MAX1706EEE [MAXIM]
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator; 1至3节电池，大电流，低噪声，升压型线性稳压器DC- DC转换器
| 型号： | MAX1706EEE |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator |
| 文件： | 总20页 (文件大小：216K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1198; Rev 0; 4/97
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
The MAX1705/MAX1706 are high-efficiency, low-noise,
s te p -up DC-DC c onve rte rs with a n a uxilia ry line a r-
regulator output. These devices are intended for use in
battery-powered wireless applications. They use a syn-
chronous 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.
♦ Up to 96% Efficiency
♦ 1.1V Guaranteed Start-Up
IN
♦ 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 non-
synchronous converters. They also feature a pulse-
frequency-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-reg-
ulator output.
♦ Voltage Monitor
♦ Pushbutton On/Off Control
______________Ord e rin g In fo rm a t io n
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
Dice*
MAX1705C/D
MAX1705EEE
MAX1706C/D
MAX1706EEE
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 volt-
age monitor.
-40°C to +85°C
0°C to +70°C
16 QSOP
Dice*
-40°C to +85°C
16 QSOP
*Dice are tested at T = +25°C, DC parameters only.
A
________________________Ap p lic a t io n s
__________Typ ic a l Op e ra t in g Circ u it
Digital Cordless Phones
Personal Communicators
Palmtop Computers
PCS Phones
Wireless Handsets
Two-Way Pagers
INPUT 0.7V TO 5.5V
Hand-Held Instruments
LX
STEP-UP OUTPUT
LBP
__________________P in Co n fig u ra t io n
POUT
LOW-BATTERY
OUT
DETECTION
TOP VIEW
LBP
LBN
1
2
3
4
5
6
7
8
16 POUT
15 ONA
14 ONB
13 LX
FB
MAX1705
MAX1706
LBO
ONA
ON/OFF CONTROL
LINEAR
REGULATOR
OUTPUT
REF
ONB
HIGH
LOW
CLK/SEL
TRACK
TRACK
GND
OUT
MAX1705
MAX1706
EFFICIENCY
NOISE
LDO
12 PGND
11 CLK/SEL
10 LBO
FBLDO
LBN
REF
GND PGND
FB
FBLDO
9 LDO
QSOP
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
ABSOLUTE MAXIMUM RATINGS
Continuous Power Dissipation (T = +70°C)
A
ONA, ONB, FBLDO, OUT, POUT to GND...................-0.3V to 6V
PGND to GND.....................................................................±0.3V
POUT to OUT......................................................................±0.3V
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, 10sec) .............................+300°C
LX to PGND ............................................-0.3V to (V
CLK/SEL, REF, FB, TRACK, LDO,
+ 0.3V)
POUT
LBN, LBP, LBO to GND.......................-0.3V to (V
+ 0.3V)
OUT
LDO Short Circuit .......................................................Continuous
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
(V
OUT
= V
= V
= 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
POUT
LBP
LX = open, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
DC-DC CONVERTER
Minimum Start-Up Voltage
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5/MAX1706
T
= +25°C, I
< 1mA, Figure 2
0.9
0.7
1.1
V
V
A
LOAD
Minimum Operating Battery
Voltage
(Note 1)
FB Regulation Voltage
FB Input Current
CLK/SEL = OUT
= 1.5V
1.219
2.5
1.233
0.01
1.247
50
V
nA
V
V
FB
OUT Adjust Range
5.5
MAX1705, 0A ≤ I ≤ 0.5A;
LX
Load Regulation
MAX1706, 0A ≤ I ≤ 0.25A;
0.65
1.25
%
LX
CLK/SEL = OUT
V
+ 0.2
V
+ 0.3
V
LDO
+ 0.4
LDO
LDO
OUT Voltage in Track Mode
Frequency in Start-Up Mode
TRACK = V
> 2.3V
= 1.5V
V
kHz
V
LDO
f
V
= V
40
150
300
LX
POUT OUT
Start-Up to Normal Mode
Transition Voltage
(Note 2)
ONA = GND, ONB = OUT, measure I
2.00
2.15
1
2.30
20
Supply Current in Shutdown
I
µA
OUT
OUT
Supply Current in
Low-Power Mode
CLK/SEL = GND, V = V
no load
= 1.5V,
FB
FBLDO
I
100
190
360
µA
OUT
V
FB
= V
= 1.5V, no load
180
2.1
µA
FBLDO
Supply Current in
Low-Noise Mode
I
CLK/SEL = OUT
OUT
FB = GND (LX switching)
mA
REFERENCE
Reference Output Voltage
Reference Load Regulation
Reference Supply Regulation
I
= 0µA
1.238
1.250
4
1.262
15
V
REF
-1µA < I
< 50µA
mV
mV
REF
2.5V < V
< 5.5V
0.2
5
OUT
2
_______________________________________________________________________________________
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
