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MAX863EEE

Dual, High-Efficiency, PFM, Step-Up DC-DC Controller

Maxim Integrated 

Dual, High-Efficiency, PFM, Step-Up

DC-DC Controller

VOUT1 OR VOUT2

R1

MAX863

FB1 OR FB2

C1

COUT

(OPTIONAL)

C2

R2

(OPTIONAL FOR HIGH-

VOLTAGE CIRCUITS)

Figure 7. Adjustable Output Circuit

Voltage ripple is the sum of contributions associated

with ESR and the capacitor value, as shown below:

VRIPPLE ≅ VRIPPLE,ESR + VRIPPLE,C

To simplify selection, assume that 75% of the ripple

results from ESR and that 25% results from the capaci-

tor value. Voltage ripple as a consequence of ESR is

approximated by:

VRIPPLE,ESR ≅ RESR x IPEAK

so:

RESR ≤

VRIPPLE,ESR

IPEAK

Estimate input and output capacitor values for a given

voltage ripple as follows:

C ≥ 0.5L x I2PEAK

VRIPPLE,C x V

where V is the input or output voltage, depending on

which capacitor is being calculated.

Choose input capacitors with working voltage ratings

over the maximum input voltage, and output capacitors

with working voltage ratings higher than their respec-

tive outputs.

Table 1. Component Suppliers

SUPPLIER

PHONE

Inductors

Coilcraft

(847) 639-6400

Coiltronics

(561) 241-7876

Dale Inductors

(605) 668-4131

Sumida USA

(847) 956-0666

MOSFETs and Diodes

Central Semiconductor (516) 435-1110

International Rectifier (310) 322-3331

Motorola

(602) 303-5454

Current-Sense Resistors

Dale/Vishay

(402) 564-3131

IRC

(512) 992-7900

Electrolytic Capacitors

AVX

(803) 946-0690

Sanyo USA

(619) 661-6835

Sprague

(603) 224-1961

Large-Value Ceramic Capacitors

Marcon/United

Chemi-Con

(847) 696-2000

TDK

Vishay/Vitramon

(847) 390-4373

(203) 268-6261

FAX

(847) 639-1469

(561) 241-9339

(605) 665-1627

(847) 956-0702

(516) 435-1824

(310) 322-3232

(602) 994-6430

(402) 563-6418

(512) 992-3377

(803) 626-3123

(619) 661-1055

(603) 224-1430

(847) 696-9278

(847) 390-4428

(203) 452-5670

Add VDD and REF Bypass Capacitors

Bypass the MAX863 with 0.1µF or higher value ceramic

capacitors placed as close to the VDD, REF, and GND

pins as possible.

Set the Output Voltage

DC-DC converter 1 operates with a 3.3V, 5V, or

adjustable output. For a preset output, connect

SENSE1 to OUT1 (Figures 2 and 4a), then set FB1 to

VDD for 3.3V operation or to GND for 5V operation. For

an adjustable output, connect a resistor voltage divider

to the FB1 pin (Figure 7). In adjustable output circuits,

connect SENSE1 to GND.

DC-DC converter 2 can be adjusted from very high

voltages down to VIN using external resistors connect-

ed to the FB2 pin, as shown in Figure 7. Select feed-

back resistor R2 in the 10kΩ to 500kΩ range. R1 is

given by:

R1

=

R2





VOUT

1.25V

− 1

where 1.25V is the voltage of the internal reference.

______________________________________________________________________________________ 13

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