EVALUATION KIT AVAILABLE
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
General Description
Benefits and Features
The MAX1709 sets a new standard of space savings
for high-power, step-up DC-DC conversion. It delivers
up to 20W at a fixed (3.3V or 5V) or adjustable (2.5V to
5.5V) output, using an on-chip power MOSFET from a
+0.7V to +5V supply.
Fixed-frequency PWM operation ensures that the
switching noise spectrum is constrained to the 600kHz
fundamental and its harmonics, allowing easy postfiltering for noise reduction. External clock synchronization
capability allows for even tighter noise spectrum control. Quiescent power consumption is less than 1mW to
extend operating time in battery-powered systems.
Two control inputs (ONA, ONB) allow simple push-on,
push-off control through a single momentary pushbutton switch, as well as conventional on/off logic control.
The MAX1709 also features programmable soft-start
and current limit for design flexibility and optimum performance with batteries.
• Integration Reduces External Component Count to
Save Space
• On-Chip 10A Power MOSFET
• 5V, 4A Output from a 3.3V Input
• Fixed 3.3V or 5V Output Voltage or
Adjustable (2.5V to 5.5V)
• Input Voltage Range Down to 0.7V
• Constant Frequency Reduces Post-Filtering
• Low-Noise, Constant-Frequency Operation
(600kHz)
• Synchronizable Switching Frequency
(350kHz to 1000kHz)
The MAX1709 is supplied in both a high-power TSSOP
package, which allows a 10ARMS switch current and a
4A output, and a narrow SO package, which supplies a
2.4A output with a switch rated at 6ARMS. Although the
narrow SO device has a lower RMS switch rating, it has
the same peak switch current rating as the TSSOP
device, and so can supply 4A loads intermittently. If
loads of 2A or less are required, refer to the MAX1708.
Routers, Servers, Workstations, Card Racks
Local 2.5V to 3.3V or 5V Conversion
Local 3.3V to 5V Conversion
3.6V or 5V RF PAs in Communications Handsets
Typical Operating Circuit
1µH
SYNC
OR
INTERNAL
CLK
LX
MAX1709
GND
SS/LIM
REF
PART
TEMP RANGE
-40°C to +85°C
16 Narrow SO
MAX1709EUI+
-40°C to +85°C
28 TSSOP-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
OUT
TOP VIEW
ONA 1
28 ONB
LX 2
27 CLK
LX 3
OUTPUT
3.3V, 5V,
OR ADJ
UP TO 4A
26 3.3/5
MAX1709
25 NC
LX 5
24 NC
LX 6
23 PGND
LX 7
22 PGND
LX 8
21 PGND
NC 9
20 PGND
NC 10
19 PGND
GND 11
18 PGND
SS/ILM 12
17 NC
REF 13
16 FB
GND 14
15 OUT
TSSOP-EP
19-1724; Rev 3; 2/15
PIN-PACKAGE
MAX1709ESE
LX 4
INPUT
1V TO 5V
ONA
Ordering Information
Pin Configuration
Applications
OFF ON
• Lower Power Consumption Extends Battery Life
• 1mW Quiescent Power
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Absolute Maximum Ratings
ONA, ONB, OUT, SS/LIM, 3.3/5 to GND ...............-0.3V to +6.0V
LX to PGND ...........................................................-0.3V to +6.0V
FB, CLK, REF to GND.............................. -0.3V to (VOUT + 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA = +70°C)
16-Pin Narrow SO (derate 16.5mW/°C above +70°C) .....1.3W
28-Pin TSSOP Exposed Pad
(derate 23.8mW/°C above +70°C) ...................................1.9W
28-Pin TSSOP Exposed Pad Junction-to-Exposed
Pad Thermal Resistance ......................................……1.2°C/W
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 = VCLK = +3.6V, ONA = ONB = FB = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
