Maxim MAX1765 800ma, low-noise, step-up dc-dc converter with 500ma linear regulator Datasheet

19-1805; Rev 0; 12/00
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
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 exceptionally low quiescent supply current (200µA). Its small
external components and tiny package make this
device an excellent choice for small hand-held applications that require the longest possible battery life.
The MAX1765 uses a synchronous-rectified pulsewidth-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 proprietary 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 currents, 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 250mΩ pass device maintains excellent dropout voltage at currents up to 500mA. The
MAX1765 also features analog soft-start and currentlimit functions to permit optimization of efficiency, external 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 Range
♦ 0.1µA Logic-Controlled Shutdown
♦ Adjustable Inductor Current Limit and Soft-Start
♦ Thermal Shutdown
♦ 1.5W, 16-Pin TSSOP-EP Package Available
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX1765EEE
-40°C to +85°C
16 QSOP
MAX1765EUE
-40°C to +85°C
16 TSSOP-EP*
*Exposed pad
Applications
Wireless Handsets
PCS Phones
Personal
Communicators
Palmtop Computers
Hand-Held Instruments
Portable Audio Players
Typical Operating Circuit
Pin Configuration
TOP VIEW
(0.7V TO 5.5V) 3.3µH
ONL
LX
ONA
POUT
INL
ONB
CLK/SEL
TRACK
OUT = 3.3V
OUT
OUTL
GND FBL PGND
16 ONL
15 TRACK
REF 3
14 OUTL
GND 4
FB
FB 5
MAX1765
REF
ILIM
FBL 1
ISET 2
OUTL = 2.85V
(ADJ 1.25V
TO 5V)
MAX1765
13 INL
12 POUT
OUT 6
11 LX
ONA 7
10 PGND
CLK/SEL 8
9
ONB
QSOP/TSSOP-EP
________________________________________________________________ Maxim Integrated Products
1
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.
MAX1765
General Description
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
ABSOLUTE MAXIMUM RATINGS
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
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.
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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
DC-DC CONVERTER
Input Voltage Range
(Note 1)
0.7
5.5
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
FB Regulation Voltage
VFB
FB Input Leakage Current
CLK/SEL = OUT, 0 < ILX < 0.55A
VFB = 1.35V
Output Voltage Adjust Range
2
1.250
1.275
V
0.01
100
nA
2.5
Load Regulation
CLK/SEL = OUT, 0 < ILOAD < 800mA
OUT Voltage in Track Mode
VOUTL > 2.0V, INL = POUT
Frequency in Startup Mode
1.215
fLX
mV/°C
5.5
-1
VOUTL
+ 0.4
VOUTL
+ 0.5
V
%
VOUTL
+ 0.6
V
1000
kHz
2.15
2.30
V
VOUT = 1.5V
125
Startup to Normal Mode
Transition Voltage
Rising edge only (Note 2)
2.00
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
Supply Current in Low-Noise
PWM Mode (Note 3)
CLK/SEL = OUT,
no load
VFB = 1.5V
130
200
µA
FB = GND (LX switching)
2.5
Supply Current in Shutdown
ONA = ONL = GND, ONB = OUT
1
_______________________________________________________________________________________
mA
10
µA
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
(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
0.1
10
µA
µA
DC-DC SWITCHES
POUT Leakage Current
VLX = 0, VOUT = 5.5V
LX Leakage Current
Switch On-Resistance
N-Channel Current Limit (Note 4)
ILIM
P-Channel Turn-Off Current
VLX = VOUT = V ONB = 5.5V, ONA = GND
0.1
10
N-channel
0.17
0.28
P-channel
0.22
0.5
1000
1250
1600
mA
10
50
120
mA
1.230
VISET = 1.25V, CLK/SEL = GND or OUT
