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MAX1765EEE+ |MAX1765EEEMAXN/a90avai800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
MAX1765EUE+T |MAX1765EUETMAXIN/a5083avai800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator


MAX1765EUE+T ,800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear RegulatorELECTRICAL CHARACTERISTICS(V = V = V = V = V = 3.6V, CLK/SEL = FBL = ONB = TRACK = PGND = GND, ISET ..
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MAX4591EPE ,High-Speed / Single-Supply / Quad / SPST Analog SwitchesFeaturesThe MAX4591/MAX4592/MAX4593 are high-speed,  Low 16Ω On-Resistanceprecision, quad, single- ..
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MAX4592CUE+ ,High-Speed, Single-Supply, Quad, SPST Analog SwitchesApplicationsMAX4591CUE 0°C to +70°C 16 TSSOPMAX4591CSE 0°C to +70°C 16 Narrow SOTest Equipment Samp ..


MAX1765EEE+-MAX1765EUE+T
800mA, Low-Noise, Step-Up DC-DC Converter with 500mA Linear Regulator
General Description
The MAX1765 is a high-efficiency, low-noise, step-up
DC-DC converter intended for use in battery-powered
wireless applications. This device operates at a high
1MHz fixed frequency while maintaining an exception-
ally low quiescent supply current (200µA). Its small
external components and tiny package make this
device an excellent choice for small hand-held applica-
tions that require the longest possible battery life.
The MAX1765 uses a synchronous-rectified pulse-
width-modulation (PWM) boost topology to generate
2.5V to 5.5V outputs from a wide range of input
sources, such as one to three alkaline or NiCd/NiMH
cells or a single lithium-ion (Li+) cell. Maxim's propri-
etary architecture significantly improves efficiency at
low load currents while automatically transitioning to
fixed-frequency PWM operation at medium to high load
currents to maintain excellent full-load efficiency.
Forced-PWM mode is available for applications that
require constant-frequency operation at all load cur-
rents, and the MAX1765 may also be synchronized to
an external clock to protect sensitive frequency bands
in communications equipment.
The MAX1765’s low-dropout (LDO) linear regulator and
DC-DC converter have separate shutdown control. The
linear regulator's 250mΩpass device maintains excel-
lent dropout voltage at currents up to 500mA. The
MAX1765 also features analog soft-start and current-
limit functions to permit optimization of efficiency, exter-
nal component size, and output voltage ripple.
The MAX1765 comes in a 16-pin QSOP package and a
thermally enhanced 16-pin TSSOP-EP.
____________________________Features
High-Efficiency Step-Up Converter
Up to 93% Efficiency
Adjustable Output from +2.5V to +5.5V
Up to 800mA Output
PWM Synchronous-Rectified Topology
1MHz Operating Frequency (or Sync)
LDO Linear Regulator
500mA LDO Linear Regulator
2.85V Linear Regulator Output or Adjustable
(1.25V to 5V)
Low 125mV Dropout at 500mA
+0.7V to +5.5V Input Range0.1μA Logic-Controlled ShutdownAdjustable Inductor Current Limit and Soft-StartThermal Shutdown1.5W, 16-Pin TSSOP-EP Package Available
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator

19-1805; Rev 1; 4/11
FBLONL
TRACK
INL
POUT
PGND
OUTL
TOP VIEW
MAX1765
QSOP/TSSOP-EP

ONB
ISET
REF
OUT
GND
ONA
CLK/SEL
Pin Configuration

Wireless Handsets
PCS Phones
Palmtop Computers
Personal
Communicators
Hand-Held Instruments
Portable Audio Players
Applications

FBL
REF
ILIM
ONLONA
(0.7V TO 5.5V)3.3μH
OUTL = 2.85V
(ADJ 1.25V
TO 5V)
OUT = 3.3V
OUT
OUTL
POUT
GNDPGND
TRACK
CLK/SEL
ONB
INL
MAX1765
Typical Operating Circuit
Ordering Information

