19-1198; Rev 1; 8/00
KIT
ATION
EVALU
E
L
B
AVAILA
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
The MAX1705/MAX1706 are high-efficiency, low-noise,
step-up DC-DC converters with an auxiliary linearregulator output. These devices are intended for use in
battery-powered wireless applications. They use a synchronous rectifier pulse-width-modulation (PWM) boost
topology to generate 2.5V to 5.5V outputs from battery
inputs, such as 1 to 3 NiCd/NiMH cells or 1 Li-Ion cell.
The MAX1705 has an internal 1A n-channel MOSFET
switch. The MAX1706 has a 0.5A switch. Both devices
also have a built-in low-dropout linear regulator that
delivers up to 200mA.
Features
♦ Up to 96% Efficiency
♦ 1.1VIN Guaranteed Startup
♦ Up to 850mA Output (MAX1705)
♦ Step-Up Output (2.5V to 5.5V Adjustable)
♦ Linear Regulator (1.25V to 5.0V Adjustable)
♦ PWM/PFM Synchronous-Rectified Topology
♦ 300kHz PWM Mode or Synchronizable
♦ 1µA Shutdown Mode
With an internal synchronous rectifier, the MAX1705/
MAX1706 deliver 5% better efficiency than similar nonsynchronous converters. They also feature a pulsefrequency-modulation (PFM) standby mode to improve
efficiency at light loads, and a 1µA shutdown mode. An
efficiency-enhancing track mode reduces the step-up
DC-DC converter output to 300mV above the linear-regulator output.
♦ Voltage Monitor
Both devices come in a 16-pin QSOP package, which
occupies the same space as an 8-pin SO. Other features
include two shutdown-control inputs for push-on/push-off
control, and an uncommitted comparator for use as a voltage monitor.
16 QSOP
MAX1705EEE
-40°C to +85°C
MAX1706C/D
Dice*
0°C to +70°C
16 QSOP
MAX1706EEE
-40°C to +85°C
*Dice are tested at TA = +25°C, DC parameters only.
________________________Applications
Digital Cordless Phones
Personal Communicators
PCS Phones
Wireless Handsets
Palmtop Computers
Handheld Instruments
Two-Way Pagers
♦ Pushbutton On/Off Control
Ordering Information
PART
TEMP RANGE
MAX1705C/D
PIN-PACKAGE
Dice*
0°C to +70°C
__________Typical Operating Circuit
INPUT 0.7V TO 5.5V
LX
Pin Configuration
TOP VIEW
LBP 1
16 POUT
LBN 2
15 ONA
REF 3
14 ONB
TRACK 4
GND 5
MAX1705
MAX1706
OUT 6
13 LX
11 CLK/SEL
FB 7
POUT
LOW-BATTERY
DETECTION
OUT
MAX1705
ON/OFF CONTROL
HIGH
EFFICIENCY
LOW
NOISE
LBO MAX1706
ONA
FB
LINEAR
REGULATOR
OUTPUT
ONB
CLK/SEL
TRACK
12 PGND
STEP-UP OUTPUT
LBP
LBN
REF
LDO
FBLDO
GND PGND
10 LBO
FBLDO 8
9
LDO
QSOP
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX1705/MAX1706
General Description
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, FBLDO, OUT, POUT to GND...................-0.3V to 6V
PGND to GND.....................................................................±0.3V
POUT to OUT ......................................................................±0.3V
LX to PGND ............................................-0.3V to (VPOUT + 0.3V)
CLK/SEL, REF, FB, TRACK, LDO,
LBN, LBP, LBO to GND.......................-0.3V to (VOUT + 0.3V)
LDO Short Circuit .......................................................Continuous
Continuous Power Dissipation (TA = +70°C)
QSOP (derate 8.70mW/°C above +70°C) ...................696mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°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 = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
LX = open, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
1.1
V
DC-DC CONVERTER
Minimum Startup Voltage
TA = +25°C, ILOAD < 1mA, Figure 2
0.9
Minimum Operating Battery
Voltage
(Note 1)
0.7
FB Regulation Voltage
CLK/SEL = OUT
FB Input Current
VFB = 1.5V
1.219
OUT Adjust Range
V
1.233
1.247
V
0.01
50
nA
5.5
V
0.65
1.25
%
2.5
Load Regulation
MAX1705, 0A ≤ ILX ≤ 0.5A;
MAX1706, 0A ≤ ILX ≤ 0.25A;
CLK/SEL = OUT
OUT Voltage in Track Mode
TRACK = VLDO > 2.3V
VLDO
+ 0.2
VLDO
+ 0.3
VLDO
+ 0.4
V
VPOUT = VOUT = 1.5V
40
150
300
kHz
2.00
2.15
2.30
V
1
20
µA
100
190
µA
VFB = VFBLDO = 1.5V, no load
180
360
µA
FB = GND (LX switching)
2.1
Frequency in Startup Mode
fLX
Startup to Normal Mode
Transition Voltage
(Note 2)
Supply Current in Shutdown
IOUT
ONA = GND, ONB = OUT, measure IOUT
Supply Current in
Low-Power Mode
IOUT
CLK/SEL = GND, VFB = VFBLDO = 1.5V,
no load
Supply Current in
Low-Noise Mode
IOUT
CLK/SEL = OUT
mA
REFERENCE
Reference Output Voltage
IREF = 0µA
Reference Load Regulation
Reference Supply Regulation
2
1.238
1.250
1.262
V
-1µA < IREF < 50µA
4
15
mV
2.5V < VOUT < 5.5V
0.2
5
mV
