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
oHigh-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)
oLDO Linear Regulator
500mA LDO Linear Regulator
2.85V Linear Regulator Output or Adjustable
(1.25V to 5V)
Low 125mV Dropout at 500mA
o+0.7V to +5.5V Input Range
o0.1μA Logic-Controlled Shutdown
oAdjustable Inductor Current Limit and Soft-Start
oThermal Shutdown
o1.5W, 16-Pin TSSOP-EP Package Available
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
________________________________________________________________
Maxim Integrated Products
1
19-1805; Rev 1; 4/11
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
FBL ONL
TRACK
INL
POUT
LX
PGND
OUTL
TOP VIEW
MAX1765
QSOP/TSSOP-EP
ONB
ISET
REF
OUT
GND
FB
ONA
CLK/SEL
Pin Configuration
Wireless Handsets
PCS Phones
Palmtop Computers
Personal
Communicators
Hand-Held Instruments
Portable Audio Players
Applications
FBL
REF
ILIM
ONL ONA
(0.7V TO 5.5V) 3.3μH
OUTL = 2.85V
(ADJ 1.25V
TO 5V)
OUT = 3.3V
OUT
OUTL
POUT
FB
GND PGND
TRACK
LX
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
2 _______________________________________________________________________________________
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
TA= +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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DC-DC CONVERTER
Input Voltage Range (Note 1) 0.7 5.5 V
INL Voltage Range (Note 1) 2.3 5.5 V
Minimum Startup Voltage ILOAD < 1mA, TA = +25°C, Figure 2 0.9 1.1 V
Temperature Coefficient of
Startup Voltage ILOAD < 1mA -2 m V /°C
FB Regulation Voltage VFB CLK/SEL = OUT, 0 < ILX < 0.55A 1.215 1.250 1.275 V
FB Input Leakage Current VFB = 1.35V 0.01 100 nA
Output Voltage Adjust Range 2.5 5.5 V
Load Regulation CLK/SEL = OUT, 0 < ILOAD < 800mA -1 %
OUT Voltage in Track Mode VOUTL > 2.0V, INL = POUT VOUTL
+ 0.4
VOUTL
+ 0.5
VOUTL
+ 0.6 V
Frequency in Startup Mode fLX VOUT = 1.5V 125 1000 kHz
Startup to Normal Mode
Transition Voltage Rising edge only (Note 2) 2.00 2.15 2.30 V
ISET Input Leakage Current VISET = 1.25V 0.01 50 nA
Supply Current in Normal Mode
(Note 3) CLK/SEL = ONL = GND, no load 100 200 μA
VFB = 1.5V 130 200 μA
Supply Current in Low-Noise
PWM Mode (Note 3)
C LK/S E L = OU T,
no l oad FB = GN D ( LX sw i tchi ng ) 2.5 mA
Supply Current in Shutdown ONA = ONL = GND, ONB = OUT 1 10 μA
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
_______________________________________________________________________________________ 3
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
TA= +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
DC-DC SWITCHES
POUT Leakage Current VLX = 0V, VOUT = 5.5V 0.1 10 µA
LX Leakage Current VLX = VOUT = V ONB = 5.5V, ONA = GND 0.1 10 µA
N-channel 0.17 0.28
Switch On-Resistance P-channel 0.22 0.5 Ω
N - C hannel C ur r ent Li m i t ( N ote 4) ILIM VISET = 1.25V, CLK/SEL = GND or OUT 1000 1250 1600 mA
P-Channel Turn-Off Current CLK/SEL = GND 10 50 120 mA
REFERENCE
Reference Output Voltage VREF IREF = 0A 1.230 1.250 1.270 V
Reference Load Regulation -1µA < IREF < 50µA 5 15 mV
Reference Supply Regulation 2.5V < VOUT < 5.5V 0.2 5 mV
LINEAR REGULATOR
INL Voltage Range (Note 1) 2.3 5.5 V
INL Startup Voltage VINL VOUT = 2V, rising edge only 2.15 2.30 2.45 V
Output Voltage in Internal
Feedback Mode FBL = GND, IOUTL = 10mA 2.80 2.85 2.90 V
FBL Dual-Mode Threshold 150 250 350 mV
FBL Regulation Voltage VFBL FBL = OUTL, IOUTL = 10mA, IREF = 0A 1.230 1.250 1.270 V
FBL Input Leakage Current VFBL = 1.5V 0.01 50 nA
OUTL Adjust Range 1.25 5 V
Short-Circuit Current Limit VFBL = 1V 550 1300 mA
Dropout Resistance VFBL = 1V, IOUTL = 500mA 0.25 0.5 Ω
Load Regulation 1mA < IOUTL < 500mA, FBL = GND 0.5 1 %
Line Regulation 2.5V < (VOUT = VINL = VPOUT) < 5.5V,
FBL = OUTL -0.5 0.5 %
INL Supply Current in Shutdown OUTL = ONA = ONL = GND 0.1 10 µA