ELECTRICAL CHARACTERISTICS (continued)
(V
OUT
= V
= V
= 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
POUT
LBP
LX = open, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
DC-DC SWITCHES
POUT Leakage Current
LX Leakage Current
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
= 0V, V
= 0V, V
= V
= 5.5V
0.1
0.1
20
20
µA
µA
ONB
ONB
OUT
LX
V
LX
= V
= 5.5V
OUT
CLK/SEL = GND
0.23
0.16
0.27
1280
750
435
435
0.45
0.28
0.50
1550
950
550
550
N-channel, I = 100mA
LX
Ω
CLK/SEL = OUT
Switch On-Resistance
P-channel, I = 100mA
LX
MAX1705
MAX1706
MAX1705
MAX1706
1000
550
250
250
CLK/SEL = OUT
CLK/SEL = GND
CLK/SEL = GND
N-Channel MOSFET
Current Limit
I
mA
mA
LIM
P-Channel Synchronous-
Rectifier Turn-Off Current
20
70
120
LINEAR REGULATOR
FBLDO Regulation Voltage
FBLDO Input Current
LDO Adjust Range
FBLDO = LDO, I
= 1mA
1.238
1.250
0.01
1.262
50
V
nA
V
LOAD
V
FBLDO
= 1.5V
1.25
220
5.0
Short-Circuit Current Limit
Dropout Resistance
FBLDO = GND
= 1V, I
300
0.5
0.4
500
1.2
mA
Ω
V
= 200mA
LDO
FBLDO
Load Regulation
10µA < I
< 200mA, FBLDO = LDO
< 5.5V, FBLDO = LDO,
1.2
%
LDO
2.5V < V
OUT
Line Regulation
0.1
0.5
%
I
= 1mA
LDO
AC Power-Supply Rejection
Thermal Shutdown
f = 300kHz
38
dB
°C
Hysteresis approximately 10°C
155
LOW-BATTERY COMPARATOR
LBN, LBP Offset
LBP falling
LBP rising
-5
5
mV
mV
LBN, LBP Hysteresis
16
LBN, LBP Common-Mode
Input Range
V
= 0.5V and 1.5V (at least one input must
LBN
0.5
1.5
50
0.4
1
V
nA
V
be within this range)
LBN, LBP Input Current
LBO Output Low Voltage
V
LBN
= VLBP = 1V
0.01
I
= 1mA, V = 2.5V, LBP = GND,
OUT
SINK
LBN = OUT
LBO High Leakage
V
LBO
= V = 5V
OUT
µA
CONTROL INPUTS
0.2V
1.2V < V
< 5.5V, ONA, ONB (Note 3)
OUT
OUT
Input Low Level
Input High Level
V
V
V
OUT
= 2.5V, CLK/SEL, TRACK
0.2V
OUT
0.8V
1.2V < V
< 5.5V, ONA, ONB (Note 3)
OUT
OUT
V
OUT
= 5.5V, CLK/SEL, TRACK
0.8V
OUT
Input Leakage Current
(CLK/SEL, ONA, ONB, TRACK)
1
µA
_______________________________________________________________________________________
3
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
ELECTRICAL CHARACTERISTICS (continued)
(V
OUT
= V
= V
= 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
POUT
LBP
LX = open, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.)
A
A
PARAMETER
SYMBOL
CONDITIONS
CLK/SEL = OUT
MIN
TYP
MAX
UNITS
Internal Oscillator Frequency
260
300
340
kHz
External Oscillator
Synchronization Range
200
80
400
90
kHz
Oscillator Maximum Duty Cycle
Minimum CLK/SEL Pulse
86
%
200
ns
Maximum CLK/SEL
Rise/Fall Time
100
ns
ELECTRICAL CHARACTERISTICS
(V
OUT
= V
= V
= 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
POUT
LBP
LX = open, T = -40°C to +85°C, unless otherwise noted, Note 4.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5/MAX1706
DC-DC CONVERTER
FB Regulation Voltage
CLK/SEL = OUT
TRACK = OUT, V
1.215
1.251
V
V
V
LDO
0.2
+
V
LDO
+
OUT Voltage in Track Mode
> 2.3V
LDO
0.4
2.3
Start-Up to Normal Mode
Transition Voltage
2.0
V
Supply Current in Shutdown
I
20
µA
µA
ONA = 0V, ONB = OUT, measure I
OUT
OUT
Supply Current in
Low-Power Mode
I
CLK/SEL = 0V, FB = FBLDO = 1.5V, no load
190
OUT
Supply Current in
Low-Noise Mode
CLK/SEL = OUT, V = V
no load
= 1.5V,
FBLDO
FB
I
360
µA
V
OUT
REFERENCE
Reference Output Voltage
DC-DC CONVERTER
I
= 0µA
1.235
1.265
REF
CLK/SEL = 0V
CLK/SEL = OUT
CLK/SEL = OUT
MAX1705
0.45
0.28
0.50
1700
950
N-channel, I = 100mA
LX
Switch On-Resistance
Ω
P-channel, I = 100mA
LX
1000
550
250
250
CLK/SEL = OUT
CLK/SEL = 0V
CLK/SEL = 0V
MAX1706
N-Channel MOSFET
Current Limit
I
mA
mA
LIM
MAX1705
570
MAX1706
570
P-Channel Synchronous-
Rectifier Turn-Off Current
20
120
4
_______________________________________________________________________________________
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
ELECTRICAL CHARACTERISTICS (continued)
(V
OUT
= V
= V
= 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22µF),
POUT
LBP
LX = open, T = -40°C to +85°C, unless otherwise noted, Note 4.)