_______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
LX = open, 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, V ONB = VOUT = 5.0V
0.1
20
µA
LX Leakage Current
VLX = V ONB = VOUT = 5.0V
0.1
20
µA
CLK/SEL = GND
0.23
0.45
CLK/SEL = OUT
0.16
0.28
n-channel, ILX = 100mA
Switch On-Resistance
p-channel, ILX = 100mA
CLK/SEL = OUT
n-Channel MOSFET
Current Limit
ILIM
CLK/SEL = GND
p-Channel SynchronousRectifier Turn-Off Current
Ω
0.27
0.50
MAX1705
1000
1280
1550
MAX1706
550
750
950
MAX1705
250
435
550
MAX1706
250
435
550
20
70
120
mA
1.238
1.250
1.262
V
50
nA
CLK/SEL = GND
mA
LINEAR REGULATOR
FBLDO Regulation Voltage
FBLDO = LDO, ILOAD = 1mA
FBLDO Input Current
VFBLDO = 1.5V
LDO Adjust Range
0.01
1.25
220
5.0
V
300
500
mA
Short-Circuit Current Limit
FBLDO = GND
Dropout Resistance
VFBLDO = 1V, ILDO = 200mA
0.5
1.2
Ω
Load Regulation
100µA < ILDO < 200mA, FBLDO = LDO
0.4
1.2
%
Line Regulation
2.5V < VOUT < 5.5V, FBLDO = LDO,
ILDO = 1mA
0.1
0.5
%
AC Power-Supply Rejection
f = 300kHz
38
dB
Thermal Shutdown
Hysteresis approximately 10°C
155
°C
LOW-BATTERY COMPARATOR
LBN, LBP Offset
LBP falling
LBN, LBP Hysteresis
LBP rising
LBN, LBP Common-Mode
Input Range
VLBN = 0.5V and 1.5V (at least one input must
be within this range)
LBN, LBP Input Current
VLBN = VLBP = 1V
LBO Output Low Voltage
ISINK = 1mA, VOUT = 2.5V, LBP = GND,
LBN = OUT
LBO High Leakage
VLBO = VOUT = 5V
-5
+5
16
0.5
0.01
mV
mV
1.5
V
50
nA
0.4
V
1
µA
CONTROL INPUTS
Input Low Level
Input High Level
Input Leakage Current
(CLK/SEL, ONA, ONB, TRACK)
1.2V < VOUT < 5.5V, ONA, ONB (Note 3)
0.2VOUT
VOUT = 2.5V, CLK/SEL, TRACK
0.2VOUT
1.2V < VOUT < 5.5V, ONA, ONB (Note 3)
0.8VOUT
VOUT = 5.5V, CLK/SEL, TRACK
0.8VOUT
V
V
1
µA
_______________________________________________________________________________________
3
MAX1705/MAX1706
ELECTRICAL CHARACTERISTICS (continued)
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
LX = open, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
Internal Oscillator Frequency
CONDITIONS
CLK/SEL = OUT
MIN
TYP
MAX
UNITS
260
300
340
kHz
400
kHz
External Oscillator
Synchronization Range
200
Oscillator Maximum Duty Cycle
80
86
90
%
Minimum CLK/SEL Pulse
200
ns
Maximum CLK/SEL
Rise/Fall Time
100
ns
ELECTRICAL CHARACTERISTICS
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF)
noted. (Note 4) LX = open, TA = -40°C to +85°C, unless otherwise noted. (Note 4)
PARAMETER
SYMBOL
CONDITIONS
DC-DC CONVERTER
FB Regulation Voltage
CLK/SEL = OUT
OUT Voltage in Track Mode
TRACK = OUT, VLDO > 2.3V
MIN
Startup to Normal Mode
Transition Voltage
TYP
MAX
UNITS
1.215
1.251
V
VLDO +
0.2
VLDO +
0.4
V
2.0
2.3
V
Supply Current in Shutdown
IOUT
ONA = 0V, ONB = OUT, measure IOUT
20
µA
Supply Current in
Low-Power Mode
IOUT
CLK/SEL = 0V, FB = FBLDO = 1.5V, no load
190
µA
Supply Current in
Low-Noise Mode
IOUT
CLK/SEL = OUT, VFB = VFBLDO = 1.5V,
no load
360
µA
1.265
V
REFERENCE
Reference Output Voltage
IREF = 0µA
1.235
DC-DC CONVERTER
n-channel, ILX = 100mA
Switch On-Resistance
p-channel, ILX = 100mA
CLK/SEL = OUT
n-Channel MOSFET
Current Limit
ILIM
CLK/SEL = 0V
p-Channel SynchronousRectifier Turn-Off Current
4
CLK/SEL = 0V
CLK/SEL = 0V
0.45
CLK/SEL = OUT
0.28
CLK/SEL = OUT
0.50
MAX1705
1000
1700
MAX1706
550
950
MAX1705
250
570
MAX1706
250
570
20
120
_______________________________________________________________________________________
Ω
mA
mA
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
LX = open, TA = -40°C to +85°C, unless otherwise noted, Note 4.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
LINEAR REGULATOR
FBLDO Regulation Voltage
FBLDO = LDO, ILOAD = 1mA
FBLDO Input Current
VFBLDO = 1.5V
Short-Circuit Current Limit
FBLDO = LDO = GND
Dropout Resistance
VFBLDO = 1V, ILDO = 200mA
1.233
0.01
220
1.268
V
50
nA
600
mA
1.2
Ω
LOW-BATTERY COMPARATOR
LBN, LBP Offset
LBP falling
-5
+5
mV
LBN, LBP Common-Mode
Input Range
LBN = 0.5V and 1.5V (at least one input must
be within this range)
0.5
1.5
V
LBO High Leakage
LBO = OUT = 5V
1
µA
CONTROL INPUTS
Input Low Level
Input High Level
Internal Oscillator Frequency
External Oscillator
Synchronization Range
Note 1:
Note 2:
Note 3:
Note 4:
1.2V < VOUT < 5.5V, ONA, ONB (Note 2)
0.15VOUT
VOUT = 2.5V, CLK/SEL, TRACK
0.15VOUT
1.2V < VOUT < 5.5V, ONA, ONB (Note 2)
0.85VOUT
VOUT = 5.5V, CLK/SEL, TRACK
0.85VOUT
CLK/SEL = OUT
V
V
260
340
kHz
200
400
kHz
Once the output is in regulation, the MAX1705/MAX1706 operate down to a 0.7V input voltage.