INL No-Load Supply Current IOUTL = 0A, VINL = 5.5V 90 250 µA
AC Power-Supply Rejection f = 10kHz 65 dB
Thermal Shutdown Hysteresis approximately 10°C 160 °C
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
4 _______________________________________________________________________________________
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
TA=+25 °C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CONTROL INPUTS
1.1V < VOUT < 1.8V 0.2
O N A, O NB, O N L
( N ote 5) 1.8V < VOUT < 5.5V 0.4
CLK/SEL 1.2V < VOUT < 5.5V 0.2 ×
VOUT
Input Low Level
TRACK 1.2V < VINL < 5.5V 0.2 ×
VINL
V
1.1V < VOUT < 1.8V VOUT
- 0.2
O N A, O NB, O N L
( N ote 5) 1.8V < VOUT < 5.5V 1.6
CLK/SEL 1.2V < VOUT < 5.5V 0.8 ×
VOUT
Input High Level
TRACK 1.2V < VINL < 5.5V 0.8 ×
VINL
V
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)
0.01 1 μA
Internal Oscillator Frequency CLK/SEL = OUT 0.8 1 1.2 MHz
External Oscillator
Synchronization Range 0.5 1.2 MHz
Oscillator Maximum Duty Cycle 80 86 90 %
Minimum CLK/SEL Pulse 200 ns
M axi m um C LK/S E L Ri se/Fal l Ti m e100 ns
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
_______________________________________________________________________________________ 5
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)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
DC-DC CONVERTER
FB Regulation Voltage VFB CLK/SEL = OUT, 0 < ILX < 0.55A
1.210 1.280
V
OUT Voltage in Track Mode VOUTL > 2.0V, INL = POUT VOUTL
+ 0.4
VOUTL
+ 0.6
V
Startup to Normal Mode
Transition Voltage Rising edge only (Note 2)
2.00 2.30
V
Supply Current in Normal Mode
(Note 3) CLK/SEL = ONL = GND, no load
200
µA
Supply Current in
Low-Noise PWM Mode (Note 3 C LK/S E L = OU T, V
FB = 1.5V , no l oad
200
µA
Supply Current in Shutdown ONA = ONL = GND, ONB = OUT 10 µA
DC-DC SWITCHES
POUT Leakage Current VLX = 0V, VOUT = 5.5V 10 µA
LX Leakage Current VLX = VOUT = V
ONB = 5.5V, ONA = GND 10 µA
N-channel
0.28
Switch On-Resistance P-channel
0.50
Ω
N - C hannel C ur r ent Li m i t ( N ote 4)
ILIM VISET = 1.25V, CLK/SEL = GND or OUT
1000 1600
mA
P-Channel Turn-Off Current CLK/SEL = GND 5
120
mA
REFERENCE
Reference Output Voltage IREF = 0A
1.225 1.275
V
LINEAR REGULATOR
Output Voltage in Internal
Feedback Mode FBL = GND, IOUTL = 10mA
2.79 2.90
V
FBL Input Threshold
150 350
mV
FBL Regulation Voltage FBL = OUTL, IOUTL = 10mA, IREF = 0A
1.225 1.275
V
LDO Startup Voltage VOUT = 2V, rising edge only
2.15 2.45
V
Dropout Resistance VFBL = 1V, IOUTL = 500mA 0.5 Ω
INL Supply Current in Shutdown
OUTL = ONA = ONL = GND 10 µA
INL No-Load Supply Current IOUTL = 0A, VINL = 5.5V
250
µA
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
6 _______________________________________________________________________________________
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)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CONTROL INPUTS
1.1V < VOUT < 1.8V 0.2
O N A, O NB, O N L
( N ote 5) 1.8V < VOUT < 5.5V 0.4
CLK/SEL 1.2V < VOUT < 5.5V 0.2 ×
VOUT
Input Low Level
TRACK 1.2V < VINL
< 5.5V 0.2 ×
VINL
V
1.1V < VOUT < 1.8V VOUT
- 0.2
O N A, O NB, O N L
( N ote 5) 1.8V < VOUT
< 5.5V 1.6
CLK/SEL 1.2V < VOUT < 5.5V 0.8 ×
VOUT
Input High Level
TRACK 1.2V < VINL
< 5.5V 0.8 ×
VINL
V
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)
1μA
Internal Oscillator Frequency CLK/SEL = OUT 0.8 1.2 MHz
Oscillator Maximum Duty Cycle 79 90 %
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 VOUT is below this value (see
Low-Voltage Startup Oscillator
section). 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
_______________________________________________________________________________________
7
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
0
0.001 10.10.01
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +5V)
30
10
70
50
90
40
20
80
60