A
PARAMETER
LINEAR REGULATOR
FBLDO Regulation Voltage
FBLDO Input Current
SYMBOL
CONDITIONS
MIN
1.233
220
TYP
MAX
UNITS
FBLDO = LDO, I
= 1mA
1.268
50
V
nA
mA
Ω
LOAD
V
= 1.5V
0.01
FBLDO
Short-Circuit Current Limit
Dropout Resistance
FBLDO = LDO = GND
= 1V, I = 200mA
600
1.2
V
FBLDO
LDO
LOW-BATTERY COMPARATOR
LBN, LBP Offset
LBP falling
-5
5
1.5
1
mV
V
LBN, LBP Common-Mode
Input Range
LBN = 0.5V and 1.5V (at least one input must
be within this range)
0.5
LBO High Leakage
LBO = OUT = 5V
µA
CONTROL INPUTS
0.15V
1.2V < V
< 5.5V, ONA, ONB (Note 2)
OUT
OUT
Input Low Level
V
V
= 2.5V, CLK/SEL, TRACK
0.15V
OUT
OUT
0.85V
1.2V < V
< 5.5V, ONA, ONB (Note 2)
OUT
OUT
Input High Level
V
V
= 5.5V, CLK/SEL, TRACK
0.85V
OUT
OUT
Internal Oscillator Frequency
CLK/SEL = OUT
260
340
400
kHz
kHz
External Oscillator
Synchronization Range
200
Note 1: Once the output is in regulation, the MAX1705/MAX1706 operate down to a 0.7V input voltage.
Note 2: The device is in start-up mode when V is below this value (see Low-Voltage Start-Up Oscillator section).
OUT
Note 3: ONA and ONB inputs have a hysteresis of approximately 0.15V
.
OUT
Note 4: Specifications to -40°C to are guaranteed by design, not production tested.
_______________________________________________________________________________________
5
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(Circuit of Figure 2, T = +25°C, unless otherwise noted.)
A
MAX1705
MAX1705
EFFICIENCY vs. OUTPUT CURRENT
(V = 5V)
MAX1705
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
EFFICIENCY vs. OUTPUT CURRENT
(V = 3.3V)
OUT
OUT
1000
100
90
100
90
L = 10µH
B.1
A.1
C.1
900
800
B.1
B.2
80
70
60
50
40
30
20
10
80
70
60
50
40
30
20
10
C.2
B.2
PWM MODE
A.2
A.2
700
600
500
400
A.1
V
OUT
= 5V
V
OUT
= 3.3V
L = 10µH
V = 5V
OUT
L = 10µH
= 3.3V
A: V = 0.9V
B: V = 2.7V
1: PFM MODE
2: PWM MODE
PFM MODE
V
OUT
A: V = 0.9V
C: V = 2.4V
IN
E: V = 3.6V
1: PFM MODE
2: PWM MODE
IN
300
200
100
0
IN
V
OUT
= 3.3V
IN
IN
V
OUT
= 5V
0
0
0.1
1
10
100
1000
0.1
1
10
100
1000
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
INPUT VOLTAGE (V)
5/MAX1706
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
MAX1706
MAX1706
MAX1706
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY vs. OUTPUT CURRENT
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
(V = 5V)
OUT
(V = 3.3V)
OUT
100
90
100
90
700
600
B.1
L = 22µH
C.1
A.1
80
70
60
50
40
30
20
10
80
70
60
50
40
30
20
10
B.2
C.2
B.2
B.1
PWM MODE
A.2
500
400
300
200
A.2
V
OUT
= 5V
A.1
V
OUT
= 3.3V
L = 22µH
OUT
V
= 5V
A: V = 0.9V
B: V = 2.4V
IN
C: V = 3.6V
1: PFM MODE
2: PWM MODE
L = 22µH
= 3.3V
A: V = 0.9V
B: V = 2.7V
IN
1: PFM MODE
2: PWM MODE
V
OUT
IN
V
OUT
= 3.3V
IN
IN
V
OUT
= 5V
100
0
PFM MODE
0
0
0.1
1
10
100
1000
0.1
1
10
100
1000
0
0.5 1.0 1.5 2.0 2.5
3
3.5
4
4.5
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
MAX1705
START-UP INPUT VOLTAGE
vs. OUTPUT CURRENT
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
LINEAR-REGULATOR DROPOUT
VOLTAGE vs. LOAD CURRENT
2.3
12
140
120
100
80
V
= 3.3V
NO-LOAD START-UP:
1.0V AT -40°C
0.79 AT +25°C
0.64V AT +85°C
CONSTANT-CURRENT LOAD
OUT
11
10
9
2.1
1.9
L = 10µH
V
LDO
= 3.3V
1.7
1.5
1.3
8
V
OUT
= 3.3V
7
V
LDO
= 2.5V
PWM MODE
L = 10µH
D1 = MBR0520L
6
60
5
V
LDO
= 5V
4
1.1
0.9
0.7
0.5
T = -40°C
A
40
3
T = +25°C
A
2
20
PFM MODE
1
T = +85°C
A
0
0
0.01
0.1
1
10
100
1000
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
160
200
OUTPUT CURRENT (mA)
LOAD CURRENT (mA)
6
_______________________________________________________________________________________
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 2, T = +25°C, unless otherwise noted.)