The device is in startup mode when VOUT is below this value (see Low-Voltage Startup Oscillator section).
ONA and ONB inputs have a hysteresis of approximately 0.15VOUT.
Specifications to -40°C to are guaranteed by design, not production tested.
_______________________________________________________________________________________
5
MAX1705/MAX1706
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
MAX1705
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 5V)
60
50
L = 10µH
VOUT = 3.3V
A: VIN = 0.9V
B: VIN = 2.7V
1: PFM MODE
2: PWM MODE
40
30
20
10
50
L = 10µH
VOUT = 5V
A: VIN = 0.9V
C: VIN = 2.4V
E: VIN = 3.6V
1: PFM MODE
2: PWM MODE
40
20
10
1
10
100
800
PWM MODE
700
VOUT = 5V
600
VOUT = 3.3V
500
400
PFM MODE
300
VOUT = 3.3V
200
VOUT = 5V
100
0
0
0.1
0.1
1000
1
10
100
1000
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
MAX1706
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 3.3V)
MAX1706
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 5V)
MAX1706
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
B.2
80
EFFICIENCY (%)
A.2
70
60
50
L = 22µH
VOUT = 3.3V
A: VIN = 0.9V
B: VIN = 2.7V
1: PFM MODE
2: PWM MODE
40
30
20
10
C.1
B.2 C.2
B.1
70
A.2
A.1
60
50
L = 22µH
VOUT = 5V
A: VIN = 0.9V
B: VIN = 2.4V
C: VIN = 3.6V
1: PFM MODE
2: PWM MODE
40
30
20
10
700
L = 22µH
1
10
100
1.5
1.3
VOUT = 3.3V
200
VOUT = 5V
100
0.1
1000
1
10
100
1000
0
0.5 1.0 1.5 2.0 2.5
3
3.5
4
MAX1705
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
LINEAR-REGULATOR DROPOUT
VOLTAGE vs. LOAD CURRENT
1.1
MAX1705/6 TOC07
TA = -40°C
0.9
TA = +25°C
0.7
TA = +85°C
0.5
0.01
300
PFM MODE
0.1
1
10
OUTPUT CURRENT (mA)
100
1000
12
VOUT = 3.3V
L = 10µH
11
10
9
8
7
6
PWM MODE
5
4
3
2
1
0
140
VLDO = 3.3V
120
DROPOUT VOLTAGE (mV)
1.7
VOUT = 3.3V
INPUT VOLTAGE (V)
NO-LOAD STARTUP:
1.0V AT -40°C
0.79 AT +25°C
0.64V AT +85°C
CONSTANT-CURRENT LOAD
VOUT = 3.3V
L = 10µH
D1 = MBR0520L
1.9
VOUT = 5V
400
OUTPUT CURRENT (mA)
2.3
2.1
PWM MODE
500
OUTPUT CURRENT (mA)
NO-LOAD SUPPLY CURRENT (mA)
0.1
600
0
0
0
MAX1705/6 TOC06
80
90
MAXIMUM OUTPUT CURRENT (mA)
A.1
100
MAX1705/6 TOC04
B.1
90
MAX1705/6 TOC05
OUTPUT CURRENT (mA)
100
EFFICIENCY (%)
A.1
60
30
0
6
B.2 C.2
A.2
70
L = 10µH
900
MAX1705/6 TOC8
EFFICIENCY (%)
70
B.1
80
EFFICIENCY (%)
A.2
MAX1705/6 TOC03
B.2
80
1000
4.5
MAX1705/6 TOC09
A.1
C.1
90
MAXIMUM OUTPUT CURRENT (mA)
B.1
90
100
MAX1705/6 TOC01
100
MAX1705
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX1705/6 TOC02
MAX1705
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 3.3V)
STARTUP INPUT VOLTAGE (V)
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
100
80
VLDO = 2.5V
60
VLDO = 5V
40
20
PFM MODE
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
0
40
80
120
LOAD CURRENT (mA)
_______________________________________________________________________________________
160
200
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
LINEAR-REGULATOR
REGION OF STABLE C6 ESR
vs. LOAD CURRENT
LINEAR-REGULATOR POWER-SUPPLY
REJECTION RATIO vs. FREQUENCY
50
MAX1705/6 TOC11
100
MAX1705/6 TOC10
60
C6 = 22µF
UNCOMPENSATED
10
C6 ESR (Ω)
30
20
STABLE REGION
VOUT = 4V TO 5V
VLDO = 3.3V
ILDO = 200mA
C5 = 0.33µF
10
0.1
0
1k
10k
100k
1M
0
10M
1
50
MAX1705
NOISE SPECTRUM AT POUT
(VOUT = 4.5V, VIN = 1.2V, 200mA LOAD)
100
150
200
250
300
LOAD CURRENT (mA)
MAX1705/6 TOC13
FREQUENCY (Hz)
NOISE (5mVRMS/div)
0V
1k
10k
100k
1M
10M
FREQUENCY (Hz)
MAX1705
LINEAR-REGULATOR OUTPUT NOISE SPECTRUM
(VLDO = 3.3V, VOUT = 4.5V, VIN = 1.2V, ILDO = 200mA)
MAX1705/6 TOC14
100
C2 = 22pF (FEED FORWARD)
1
NOISE (50µV/div)
PSRR (dB)
40
0V
1k
10k
100k
1M
10M
FREQUENCY (Hz)
_______________________________________________________________________________________
7
MAX1705/MAX1706
____________________________Typical Operating Characteristics (continued)
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
MAX1705/6 TOC17
MAX1705/6 TOC16
MAX1705/6 TOC15
A
MAX1705
POWER-ON DELAY
(PWM MODE)
MAX1705
LOAD-TRANSIENT RESPONSE
MAX1705
LINE-TRANSIENT RESPONSE
A
B
A
3V
2.5V
3.3V
C
B
B
0mA
D
VIN = 1.2V, LOAD = 1kΩ, ONB TIED TO OUT
A = ONA, 2V/div
B = VLDO, 2V/div
C = VOUT, 2V/div
D = INDUCTOR CURRENT, 500mA/div
VIN = 1.2V, VOUT = 3.3V
A = VOUT, 50mV/div, 3.3V DC OFFSET
B = IOUT, 0mA TO 200mA, 200mA/div
MAX1705
LINEAR-REGULATOR
OUTPUT NOISE
B
MAX1705/6 TOC19
MAX1705
PFM SWITCHING WAVEFORMS
1A
A
DC TO 500kHz
0mA
0V
B
0V
C
D
8
MAX1705/6 TOC20
MAX1705