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
0
0.05
0.10
0.15
0.20
0.25
0.30
0 200100 300 400 500 600 700 800
LINEAR REGULATOR DROPOUT
VOLTAGE vs. LOAD CURRENT
MAX1765 toc07
LOAD CURRENT (mA)
DROPOUT VOLTAGE (V)
VOUTL = +2.5V
VOUTL = +2.85V
VOUTL = +5V
0
1 100010010
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT
2.5
1.0
0.5
2.0
1.5
MAX1765 toc08
OUTPUT CURRENT (mA)
STARTUP INPUT VOLTAGE (V)
TA = +25°C
TA = -40°C
TA = +85°C
0
4
2
10
8
6
16
14
12
18
0 1.0 1.50.5 2.0 2.5 3.0 3.5
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1765 toc09
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
FPWM MODE
NORMAL MODE
90
0
0.001 10.10.01
EFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)
30
10
70
50
100
40
20
80
60
MAX1765 toc01
LOAD CURRENT (A)
EFFICIENCY (%)
VIN = +2.4V
NORMAL
MODE
VIN = +1.2V
VIN = +2.4V
VIN = +1.2V
PWM
MODE
90
0
0.001 10.10.01
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5V)
30
10
70
50
100
40
20
80
60
MAX1765 toc02
LOAD CURRENT (A)
EFFICIENCY (%)
PWM
MODE
VIN = +3.6V
VIN = +2.4V
VIN = +1.2V
VIN = +3.6V NORMAL MODE
VIN = +2.4V
VIN = +1.2V
90
0
0.001 10.10.01
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +2.85V)
30
10
70
50
100
40
20
80
60
MAX1765 toc03
LOAD CURRENT (A)
EFFICIENCY (%)
NORMAL MODE
VIN = +1.2V
VIN = +2.4V
VIN = +1.2V
VIN = +2.4V
PWM
MODE
0
0.001 10.10.01
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +3.3V)
30
10
70
50
90
40
20
80
60
MAX1765 toc04
LOAD CURRENT (A)
EFFICIENCY (%)
VIN = +1.2V
VIN = +1.2V
VIN = +2.4V
VIN = +3.6V
VIN = +2.4V
NORMAL
MODE NORMAL MODE/
PWM MODE
PWM
MODE
0
600
400
200
800
1000
1200
02.01.50.5 1.0 2.5 3.0 3.5 4.0 4.5 5.0
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
8 _______________________________________________________________________________________
LOAD TRANSIENT RESPONSE
MAX1765 toc14
A: IOUT, 500mA/div
B: VOUT,100mV/div
A
B
50μs/div
VIN = +2.4V, VOUT = +3.3V, IOUT = 0 TO 500mA
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
0
-10
-20
-30
-40
-50
-60
-70
-80
0.1 10 1001 1000
LDO PSRR vs. FREQUENCY
(100Hz TO 1MHz)
MAX1765 toc10
FREQUENCY (kHz)
LDO PSRR (dB)
16
0.1 1 10
BOOST FOLLOWED BY LDO
OUTPUT NOISE SPECTRUM
0
MAX1765 toc11
FREQUENCY (MHz)
NOISE (mVRMS)
4
2
8
10
6
12
14
VIN = +2.4V
VOUT = +3.3V
LINE TRANSIENT RESPONSE
(DC-DC)
MAX1765 toc12
100μs/div
A: VIN, 500mV/div
B: VOUT, 1mV/div, AC-COUPLED
A
B
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
A
B
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
A
B
C
SOFT-START WAVEFORMS
(RSS = 500kΩ, CSS = 0.1μF)
MAX1765 toc15b
A: 0NA, 5V/div
B: INPUT CURRENT, 100mA/div
C: VOUT, 1V/div
A
B
C
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
C: OUTPUT RIPPLE, 50mV/div, AC-COUPLED
A
B
C
500ns/div
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
_______________________________________________________________________________________
9
PIN NAME FUNCTION
1 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.
2 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.
3 REF 1.25V 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.
4 GND Ground. Connect to PGND with short trace.
5FB
Boost 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.
6 OUT Boost 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.
7 ONA ON Input. When high, the DC-DC is operational (Table 2).
8 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
0
0.4
0.2
0.8
0.6
1.2
1.0
1.4
0 0.4 0.60.2 0.8 1.0 1.2 1.4
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
A
B
C
500ns/div
450
0.1 1 10
LINEAR-REGULATOR OUTPUT NOISE
50
0
MAX1765 toc18
FREQUENCY (MHz)
NOISE (mVRMS)
150
250
350
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
10 ______________________________________________________________________________________
PIN NAME FUNCTION
9ONB ON Input. When low, the DC-DC is operational (Table 2).