*EP = Exposed pad.
+Denotes a lead(Pb)-free/RoHS-compliant package.PART TEMP RANGE PIN-PACKAGE
MAX1765EEE+-40°C to +85°C16 QSOP
MAX1765EUE+-40°C to +85°C16 TSSOP-EP*
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(VOUT= VPOUT= VINL= VONA= VONL= 3.6V, CLK/SEL = FBL = ONB= TRACK = PGND = GND, ISET = REF (bypassed with
0.22µF), LX = open, OUTL = open (bypassed with 4.7µF), TA= 0°C to +85°C, unless otherwise noted. Typical values are at= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ONA, ONB, ONL, TRACK, OUT, INL to GND..............-0.3V, +6V
PGND to GND.....................................................................±0.3V
LX to GND...............................................-0.3V to (POUT + 0.3V)
OUTL to GND..............................................-0.3V to (INL + 0.3V)
CLK/SEL, REF, FB, FBL, ISET, POUT
to GND...................................................-0.3V to (OUT + 0.3V)
OUTL Short Circuit.....................................................Continuous
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
16-Pin TSSOP-EP (derate 19mW/°C above +70°C)....1500mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow).......................................+260°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
DC-DC CONVERTER

Input Voltage Range(Note 1)0.75.5V
INL Voltage Range(Note 1)2.35.5V
Minimum Startup VoltageILOAD < 1mA, TA = +25°C, Figure 20.91.1V
Temperature Coefficient of
Startup VoltageILOAD < 1mA-2m V /°C
FB Regulation VoltageVFBCLK/SEL = OUT, 0 < ILX < 0.55A1.2151.2501.275V
FB Input Leakage CurrentVFB = 1.35V0.01100nA
Output Voltage Adjust Range2.55.5V
Load RegulationCLK/SEL = OUT, 0 < ILOAD < 800mA-1%
OUT Voltage in Track ModeVOUTL > 2.0V, INL = POUTVOUTL
+ 0.4
VOUTL
+ 0.5
VOUTL
+ 0.6V
Frequency in Startup ModefLXVOUT = 1.5V1251000kHz
Startup to Normal Mode
Transition VoltageRising edge only (Note 2)2.002.152.30V
ISET Input Leakage CurrentVISET = 1.25V0.0150nA
Supply Current in Normal Mode
(Note 3)CLK/SEL = ONL = GND, no load100200μA
VFB = 1.5V130200μASupply Current in Low-Noise
PWM Mode (Note 3)LK/S E L = OU T,
no l oad FB = GN D ( LX sw i tchi ng ) 2.5mA
Supply Current in ShutdownONA = ONL = GND, ONB = OUT110μA
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)

(VOUT= VPOUT= VINL= VONA= VONL= 3.6V, CLK/SEL = FBL = ONB= TRACK = PGND = GND, ISET = REF (bypassed with
0.22µF), LX = open, OUTL = open (bypassed with 4.7µF), TA= 0°C to +85°C, unless otherwise noted. Typical values are at= +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
DC-DC SWITCHES

POUT Leakage CurrentVLX = 0V, VOUT = 5.5V0.110µA
LX Leakage CurrentVLX = VOUT = V ONB = 5.5V, ONA = GND0.110µA
N-channel0.170.28Switch On-ResistanceP-channel0.220.5Ω- C hannel C ur r ent Li m i t ( N ote 4) ILIMVISET = 1.25V, CLK/SEL = GND or OUT100012501600mA
P-Channel Turn-Off CurrentCLK/SEL = GND1050120mA
REFERENCE

Reference Output VoltageVREFIREF = 0A1.2301.2501.270V
Reference Load Regulation-1µA < IREF < 50µA515mV
Reference Supply Regulation2.5V < VOUT < 5.5V0.25mV
LINEAR REGULATOR

INL Voltage Range(Note 1)2.35.5V
INL Startup VoltageVINLVOUT = 2V, rising edge only2.152.302.45V
Output Voltage in Internal
Feedback ModeFBL = GND, IOUTL = 10mA2.802.852.90V
FBL Dual-Mode Threshold150250350mV
FBL Regulation VoltageVFBLFBL = OUTL, IOUTL = 10mA, IREF = 0A1.2301.2501.270V
FBL Input Leakage CurrentVFBL = 1.5V0.0150nA
OUTL Adjust Range1.255V
Short-Circuit Current LimitVFBL = 1V5501300mA
Dropout ResistanceVFBL = 1V, IOUTL = 500mA0.250.5Ω
Load Regulation1mA < IOUTL < 500mA, FBL = GND0.51%
Line Regulation2.5V < (VOUT = VINL = VPOUT) < 5.5V,
FBL = OUTL-0.50.5%
INL Supply Current in ShutdownOUTL = ONA = ONL = GND0.110µA
INL No-Load Supply CurrentIOUTL = 0A, VINL = 5.5V90250µA
AC Power-Supply Rejectionf = 10kHz65dB
Thermal ShutdownHysteresis approximately 10°C160°C
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)