PWM SWITCHING WAVEFORMS
A
2ms
200µs/div
200µs/div
IOUT = 0mA, VOUT = 3.3V
A = VIN, 1.5V TO 2.0V, 200mV/div
B = VOUT, 10mV/div, 3.3V DC OFFSET
MAX1705/6 TOC18
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
VOUT
C
VOUT
VLDO
D
VLDO
1µs/div
2µs/div
VIN = 1.2V, VOUT = 4.5V, VLDO = 3.3V, ILDO = 200mA
A = INDUCTOR CURRENT, 500mA/div
B = LX VOLTAGE, 5V/div
C = VOUT RIPPLE, 50m/div AC-COUPLED
D = VLDO RIPPLE, 5m/div AC-COUPLED
C5 = 0.33µF
VIN = 1.2V, VOUT = 4.5V, VLDO = 3.3V, ILDO = 40mA
A = INDUCTOR CURRENT, 500mA/div
B = LX VOLTAGE, 5V/div
C = VOUT RIPPLE, 50mV/div AC-COUPLED
D = VLDO RIPPLE, 5mV/div AC-COUPLED
C5 = 0.33µF
VLDO
1ms/div
VLDO IS AC-COUPLED, 1mv/div
ILDO = 200mA
C5 = 0.33µF
_______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
PIN
NAME
FUNCTION
1
LBP
Low-Battery Comparator Noninverting Input. Common-mode range is 0.5V to 1.5V.
2
LBN
Low-Battery Comparator Inverting Input. Common-mode range is 0.5V to 1.5V.
3
REF
1.250V Reference Output. Bypass REF with a 0.33µF capacitor to GND. REF can source up to 50µA.
4
TRACK
5
GND
Ground
6
OUT
Step-Up Converter Feedback Input, Used During Track Mode. IC power and low-dropout linear-regulator
input. Bypass OUT to GND with a 0.1µF ceramic capacitor placed as close to the IC as possible.
7
FB
Step-Up DC-DC Converter Feedback Input. Connect FB to a resistor voltage-divider between POUT and
GND to set the output voltage between 2.5V and 5.5V. FB regulates to 1.233V.
8
FBLDO
9
LDO
Low-Dropout Linear-Regulator Output. LDO sources up to 200mA. Bypass to GND with a 22µF capacitor.
10
LBO
Low-Battery Comparator Output. This open-drain, n-channel output is low when LBP < LBN.
Input hysteresis is 16mV.
Track-Mode Control Input for DC-DC Converter. In track mode, the boost-converter output is sensed at
OUT and set 0.3V above LDO to improve efficiency. Set TRACK to OUT for track mode. Connect TRACK to
GND for normal operation.
Low-Dropout Linear-Regulator Feedback Input. Connect FBLDO to a resistor voltage-divider between LDO
to GND to set the output voltage from 1.25V to VOUT - 0.3V (5.0V max). FBLDO regulates to 1.250V.
Switching-Mode Selection and External-Clock Synchronization Input:
• CLK/SEL = low: low-power, low-quiescent-current PFM mode.
• CLK/SEL = high: low-noise, high-power PWM mode. Switches at a constant frequency (300kHz). Full
output power is available.
• CLK/SEL = driven with an external clock: low-noise, high-power synchronized PWM mode.
Synchronizes to an external clock (from 200kHz to 400kHz).
Turning on the DC-DC converter with CLK/SEL = GND also serves as a soft-start function,
since peak inductor current is reduced.
11
CLK/SEL
12
PGND
13
LX
14
ONB
Off-Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal
operation (Table 2).
15
ONA
On-Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal
operation (Table 2).
16
POUT
Boost DC-DC Converter Power Output. POUT is the source of the p-channel synchronous-rectifier MOSFET
switch. Connect an external Schottky diode from LX to POUT. The output current available from POUT is
reduced by the current drawn from the LDO linear-regulator output.
Power Ground for the Source of the n-channel power MOSFET switch
Inductor Connection to the Drains of the p-Channel Synchronous Rectifier and n-Channel Switch
_______________________________________________________________________________________
9
MAX1705/MAX1706
Pin Description
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
Detailed Description
The MAX1705/MAX1706 are designed to supply both
power and low-noise circuitry in portable RF and dataacquisition instruments. They combine a linear regulator, step-up switching regulator, n-channel power
MOSFET, p-channel synchronous rectifier, precision
reference, and low-battery comparator in a single 16pin QSOP package (Figure 1). The switching DC-DC
converter boosts a 1- or 2-cell input to an adjustable
output between 2.5V and 5.5V. The internal low-dropout
regulator provides linear postregulation for noisesensitive circuitry, as well as outputs from 1.25V to
300mV below the switching-regulator output. The
MAX1705/MAX1706 start from a low, 1.1V input and
remain operational down to 0.7V.
These devices are optimized for use in cellular phones
and other applications requiring low noise during fullpower operation, as well as low quiescent current for
LBO
maximum battery life during standby and shutdown.