10 PGND Power Ground
11 LX Inductor connection to the drain of P-channel synchronous rectifier and N-channel switch.
12 POUT 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.
13 INL Linear Regulator Power Input. Source of PFET pass device connected between INL and OUTL. Connect
INL to POUT.
14 OUTL Linear Regulator Output. OUTL can source up to 500mA. Bypass OUTL to GND with a 4.7µF capacitor.
15 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).
16 ONL 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.
— EP Exposed Pad (TSSOP Only). Internally connected to GND and PGND. Connect to a large ground plane.
Pin Description (continued)
Light-Load Operation in Normal Mode
At light loads, the MAX1765 operates by turning on the
DC-DC converter’s N-channel field-effect transistor
(FET) when VFB < VREF, synchronized with the rising
edge of the oscillator. The N-channel FET will remain
on, ramping up the inductor current past the minimum
inductor current, until the internal error amplifier and
current mode circuitry determine that the needs of the
system have been met or the device hits the ISET cur-
rent limit. The N-channel is then turned off and the P-
channel is turned on until current decays to the
P-channel turn-off current level. The N-channel will
remain off until VFB is again less than VREF, and a rising
edge of the oscillator occurs.
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
______________________________________________________________________________________ 11
2.15V
ON
OUTL
POUT
LX
PGND
REF
SHUTDOWN
LOGIC
THERMAL
SENSOR
MAX1765
ERROR
AMP
STARTUP
OSCILLATOR
EN QP
P
N
MOSFET DRIVER
WITH CURRENT
LIMITING
EN
1MHz
OSCILLATOR
EN
D
OSC
MODE
SKIP/PWM
Q
Q
IFB
PWM
CONTROLLER
RDY
1.250V
REFERENCE
IC PWR
IREF
ICS
FBL
OUT
VOUT
ONL
INL
ONB
GND
ONA
VOUT - 300mV ISET
ONL
REF
CLK/SEL
FB
TRACK
TRACK
ISET
Figure 1. Functional Diagram
Table 1. Selecting the Operating Mode
CLK/SEL MODE FEATURES
0Normal
Operation
High-efficiency pulse
skipping at light loads,
PWM at medium and
heavy loads
1 Forced PWM Low noise, fixed
frequency at all loads
E xter nal C l ock
500kH z to
1.2M H z
Synchronized
PWM
Low noise, fixed
frequency at all loads
MAX1765
PWM Operation in Normal Mode
The MAX1765 transitions to fixed-frequency PWM oper-
ation under medium and heavy loads. The N-channel
FET is engaged when VFB < VREF and is kept on to
ramp up the current in the inductor until one of the fol-
lowing conditions occurs: the system needs are met,
the next falling edge of the internal oscillator is
achieved, or the maximum inductor current (ISET) is
reached. The N-channel is turned off, activating the P-
channel synchronous rectifier that remains on until the
inductor current gets to the P-channel turn-off current
level, or VFB < VREF and there is a rising oscillator
clock edge. The 1MHz fixed-frequency operation pro-
duces an easily filtered fixed-noise spectrum.
Forced PWM Operation
When CLK/SEL is high, the MAX1765 operates in a low-
noise PWM-only mode. The N-channel FET is turned on
when VFB < VREF and is kept on to ramp up the induc-
tor current until one of the following conditions occurs:
the system needs are met, the next falling edge of the
internal oscillator is achieved, or the ISET is reached.
The N-channel is then turned off, activating the P-chan-
nel synchronous rectifier that remains on until the next
rising edge of the oscillator, where the N-channel is
again turned on under most conditions. The P-channel
zero detect circuitry is deactivated in forced PWM
mode. This means an N- or P-channel FET is on all the
time for most load conditions.
At light loads, the P-channel will remain on so the
device can pass current back to the input from the out-
put. The P-channel will only pass current for two cycles
before it is disabled. Then, the device remains inactive
until VFB < VREF.
During forced PWM operation, the MAX1765 switches
at a constant frequency (1MHz) and modulates the
MOSFET switch pulse width to control the power trans-
ferred per cycle in order to regulate the output voltage
for most output currents. Switching harmonics generat-
ed by fixed-frequency operation are consistent and
easily filtered. (See the Boost Followed by LDO Output
Noise Spectrum plot in the
Typical Operating
Characteristics.