A
LINEAR-REGULATOR
REGION OF STABLE C6 ESR
vs. LOAD CURRENT
LINEAR-REGULATOR POWER-SUPPLY
REJECTION RATIO vs. FREQUENCY
60
100
10
1
C6 = 22µF
50
40
30
20
UNCOMPENSATED
C2 = 22pF (FEED FORWARD)
STABLE REGION
V
V
LDO
= 4V TO 5V
= 3.3V
OUT
0.1
0
10
0
I
= 200mA
LDO
C5 = 0.33µF
100
1k
10k
100k 1M
10M
1
50
100
150
200
250
300
FREQUENCY (Hz)
LOAD CURRENT (mA)
MAX1705
NOISE SPECTRUM AT POUT
(V = 4.5V, V = 1.2V, 200mA LOAD)
OUT
IN
0V
1k
10k
100k
1M
10M
FREQUENCY (Hz)
MAX1705
LINEAR-REGULATOR OUTPUT NOISE SPECTRUM
(V = 3.3V, V = 4.5V, V = 1.2V, I = 200mA)
LDO
OUT
IN
LDO
0V
1k
10k
100k
FREQUENCY (Hz)
1M
10M
_______________________________________________________________________________________
7
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 2, T = +25°C, unless otherwise noted.)
A
MAX1705
POWER-ON DELAY
(PWM MODE)
MAX1705
LOAD-TRANSIENT RESPONSE
MAX1705
LINE-TRANSIENT RESPONSE
3V
A
B
2.5V
A
B
A
B
3.3V
0mA
C
D
200µs/div
200µs/div
200µs/div
5/MAX1706
V
IN
= 1.2V, V = 3.3V
OUT
V = 1.2V, LOAD = 1kΩ
IN
I
= 0mA, V = 3.3V
OUT
OUT
A = V , 50mV/div, 3.3V DC OFFSET
A = ONA, 2V/div
A = V , 1.5V TO 2.0V, 200mV/div
OUT
IN
B = I , 0mA TO 200mA, 200mA/div
OUT
B = V , 2V/div
B = V 10mV/div, 3.3V DC OFFSET
OUT,
LDO
C = V , 2V/div
OUT
D = INDUCTOR CURRENT, 500mA/div
MAX1705
LINEAR-REGULATOR
OUTPUT NOISE
MAX1705
PWM SWITCHING WAVEFORMS
MAX1705
PFM SWITCHING WAVEFORMS
DC TO 500kHz
A
1A
0V
A
B
C
0mA
0V
B
C
V
LDO
V
OUT
V
OUT
D
V
LDO
D
V
LDO
1µs/div
2µs/div
1ms/div
V = 1.2V, V = 4.5V, V = 3.3V, I = 40mA
IN OUT LDO LDO
A = INDUCTOR CURRENT, 500mA/div
B = LX VOLTAGE, 5V/div
V
I
IS AC COUPLED, 1mv/div
= 200mA
V
= 1.2V, V = 4.5V, V = 3.3V, I = 200mA
LDO
IN
OUT
LDO
LDO
A = INDUCTOR CURRENT, 500mA/div
B = LX VOLTAGE, 5V/div
LDO
C5 = 0.33µF
C = V RIPPLE, 50m/div AC COUPLED
C = V
RIPPLE, 50mV/div AC COUPLED
OUT
OUT
D = V RIPPLE, 5m/div AC COUPLED
D = V RIPPLE, 5mV/div AC COUPLED
LDO
LDO
C5 = 0.33µF
C5 = 0.33µF
8
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5/MAX1706
______________________________________________________________P in De s c rip t io n
PIN
1
NAME
LBP
FUNCTION
Low-Battery Comparator Noninverting Input. Common-mode range is 0.5V to 1.5V.
Low-Battery Comparator Inverting Input. Common-mode range is 0.5V to 1.5V.
1.250V Reference Output. Bypass REF with a 0.33µF capacitor to GND. REF can source up to 50µA.
2
LBN
REF
3
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.
4
TRACK
5
6
GND
OUT
Ground
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.
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.
7
FB
Low-Dropout Linear-Regulator Feedback Input. Connect FBLDO to a resistor voltage divider between LDO
8
9
FBLDO
LDO
to GND to set the output voltage from 1.25V to V
- 0.3V (5.0V max). FBLDO regulates to 1.250V.