They feature constant-frequency (300kHz), low-noise
pulse-width-modulation (PWM) operation with 300mA or
730mA output capability from 1 or 2 cells, respectively,
with 3.3V output. A low-quiescent-current standby
pulse-frequency-modulation (PFM) mode offers an output up to 60mA and 140µA, respectively, and reduces
quiescent power consumption to 500µW. In shutdown
mode, the quiescent current is further reduced to just
1µA. Figure 2 shows the standard application circuit for
the MAX1705 configured in high-power PWM mode.
Additional features include synchronous rectification for
high efficiency and improved battery life, and an
uncommitted comparator for low-battery detection. A
CLK/SEL input allows frequency synchronization to
reduce interference. Dual shutdown controls allow shutdown using a momentary pushbutton switch and microprocessor control.
MAX1705
MAX1706
THERMAL
SENSOR
LBP
N
SHUTDOWN
LOGIC
LBN
OUT
FBLDO
MOSFET DRIVER
WITH CURRENT
LIMITING
ERROR
AMP
OUT
REF
P
LDO
IC PWR
POUT
2.15V
EN
GND
START-UP
OSCILLATOR
Q
D
Q
P
PFM/PWM
CONTROLLER
ONA
ON
ONB
REF
OSC
EN
300kHz
OSCILLATOR
CLK/SEL
VLDO
LX
EN
RDY
1.250V
REFERENCE
PFM/PWM
MODE
Q
ICS
IREF
FB
TRACK
PGND
VOUT - 300mV
IFB
Figure 1. Functional Diagram
10
N
______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
MAX1705/MAX1706
INPUT 0.9V TO 3.6V
L1 10µH (22µH)
C7
22µF
D1
R5
LX
BOOST OUTPUT 3.6V
POUT
(TO PGND)
R6
LBP
OUT
LBN
TRACK
REF
C8
0.33µF
C9
0.33µF
C3
R1
0.1µF 191kΩ
PGND
(TO PGND)
MAX1705
MAX1706
R2
100kΩ
FB
ONA
(TO OUT)
LDO OUTPUT 3.3V
ONB
LDO
CLK/SEL
FBLDO
C5*
0.33µF
LBO
GND
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATH.
C4
220µF
(100µF)
C1*
R7
100kΩ
R3
165kΩ
C6
22µF
C2*
R4
100kΩ
*OPTIONAL.
( ) ARE FOR MAX1706.
Figure 2. Typical Operating Circuit (PFM Mode)
Step-Up Converter
The step-up switching DC-DC converter generates an
adjustable output to supply both power circuitry (such
as RF power amplifiers) and the internal low-dropout
linear regulator. During the first part of each cycle, the
internal n-channel MOSFET switch is turned on. This
allows current to ramp up in the inductor and store
energy in a magnetic field. During the second part of
each cycle, when the MOSFET is turned off, the voltage
across the inductor reverses and forces current
through the diode and synchronous rectifier to the output filter capacitor and load. As the energy stored in
the inductor is depleted, the current ramps down, and
the output diode and synchronous rectifier turn off.
Voltage across the load is regulated using either PWM
or PFM operation, depending on the CLK/SEL pin setting (Table 1).
Low-Noise, High-Power PWM Operation
When CLK/SEL is pulled high, the MAX1705/MAX1706
operate in a high-power, low-noise PWM mode. During
PWM operation, they switch at a constant frequency
(300kHz), and modulate the MOSFET switch pulse
width to control the power transferred per cycle and
regulate the voltage across the load. In PWM mode, the
Table 1. Selecting the Operating Mode
CLK/SEL
MODE
FEATURES
0
PFM
Low supply current
1
PWM
Low noise,
high output current
External Clock
(200kHz to 400kHz)
Synchronized
PWM
Low noise,
high output current
devices can output up to 850mA. Switching harmonics
generated by fixed-frequency operation are consistent
and easily filtered.
During PWM operation, each of the internal clock’s rising edges sets a flip-flop, which turns on the n-channel
MOSFET switch (Figure 3). The switch is turned off
when the sum of the voltage-error and currentfeedback signals trips a multi-input comparator and
resets the flip-flop; the switch remains off for the rest of
the cycle. When a change occurs in the output voltage
error signal into the comparator, it shifts the level that
the inductor current is allowed to ramp to during each
cycle and modulates the MOSFET switch pulse width.
A second comparator enforces a 1.55A (max) inductor-
______________________________________________________________________________________
11
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
POUT
Q
POUT
Q
P
IFB*
LOGIC HIGH
D
R
IREF*
R
P
LX
Q
N
S
LX
IFB*
ICS
S
N
Q
IREF*
CURRENTLIMIT LEVEL
R
PGND
OSC
CURRENTLIMIT LEVEL
PGND
*SEE FIGURE 1
Figure 3. Simplified PWM Controller Block Diagram
current limit for the MAX1705, and 950mA (max) for the
MAX1706. During PWM operation, the circuit operates
with a continuous inductor current.
Synchronized PWM Operation
The MAX1705/MAX1706 can also be synchronized to a
200kHz to 400kHz frequency by applying an external
clock to CLK/SEL. This allows the user to set the harmonics, to avoid IF bands in wireless applications. The
synchronous rectifier is also active during synchronized
PWM operation.
Low-Power PFM Operation
Pulling CLK/SEL low places the MAX1705/MAX1706 in
low-power standby mode. During standby mode, PFM
operation regulates the output voltage by transferring a
fixed amount of energy during each cycle, and then
modulating the switching frequency to control the
power delivered to the output. The devices switch only
as needed to service the load, resulting in the highest
possible efficiency at light loads. Output current capability in PFM mode is 140mA (from 2.4V input to 3.3V
output). The output is regulated at 1.3% above the
PWM threshold.