)
Synchronized PWM Operation
The MAX1765 can be synchronized in PWM mode to
an external frequency of 500kHz to 1.2MHz by applying
an external clock signal to CLK/SEL. This allows inter-
ference to be minimized in wireless applications. The
synchronous rectifier is active during synchronized
PWM operation.
Synchronous Rectifier
The MAX1765 features an internal 250mΩ, P-channel
synchronous rectifier to enhance efficiency. Synchronous
rectification provides a 5% efficiency improvement over
similar nonsynchronous boost regulators. In PWM mode,
the synchronous rectifier is turned on during the second
portion of each switching cycle. At light loads (in normal
mode), an internal comparator turns on the synchronous
rectifier when the voltage at LX exceeds the boost regu-
lator output, and turns it off when the inductor current
drops below 50mA.
Low-Voltage Startup Oscillator
The MAX1765 uses a low-voltage startup oscillator for a
1.1V guaranteed minimum input startup input voltage.
A Schottky diode placed across LX and POUT reduces
the startup voltage to 0.9V. At startup, the low-voltage
oscillator switches the N-channel MOSFET until the out-
put voltage reaches 2.15V. Above this level, the normal
boost-converter feedback and control circuitry takes
over. Once the device is in regulation, it can operate
down to 0.7V input since internal power for the IC is
bootstrapped from the OUT pin. Do not apply full load
until the output exceeds 2.3V.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
12 ______________________________________________________________________________________
Figure 2. Typical Application Circuit
CLK/SEL PGNDGND
ONL
TRACK
ONB
4.7μF
FBL
OUTL
33μF
3.3μH
REF
ILIM 4.7Ω
LX
POUT
OUT
FB
LOGIC INPUTS
0.22μF
100μF
0.68μF
0.7V to 3.2V
MAX1765
ONA
VIN
VOUTL =
2.85V
100k
165k
VOUT
3.3V
INL
Linear Regulator
The MAX1765 contains an LDO with a fixed 2.85V (or
adjustable) output. The MAX1765 linear regulator fea-
tures a 250mΩ, P-channel MOSFET pass transistor.
This provides several advantages, including longer bat-
tery life, over similar designs using a PNP pass transis-
tor. The P-channel MOSFET requires no base-drive
current. This reduces quiescent current considerably,
since PNP-based regulators tend to waste base-drive
current in dropout when the pass transistor saturates.
Connect the input of the linear regulator (INL) to POUT.
The linear regulator can be used to postfilter the switch-
ing regulator or regulate a separate supply voltage.
This regulated output is intended to power noise-sensi-
tive analog circuitry, such as low-noise amplifiers and
IF stages in cellular phones and other instruments, and
can deliver up to 500mA. Use a 4.7µF capacitor with
less than a 1Ωequivalent series resistance (ESR) on
the output to provide stability. The linear regulator has
an internal 1.3A (max) current limit and thermal-over-
load protection circuitry to protect this output.
Configurations
There are several useful circuit configurations that can
be implemented with the MAX1765. The TRACK input
divides the circuit configurations into two types, one
where the DC-DC converter tracks to the LDO output,
and the other where the boost and the LDO regulate
independently.
Track Mode
Asserting the TRACK input places the MAX1765 into
track mode, where the DC-DC switching regulator’s
feedback pin (FB) is ignored, and the boost output
(POUT) “tracks” to 500mV above the linear regulator
output. The primary use of the MAX1765 in TRACK
mode is as a simple or very-low-noise step-up/down
power supply (see Figures 3 and 4; also see the
Maximum Output Current vs. Input Voltage plot in the
Typical Operating Characteristics.
)
This circuit operates as a linear regulator when the
input supply (a battery) is greater than VLDO. When the
battery discharges below VLDO, the DC-DC converter
turns on, boosting POUT to a constant 500mV above
the linear regulator output. This configuration also
allows for true shutdown (see
True Shutdown
).
Dual-Supply Mode
When the TRACK input is low, the MAX1765 operates
two independent power supplies, a DC-DC converter,
and a linear regulator. One such application of this con-
figuration is shown in Figure 4. In this mode, the device
generates two boosted voltages from a single battery
supply. The DC-DC converter could be used to supply
the power amplifier (PA) of a cell phone, while the linear
regulator powers the baseband functions within the
phone. Asserting TRACK switches the device into track
mode when the high-voltage supply for the PA is no
longer needed, thus improving efficiency in standby-
receive mode. When the PA again needs 5V, deassert
the TRACK input.
Shutdown
The MAX1765 has a shutdown mode that reduces qui-
escent current to 1µA. During shutdown, the reference,
LDO, DC-DC converter, and all feedback and control
circuitry are off. Table 2 shows the MAX1765 shutdown
truth table. If ONA, ONB, and ONL are all deasserted,
the device is shut down.
