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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

__________Applications Information

Low-Input-Voltage Operation

When the voltage at VDD falls and EXT1 or EXT2

approaches the MOSFET gate-to-source threshold volt-

age, the MOSFET may operate in its linear region and

dissipate excessive power. Prolonged operation in this

mode may damage the MOSFET if power dissipation

ratings are inadequate. This effect is more significant in

non-bootstrapped mode, but can occur in boot-

strapped mode if the input voltage drops so low that it

cannot support the load and causes the output voltage

to collapse. To avoid this condition, use logic-level or

low-threshold MOSFETs.

Starting Up Under Load

The Typical Operating Characteristics show the

Bootstrapped-Mode Minimum Start-Up Input Voltage

vs. Output Current graph. The MAX863 is not intended

to start up under full load in bootstrapped mode with

low input voltages.

________________Application Circuits

Bootstrapped 5V Logic and

24V LCD Bias Supply

The circuit in Figure 8 operates from two AA or AAA

cells, and generates 5V (up to 750mA) for logic and

24V (up to 35mA) for an LCD bias supply. OUT1 is

used to bootstrap the MAX863 for better MOSFET gate

drive. VOUT1 can be set to 3.3V if low threshold

MOSFETs are used.

VIN = 2.0V TO 11V OR VOUT2

T1

10µH, 2.5A

CTX10-4

FLYBACK OR SEPIC

OUTPUT

D1

C9

VOUT1 = 3.3V, 600mA MBRS340T3 10µF

C1

330µF

10V

≤0.1Ω

N1A

R1

50mΩ

R7

100k

C3

100µF

10V

≤0.1Ω

D3

CMPSH-3C

C4

100µF

10V

≤0.1Ω

C2

1µF

L2

10µH

2A

D2

MBRS340T3

SENSE1 FB1 VDD BOOT

EXT1

EXT2

CS1

CS2

N1B

IRF7301

R5

R2

R3

50mΩ

1M

MAX863

1%

LBI

FB2

R6

R4

SHDN1

SHDN2

ON/OFF

115k

1%

LOW-BATTERY

DETECTOR OUTPUT

LBO

REF

PGND GND

C7

0.1µF

VOUT2 = 12V

C5

100µF

20V

≤0.1Ω

C6

10pF

C8

82pF

Figure 9. 3-Cell to 3.3V Step-Up/Step-Down Logic Supply with 12V for Flash Memory or Analog Functions

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