OUT
Low-Dropout Linear-Regulator Output. LDO sources up to 200mA. Bypass to GND with a 22µF capacitor.
Low-Battery Comparator Output. This open-drain, N-channel output is low when LBP < LBN.
Input hysteresis is 16mV.
10
LBO
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).
11
CLK/SEL
Turning on the DC-DC converter with CLK/SEL = GND also serves as a soft-start function,
since peak inductor current is reduced.
12
13
PGND
LX
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
Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal
operation (Table 2).
14
15
ONB
On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal
operation (Table 2).
ONA
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.
16
POUT
_______________________________________________________________________________________
9
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
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maximum battery life during standby and shutdown.
_______________De t a ile d De s c rip t io n
They feature constant-frequency (300kHz), low-noise
The MAX1705/MAX1706 are designed to supply both
pulse-width-modulation (PWM) operation with 300mA or
power and low-noise circuitry in portable RF and data-
730mA output capability from one or two cells, respec-
acquisition instruments. They combine a linear regula-
tively, with 3.3V output. A low-quiescent-current stand-
tor, s te p -up s witc hing re g ula tor, N-c ha nne l p owe r
by pulse-frequency-modulation (PFM) mode offers an
MOSFET, P-channel synchronous rectifier, precision
outp ut up to 60mA a nd 140µA, re s p e c tive ly, a nd
reference, and low-battery comparator in a single 16-
reduces quiescent power consumption to 500µW. In
pin QSOP package (Figure 1). The switching DC-DC
s hutd own mod e , the q uie s c e nt c urre nt is furthe r
converter boosts a 1- or 2-cell input to an adjustable
reduced to just 1µA. Figure 2 shows the standard appli-
output between 2.5V and 5.5V. The internal low-dropout
c a tion c irc uit for the MAX1705 c onfig ure d in hig h-
re g ula tor p rovid e s line a r p os t-re g ula tion for nois e -
power PWM mode.
sensitive circuitry, as well as outputs from 1.25V to
Additional features include synchronous rectification for
hig h e ffic ie nc y a nd imp rove d b a tte ry life , a nd a n
uncommitted comparator for low-battery detection. A
CLK/SEL input allows frequency synchronization to
reduce interference. Dual shutdown controls allow shut-
down using a momentary pushbutton switch and micro-
processor control.
300mV b e low the s witc hing -re g ula tor outp ut. 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 full-
power operation, as well as low quiescent current for
5/MAX1706
LBO
MAX1705
MAX1706
THERMAL
SENSOR
LBP
N
SHUTDOWN
LOGIC
LBN
OUT
FBLDO
OUT
MOSFET DRIVER
WITH CURRENT
LIMITING
ERROR
AMP
P
LDO
REF
EN
IC PWR
2.15V
POUT
START-UP
OSCILLATOR
D
P
Q
Q
GND
PFM/PWM
CONTROLLER
ONA
ONB
LX
ON
EN
RDY
1.250V
REFERENCE
OSC
REF
N
Q
EN
300kHz
OSCILLATOR
PFM/PWM
CLK/SEL
ICS
MODE
IREF
V
LDO
FB
PGND
IFB
V
OUT
- 300mV
TRACK
Figure 1. Functional Diagram
10 ______________________________________________________________________________________
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5/MAX1706
INPUT 0.9V TO 3.6V
L1 10µH (22µH)
D1
C7
22µF
R5
LX
BOOST OUTPUT 3.6V
POUT
OUT
LBP
C4
220µF
(100µF)
(TO PGND)
C3
0.1µF
C9
0.33µF
LBN
REF
R1
191k
TRACK
PGND
R6
C1*
C8
0.33µF
(TO PGND)
MAX1705
MAX1706
R2
100k
FB
ONA
ONB
LDO OUTPUT 3.3V
LDO
CLK/SEL
LBO
FBLDO
C5*
0.33µF
C6
22µF
R3
165k
GND
C2*
R4
100k
R7
100k
*OPTIONAL.
( ) ARE FOR MAX1706.
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATH.
Figure 2. Typical Operating Circuit (PWM Mode)
S t e p -Up Co n ve rt e r
Table 1. Selecting the Operating Mode
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
a c ros s the ind uc tor re ve rs e s a nd forc e s c urre nt
through the diode and synchronous rectifier to the out-
put 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 set-
ting (Table 1).