(VOUT= VPOUT= VINL= VONA= VONL= 3.6V, CLK/SEL = FBL = ONB= TRACK = PGND = GND, ISET = REF (bypassed with
0.22µF), LX = open, OUTL = open (bypassed with 4.7µF), TA= 0°C to +85°C, unless otherwise noted. Typical values are at=+25 °C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
CONTROL INPUTS

1.1V < VOUT < 1.8V0.2O N A, O NB, O N LN ote 5) 1.8V < VOUT < 5.5V0.4
CLK/SEL1.2V < VOUT < 5.5V0.2 ×
VOUTInput Low Level
TRACK1.2V < VINL < 5.5V0.2 ×
VINL
1.1V < VOUT < 1.8VVOUT
- 0.2O N A, O NB, O N LN ote 5)
1.8V < VOUT < 5.5V1.6
CLK/SEL1.2V < VOUT < 5.5V0.8 ×
VOUT
Input High Level
TRACK1.2V < VINL < 5.5V0.8 ×
VINL
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)
0.011μA
Internal Oscillator FrequencyCLK/SEL = OUT0.811.2MHz
External Oscillator
Synchronization Range0.51.2MHz
Oscillator Maximum Duty Cycle808690%
Minimum CLK/SEL Pulse200nsaxi m um C LK/S E L Ri se/Fal l Ti m e100ns
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS

(VOUT= VPOUT= VINL= VONA= VONL= 3.6V, CLK/SEL = FBL = ONB= TRACK = PGND = GND, ISET = REF (bypassed with
0.22µF), LX = open, OUTL = open (bypassed with 4.7µF), TA= -40°C to +85°C, unless otherwise noted.) (Note 6)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
DC-DC CONVERTER

FB Regulation VoltageVFBCLK/SEL = OUT, 0 < ILX < 0.55A1.2101.280V
OUT Voltage in Track ModeVOUTL > 2.0V, INL = POUTVOUTL
+ 0.4
VOUTL
+ 0.6V
Startup to Normal Mode
Transition VoltageRising edge only (Note 2)2.002.30V
Supply Current in Normal Mode
(Note 3)CLK/SEL = ONL = GND, no load200µA
Supply Current in
Low-Noise PWM Mode (Note 3C LK/S E L = OU T, V FB = 1.5V , no l oad 200µA
Supply Current in ShutdownONA = ONL = GND, ONB = OUT10µA
DC-DC SWITCHES

POUT Leakage CurrentVLX = 0V, VOUT = 5.5V10µA
LX Leakage CurrentVLX = VOUT = V ONB = 5.5V, ONA = GND10µA
N-channel0.28Switch On-ResistanceP-channel0.50Ω- C hannel C ur r ent Li m i t ( N ote 4) ILIMVISET = 1.25V, CLK/SEL = GND or OUT10001600mA
P-Channel Turn-Off CurrentCLK/SEL = GND5120mA
REFERENCE

Reference Output VoltageIREF = 0A1.2251.275V
LINEAR REGULATOR

Output Voltage in Internal
Feedback ModeFBL = GND, IOUTL = 10mA2.792.90V
FBL Input Threshold150350mV
FBL Regulation VoltageFBL = OUTL, IOUTL = 10mA, IREF = 0A1.2251.275V
LDO Startup VoltageVOUT = 2V, rising edge only2.152.45V
Dropout ResistanceVFBL = 1V, IOUTL = 500mA0.5Ω
INL Supply Current in ShutdownOUTL = ONA = ONL = GND10µA
INL No-Load Supply CurrentIOUTL = 0A, VINL = 5.5V250µA
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)

(VOUT= VPOUT= VINL= VONA= VONL= 3.6V, CLK/SEL = FBL = ONB= TRACK = PGND = GND, ISET = REF (bypassed with
0.22µF), LX = open, OUTL = open (bypassed with 4.7µF), TA= -40°C to +85°C, unless otherwise noted.) (Note 6)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
CONTROL INPUTS

