MAX1748 データシートの表示（PDF） - Maxim Integrated

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MAX1748

Triple-Output TFT-LCD DC-DC Converters

Maxim Integrated 

Triple-Output TFT-LCD

DC-DC Converters

L1

VIN = 2.7V TO 5.5V

VOUT = [1 + (R1 / R2)] x VREF

VREF = 1.25V

OSC

S

IN

D1

LX

VMAIN

(UP TO 13V)

INTG

CINTG

R

Q

-

+

ILIM

+

+

-

MAX1748

MAX8726

-

Gm

+

+-

1.25V

PGND

R1

C1

FB

RCOMP

REF

R2

C2

GND

CCOMP

Figure 1. PWM Boost Converter Block Diagram

Soft-Start

For the main boost regulator, soft-start allows a gradual

increase of the internal current-limit level during startup

to reduce input surge currents. The MAX1748/MAX8726

divide the soft-start period into four phases. During

phase 1, the MAX1748/MAX8726 limit the current limit to

only 0.38A (see the Electrical Characteristics tables),

approximately a quarter of the maximum current limit

(ILX(MAX)). If the output does not reach regulation within

1ms, soft-start enters phase II and the current limit is

increased by another 25%. This process is repeated for

phase III. The maximum 1.5A (typ) current limit is

reached at the end of phase III or when the output

reaches regulation, whichever occurs first (see the start-

up waveforms in the Typical Operating Characteristics).

For the charge pumps, soft-start is achieved by control-

ling the rise rate of the output voltage. The output volt-

age regulates within 4ms, regardless of output

capacitance and load, limited only by the regulator’s

output impedance.

Shutdown

A logic-low level on SHDN disables all three

MAX1748/MAX8726 converters and the reference.

When shut down, supply current drops to 0.1µA to

maximize battery life and the reference is pulled to

ground. The output capacitance and load current

determine the rate at which each output voltage will

decay. A logic-level high on SHDN power activates the

MAX1748/MAX8726 (see the Power-Up Sequencing

section). Do not leave SHDN floating. If unused,

connect SHDN to IN.

Power-Up Sequencing

Upon power-up or exiting shutdown, the MAX1748 and

MAX8726 start their respective power-up sequences.

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