Rainbow Electronics MAX1760 - Manual (Page 7)

MAX1760
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
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Detailed Description
The MAX1760 is a highly efficient, low-noise power sup-
ply for portable RF and hand-held instruments. It com-
bines a boost switching regulator, N-channel power
MOSFET, P-channel synchronous rectifier, precision
reference, and shutdown control (Figure 1).
The DC-DC converter boosts a 1-cell to 3-cell battery
voltage input to a fixed 3.3V or adjustable voltage
between 2.5V and 5.5V. An external Schottky diode is
required for output voltages greater than 4V. The
MAX1760 guarantees startup with an input voltage as
low as 1.1V and remains operational down to an input
of just 0.7V. It is optimized for use in cellular phones
and other applications requiring low noise and low qui-
escent current for maximum battery life. It features
fixed-frequency operation at medium and heavy loads,
but at light loads, switches only as needed for optimum
efficiency. This device is also capable of constant-fre-
quency (1MHz), low-noise PWM operation at all load
currents, or frequency-synchronized PWM operation
when connected to an external clock. Table 1 lists
some typical outputs. Shutdown reduces quiescent cur-
rent to just 1µA. Figure 2 shows the standard applica-
tion circuit for the MAX1760.
Step-Up Converter
During DC-DC converter operation, the internal N-chan-
nel MOSFET switch turns on for the first part of each
cycle, allowing current to ramp up in the inductor and
store energy in a magnetic field. During the second
part of each cycle, the MOSFET turns off and inductor
current flows through the synchronous rectifier to the
2.15V
IC POWER
1.25V
REFERENCE
UNDERVOLTAGE LOCKOUT
STARTUP
OSCILLATOR
OSCILLATOR
1MHz
CONTROLLER
MODE
PCH
NCH
EN D
EN
POUT
LX
PGND
OSC OSC
MODE CLK/SEL
ISET FB
EN
Q
REF
FB
ISET
GND
CLK/SEL
ON RDY
REF GND
ON
OUT
MAX1760
Figure 1. Functional Diagram
FB PGND GND
POUT
LX
ISET
OUT
REF
CLK/SEL
V IN = 2.4V
V OUT = 3.3V,
800mA
ON
MAX1760
3.3 µH
0.68 µF
4.7 Ω
33 µF
0.22 µF
100 µF
Figure 2. Standard Application Circuit