1.1V < VOUT < 1.8V0.2O N A, O NB, O N LN ote 5) 1.8V < VOUT < 5.5V0.4
CLK/SEL1.2V < VOUT < 5.5V 0.2 ×
VOUTInput Low Level
TRACK1.2V < VINL < 5.5V 0.2 ×
VINL
1.1V < VOUT < 1.8VVOUT
- 0.2O N A, O NB, O N LN ote 5) 1.8V < VOUT < 5.5V1.6
CLK/SEL1.2V < VOUT < 5.5V0.8 ×
VOUT
Input High Level
TRACK1.2V < VINL < 5.5V0.8 ×
VINL
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)μA
Internal Oscillator FrequencyCLK/SEL = OUT0.81.2MHz
Oscillator Maximum Duty Cycle7990%
Note 1:
Operating voltage. Since the regulator is bootstrapped to the output, once started it will operate down to 0.7V input.
Note 2:
The device is in startup mode when VOUTis below this value (see Low-Voltage Startup Oscillatorsection). Do not apply full
load current.
Note 3:
Supply current into the OUT and POUT pins. This current correlates directly to the actual battery-supply current, but is
reduced in value according to the step-up ratio and efficiency.
Note 4:
Minimum recommended ISET voltage in normal mode is 0.625V.
Note 5:
ONA, ONB, ONL have hysteresis of approximately 0.15 ✕VOUT.
Note 6:
Specifications to -40°C are guaranteed by design and not production tested.
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +5V)
MAX1765 toc05
LOAD CURRENT (A)
EFFICIENCY (%)
VIN = +1.2V
VIN = +1.2V
VIN = +3.6V
NORMAL MODE
VIN = +2.4V
VIN = +3.6V
VIN = +2.4V
PWM
MODE
LINEAR REGULATOR DROPOUT
VOLTAGE vs. LOAD CURRENT
MAX1765 toc07
DROPOUT VOLTAGE (V)
VOUTL = +2.5V
VOUTL = +2.85V
VOUTL = +5V100010010
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT

MAX1765 toc08
STARTUP INPUT VOLTAGE (V)
TA = +25°C
TA = -40°C
TA = +85°C1.01.50.52.02.53.03.5
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE

MAX1765 toc09
SUPPLY CURRENT (mA)
FPWM MODE
NORMAL MODE
EFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)
MAX1765 toc01
LOAD CURRENT (A)
EFFICIENCY (%)
VIN = +2.4V
NORMAL
MODE
VIN = +1.2V
VIN = +2.4V
VIN = +1.2V
PWM
MODE
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5V)
MAX1765 toc02
LOAD CURRENT (A)
EFFICIENCY (%)
PWM
MODE
VIN = +3.6V
VIN = +2.4V
VIN = +1.2V
VIN = +3.6VNORMAL MODE
VIN = +2.4V
VIN = +1.2V
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +2.85V)
MAX1765 toc03
LOAD CURRENT (A)
EFFICIENCY (%)
NORMAL MODE
VIN = +1.2V
VIN = +2.4V
VIN = +1.2V
VIN = +2.4V
PWM
MODE
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +3.3V)
MAX1765 toc04
LOAD CURRENT (A)
EFFICIENCY (%)
VIN = +1.2V
VIN = +1.2V
VIN = +2.4V
VIN = +3.6VVIN = +2.4V
NORMAL
MODENORMAL MODE/
PWM MODE
PWM
MODE
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX1765 toc06
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
VOUT = +5V, ISET = REF
VOUT = +3.3V, ISET = REF
VOUT = +3.3V, ISET = 0.5 REF
VOUT = +5V, ISET = 0.5 REF
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
LOAD TRANSIENT RESPONSE

MAX1765 toc14
A: IOUT, 500mA/div
B: VOUT,100mV/div
50μs/div
VIN = +2.4V, VOUT = +3.3V, IOUT = 0 TO 500mA
Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)
LDO PSRR vs. FREQUENCY
(100Hz TO 1MHz)
MAX1765 toc10
FREQUENCY (kHz)
LDO PSRR (dB)
BOOST FOLLOWED BY LDO
OUTPUT NOISE SPECTRUM
MAX1765 toc11
FREQUENCY (MHz)
NOISE (mV
RMSVIN = +2.4V
VOUT = +3.3V
LINE TRANSIENT RESPONSE
(DC-DC)

MAX1765 toc12
100μs/div
A: VIN, 500mV/div
B: VOUT, 1mV/div, AC-COUPLED
VOUT = +3.3V, I = 0mA
VIN = +1.4V TO +2.4V
LINE TRANSIENT RESPONSE
(LINEAR)

MAX1765 toc13
A: VIN, 2V/div
B: VOUT, 5mV/div, AC-COUPLED
I = 0mA, VIN = +3V TO +5V, VOUT = +3.3V
TURN-ON WAVEFORMS
NO SOFT-START COMPONENTS

