MAX1765EUE-T Maxim Integrated Products, MAX1765EUE-T Datasheet - Page 10
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MAX1765EUE-T
Manufacturer Part Number
MAX1765EUE-T
Description
DC/DC Switching Converters 800mA Step-Up w/500mA Linear Reg
Manufacturer
Maxim Integrated Products
Datasheet
1.MAX1765EEE.pdf
(19 pages)
The MAX1765 is a highly efficient, low-noise power
supply for portable RF hand-held instruments. This
boost power supply combines an LDO linear regulator,
a low-noise, high-power, step-up switching regulator,
an N-channel power MOSFET, a P-channel synchro-
nous rectifier, shutdown control, and a precision volt-
age reference in a single 16-pin QSOP or a thermally
enhanced TSSOP-EP (Figure 1).
The switching DC-DC converter boosts a 1-cell to 3-cell
NiMH/NiCd or a single Li+ battery input to an
adjustable output voltage between 2.5V and 5.5V. The
MAX1765 guarantees startup with voltages as low as
1.1V and will remain operational down to 0.7V (Figure
2). The internal LDO regulator provides linear postregu-
lation for noise-sensitive circuitry, or it can be used as a
separate voltage output adjustable from 1.25V up to
POUT.
The MAX1765 is 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.
The device automatically transitions to a low-quiescent-
current pulse-skipping control scheme during light
loads that reduces the quiescent power consumption to
360µW. The supply current of the device can be further
reduced to 1µA when the device is shut down. Figure 2
shows a typical application of the MAX1765 in normal
mode.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
10
PIN
10
11
12
13
14
15
16
9
______________________________________________________________________________________
TRACK
NAME
PGND
POUT
OUTL
ONB
ONL
INL
LX
Detailed Description
ON Input. When low, the DC-DC is operational (Table 2).
Power Ground
Inductor connection to the drain of P-channel synchronous rectifier and N-channel switch.
Boost Converter Power Output. POUT is the source of the P-channel synchronous-rectifier MOSFET
switch. Connect POUT to INL. Bypass POUT to PGND with a 100µF capacitor.
Linear Regulator Power Input. Source of PFET pass device connected between INL and OUTL.
Connect INL to POUT.
Linear Regulator Output. OUTL can source up to 500mA. Bypass OUTL to GND with a 4.7µF
capacitor.
Track-Mode Control Input for DC-DC Converter. In track mode, the boost converter output is sensed
at OUT and set to 0.5V above OUTL to improve efficiency. Set TRACK to OUT for track mode and to
GND for normal operation (Table 2).
Linear Regulator ON Input. Enables the linear regulator output when TRACK = LOW. ONA and ONB
determine the linear regulator’s output state when TRACK = HIGH.
The switching regulator supports two low-noise modes:
fixed-frequency PWM for low noise in all load condi-
tions, and synchronization of the internal oscillator to an
external clock driving the CLK input. In TRACK mode,
the DC and linear regulator work together to maintain
excellent PSRR without excessive efficiency loss.
Additional MAX1765 features include synchronous rec-
tification for high efficiency and increased battery life,
dual boost shutdown controls for µP or a pushbutton
momentary switch, and a separate shutdown control for
the linear regulator.
During DC-DC converter operation, the internal N-chan-
nel MOSFET 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 output filter
capacitor and the load. As the energy stored in the
inductor is depleted, the current ramps down and the
synchronous rectifier turns off. The CLK/SEL pin deter-
mines whether a pulse-skipping or PWM control method
is used at light loads (Table 1).
Pulling CLK/SEL low selects the MAX1765’s normal
operating mode. In this mode, the device operates in
PWM when driving medium to heavy loads and auto-
matically switches to SKIP mode if the load requires
FUNCTION
Pin Description (continued)
Step-Up Converter
Normal Operation