MAX1705 Maxim, MAX1705 Datasheet - Page 10

• Manufacturer Part Number: MAX1705
• Description: 1- to 3-Cell / High-Current / Low-Noise / Step-Up DC-DC Converters with Linear Regulator
• Manufacturer: Maxim

The MAX1705/MAX1706 are designed to supply both
power and low-noise circuitry in portable RF and data-
acquisition instruments. They combine a linear regula-
tor, step-up switching regulator, N-channel power
MOSFET, P-channel synchronous rectifier, precision
reference, and low-battery comparator in a single 16-
pin QSOP package (Figure 1). The switching DC-DC
converter boosts a 1- or 2-cell input to an adjustable
output between 2.5V and 5.5V. The internal low-dropout
regulator provides linear post-regulation for noise-
sensitive circuitry, as well as outputs from 1.25V to
300mV below the switching-regulator output. The
MAX1705/MAX1706 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
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
Figure 1. Functional Diagram
10
_______________Detailed Description
CLK/SEL
TRACK
FBLDO
______________________________________________________________________________________
LBO
LBN
OUT
GND
ONA
REF
LBP
ONB
FB
2.15V
V
IC PWR
OUT
- 300mV
V
LDO
ON
REFERENCE
1.250V
N
RDY
SHUTDOWN
THERMAL
SENSOR
LOGIC
maximum battery life during standby and shutdown.
They feature constant-frequency (300kHz), low-noise
pulse-width-modulation (PWM) operation with 300mA or
730mA output capability from one or two cells, respec-
tively, with 3.3V output. A low-quiescent-current stand-
by pulse-frequency-modulation (PFM) mode offers an
output up to 60mA and 140µA, respectively, and
reduces quiescent power consumption to 500µW. In
shutdown mode, the quiescent current is further
reduced to just 1µA. Figure 2 shows the standard appli-
cation circuit for the MAX1705 configured in high-
power PWM mode.
Additional features include synchronous rectification for
high efficiency and improved battery life, and an
uncommitted comparator for low-battery detection. A
CLK/SEL input allows frequency synchronization to
reduce interference. Dual shutdown controls allow shut-
down using a momentary pushbutton switch and micro-
processor control.
EN
REF
EN
OSCILLATOR
300kHz
OSCILLATOR
START-UP
ERROR
AMP
PFM/PWM
Q
MOSFET DRIVER
WITH CURRENT
D
EN
OSC
IFB
MODE
IREF
CONTROLLER
LIMITING
PFM/PWM
MAX1705
MAX1706
ICS
Q
Q
OUT
N
P
P
POUT
PGND
LDO
LX