3.26
3.34
3.42
5.05
5.17
-0.25
-0.45
1.240
1.265
V
1
200
nA
5.5
V
Measured between 1A < ISW < 3A (Note 2)
ISW = 1A
UNITS
4.92
Load Regulation
VFB = +1.5V
MAX
3.3/5 = GND, ISW = 1A
VFB < 0.1V (Note 1)
FB Input Current
TYP
3.3/5 = OUT, ISW = 1A
Output Voltage
FB Regulation Voltage
MIN
Output Voltage Adjust Range
1.215
2.5
V
%/A
Output Undervoltage Lockout
(Note 3)
2.0
2.3
V
Frequency in Startup Mode
VOUT =1.5V
40
400
kHz
Minimum Startup Voltage
IOUT < 1mA (Note 1), TA = +25°C (Note 4)
1.1
V
Minimum Operating Voltage
(Note 5)
Soft-Start Pin Current
VSS/LIM = 1V
4
5.0
µA
OUT Supply Current
VFB = 1.5V (Note 6)
200
440
µA
V ONB = 3.6V
0.1
5
µA
VLX = V ONB = VOUT = +5.5V
0.1
40
µA
22
40
mΩ
OUT Leakage Current In
Shutdown
LX Leakage Current
n-Channel Switch
On-Resistance
n-Channel Current Limit
RMS Switch Current
0.7
3.2
SS/LIM = open
7.5
SS/LIM = 150kΩ to GND
3.5
V
9
12
5
6.5
MAX1709EUI+
10
MAX1709ESE
6
Reference Voltage
IREF = 0
Reference Load Regulation
-1µA < IREF < 50µA
Reference Supply Rejection
+2.5V < VOUT < +5.5V
1.245
A
ARMS
1.260
1.275
V
4
10
mV
0.2
5
mV
ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V
0.2 ×
VOUT
CLK, 2.7V < VOUT < 5.5V
0.2 ×
VOUT
Input Low Level (Note 7)
www.maximintegrated.com
0.9
V
Maxim Integrated | 2
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Electrical Characteristics (continued)
(VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
Input High Level
Logic Input Current
CONDITIONS
MIN
ONA, ONB, 3.3/5, 1.2V < VOUT <5.5
0.8 × VOUT
CLK, 2.7 V< VOUT < 5.5V
0.8 × VOUT
TYP
MAX
UNITS
V
ONA, ONB, CLK, 3.3/5
1
µA
Internal Oscillator Frequency
520
600
680
kHz
Maximum Duty Cycle
82
90
94
%
1000
kHz
50
ns
External Clock Frequency
Range
CLK Pulse Width
(Note 8)
CLK Rise/Fall Time
(Note 8)
350
100
ns
Electrical Characteristics
(VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 9)
PARAMETER
Output Voltage
CONDITIONS
MIN
3.45
(Note 1)
3.3/5 = OUT, ISW = 1A
4.9
5.2
1.21
1.27
V
200
nA
-0.45
%/A
5.2
µA
5
µA
400
µA
40
mΩ
ISW = 1A
VFB = +1.5V
Load Regulation
Measured between 1A < ISW < 5A (Note 2)
Soft-Start Pin Current
SS/LIM = 1V
OUT Leakage Current in
Shutdown
V ONB = 3.6V
OUT Supply Current
VFB = 1.5V (Note 6)
3.2
n-Channel Switch
On-Resistance
www.maximintegrated.com
UNITS
3.24
FB Input Current
Reference Voltage
MAX
3.3/5 = GND, ISW = 1A
FB Regulation Voltage
n-Channel Current Limit
TYP
VFB < 0.1V, VIN = +2.4V
SS/LIM = unconnected
7.5
15
SS/LIM = 150kΩ to GND
3.5
7
IREF = 0
1.24
1.28
V
V
V
Maxim Integrated | 3
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Electrical Characteristics (continued)
(VOUT = VCLK = +3.6V, ONA = ONB = FB = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 9)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V
0.2 ×
VOUT
V
CLK, 2.7V < VOUT < 5.5V
0.2 ×
VOUT
Input Low Level (Note 7)
ONA, ONB, 3.3/5, 1.2V < VOUT < 5.5V
0.8 ×
VOUT
CLK, VOUT = 5.5V
0.8 ×
VOUT
Input High Level
Logic Input Current
ONA, ONB, CLK, 3.3/5
TYP
V
1
µA
Internal Oscillator Frequency
500
700
kHz
Maximum Duty Cycle
80
95
%
External Clock Frequency
Range
350
1000
kHz
50
ns
CLK/SEL Pulse Width
(Note 8)
CLK/SEL Rise/Fall Time
(Note 8)
100
ns
Note 1: Output voltage is specified at 1A switch current ISW, which is equivalent to approximately 1A (VIN / VOUT) of load current.