CLK/SEL = GND
Ω
REFERENCE
Reference Output Voltage
1.250
1.270
V
Reference Load Regulation
VREF
-1µA < IREF < 50µA
IREF = 0
5
15
mV
Reference Supply Regulation
2.5V < VOUT < 5.5V
0.2
5
mV
LINEAR REGULATOR
INL Voltage Range
(Note 1)
INL Startup Voltage
VINL
Output Voltage in Internal
Feedback Mode
2.3
5.5
V
VOUT = 2V, rising edge only
2.15
2.30
2.45
V
FBL = GND, IOUTL = 10mA
2.80
2.85
2.90
V
150
250
350
mV
1.230
1.250
1.270
V
0.01
50
nA
FBL Dual-Mode Threshold
FBL Regulation Voltage
FBL Input Leakage Current
VFBL
FBL = OUTL, IOUTL = 10mA, IREF = 0
VFBL = 1.5V
OUTL Adjust Range
1.25
5
V
550
1300
mA
Short-Circuit Current Limit
VFBL = 1V
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
%
INL Supply Current in Shutdown
OUTL = ONA = ONL = GND
0.1
10
µA
INL No-Load Supply Current
IOUTL = 0, VINL = 5.5V
90
250
µA
-0.5
AC Power-Supply Rejection
f = 10kHz
65
dB
Thermal Shutdown
Hysteresis approximately 10°C
160
°C
_______________________________________________________________________________________
3
MAX1765
ELECTRICAL CHARACTERISTICS (continued)
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
TA =+25 °C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CONTROL INPUTS
Input Low Level
Input High Level
ONA, ONB, ONL
(Note 5)
1.1V < VOUT < 1.8V
0.2
1.8V < VOUT < 5.5V
0.4
CLK/SEL
1.2V < VOUT < 5.5V
0.2 ×
VOUT
TRACK
1.2V < VINL < 5.5V
0.2 ×
VINL
ONA, ONB, ONL
(Note 5)
1.1V < VOUT < 1.8V
VOUT
- 0.2
1.8V < VOUT < 5.5V
1.6
CLK/SEL
1.2V < VOUT < 5.5V
0.8 ×
VOUT
TRACK
1.2V < VINL < 5.5V
0.8 ×
VINL
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)
Internal Oscillator Frequency
CLK/SEL = OUT
0.8
External Oscillator
Synchronization Range
0.5
Oscillator Maximum Duty Cycle
80
V
V
0.01
1
µA
1
1.2
MHz
1.2
MHz
86
90
%
Minimum CLK/SEL Pulse
200
ns
Maximum CLK/SEL Rise/Fall Time
100
ns
4
_______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
(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
CLK/SEL = OUT, VFB = 1.5V, no load
200
µA
Supply Current in Shutdown
ONA = ONL = GND, ONB = OUT
10
µA
POUT Leakage Current
VLX = 0, VOUT = 5.5V
10
µA
LX Leakage Current
VLX = VOUT = V ONB = 5.5V, ONA = GND
10
µA
DC-DC SWITCHES
Switch On-Resistance
N-Channel Current Limit (Note 4)
P-Channel Turn-Off Current
ILIM
N-channel
0.28
P-channel
0.50
VISET = 1.25V, CLK/SEL = GND or OUT
Ω
1000
1600
mA
5
120
mA
IREF = 0
1.225
1.275
V
FBL = GND, IOUTL = 10mA
2.79
2.90
V
150
350
mV
V
CLK/SEL = GND
REFERENCE
Reference Output Voltage
LINEAR REGULATOR
Output Voltage in Internal
Feedback Mode
FBL Input Threshold
FBL Regulation Voltage
FBL = OUTL, IOUTL = 10mA, IREF = 0
1.225
1.275
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 = 0, VINL = 5.5V
250
µA
_______________________________________________________________________________________
5
MAX1765
ELECTRICAL CHARACTERISTICS
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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CONTROL INPUTS
Input Low Level
Input High Level
ONA, ONB, ONL
(Note 5)
1.1V < VOUT < 1.8V
0.2
1.8V < VOUT < 5.5V
0.4
CLK/SEL
1.2V < VOUT < 5.5V
0.2 ×
VOUT
TRACK
1.2V < VINL < 5.5V
0.2 ×
VINL
ONA, ONB, ONL
(Note 5)
1.1V < VOUT < 1.8V
1.8V < VOUT < 5.5V
VOUT
- 0.2
1.6
CLK/SEL
1.2V < VOUT < 5.5V
0.8 ×
VOUT
TRACK
1.2V < VINL < 5.5V
0.8 ×
VINL
Input Leakage Current
(CLK/SEL, ONA, ONB,
ONL, TRACK)
Internal Oscillator Frequency
Oscillator Maximum Duty Cycle
CLK/SEL = OUT
V
V
1
µA
0.8
1.2
MHz
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.