During PFM operation, the error comparator detects
output voltage falling out of regulation and sets a
flip-flop, turning on the n-channel MOSFET switch
(Figure 4). When the inductor current ramps to the PFM
mode current limit (435mA) and stores a fixed amount
of energy, the current-sense comparator resets a flipflop. The flip-flop turns off the n-channel switch and
turns on the p-channel synchronous rectifier. A second
flip-flop, previously reset by the switch’s “on” signal,
inhibits the error comparator from initiating another
12
*SEE FIGURE 1
Figure 4. Controller Block Diagram in PFM Mode
cycle until the energy stored in the inductor is dumped
into the output filter capacitor and the synchronous rectifier current ramps down to 70mA. This forces operation with a discontinuous inductor current.
Synchronous Rectifier
The MAX1705/MAX1706 feature an internal 270mΩ,
p-channel synchronous rectifier to enhance efficiency.
Synchronous rectification provides a 5% efficiency
improvement over similar nonsynchronous step-up
regulators. In PWM mode, the synchronous rectifier is
turned on during the second half of each cycle. In PFM
mode, an internal comparator turns on the synchronous
rectifier when the voltage at LX exceeds the step-up
converter output, and then turns it off when the inductor
current drops below 70mA.
Linear Regulator
The internal low-dropout linear regulator steps down the
output from the step-up converter and reduces switching
ripple. It 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
200mA. However, in practice, the maximum output current is further limited by the current available from the
boost converter and by the voltage differential between
OUT and LDO. Use a 22µF capacitor with a 1Ω or less
equivalent series resistance (ESR) at the output for stability (see the Linear Regulator Region of Stable C6 ESR
vs. Load Current graph in the Typical Operating
Characteristics). When the MAX1705/1706 are activated
by logic control (ONA, ONB), the linear regulator (LDO)
remains off until the step-up converter (POUT) goes into
______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
Low-Voltage Startup Oscillator
The MAX1705/MAX1706 use a CMOS, low-voltage startup oscillator for a 1.1V guaranteed minimum startup
input voltage at +25°C. On startup, the low-voltage oscillator switches the n-channel MOSFET until the output
voltage reaches 2.15V. Above this level, the normal stepup converter feedback and control circuitry take over.
Once the device is in regulation, it can operate down to a
0.7V input, since internal power for the IC is bootstrapped from the output using the OUT pin.
To reduce current loading during step-up, the linear
regulator is kept off until the startup converter goes into
regulation. Minimum startup voltage is influenced by
load and temperature (see the Typical Operating
Characteristics). To allow proper startup, do not apply
a full load at POUT until after the device has exited
startup mode and entered normal operation.
Table 2. On/Off Logic Control
ONA
ONB
MAX1705/MAX1706
0
0
On
0
1
Off
1
0
On
1
1
On
below the input, but the linear regulator output is
turned off.
Entry into shutdown mode is controlled by logic input
pins ONA and ONB (Table 2). Both inputs have trip
points near 0.5VOUT with 0.15VOUT hysteresis.
Tracking
Connecting TRACK to the step-up converter output
implements a tracking mode that sets the step-up
converter output to 300mV above the linear-regulator
output, improving efficiency. In track mode, feedback
for the step-up converter is derived from the OUT pin.
When TRACK is low, the step-up converter and linear
regulator are separately controlled by their respective
feedback inputs, FB and FBLDO. TRACK is a logic
input with a 0.5VOUT threshold, and should be hardwired or switched with a slew rate exceeding 1V/µs.
VLDO must be set above 2.3V for track mode to operate
properly.
On power-up with TRACK = OUT, the step-up converter initially uses the FB input to regulate its output. After
the step-up converter goes into regulation for the first
time, the linear regulator turns on. When the linear regulator reaches 2.3V, track mode is enabled and the stepup converter is regulated to 300mV above the linearregulator output.
Low-Battery Comparator
The internal low-battery comparator has uncommitted
inputs and an open-drain output capable of sinking
1mA. To use it as a low-battery-detection comparator,
connect the LBN input to the reference, and connect
the LBP input to an external resistor-divider between
the positive battery terminal and GND (Figure 2). The
resistor values are then as follows:
Shutdown
The MAX1705/MAX1706 feature a shutdown mode that
reduces quiescent current to less than 1µA, preserving
battery life when the system is not in use. During shutdown, the reference, the low-battery comparator, and
all feedback and control circuitry are off. The step-up
converter’s output drops to one Schottky diode drop
⎛ VIN,TH
⎞
R5 = R6 ⎜
- 1⎟
⎝ VLBN
⎠
where VIN,TH is the desired input voltage trip point and
VLBN = VREF = 1.25V. Since the input bias current into
______________________________________________________________________________________
13
MAX1705/MAX1706
regulation for the first time. However when power is first
applied, LDO may be on before POUT reaches regulation. If this is not acceptable, the chip should be held in
shutdown when input voltage is first appled to ensure
that the linear regulator is off until POUT is ready.
The linear regulator in the MAX1705/MAX1706 features
a 0.5Ω, p-channel MOSFET pass transistor. This provides several advantages, including longer battery life,
over similar designs using a pnp pass transistor. The pchannel MOSFET requires no base-drive current, which
reduces quiescent current considerably. PNP-based
regulators tend to waste base-drive current in dropout
when the pass transistor saturates. The
MAX1705/MAX1706 eliminate this problem.
The linear-regulator error amplifier compares the output
feedback sensed at the FBLDO input against the internal 1.250V reference, and amplifies the difference
(Figure 1). The MOSFET driver reads the error signal
and applies the appropriate drive to the p-channel
pass transistor. If the feedback signal is lower than the
reference, the pass-transistor gate is pulled lower,
allowing more current to pass to the output, thereby
increasing the output voltage. If the feedback voltage is
too high, the pass-transistor gate is pulled up, allowing
less current to pass to the output. Additional blocks
include a current-limiting block and a thermal-overload
protection block.
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
LBP is less than 50nA, R6 can be a large value (such
as 270kΩ or less) without sacrificing accuracy.
Connect the resistor voltage-divider as close to the IC
as possible, within 0.2in. (5mm) of the LBP pin. The
inputs have a 0.5V to 1.5V common-mode input range,
and a 16mV input-referred hysteresis.
