339

605-665-1627

310-322-3332

602-994-6430

619-661-1055

408-970-3950

847-956-0702

Layout Considerations

High-frequency switching regulators are sensitive to PC

board layout. Poor layout introduces switching noise

into the current and voltage-feedback signals, resulting

in jitter, instability, or degraded performance. Place the

anode of the Schottky diode and the ground pins of the

input and output capacitors close together, and route

them to a common “star-ground” point. Place compo-

nents and route ground paths so as to prevent high

currents from causing large voltage gradients between

the ground pin of the output filter capacitor, the con-

troller IC, and the reference bypass capacitor. Keep

the extra copper on the component and solder sides of

the PC board rather than etching it away, and connect

it to ground for use as a pseudoground plane. Refer to

the MAX886/MAX888 evaluation kit for a two-layer PC

board layout example.

Component Suppliers

Table 7 lists component suppliers.

18 ______________________________________________________________________________________

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