6
_______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
0.7
NORMAL
MODE
0.6
PWM
MODE
0.4
VIN = +2.4V
0.3
0.2
40
VIN = +1.2V
VIN = +2.4V
0.01
0.1
1
VIN = +2.4V
70
60
VIN = +1.2V
PWM
MODE
50
40
VIN = +1.2V
30
VIN = +2.4V
20
VIN = +3.6V
10
0
0.001
0
0.001
0.01
0.1
1
0.001
0.01
0.1
1
LOAD CURRENT (A)
LOAD CURRENT (A)
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +3.3V)
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +5V)
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
NORMAL
MODE
VIN = +1.2V
VIN = +1.2V
NORMAL MODE/
PWM MODE
30
60
VIN = +1.2V
40
30
20
20
10
10
0
0
0.01
0.1
1
VIN = +1.2V
VIN = +2.4V
VOUT = +3.3V, ISET = REF
800
600
400
200
VOUT = +5V, ISET = 0.5 REF
VIN = +3.6V
0
0.001
0.01
0.1
0
1
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
LOAD CURRENT (A)
LOAD CURRENT (A)
INPUT VOLTAGE (V)
LINEAR REGULATOR DROPOUT
VOLTAGE vs. LOAD CURRENT
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1765 toc07
0.30
0.25
VOUTL = +2.5V
0.20
VOUTL = +2.85V
0.15
0.10
VOUTL = +5V
0.05
2.5
STARTUP INPUT VOLTAGE (V)
0.001
VIN = +2.4V
50
PWM
MODE
VOUT = +3.3V, ISET = 0.5 REF
TA = +25°C
2.0
TA = -40°C
1.5
18
1.0
TA = +85°C
MAX1765 toc09
40
PWM
MODE
VOUT = +5V, ISET = REF
1000
16
SUPPLY CURRENT (mA)
50
EFFICIENCY (%)
60
14
FPWM MODE
12
10
8
6
4
0.5
2
0
100 200 300 400 500 600 700 800
LOAD CURRENT (mA)
NORMAL MODE
0
0
0
MAX1765 toc06
70
VIN = +2.4V
1200
OUTPUT CURRENT (mA)
70
VIN = +3.6V
NORMAL MODE
80
MAX1765 toc08
80
90
MAX1765 toc04
VIN = +3.6V
VIN = +2.4V
MAX1765 toc05
LOAD CURRENT (A)
90
EFFICIENCY (%)
PWM
MODE
50
NORMAL MODE
80
10
0
DROPOUT VOLTAGE (V)
VIN = +1.2V
60
20
0.1
90
VIN = +2.4V
70
30
VIN = +1.2V
100
MAX1765 toc03
80
VIN = +1.2V
0.5
VIN = +3.6V NORMAL MODE
90
EFFICIENCY (%)
EFFICIENCY (%)
0.8
TRACK MODE EFFICIENCY vs. LOAD CURRENT
(VOUTL = +2.85V)
EFFICIENCY (%)
VIN = +2.4V
0.9
100
MAX1765 toc01
1.0
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5V)
MAX1765 toc02
EFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)
1
10
100
OUTPUT CURRENT (mA)
1000
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
INPUT VOLTAGE (V)
_______________________________________________________________________________________
7
MAX1765
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
LDO PSRR vs. FREQUENCY
(100Hz TO 1MHz)
LINE TRANSIENT RESPONSE
(DC-DC)
BOOST FOLLOWED BY LDO
OUTPUT NOISE SPECTRUM
12
NOISE (mVRMS)
-40
-50
VIN = +2.4V
VOUT = +3.3V
14
-20
-30
MAX1765 toc11
-10
MAX1765 toc12
16
MAX1765 toc10
0
LDO PSRR (dB)
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
10
A
8
6
4
2
-60
0
B
-70
-80
0.1
1
10
100
1000
0.1
1
10
100µs/div
A: VIN, 500mV/div
VOUT = +3.3V, I = 0mA
B: VOUT, 1mV/div, AC-COUPLED VIN = +1.4V TO +2.4V
FREQUENCY (kHz)
FREQUENCY (MHz)
LINE TRANSIENT RESPONSE
(LINEAR)
LOAD TRANSIENT RESPONSE
MAX1765 toc13
TURN-ON WAVEFORMS
NO SOFT-START COMPONENTS
MAX1765 toc15a
MAX1765 toc14
A
A
A
B
B
C
B
I = 0mA, VIN = +3V TO +5V, VOUT = +3.3V
A: VIN, 2V/div
B: VOUT, 5mV/div, AC-COUPLED
A: 0NA, 5V/div
B: VOUT, 2V/div
C: INPUT CURRENT, 1A/div
50µs/div
VIN = +2.4V, VOUT = +3.3V, IOUT = 0 TO 500mA
A: IOUT, 500mA/div
B: VOUT,100mV/div
HEAVY-LOAD SWITCHING WAVEFORMS
(IOUT = 650mA, VIN = +2.4V, VOUT = 3.3V)
SOFT-START WAVEFORMS
(RSS = 500kΩ, CSS = 0.1µF)
MAX1765 toc16
MAX1765 toc15b
A
A
B
B
C
C
2.5ms/div
A: 0NA, 5V/div
B: INPUT CURRENT, 100mA/div
C: VOUT, 1V/div
8
500ns/div
A: LX, 5V/div
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT RIPPLE, 50mV/div, AC-COUPLED
_______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
LINEAR-REGULATOR OUTPUT NOISE
MAX1765 toc17
ILDO = 200mA
VLDO = 2.85V
A
250
150
C
50
0.1
A: LX NODE, 5V/div