The low-battery comparator can also be used to monitor the output voltage, as shown in Figure 5.
To set the low-battery threshold to a voltage below the
1.25V reference, insert a resistor-divider between REF
and LBN, and connect the battery to the LBP input
through a 10kΩ current-limiting resistor (Figure 6). The
equation for setting the resistors for the low-battery
threshold is then as follows:
⎛ V
⎞
R5 = R6 ⎜ REF - 1⎟
⎝ VIN,TH
⎠
POUT
LDO
MAX1705
MAX1706
LBO
R5
LBP
LBN
R6
REF
GND
0.33µF
Figure 5. Using the Low-Battery Comparator to Sense
the Output Voltage
Alternatively, the low-battery comparator can be used
to check the output voltage or to control the load directly on POUT during startup (Figure 7). Use the following
equation to set the resistor values:
POUT
REF
MAX1705
MAX1706
⎛ VOUT,TH
⎞
R5 = R6 ⎜
- 1⎟
⎝ VLBP
⎠
LBO
LBN
R8
10kΩ
R6
LBP
where VOUT,TH is the desired output voltage trip point
and VLBP is connected to the reference or 1.25V.
0.33µF
R5
GND
BATTERY
VOLTAGE
Reference
The MAX1705/MAX1706 have an internal 1.250V, 1%
bandgap reference. Connect a 0.33µF bypass capacitor to GND within 0.2in. (5mm) of the REF pin. REF can
source up to 50µA of external load current.
Figure 6. Detecting Battery Voltages Below 1.25V
_________________ Design Procedure
Setting the Output Voltages
Set the step-up converter output voltage between 2.5V
and 5.5V by connecting a resistor voltage-divider to FB
from OUT to GND, as shown in Figure 8. The resistor
values are then as follows:
STEP-UP OUTPUT
P
C5
270kΩ
C3
0.1µF
OUT
POUT
R5
LBN
C4
MAX1705
R6
LBO MAX1706
LBP
⎛V
⎞
R1 = R2 ⎜ POUT - 1⎟
⎝ VFB
⎠
where VFB, the step-up regulator feedback setpoint, is
1.233V. Since the input bias current into FB is less than
50nA, R2 can have a large value (such as 270kΩ or
14
REF
GND
0.33µF
Figure 7. Using the Low-Battery Comparator for Load Control
During Startup
______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
⎛ V
⎞
R3 = R4 ⎜ LDO - 1⎟
⎝ VFBLDO
⎠
where VFBLDO, the linear-regulator feedback trip point,
is 1.250V. Since the input bias current into FBLDO is
less than 50nA, R4 can be a large value (such as
270kΩ or less). Connect the resistor voltage-divider as
close to the IC as possible, within 0.2in. (5mm) of the
FBLDO pin.
Inductor Selection
The MAX1705/MAX1706s’ high switching frequency
allows the use of a small surface-mount inductor. Use a
10µH inductor for the MAX1705 and a 22µH inductor
for the MAX1706. Make sure the saturation-current rating exceeds the n-channel switch current limit of 1.55A
for the MAX1705 and 950mA for the MAX1706. For high
efficiency, chose an inductor with a high-frequency
core material, such as ferrite, to reduce core losses. To
minimize radiated noise, use a torroid, pot core, or
shielded-bobbin inductor. See Table 3 for suggested
parts and Table 4 for a list of inductor suppliers.
Connect the inductor from the battery to the LX pin as
close to the IC as possible.
500mA. Attach the diode between the LX and POUT
pins, as close to the IC as possible.
In high-temperature applications, some Schottky
diodes may be unsuitable due to high reverse-leakage
currents. Try substituting a Schottky diode with a higher
reverse voltage rating, or use an ultra-fast silicon rectifier with reverse recover times less than 60ns (such as a
MUR150 or EC11FS1). Do not use ordinary rectifier
diodes, since slow switching speeds and long reverse recovery times compromise efficiency and load
regulation.
Choose Input and Output
Filter Capacitors
Choose input and output filter capacitors that 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-ESR tantalum capacitor is recommended at the MAX1706’s step-up output. For the
MAX1705, use two in parallel or a 220µF low-ESR tantalum capacitor. The input filter capacitor (C7) also
LINEARREGULATOR
OUTPUT
C2*
LDO
MAX1705
MAX1706
R3
STEP-UP
OUTPUT
POUT
R1
C1*
OUT
FBLDO
R4
GND
FB
PGND
R2
Attaching the Output Diode
Use a Schottky diode, such as a 1N5817, MBR0520L,
or equivalent. The Schottky diode carries current during
startup, and in PFM mode after the synchronous rectifier turns off. Thus, the current rating only needs to be
* OPTIONAL COMPENSATION CAPACITORS
Figure 8. Feedback Connections for the MAX1705/MAX1706
Table 3. Component Selection Guide
PRODUCTION
INDUCTORS
CAPACITORS
DIODES
Surface Mount
Sumida CDR63B, CD73, CDR73B, CD74B series
Coilcraft DO1608, DO3308, DT3316 series
Matsuo 267 series
Sprague 595D series
AVX TPS series
Motorola MBR0520L
Through Hole
Sumida RCH654 series
Sanyo OS-CON series
Nichicon PL series
Motorola 1N5817
______________________________________________________________________________________
15
MAX1705/MAX1706
less) without sacrificing accuracy. Connect the resistor
voltage-divider as close to the IC as possible, within
0.2in. (5mm) of the FB pin.
Alternatively, set the step-up converter output to track
the linear regulator by 300mV. To accomplish this, set
TRACK to OUT.