True Shutdown
When a typical boost converter is placed into shut-
down, current can flow through the body diode of the
synchronous rectifier to the load. The MAX1765 can be
configured to allow true shutdown as shown in Figure 5.
The shutdown function is active low and is connected
to both ONA and ONL. When asserted, both the DC-DC
converter and the LDO are shut down simultaneously.
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
______________________________________________________________________________________ 13
Figure 3. Simple Step-Up/Step-Down Converter
PGND
GND
MAX1765
FB
VOUT = 2.5V - 5.0V
AT 500mA
4.7μF
33μF
LX
OUT
POUT
TRACK
INL
OUTL
ILIM
REF
ONL
CLK/SEL
ONB
ONA
SHDN
INPUT
0.7V TO 5.5V
*
*
* OPTIONAL COMPONENTS
FBL
0.22μF
*
MAX1765
The LDO acts like a switch in this situation and discon-
nects the input from the load. Connect FBL to a resis-
tor-divider from VREF to GND (R3 and R4 in Figure 5) so
that VFBL = 0.5V (above the Dual Mode™ threshold)
when OUTL is regulated, to ensure that the linear regu-
lator is saturated. Another method to configure the
MAX1765 for true shutdown is shown in Figure 6. This
shutdown function is active high and connects to the
gate of a low-impedance PFET and ONB. The PFET
acts like a switch in this situation and disconnects the
input from the load.
Reference
The MAX1765 has an internal 1.25V, 1% reference.
Connect a 0.22µF ceramic bypass capacitor to GND
within 0.2in (5mm) of the REF pin. REF can source up
to 50µA of external load current. Typically connect ISET
to REF to give the MAX1765 full inductor current limit.
Design Procedure
Setting DC-DC Converter Voltage
Set the output voltage between +2.5V and +5.5V by
connecting a resistor voltage-divider from OUT to FB to
GND (Figure 7). Connect the resistor voltage-divider as
close to the IC as possible, within 0.2in (5mm) of FB.
Choose R2 of 40kΩor less, then calculate R1 using:
where VFB, the boost-regulator feedback set point, is
+1.25V.
For output voltages above 4V, connect a Schottky
diode between LX and POUT to prevent voltage transi-
tion from exceeding the LX voltage rating.
Setting the Linear Regulator Voltage
The LDO regulation voltage can also be set similarly to
the DC-DC converter. Connecting FBL to GND sets the
LDO output to 2.85V. To set other output voltages
between 1.25V and POUT, connect a resistor-divider
from OUTL to FBL to GND (Figure 7). Connect the
resistor voltage-divider as close to the IC as possible,
within 0.2in (5mm) of FBL. The maximum input bias cur-
rent for the FBL input is 50nA. Choose R4 of 40kΩor
less, then calculate R3 using:
where VFBL, the linear regulator feedback set point, is
+1.25V.
Setting the Switch Current
Limit and Soft-Start
The ISET pin adjusts the inductor current limit and
implements soft-start. With ISET connected to REF, the
inductor current limits at 1.25A. With ISET connected to
a resistive divider set from REF to GND, the current limit
is reduced according to:
I =
LIM 125 2
12
.A R
RR
SS
SS SS
+
⎛
⎝
⎜
⎞
⎠
⎟
RR
V
V
OUTL
FBL
34 =⎛
⎝
⎜
⎞
⎠
⎟
- 1
RR
V
V
OUT
FB
12 =⎛
⎝
⎜
⎞
⎠
⎟
- 1
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
14 ______________________________________________________________________________________
Table 2. Operating Mode Truth Table
OPERATING
MODE TRACK ONA ONB ONL LINEAR
REGULATOR
DC-DC
CONVERTER REF
Shutdown X L H L OFF OFF OFF
HHX X
Track
HXLX
ON ON ON
LHXH
Independent Regulation
LXLH
ON ON ON
LHX L
DC-DC Only
LXLL
OFF ON ON
LDO Only X L H H ON OFF ON
Dual Mode is a trademark of Maxim Integrated Products
Implement soft-start by placing a resistor from ISET to
REF and a capacitor from ISET to GND (Figure 8). In
shutdown, ISET is discharged to GND through an
on-chip 100kΩresistor. At power-up, ISET is 0V and the
current limit is zero. As the capacitor voltage rises, the
current limit increases and the output voltage rises. The
soft-start time constant is:
Placing a capacitor across the lower resistor of the cur-
rent-limiting resistive divider provides both features
simultaneously (Figure 9).
Package Selection
The MAX1765 is available in two packages, a 16-pin
QSOP and a thermally enhanced TSSOP-EP. The
QSOP is the less expensive of the two packages, and
requires a less complex layout design. This layout
allows the designer to route underneath the device. The
power dissipation for the QSOP is 0.7W.