Note 2: Load regulation is measured by forcing specified switch current and straight-line calculation of change in output voltage in
external feedback mode. Note that the equivalent load current is approximately ISW (VIN / VOUT).
Note 3: Until undervoltage lockout is reached, the device remains in startup mode. Do not apply full load until this voltage is
reached.
Note 4: Startup is tested with Figure 1’s circuit. Output current is measured when both the input and output voltages are applied.
Note 5: Minimum operating voltage. The MAX1709 is bootstrapped and will operate down to a 0.7V input once started.
Note 6: Supply current is measured from the OUT pin to the output voltage (+3.3V). This correlates directly with actual input supply
current but is reduced in value according to the step-up ratio and efficiency.
Note 7: ONA and ONB inputs have approximately 0.15V hysteresis.
Note 8: Guaranteed by design, not production tested.
Note 9: Specifications to -40°C are guaranteed by design, not production tested.
www.maximintegrated.com
Maxim Integrated | 4
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
70
60
50
40
70
50
40
30
20
20
10
10
0
VIN = 2.5V
60
30
86.0
85.5
0.01
0.1
1
10
85.0
84.5
84.0
83.5
83.0
0
0.001
0.01
0.1
1
0.4
10
0.5
0.6
0.7
0.8
0.9
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OPERATING FREQUENCY (MHz)
LOAD REGULATION
(VIN = 3.3V, VOUT = 5V)
LINE REGULATION
(VOUT = 5V, IOUT = 1A)
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
0.6
0
0.4
INPUT VOLTAGE
INCREASING
INPUT CURRENT (mA)
VOUT REGULATION (%)
1
1000
0.2
0
-0.2
1.0
MAX1709 TOC06
0.8
MAX1709 TOC04
2
MAX1709 TOC05
0.001
VOUT REGULATION (%)
VIN = 3.3V
80
EFFICIENCY (%)
VIN = 1.2V
90
EFFICIENCY (%)
VIN = 2.5V
80
EFFICIENCY (%)
100
MAX1709 TOC02
90
MAX1709 TOC01
100
EFFICIENCY vs. SWITCHING FREQUENCY
(VIN = 3.3V, VOUT = 5V, IOUT = 2A)
EFFICIENCY
vs. OUTPUT CURRENT (VOUT = 5V)
MAX1709 TOC03
EFFICIENCY
vs. OUTPUT CURRENT (VOUT = 3.3V)
100
INPUT VOLTAGE
DECREASING
10
VOUT = 5V
-0.4
-1
1
-0.6
2
3
4
3.5
VOUT = 3.3V
1.4
TA = -40°C
1.0
TA = +25°C
VOUT = 5V
0.01
0.1
www.maximintegrated.com
1
10
2.0
1.5
2.5
3.0
3.5
25
20
-0.5
-1.0
15
10
5
0
VOUT = 3.3V
-5
-10
-2.0
LOAD CURRENT (A)
1.0
NOISE vs. FREQUENCY
0
-1.5
TA = +85°C
0.5
30
NOISE (mVRMS)
1.8
1.6
0.5
FREQUENCY CHANGE (%)
2.0
0
4.0
INPUT VOLTAGE (V)
1.0
MAX1709 TOC07
2.2
0.001
3.0
SWITCHING FREQUENCY
vs. TEMPERATURE
2.4
0.8
2.5
STARTUP VOLTAGE
vs. LOAD CURRENT
2.6
0.6
2.0
INPUT VOLTAGE (V)
2.8
STARTUP VOLTAGE (V)
5
OUTPUT CURRENT (A)
MAX1709 TOC09
1
MAX1709 TOC08
0
1.2
VOUT = 3.3V
0.1
-0.8
-2
-40
-15
10
35
TEMPERATURE (°C)
60
85
0.1
1
10
FREQUENCY (MHz)
Maxim Integrated | 5
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
