MAX8969(2011) データシートの表示（PDF） - Maxim Integrated

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MAX8969
(Rev.:2011)

Step-Up Converter for Handheld Applications

Maxim Integrated 

Step-Up Converter

for Handheld Applications

MAX8969

IN

CIN

4.7µF

TREN

EN

REFERENCE

ATM

COMPARATOR

RAMP

GENERATOR

IN

0.95 x

VOUT_TARGET

CONTROL

LOGIC

IN

ATM

TRACK

ENABLE

PWM

LOGIC

CURRENT

LIMIT

L1

1µH

OUT_

COUT

22µF

P1

TRUE

SHUTDOWN

N1

GND_ LX_

Figure 1. Functional Diagram

Detailed Description

The MAX8969 is a step-up DC-DC switching converter

that utilizes a fixed-frequency PWM architecture with

True Shutdown. With an advanced voltage-positioning

control scheme and high 3MHz switching frequency, the

IC is inexpensive to implement and compact, using only

a few small easily obtained external components. Under

light-load conditions, the IC switches only when needed,

consuming only 45FA (typ) of quiescent current. The IC

is highly efficient with an internal switch and synchronous

rectifier. Shutdown typically reduces the quiescent current

to 1FA (typ). Low quiescent current and high efficiency

make this device ideal for powering portable equipment.

Internal soft-start limits inrush current to less than 720mA

(typ), while output voltage is less than input voltage. Once

output voltage approaches input voltage approaches

input voltage after a brief delay, output voltage is boosted

to its final value at a rate of approximately 25mV/µs.

During this period, as well as being limited by the volt-

age, ramp rate current is limited by the normal 2.6A boost

mode current limit.

In boost mode, the step-up converter boosts to

VOUT_TARGET from battery input voltages ranging from

2.5V to VOUT_TARGET. When the input voltage ranges

from 0.95 x VOUT_TARGET to 5.5V, the IC enters ATM and

the output voltage approximately follows the input volt-

age. During boost mode, the input current limit is set to

2.6A to guarantee delivery of the rated out current (e.g.,

1A output current when boosting from a 2.5V input supply

to a 3.7V output).

Control Scheme

The step-up converter uses a load/line control scheme.

The load/line control scheme allows the output voltage

to sag under load, but prevents overshoot when the

load is suddenly removed. The load/line control scheme

reduces the total range of voltages reached during

transients at the expense of DC output impedance.

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