B: INDUCTOR CURRENT, 200mA/div, AC-COUPLED
C: OUTPUT RIPPLE, 20mV/div, AC-COUPLED
1.0
0.8
0.6
0.4
0.2
0
500ns/div
VOUT = +3.3
1.2
SWITCH CURRENT LIMIT (A)
NOISE (mVRMS)
350
B
SWITCH CURRENT LIMIT vs. VISET
1.4
MAX1765 toc18
450
MAX1765 toc19
LIGHT-LOAD SWITCHING WAVEFORMS
(VIN = +2.4V, VOUT = +3.3V, IOUT = 10mA)
1
10
FREQUENCY (MHz)
0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
VISET (V)
Pin Description
PIN
NAME
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.
5
FB
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
FUNCTION
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 lowpower (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.
_______________________________________________________________________________________
9
MAX1765
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Pin Description (continued)
PIN
NAME
FUNCTION
9
ONB
10
PGND
11
LX
12
POUT
13
INL
14
OUTL
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.
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.
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 synchronous rectifier, shutdown control, and a precision voltage 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 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 fullpower operation, as well as low quiescent current for
maximum battery life during standby and shutdown.
The device automatically transitions to a low-quiescentcurrent 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.
10
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 rectification 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-channel 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 determines 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 automatically switches to SKIP mode if the load requires
______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
MAX1765
MAX1765
THERMAL
SENSOR
SHUTDOWN
LOGIC
INL
FBL
OUT
ONL
MOSFET DRIVER
WITH CURRENT
LIMITING
ERROR
AMP
P
OUTL
REF
IC PWR
POUT
2.15V
TRACK
EN
GND
STARTUP
OSCILLATOR
Q
D
Q
P
PWM
CONTROLLER
ONA
ONB
ON
ONL
RDY
1.250V
REFERENCE
REF
OSC
VOUT
Q
EN
1MHz
OSCILLATOR
CLK/SEL
LX
EN
SKIP/PWM
MODE
N
ICS
IREF
FB
PGND
IFB
VOUT - 300mV
TRACK
ISET
ISET
Figure 1. Functional Diagram
Table 1. Selecting the Operating Mode
CLK/SEL
MODE
FEATURES
0
Normal
Operation
High-efficiency pulse
skipping at light loads,
PWM at medium and
heavy loads
1
Forced PWM
Low noise, fixed
frequency at all loads
External Clock
500kHz to
1.2MHz
Synchronized
PWM
Low noise, fixed
frequency at all loads
less power. SKIP mode allows higher efficiency than
PWM under light-load conditions.
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 current limit. The N-channel is then turned off and the Pchannel 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.
______________________________________________________________________________________
11
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
VIN
0.7V to 3.2V
3.3µH
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.
VOUT
3.3V
33µF
100µF
REF
LX
POUT
ILIM
INL
0.22µF
ONA
LOGIC INPUTS
4.7Ω
OUT
0.68µF
MAX1765
ONB
TRACK
ONL
165k
FB
100k
VOUTL =
2.85V
OUTL
4.7µF
FBL
GND CLK/SEL PGND
Figure 2. Typical Application Circuit
At light loads, the P-channel will remain on so the
device can pass current back to the input from the output. 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 transferred per cycle in order to regulate the output voltage
for most output currents. Switching harmonics generated 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 interference to be minimized in wireless applications. The
synchronous rectifier is active during synchronized
PWM operation.