The TSSOP-EP comes with an exposed metal pad that
is connected to the substrate of the IC. This increases
the power dissipation up to 1.5W for the TSSOP-EP. To
achieve maximum power capability, the exposed pad
of the TSSOP-EP should be reflowed to a pad with low
thermal resistance. For convenience, this pad can be
connected to AGND or PGND.
Inductor Selection
The MAX1765’s high switching frequency allows the
use of a small surface-mount inductor. For most appli-
cations, a 3.3µH inductor works well. The inductor
t =
RISE RC
SS SS
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Figure 4. Dual-Output Power Supply
MAX1765
INPUT
0.7V TO 5.5V
GND CLK/SEL FBL PGND
OUTL
POUT
LX
OUT
REF
ILIM
4.7Ω
0.68μF150k
VLDO = 2.85V
FB
33μF x 2
3.3μH
TRACK
ONL
ONB
ONA
OFF
ON
ON
OFF
TRACK
TRACK = LOW, VOUT = 5.0V
TRACK = HIGH, VOUT = 3.35V
0.22μF
50k
4.7μF
INL
Figure 5. LDO Enable Allows True Boost Shutdown
LX
POUT
INL
OUTL OUTPUT
INPUT
MAX1765
ONL
ONA
SHDN
ON
OFF
FBL
R3
R4
Figure 6. PFET Allows True Boost Shutdown
LX
POUT
FB
OUT
OUTPUT
INPUT
MAX1765 SHDN
ONB
OFF
ON
______________________________________________________________________________________ 15
MAX1765
should have a saturation current rating exceeding the
N-channel switch current limit; however, it is accept-
able to bias the inductor current into saturation by as
much as 20% if a slight reduction in efficiency is
acceptable. Lower current-rated inductors may be
used if ISET is employed to reduce the peak inductor
current (see
Setting the Switch Current Limit and Soft-
Start
). For high efficiency, choose an inductor with a
high-frequency core material to reduce core losses. To
minimize radiated noise, use a toroid or shielded induc-
tor. See Table 3 for suggested components and Table
4 for a list of component suppliers.
Output Diode
To assist startup with input voltages below 1.1V or
when VOUT is set for >4V, use a Schottky diode—such
as a 1N5817, MBR0520L or equivalent—between LX
and POUT (Figure 2). The Schottky diode carries cur-
rent after the synchronous rectifier turns off. Thus, its
current rating only needs to be 500mA. Connect the
diode as close to the IC as possible. Do not use ordi-
nary rectifier diodes; their slow switching speeds and
long reverse-recovery times render them unacceptable.
For input voltages over 1.8V, the Schottky diode may
improve light-load efficiency.
Input and Output Filter Capacitors
Choose input and output filter capacitors that will ser-
vice the input and output peak currents with accept-
able voltage ripple. Choose input capacitors with
working voltage ratings over the maximum input volt-
age and output capacitors with working voltage ratings
higher than the output. A 100µF, 100mΩ, low equiva-
lent-series-resistance (ESR) tantalum output capacitor
is recommended for most applications. At the output of
the linear regulator (OUTL), use a 4.7µF ceramic
capacitor for stability at loads up to 500mA.
The input filter capacitor reduces peak currents drawn
from the input source and also reduces input switching
noise. The input voltage source impedance determines
the required size of the input capacitor. When operat-
ing directly from one or two NiMH cells placed close to
the MAX1765, use a single 33µF low-ESR input filter
capacitor.
The Sanyo POSCAP, Panasonic SP/CB, and Kemet
T510 are good low-ESR capacitors. Low-ESR tantalum
capacitors offer a good trade-off between price and
performance. Do not exceed the ripple current ratings
of tantalum capacitors. Avoid aluminum electrolytic
capacitors; their high ESR typically results in higher
output ripple voltage.
Bypass Capacitors
Bypass REF to GND with 0.22µF. Also, bypass OUT to
GND with a 0.68µF ceramic capacitor, and connect
OUT to POUT with a 4.7Ωresistor. Each of these com-
ponents should be placed as close to its respective IC
pins as possible, within 0.2in (5mm).
Layout Considerations
High switching frequencies and large peak currents
make PC board layout a critical part of design. Poor
design will cause excessive EMI and ground bounce,
both of which can cause instability or regulation errors
by corrupting the voltage and current feedback signals.
Power components—such as the inductor, converter
IC, filter capacitors, and output diode—should be
placed as close together as possible, and their traces
should be kept short, direct, and wide. Connect the
inductor from the battery to the LX pins as close to the
IC as possible.
