MAX863EEE 查看數據表（PDF） - Maxim Integrated

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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

VIN = 1.5V TO THE LOWER OF VOUT1 OR VOUT2

L1

10µH

2A

C3

100µF

10V

≤0.1Ω

C4

100µF

10V

≤0.1Ω

VOUT1 = 5V

C1

220µF

10V

≤0.1Ω

R5

C2

0.1µF

D1

MBRS340T3

SENSE1 VDD

N1A

EXT1

BOOT

EXT2

CS1

CS2

R7

100k

R1

50mΩ

MAX863

L2

10µH

2A

D2

MBRS340T3

N1B

IRF7301

R2

R3

50mΩ

165k

1%

LOW-BATTERY

DETECTOR OUTPUT

LBO

FB2

SHDN1

LBI

ON/OFF

SHDN2

R6

REF

C7

FB1 PGND GND

0.1µF

VOUT2 = 3.3V

C5

330µF

10V

≤0.1Ω

C6

10pF

R4

100k

1%

Figure 2. Bootstrapped Typical Operating Circuit

Continuous/Discontinuous-Conduction

Modes

Each converter in the MAX863 determines from moment

to moment whether to switch or not, waiting until the out-

put voltage drops before initiating another cycle. Under

light loads, the inductor current ramps to zero before the

next cycle; this is discontinuous-conduction mode.

Continuous-conduction mode occurs when the next

switching cycle begins while current is still flowing

through the inductor. The transition point between dis-

continuous- and continuous-conduction mode is deter-

mined by input and output voltages, and by the size of

the inductor relative to the peak switching current. In

general, reducing inductance toward the minimum rec-

ommended value pushes the transition point closer to

the maximum load current. If the inductor value is low

enough or the output/input voltage ratio high enough,

the DC-DC converter may remain in discontinuous-con-

duction mode throughout its entire load range.

The MAX863 transitions into continuous-conduction

mode in two ways, depending on whether preset or

adjustable mode is used and how the external feed-

back network is compensated. Under light loads, the IC

switches in single pulses (Figure 3a). The threshold of

transition into continuous-conduction mode is reached

when the inductor current waveforms are adjacent to

one another, as shown in Figure 3b. As the load

increases, the transition into continuous-conduction

mode progresses by raising the minimum inductor cur-

rent (Figures 3c, 3d). Depending on feedback compen-

sation, transition into continuous-conduction mode may

also progress with grouped pulses (Figures 3e, 3f).

Pulse groups should be separated by less than two or

three switching cycles. Output ripple should not be

significantly more than the single-cycle no-load case.

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