Synchronous Rectifier
PWM Operation in Normal Mode
The MAX1765 transitions to fixed-frequency PWM operation 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 following 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 Pchannel 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 produces an easily filtered fixed-noise spectrum.
Forced PWM Operation
When CLK/SEL is high, the MAX1765 operates in a lownoise PWM-only mode. The N-channel FET is turned on
when VFB < VREF and is kept on to ramp up the inductor 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-channel 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
12
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 regulator 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 output 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.
Linear Regulator
The MAX1765 contains an LDO with a fixed 2.85V (or
adjustable) output. The MAX1765 linear regulator fea-
______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
INPUT
0.7V TO 5.5V
LX
*
OUT
ONB
SHDN
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 configuration 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
MAX1765
ONA
POUT
CLK/SEL
TRACK
ONL
INL
33µF
REF
VOUT = 2.5V - 5.0V
AT 500mA
OUTL
4.7µF
ILIM
*
0.22µF
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.
MAX1765
tures a 250mΩ, P-channel MOSFET pass transistor.
This provides several advantages, including longer battery life, over similar designs using a PNP pass transistor. 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 switching regulator or regulate a separate supply voltage.
This regulated output is intended to power noise-sensitive 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 1Ω equivalent series resistance (ESR) on
the output to provide stability. The linear regulator has
an internal 1.3A (max) current limit and thermal-overload protection circuitry to protect this output.
GND
FB
FBL
PGND
*
* OPTIONAL COMPONENTS
Figure 3. Simple Step-Up/Step-Down Converter
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 standbyreceive mode. When the PA again needs 5V, deassert
the TRACK input.
Shutdown
The MAX1765 has a shutdown mode that reduces quiescent 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 shutdown, 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.
The LDO acts like a switch in this situation and disconnects the input from the load. Connect FBL to a resistor-divider from VREF to GND (R3 and R4 in Figure 5) so
______________________________________________________________________________________
13
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
Table 2. Operating Mode Truth Table
OPERATING
MODE
Shutdown
TRACK
ONA
ONB
ONL
LINEAR
REGULATOR
DC-DC
CONVERTER
REF
X
L
H
L
OFF
OFF
OFF
H
H
X
X
ON
ON
ON
H
X
L
X
L
H
X
H
ON
ON
ON
L
X
L
H
L
H
X
L
OFF
ON
ON
L
X
L
L
X
L
H
H
ON
OFF
ON
Track
Independent Regulation
DC-DC Only
LDO Only
that VFBL = 0.5V (above the Dual Mode™ threshold)
when OUTL is regulated, to ensure that the linear regulator 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 40kΩ or less, then calculate R1 using:
V

R1 = R2  OUT - 1
 VFB

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 transition 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 current for the FBL input is 50nA. Choose R4 of 40kΩ or
less, then calculate R3 using:
V

R3 = R4  OUTL - 1
 VFBL

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:


RSS2
ILIM = 1.25A 

 RSS1 + RSS2 
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 onchip 100kΩ resistor. At power-up, ISET is 0V and the
current limit is zero. As the capacitor voltage rises, the
Dual Mode is a trademark of Maxim Integrated Products
14
______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
MAX1765
INPUT
0.7V TO 5.5V
INPUT
3.3µH
TRACK = LOW, VOUT = 5.0V
TRACK = HIGH, VOUT = 3.35V
LX
33µF x 2
4.7Ω
OFF
MAX1765
LX
ON
ONB
OUTPUT
POUT
OUT
SHDN
OUT
MAX1765
0.68µF
TRACK
150k
FB
TRACK
ON
OFF
OFF
ON
ONL
FB
ONB
50k
ONA
POUT
0.22µF
REF
INL
ILIM
OUTL
GND CLK/SEL FBL
PGND
Figure 6. PFET Allows True Boost Shutdown
VLDO = 2.85V
current limit increases and the output voltage rises. The
soft-start time constant is:
4.7µF
tRISE = RSSCSS
Placing a capacitor across the lower resistor of the current-limiting resistive divider provides both features
simultaneously (Figure 9).