Keep the voltage feedback network very close to the
IC, within 0.2in (5mm) of the FB pins. Keep noisy
traces, such as those from the LX pin, away from the
voltage feedback networks and guarded from them
using grounded copper. Refer to the MAX1765 EV kit
for a full PC board example.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
16 ______________________________________________________________________________________
Figure 7. Feedback Connections
MAX1765
INLOUTL POUT
OUT
FBL FB
GND PGND
R3
R4 R2
R1
STEP-UP
OUTPUT
LINEAR-
REGULATOR
OUTPUT
Applications Information
Use in a Typical Wireless
Phone Application
The MAX1765 is ideal for use in digital cordless and
PCS phones. The PA is connected directly to the step-
up converter output for maximum voltage swing and
power efficiency (Figure 10). The internal linear regula-
tor is used for postregulation to generate low-noise
power for DSP, control, and RF circuitry. The following
equations may be used to estimate the typical available
output current under conditions other than those listed
here:
where ILIM is the peak inductor current limit, fSW is the
operating frequency (typically 1.2MHz), L is the induc-
tance of the chosen inductor, LRESR is the resistance of
the chosen inductor, RNCH and RPCH are the resis-
tances of the internal N-channel and P-channel,
respectively.
II
IID
If
D
LVI R L
DVVI RL
VIRR
OUT MAX LIM RIPPLE
RIPPLE SW IN LIM NCH ESR
OUT IN LIM NCH ESR
OUT LIM PCH NCH
,=−
⎛
⎝
⎜⎞
⎠
⎟−
()
=××−× +
()
[]
=−+ × +
()
+−
()
2
1
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
______________________________________________________________________________________ 17
Figure 9. Soft-Start, Maximum Current Limit
CSS
RSS
ILIM = 1.25A
tSS = RSS CSS
500kΩ < RSS < 1MΩ
MAX1765
REF
ISET
0.22μF
Figure 8. Soft-Start, Reduced Current Limit
CSS
MAX1765
REF
ISET
0.22μFRSS1
RSS2
ILIM = 1.25A
tSS = (RSS1 || RSS2) CSS
( )
RSS2
RSS1 + RSS2
Table 3. Component Selection Guide
PRODUCTION 3.3μH INDUCTORS CAPACITORS SCHOTTKY DIODES
Surface Mount Coilcraft DS3316P
Coilcraft LPT3305
AVX TPS series
Kemet T510 series
Sanyo POSCAP series
Motorola MBR0520L
Nihon EP10QY03
Table 4. Component Suppliers
SUPPLIER COUNTRY PHONE
AVX USA 843-448-9411
Coilcraft USA 847-639-6400
Kemet USA 810-287-2536
USA 408-629-4789
Motorola Japan 81-45-474-7030
USA 847-956-0666
Sumida Japan 81-3-3607-3302
Note: Please indicate that you are using the MAX1765 when
contacting these component suppliers.
MAX1765
Table 5 lists the typical available output current when oper-
ating with one or more NiCd/NiMH cells or one Li+ cell.
Adding a Manual Power Reset
A momentary pushbutton switch can be used to turn
the MAX1765 on and off (Figure 11). ONA is pulled low
and ONB is pulled high to turn the device off. When the
momentary switch is pressed, ONB is pulled low and
the regulator turns on. The switch must be pressed
long enough for the microcontroller (µC) to exit reset
and drive ONA high. A small capacitor is added to help
debounce the switch. The µC issues a logic high to
ONA, which holds the device on, regardless of the
switch state. To turn the regulator off, press the switch
again, allowing the µC to read the switch status and
pull ONA low. When the switch is released, ONB is
pulled high.
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
18 ______________________________________________________________________________________
Table 5. Typical Available Output Current
NUMBER OF CELLS INPUT VOLTAGE
(V)
OUTPUT VOLTAGE
(V)
OUTPUT CURRENT
(mA)
1 NiCd/NiMH 1.2 3.3 330
2.4 3.3 730
2 NiCd/NiMH
2.4 5.0 460
3 NiCd/NiMH or 1 Li+ 3.6 5.0 720
PA
RF
LX POUT
GND OUTL
CONTROL
INPUTS
μC
I/O
MAX1765
INL
μC
VDD
I/O
ONA
ONB POUT
I/O
0.1μF
ON/OFF
270k
270k
MAX1765
Figure 10. Typical Phone Application
Figure 11. Momentary Pushbutton On/Off Switch
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
16 QSOP E16+1 21-0055 90-0167
16 QSOP-EP U16E+3 21-0108 90-0120
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________
19
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products.
MAX1765
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 12/00 Initial release —
1 4/11 Added lead-free designation, updated TOCs 1 and 2, and updated Pin Description
section 1, 7, 10
