1-Cell to 3-Cell, High-Power (1A),

Low-Noise, Step-Up DC-DC Converters

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9

_______________Detailed Description

The MAX1700/MAX1701 are highly efficient, low-noise

power supplies for portable RF and data acquisition

instruments. The MAX1700 combines a boost switching

regulator, N-channel power MOSFET, P-channel syn-

chronous rectifier, precision reference, and shutdown

control. The MAX1701 contains all of the MAX1700 fea-

tures plus a versatile gain amplifier, POK output, and a

low-battery comparator (Figure 1). The MAX1700/

MAX1701 come in a 16-pin QSOP package, which

occupies no more space than an 8-pin SO.

The switching DC-DC converter boosts a 1- to 3-cell

input to an adjustable output between 2.5V and 5.5V.

The MAX1700/MAX1701 start from a low 1.1V input and

remain operational down to 0.7V.

These devices are optimized for use in cellular phones

and other applications requiring low noise during full-

power operation, as well as low-quiescent current for

maximum battery life during standby and shutdown

modes. They feature constant-frequency (300kHz), low-

noise PWM operation with up to 800mA output capabili-

ty. See Table 1 for typical available output current. A

low-quiescent-current, low-power mode offers an out-

put up to 100mA and reduces quiescent power con-

sumption to 200µW. In shutdown mode, the quiescent

current is further reduced to just 3µA. Figure 2 shows

the

standard

application

circuit

for

the

MAX1700/MAX1701.

Additional features include synchronous rectification for

high efficiency and improved battery life, a POK output,

and an uncommitted comparator for low-battery detec-

tion (MAX1701). A CLK input allows frequency synchro-

nization to reduce interference. Dual shutdown controls

allow shutdown using a momentary pushbutton switch

and microprocessor control (MAX1701).

2.25V

IC PWR

1.25V

FEEDBACK AND

POWER-GOOD

SELECT

REFERENCE

UNDERVOLTAGE LOCKOUT

COMPARATOR

GAIN

BLOCK

FEEDBACK

START-UP

OSCILLATOR

OSCILLATOR

300kHz

PFM/PWM

CONTROLLER

PFM/PWM

PCH

0.25

Ω

NCH

0.13

Ω

REF

EN

D

EN

POUT

LX

PGND

POK*

AO*

LBO*

N

N

N

OSC

MODE

FB

EN

Q

Q

Q

*MAX1701 ONLY

LBP*

LBN*

ONA

REF

FB

GND

CLK/SEL

ON

RDY

REF

AIN*

ONB

OUT

Figure 1. Functional Diagram