CLK/SEL
MODE
FEATURES
0
PFM
Low supply current
Low noise,
high output current
1
PWM
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 ris-
ing edges sets a flip-flop, which turns on the N-channel
MOSFET switch (Figure 3). The switch is turned off
whe n the s um of the volta g e -e rror a nd c urre nt-
feedback 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-
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), a nd mod ula te the MOSFET s witc h p uls e
width to control the power transferred per cycle and
regulate the voltage across the load. In PWM mode, the
______________________________________________________________________________________ 11
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POUT
LOGIC HIGH
Q
Q
D
POUT
IFB*
P
N
R
IREF*
P
LX
R
S
Q
LX
IFB*
N
S
Q
ICS
IREF*
R
PGND
CURRENT
LIMIT LEVEL
CURRENT
OSC
LIMIT LEVEL
PGND
*SEE FIGURE 1
*SEE FIGURE 1
Figure 3. Simplified PWM Controller Block Diagram
5/MAX1706
Figure 4. Controller Block Diagram in PFM Mode
current limit for the MAX1705, and 950mA (max) for the
MAX1706. During PWM operation, the circuit operates
with a continuous inductor current.
cycle until the energy stored in the inductor is dumped
into the output filter capacitor and the synchronous rec-
tifier current ramps down to 70mA. This forces opera-
tion with a discontinuous 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 har-
monics, to avoid IF bands in wireless applications. The
synchronous rectifier is also active during synchronized
PWM operation.
Synchronous Rectifier
The MAX1705/MAX1706 feature an internal 270mΩ,
P-channel synchronous rectifier to enhance efficiency.
Sync hronous re c tific a tion provide s a 5% e ffic ie nc y
imp rove me nt ove r s imila r nons ync hronous s te p -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.
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
mod ula ting the s witc hing fre q ue nc y to c ontrol 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 capa-
bility in PFM mode is 140mA (from 2.4V input to 3.3V
output). The output is regulated at 1.3% above the
PWM threshold.
Lin e a r Re g u la t o r
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 cir-
cuitry, such as low-noise amplifiers and IF stages in cel-
lular phones and other instruments, and can deliver up to
200mA. However, in practice, the maximum output cur-
rent 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 sta-
bility (see the Linear Regulator Region of Stable C6 ESR
vs . Loa d Curre nt g ra p h in the Typ ic a l Op e ra ting
Characteristics). During power-up, the linear regulator
remains off until the step-up converter goes into regula-
tion for the first time.
During PFM operation, the error comparator detects
outp ut volta g e fa lling out of re g ula tion a nd s e ts a
flip -flop , turning on the N-c ha nne l MOSFET s witc h
(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 flip-
flop. 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 ______________________________________________________________________________________
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5/MAX1706
The linear regulator in the MAX1705/MAX1706 features
a 0.5Ω, P-channel MOSFET pass transistor. This pro-
Table 2. On/Off Logic Control
vides several advantages, including longer battery life,
over similar designs using a PNP pass transistor. The
P-channel MOSFET requires no base-drive current,
which reduces quiescent current considerably. PNP-
based regulators tend to waste base-drive current in
d rop out whe n the p a s s tra ns is tor s a tura te s . The
MAX1705/MAX1706 eliminate this problem.
ONA
MAX1705/MAX1706
ONB
0
0
1
1
0
1
0
1
On
Off
On
On
The linear-regulator error amplifier compares the output
feedback sensed at the FBLDO input against the inter-
na l 1.250V re fe re nc e , a nd a mp lifie s the d iffe re nc e
(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.
Tra c k in g
Connecting TRACK to the step-up converter output
imp le me nts a tra c king mod e tha t s e ts the s te p -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 0.5V
threshold, and should be hard-
wired or switched with a slew rate exceeding 1V/µs.
must be set above 2.3V for track mode to operate
OUT
V
LDO
Lo w -Vo lt a g e S t a rt -Up Os c illa t o r
The MAX1705/MAX1706 us e a CMOS, low-volta g e
start-up oscillator for a 1.1V guaranteed minimum start-
up input voltage at +25°C. On start-up, the low-voltage
oscillator switches the N-channel MOSFET until the out-
put voltage reaches 2.15V. Above this level, the normal
step-up 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.
properly.
On power-up with TRACK = OUT, the step-up convert-
er 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 regu-
lator reaches 2.3V, track mode is enabled and the step-
up converter is regulated to 300mV above the linear-
regulator output.
Lo w -Ba t t e ry Co m p a ra t o r
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:
To reduce current loading during step-up, the linear
regulator is kept off until the start-up converter goes
into regulation. Minimum start-up voltage is influenced
by load and temperature (see the Typical Operating
Characteristics). To allow proper start-up, do not apply
a full load at POUT until after the device has exited
start-up mode and entered normal operation.
S h u t d o w n
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 shut-
down, 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
b e low the inp ut, b ut the line a r re g ula tor outp ut is
turned off.
V
IN,TH
R5 = R6
- 1
V
LBN
where V
is the desired input voltage trip point and
= 1.25V. Since the input bias current into
IN,TH
REF
V
= V
LBN
LBP is less than 50nA, R6 can be a large value (such
a s 270kΩ or le s s ) without s a c rific ing a c c ura c y.
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.
Entry into shutdown mode is controlled by logic input
pins ONA and ONB (Table 2). Both inputs have trip
points near 0.5V
with 0.15V
hysteresis.
OUT
OUT
______________________________________________________________________________________ 13
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
The low-battery comparator can also be used to moni-
tor the output voltage, as shown in Figure 5.