Figure 4. Dual-Output Power Supply
INPUT
Package Selection
LX
MAX1765
ON
POUT
OFF
SHDN
ONL
INL
ONA
OUTL
FBL
R4
R3
OUTPUT
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
Figure 5. LDO Enable Allows True Boost Shutdown
The MAX1765’s high switching frequency allows the
use of a small surface-mount inductor. For most applications, a 3.3µH inductor works well. The inductor
should have a saturation current rating exceeding the
N-channel switch current limit; however, it is acceptable 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
______________________________________________________________________________________
15
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
used if ISET is employed to reduce the peak inductor
current (see Setting the Switch Current Limit and SoftStart). 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 inductor. 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 current 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 ordinary 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.
LINEARREGULATOR
OUTPUT
OUTL
INL
STEP-UP
OUTPUT
POUT
MAX1765
R1
R3
OUT
FBL
R4
FB
GND
PGND
R2
Figure 7. Feedback Connections
Input and Output Filter Capacitors
Layout Considerations
Choose input and output filter capacitors that will service the input and output peak currents with acceptable voltage ripple. Choose input capacitors with
working voltage ratings over the maximum input voltage and output capacitors with working voltage ratings
higher than the output. A 100µF, 100mΩ, low equivalent-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.
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.
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 operating 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 4.7Ω resistor. Each of these components should be placed as close to its respective IC
pins as possible, within 0.2in (5mm).
16
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.
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 stepup converter output for maximum voltage swing and
power efficiency (Figure 10). The internal linear regulator 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:
______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
(
0.22µF
RSS1
)
REF
0.22µF
ILIM = 1.25A
tSS = RSS CSS
500kΩ < RSS < 1MΩ
RSS
MAX1765
MAX1765
ISET
CSS
MAX1765
RSS2
ILIM = 1.25A RSS1 + RSS2
tSS = (RSS1 || RSS2) CSS
REF
ISET
CSS
RSS2
Figure 9. Soft-Start, Maximum Current Limit
Figure 8. Soft-Start, Reduced Current Limit
Table 3. Component Selection Guide
PRODUCTION
3.3µH INDUCTORS
Coilcraft DS3316P
Coilcraft LPT3305
Surface Mount
Table 4. Component Suppliers
COUNTRY
PHONE
AVX
SUPPLIER
USA
843-448-9411
Coilcraft
USA
847-639-6400
Kemet
USA
810-287-2536
USA
408-629-4789
Japan
81-45-474-7030
Motorola
Sumida
USA
847-956-0666
Japan
81-3-3607-3302
Note: Please indicate that you are using the MAX1765 when
contacting these component suppliers.
CAPACITORS
SCHOTTKY DIODES
AVX TPS series
Kemet T510 series
Sanyo POSCAP series
Motorola MBR0520L
Nihon EP10QY03
I


IOUT,MAX =  ILIM − RIPPLE  (I − D)

2 
IRIPPLE =
D=
[
]
D
1
×
× VIN − ILIM × (RNCH + LESR )
fSW
L
VOUT − VIN + ILIM × (RNCH + LESR )
VOUT + ILIM (RPCH − RNCH )
where ILIM is the peak inductor current limit, fSW is the
operating frequency (typically 1.2MHz), L is the inductance of the chosen inductor, LRESR is the resistance of
the chosen inductor, RNCH and RPCH are the resistances of the internal N-channel and P-channel,
respectively.
Table 5 lists the typical available output current when operating 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
______________________________________________________________________________________
17
MAX1765
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
µC
270k
LX
CONTROL
INPUTS
POUT
INL
MAX1765
GND
MAX1765
ONB
ON/OFF
VDD
POUT
I/O
OUTL
ONA
I/O µC
I/O
PA
RF
0.1µF
270k
Figure 10. Typical Phone Application
Figure 11. Momentary Pushbutton On/Off Switch
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
2.4
5.0
460
3.6
5.0
720
2 NiCd/NiMH
3 NiCd/NiMH or 1 Li+
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.
18
Chip Information
TRANSISTOR COUNT: 1735
______________________________________________________________________________________
800mA, Low-Noise, Step-Up DC-DC Converter
with 500mA Linear Regulator
QSOP.EPS
TSSOP, 4.0,EXP PADS.EPS
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX1765
Package Information