To set the low-dropout linear-regulator output, use a
resistor voltage-divider connected to FBLDO from LDO
to GND. Set the output to a value at least 300mV less
than the step-up converter output using the following
formula:
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
reduces peak currents drawn from the input source
and reduces input switching noise. The input voltage
source impedance determines the size required for the
input capacitor. When operating directly from one or
two NiCd cells placed close to the MAX1705/MAX1706,
use a 22µF, low-ESR input filter capacitor. When
operating from a power source placed farther away, or
from higher impedance batteries, consider using one or
two 100µF, 100mΩ, low-ESR tantalum capacitors.
Low-ESR capacitors are recommended. Capacitor ESR
is a major contributor to output ripple—often more than
70%.
Ceramic, Sanyo OS-CON, and Panasonic SP/CB-series
capacitors offer the lowest ESR. Low-ESR tantalum
capacitors are second best and generally offer a good
trade-off between price and performance. Do not
exceed the ripple-current ratings of tantalum capacitors. Avoid aluminum-electrolytic capacitors, since their
ESR is too high.
Adding Bypass Capacitors
Several ceramic bypass capacitors are required for
proper operation of the MAX1705/MAX1706. Bypass
REF with a 0.33µF capacitor to GND. Connect a 0.1µF
ceramic capacitor from OUT to GND and a 0.33µF
ceramic capacitor from POUT to PGND. Place a 22µF,
low-ESR capacitor and an optional 0.33µF ceramic
capacitor from the linear-regulator output LDO to GND.
An optional 22pF ceramic capacitor can be added to
the linear-regulator feedback network to reduce noise
(C2, Figure 2). Place each of these as close to their
respective pins as possible, within 0.2in. (5mm) of the
DC-DC converter IC. High-value, low-voltage, surfacemount ceramic capacitors are now readily available in
small packages; see Table 4 for suggested suppliers.
Designing a PC Board
High switching frequencies and large peak currents
make PC board layout an important part of design.
Poor design can cause excessive EMI and groundbounce, both of which can cause instability or
regulation errors by corrupting voltage- and currentfeedback signals. It is highly recommended that the PC
board example of the MAX1705 evaluation kit (EV kit)
be followed.
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. Place the LDO
output capacitor as close to the LDO pin as possible.
Make the connection between POUT and OUT very
16
Table 4. Component Suppliers
SUPPLIER
PHONE
FAX
AVX
USA: 803-946-0690
800-282-4975
803-626-3123
Coilcraft
USA: 847- 639-6400
847-639-1469
Matsuo
USA: 714-969-2491
714-960-6492
Motorola
USA: 602-303-5454
602-994-6430
Sanyo
USA: 619-661-6835
Japan: 81-7-2070-6306
619-661-1055
81-7-2070-1174
Sumida
USA: 847-956-0666
Japan: 81-3-3607-5111
847-956-0702
81-3-3607-5144
short. Keep the extra copper on the board, and integrate it into ground as a pseudo-ground plane.
On multilayer boards, do not connect the ground pins
of the power components using vias through an internal
ground plane. Instead, place them close together and
route them in a star-ground configuration using component-side copper. Then connect the star ground to the
internal ground plane using vias.
Keep the voltage-feedback networks very close to the
MAX1705/MAX1706—within 0.2in. (5mm) of the FB and
FBLDO pins. Keep noisy traces, such as from the LX
pin, away from the reference and voltage-feedback networks, especially the LDO feedback, and separated
from them using grounded copper. Consult the
MAX1705/MAX1706 EV kit for a full PC board example.
Applications Information
Use in a Typical
Wireless Phone Application
The MAX1705/MAX1706 are ideal for use in digital cordless and PCS phones. The power amplifier (PA) is connected directly to the step-up converter output for
maximum voltage swing (Figure 10). The internal linear
regulator is used for postregulation to generate lownoise power for DSP, control, and RF circuitry. Typically,
RF phones spend most of their life in standby mode and
short periods in transmit/receive mode. During standby,
maximize battery life by setting CLK/SEL = GND and
TRACK = OUT; this places the IC in PFM and track
modes (for lowest quiescent power consumption). In
transmit/receive mode, set TRACK = GND and CLK/SEL
= OUT to increase the PA supply voltage and initiate
high-power, low-noise PWM operation. Table 5 lists the
typical available output current when operating with
one or more NiCd/NiMH cells or one Li-Ion cell.
______________________________________________________________________________________
1 to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
LX
CONTROL
INPUTS
MAX1705
MAX1706
POUT
GND
ONB
ON/OFF
MAX1705
MAX1706
MAX1705/MAX1706
µC
270kΩ
OUT
VDD
I/O
LDO
ONA
PA
I/O µC
0.1µF
RF
I/O
270kΩ
Figure 11. Momentary Pushbutton On/Off Switch
Figure 10. Typical Phone Application
Table 5. Typical Available Output Current
NO. OF CELLS
INPUT VOLTAGE
(V)
STEP-UP OUTPUT VOLTAGE:
(PA POWER SUPPLY)
(V)
TOTAL OUTPUT CURRENT
(mA)
MAX1705
MAX1706
1 NiCd/NiMH
1.2
3.3
300
200
2 NiCd/NiMH
2.4
3.3
730
450
2 NiCd/NiMH
2.4
5.0
500
350
3 NiCd/NiMH or 1 Li-Ion
3.6
5.0
850
550
Implementing Soft-Start
To implement soft-start, set CLK/SEL low on power-up;
this forces PFM operation and reduces the peak switching current to 435mA. Once the circuit is in regulation,
CLK/SEL can be set high for full-power operation.
Chip Information
TRANSISTOR COUNT: 1649
SUBSTRATE CONNECTED TO GND
Adding a Manual Power Reset
A momentary pushbutton switch can be used to turn
the MAX1705/MAX1706 on and off (Figure 11). ONA is
pulled low and ONB is pulled high to turn the part 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 (200ms) 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 part 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.
______________________________________________________________________________________
17
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
QSOP.EPS
MAX1705/MAX1706
1- to 3-Cell, High-Current, Low-Noise,
Step-Up DC-DC Converters with Linear Regulator
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
21-0055
F
1
1
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.
18 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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