POUT
To set the low-battery threshold to a voltage below the
LDO
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:
MAX1705
MAX1706
R5
R6
LBO
LBP
LBN
REF
GND
0.33µF
V
REF
R5 = R6
- 1
V
IN,TH
Alternatively, the low-battery comparator can be used
to check the output voltage or to control the load direct-
ly on POUT during start-up (Figure 7). Use the following
equation to set the resistor values:
Figure 5. Using the Low-Battery Comparator to Sense
the Output Voltage
5/MAX1706
V
OUT,TH
R5 = R6
- 1
V
POUT
REF
LBP
where V
is the desired output voltage trip point
is connected to the reference or 1.25V.
MAX1705
R5
OUT,TH
0.33µF
MAX1706
and V
LBP
LBO
LBN
Re fe re n c e
R8
10k
The MAX1705/MAX1706 have an internal 1.250V, 1%
bandgap reference. Connect a 0.33µF bypass capaci-
tor to GND within 0.2in. (5mm) of the REF pin. REF can
source up to 50µA of external load current.
R6
LBP
GND
BATTERY
VOLTAGE
_________________ De s ig n P ro c e d u re
S e t t in g t h e Ou t p u t Vo lt a g e s
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:
Figure 6. Detecting Battery Voltages Below 1.25V
STEP-UP OUTPUT
P
C3
0.1µF
C5
POUT
OUT
R5
V
270k
POUT
R1 = R2
- 1
V
LBN
FB
C4
MAX1705
MAX1706
R6
where V , the step-up regulator feedback setpoint, is
FB
LBO
LBP
REF
1.233V. Since the input bias current into FB is less than
50nA, R2 can have 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 FB pin.
GND
0.33µF
Alternatively, set the step-up converter output to track
the linear regulator by 300mV. To accomplish this, set
TRACK to OUT.
Figure 7. Using the Low-Battery Comparator for Load Control
During Start-Up
14 ______________________________________________________________________________________
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5/MAX1706
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:
MUR150 or EC11FS1). Do not use ordinary rectifier
d iod e s , s inc e s low s witc hing s p e e d s a nd long re -
verse recovery times compromise efficiency and load
regulation.
Ch o o s e In p u t a n d Ou t p u t
Filt e r Ca p a c it o rs
V
LDO
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.
R3 = R4
- 1
V
FBLDO
where V
, the linear-regulator feedback trip point,
FBLDO
is 1.250V. Since the input bias current into FBLDO is
le s s tha n 50nA, R4 c a n b e a la rg e va lue (s uc h a s
270kΩ or less). Connect the resistor voltage-divider as
close to the IC as possible, within 0.2in. (5mm) of the
FBLDO pin.
A 100µF, 100mΩ, low-ESR tantalum capacitor is recom-
me nd e d a t the MAX1706’s s te p -up outp ut. For the
MAX1705, use two in parallel or a 220µF low-ESR tanta-
lum c a p a c itor. The inp ut filte r c a p a c itor (C7) a ls o
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,
us e a 22µF, low-ESR inp ut filte r c a p a c itor. Whe n
operating from a power source placed farther away, or
In d u c t o r S e le c t io n
The MAX1705/MAX1706’s 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 rat-
ing 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
p a rts a nd Ta b le 4 for a lis t of ind uc tor s up p lie rs .
Connect the inductor from the battery to the LX pin as
close to the IC as possible.
LINEAR-
REGULATOR
OUTPUT
STEP-UP
OUTPUT
LDO
POUT
OUT
MAX1705
MAX1706
C2*
C1*
R3
R4
R1
R2
At t a c h in g t h e Ou t p u t Dio d e
Use a Schottky diode, such as a 1N5817, MBR0520L,
or equivalent. The Schottky diode carries current during
start-up, and in PFM mode after the synchronous rectifi-
er turns off. Thus, the current rating only needs to be
500mA. Attach the diode between the LX and POUT
pins, as close to the IC as possible.
FB
FBLDO
GND
PGND
In hig h-te mp e ra ture a p p lic a tions , s ome Sc hottky
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 rectifi-
er with reverse recover times less than 60ns (such as a
* OPTIONAL COMPENSATION CAPACITORS
Figure 8. Feedback Connections for the MAX1705/MAX1706
Table 3. Component Selection Guide
PRODUCTION
INDUCTORS
CAPACITORS
Matsuo 267 series
Sprague 595D series
AVX TPS series
DIODES
Sumida CDR63B, CD73, CDR73B, CD74B series
Coilcraft DO1608, DO3308, DT3316 series
Surface Mount
Motorola MBR0520L
Sanyo OS-CON series
Nichicon PL series
Through Hole
Sumida RCH654 series
Motorola 1N5817
______________________________________________________________________________________ 15
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
from higher-impedance batteries, consider using one
or two 100µF, 100mΩ, low-ESR tantalum capacitors.
Table 4. Component Suppliers
SUPPLIER
PHONE
FAX
Low-ESR capacitors are recommended. Capacitor ESR
is a major contributor to output ripple—often more than
70%.