MAX1765 toc15a
A: 0NA, 5V/div
B: VOUT, 2V/div
C: INPUT CURRENT, 1A/div
SOFT-START WAVEFORMS
(RSS = 500kΩ, CSS = 0.1μF)

MAX1765 toc15b
A: 0NA, 5V/div
B: INPUT CURRENT, 100mA/div
2.5ms/div
HEAVY-LOAD SWITCHING WAVEFORMS
(IOUT = 650mA, VIN = +2.4V, VOUT = 3.3V)

MAX1765 toc16
A: LX, 5V/div
B: INDUCTOR CURRENT, 200mA/div
500ns/div
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
PINNAMEFUNCTION
FBL
Low-Dropout Linear Regulator Dual-Mode Feedback Input. Connect FBL to ground for 2.85V nominal
output voltage. Connect FBL to a resistor-divider from OUTL to ground for an adjustable output voltage.
FBL regulates to 1.25V.ISET
Set N-Channel Current Limit. For maximum current limit, connect ISET to REF. To reduce current limit,
use a resistor-divider from REF to GND. If soft-start is desired, a capacitor can be added from ISET to
GND. When ONA = LO and ONB = HI or VREF < 80% of nominal value, an on-chip 100kΩ switchable
resistor discharges ISET to GND.REF1.25V Reference Output. Connect a 0.22µF bypass capacitor to GND; 50µA of external load current is
allowed. The reference is enabled if ONA = HI, ONB = LO, or ONL = HI.GNDGround. Connect to PGND with short trace.
5FBBoost Converter Feedback Input. Connect a resistor-divider between OUT and GND to set the output
voltage in the range of 2.5V to 5V. In track mode, FB is disabled after OUTL is in regulation.OUTBoost Converter IC power is derived from OUT. Connect OUT to POUT through a 4.7Ω resistor and
bypass to GND with a 0.68µF capacitor.ONAON Input. When high, the DC-DC is operational (Table 2).CLK/SEL
CLOCK Input for the DC-DC Converter. Also serves to program operating mode of switch as follows:
CLK/SEL = LOW: Normal mode. Operates at a fixed frequency, automatically switching to low-power

(SKIP) mode when the load is minimized.
CLK/SEL = HI: Forced PWM mode. Operates in low-noise, constant-frequency mode at all loads.
CLK/SEL = Clocked: Synchronized forced PWM mode. The internal oscillator is synchronized to an

external clock in the 500kHz to 1200kHz frequency range.
Pin Description

SWITCH CURRENT LIMIT vs. VISET
MAX1765 toc19
VISET (V)
SWITCH CURRENT LIMIT (A)
VOUT = +3.3
Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)
LIGHT-LOAD SWITCHING WAVEFORMS
(VIN = +2.4V, VOUT = +3.3V, IOUT = 10mA)

MAX1765 toc17
A: LX NODE, 5V/div
B: INDUCTOR CURRENT, 200mA/div, AC-COUPLED
C: OUTPUT RIPPLE, 20mV/div, AC-COUPLED
500ns/div
LINEAR-REGULATOR OUTPUT NOISE
MAX1765 toc18
FREQUENCY (MHz)
NOISE (mV
RMS
ILDO = 200mA
VLDO = 2.85V
MAX1765
Detailed Description

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 postregulation for noise-
sensitive circuitry, or it can be used as a separate volt-
age 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.
The switching regulator supports two low-noise modes:
fixed-frequency PWM for low noise in all load conditions,
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.
Step-Up Converter

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).
Normal Operation

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
less power. SKIP mode allows higher efficiency than
PWM under light-load conditions.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
PINNAMEFUNCTION
ONBON Input. When low, the DC-DC is operational (Table 2).PGNDPower GroundLXInductor connection to the drain of P-channel synchronous rectifier and N-channel switch.POUTBoost 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.INLLinear Regulator Power Input. Source of PFET pass device connected between INL and OUTL. Connect
INL to POUT.OUTLLinear Regulator Output. OUTL can source up to 500mA. Bypass OUTL to GND with a 4.7µF capacitor.TRACK
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).ONLLinear Regulator ON Input. Enables the linear regulator output when TRACK = LOW. ONA and ONB
determine the linear regulator’s output state when TRACK = HIGH.EPExposed Pad (TSSOP Only). Internally connected to GND and PGND. Connect to a large ground plane.
Pin Description (continued)
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