USA: (803) 946-0690
(800) 282-4975
(803) 626-3123
AVX
Coilcraft
Matsuo
USA: (847) 639-6400
USA: (714) 969-2491
USA: (602) 303-5454
(847) 639-1469
(714) 960-6492
(602) 994-6430
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
tra d e -off b e twe e n p ric e a nd p e rforma nc e . Do not
exceed the ripple-current ratings of tantalum capaci-
tors. Avoid aluminum-electrolytic capacitors, since their
ESR is too high.
Motorola
USA: (619) 661-6835
Japan: 81-7-2070-6306
(619) 661-1055
81-7-2070-1174
Sanyo
USA: (847) 956-0666
Japan: 81-3-3607-5111
(847) 956-0702
81-3-3607-5144
Sumida
Ad d in g Byp a s s Ca p a c it o rs
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, surface-
mount ceramic capacitors are now readily available in
small packages; see Table 4 for suggested suppliers.
ground plane. Instead, place them close together and
route them in a star-ground configuration using compo-
nent-side copper. Then connect the star ground to the
internal ground plane using vias.
5/MAX1706
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 net-
works, especially the LDO feedback, and separated
from the m us ing g round e d c op p e r. Cons ult the
MAX1705/MAX1706 EV kit for a full PC board example.
__________ Ap p lic a t io n s In fo rm a t io n
Us e in a Typ ic a l
Wire le s s P h o n e Ap p lic a t io n
De s ig n in g a P C Bo a rd
High switching frequencies and large peak currents
make PC board layout an important part of design.
Poor design can cause excessive EMI and ground-
b ounc e , b oth of whic h c a n c a us e ins ta b ility or
regulation errors by corrupting voltage- and current-
feedback signals. It is highly recommended that the PC
board example of the MAX1705 evaluation kit (EV kit)
be followed.
The MAX1705/MAX1706 are ideal for use in digital cord-
less and PCS phones. The power amplifier (PA) is con-
ne c te d d ire c tly to the s te p -up c onve rte r outp ut for
maximum voltage swing (Figure 9). The internal linear
regulator is used for post-regulation to generate low-
noise 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.
Power components—such as the inductor, converter
IC, filte r c a p a c itors , a nd outp ut d iod e —s hould b e
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
short. Keep the extra copper on the board, and inte-
grate 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
16 ______________________________________________________________________________________
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
µC
270k
MAX1705
MAX1706
LX
POUT
V
DD
OUT
CONTROL
INPUTS
ONB
ON/OFF
MAX1705
MAX1706
I/O
I/O
GND
LDO
ONA
PA
µC
RF
I/O
0.1µF
270k
Figure 10. Momentary Pushbutton On/Off Switch
Figure 9. Typical Phone Application
Table 5. Typical Available Output Current
TOTAL OUTPUT CURRENT
(mA)
STEP-UP OUTPUT VOLTAGE:
(PA POWER SUPPLY)
(V)
INPUT VOLTAGE
NUMBER OF CELLS
(V)
MAX1705
300
MAX1706
200
1 NiCd/NiMH
1.2
2.4
2.4
3.6
3.3
3.3
5.0
5.0
2 NiCd/NiMH
730
450
2 NiCd/NiMH
500
350
3 NiCd/NiMH or 1 Li-Ion
850
550
Im p le m e n t in g S o ft -S t a rt
___________________Ch ip In fo rm a t io n
TRANSISTOR COUNT: 1649
To implement soft-start, set CLK/SEL low on power-up;
this forces PFM operation and reduces the peak switch-
ing current to 435mA. Once the circuit is in regulation,
CLK/SEL can be set high for full-power operation.
SUBSTRATE CONNECTED TO GND
Ad d in g a Ma n u a l P o w e r Re s e t
A momentary pushbutton switch can be used to turn
the MAX1705/MAX1706 on and off (Figure 10). 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
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
__________________________________________________Ta p e -a n d -Re e l In fo rm a t io n
4.0 ±0.1
1.0 ±0.1
1.75 ±0.1
2.0 ±0.05
1.5 +0.1/-0.0 DIAMETER
A
3.5 ±0.05
8.0 ±0.3
2.2 ±0.1
0.5 RADIUS
TYPICAL
A0
1.0 MINIMUM
4.0 ±0.1
A
Bo
5/MAX1706
Ao = 3.1mm ±0.1
Bo = 2.7mm ±0.1
Ko = 1.2mm ±0.1
NOTE: DIMENSIONS ARE IN MM.
AND FOLLOW EIA481-1 STANDARD.
Ko
0.30 ±0.05
0.8 ±0.05
0.30R MAX.
18 ______________________________________________________________________________________
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S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
5/MAX1706
________________________________________________________P a c k a g e In fo rm a t io n
______________________________________________________________________________________ 19
1 - t o 3 -Ce ll, Hig h -Cu rre n t , Lo w -No is e ,
S t e p -Up DC-DC Co n ve rt e rs w it h Lin e a r Re g u la t o r
NOTES
5/MAX1706
20 ______________________________________________________________________________________
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