SWITCH CURRENT LIMIT
vs. SS/LIM RESISTANCE
SWITCH CURRENT LIMIT
vs. TEMPERATURE
11.0
5V
VLX
5V/div
0
CURRENT LIMIT (A)
8
CURRENT LIMIT (A)
MAX1709-13a
MAX1709-12
9
HEAVY SWITCHING WAVEFORM
11.5
MAX1709 TOC10
10
7
6
5
10.5
10.0
9.0
4
VOUT
100mV/div
5V
9.5
3
8.5
2
8.0
VOUT = 3.3V
4A
IL
2A/div
2A
IOUT = 2A
50
100
150
200
250
-40
300
-15
10
35
SS/LIM RESISTANCE (kΩ)
TEMPERATURE (°C)
HEAVY SWITCHING WAVEFORM
(WITH LC FILTER)
LINE-TRANSIENT
RESPONSE
60
85
1μs/div
LOAD-TRANSIENT
RESPONSE
MAX1709-14
MAX1709-13b
MAX1709-15
3A
5V
VLX
5V/div
0
IOUT
2A/div
1A
3.5V
VIN
0.5V/div
3V
VOUT
100mV/div
5V
VOUT
100mV/
5V
6A
4A
IL
2A/div
2A
VOUT
50mV/d
5V
IL
2A/div
4A
2A
IOUT = 1A
100μs/div
1μs/div
20μs/div
IOUT = 2A
L = 12.5nH (COILCRAFT A04T)
C = 1μF
SHUTDOWN WITH SOFT-START
(CSS = 0.1μF)
SHUTDOWN WITH SOFT-START
(CSS = 0.01μF)
MAX1709-16
5V
VONA
5V/div
0
SHUTDOWN WITHOUT SOFT-START
MAX1709-18
MAX1709-17
5V
VONA
5V/div
0
2A
4A
IIN
2A/div
2A
VOUT
2V/div
4V
0
IIN
2A/div
2V
VOUT
2V/div
www.maximintegrated.com
IIN
2A/div
2A
VOUT
2V/div
4V
2V
2V
1ms/div
CSS = 0.1μF
ROUT = 5Ω
VONB = VOUT
4A
0
0
4V
VONA
5V/div
0
6A
6A
4A
5V
1ms/div
1ms/div
CSS = 0.01μF
ROUT = 5Ω
VONB = VOUT
CSS = 0
ROUT = 5Ω
VONB = VOUT
Maxim Integrated | 6
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Pin Description
PIN
TSSOP
NARROW SO
NAME
1
1
ONA
2–8
2, 3, 4
LX
11, 14
5, 8
GND
FUNCTION
On-Control Input. When ONA = high OR ONB = low, the device turns on
Drain of n-Channel Power Switch. Connect pins 2, 3, and 4 together.
Connect external Schottky diode from LX to OUT.
Ground. Connect ground inputs together, then connect to PGND.
Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to
GND to control the rate at which the device reaches current limit (soft-start).
To reduce the current limit from the preset values, connect a resistor from
SS/LIM to GND (see Design Procedure). During shutdown, this pin is
internally pulled to GND to discharge the soft-start capacitor.
12
6
SS/LIM
13
7
REF
1.26V Voltage Reference Output. Bypass with a 0.22µF capacitor to GND.
Maximum REF load is 50µA.
15
9
OUT
Output Voltage Sense Input. The device is powered from OUT. Bypass with
a 0.1µF to PGND with less than 5mm trace length. Connect a 2Ω series
resistor from the output filter capacitor to OUT (Figure 1).
DC-DC Converter Feedback Input. Connect FB to GND for internally set
output voltage (see 3.3/5 pin description). Connect a resistor-divider from
the output to set the output voltage in the +2.5V to +5.5V range. FB
regulates to +1.25V (Figure 4).
16
10
FB
18–23
11, 12, 13
PGND
Power Ground. Source of n-channel power MOSFET switch. Connect PGND
inputs together, then connect to GND.
26
14
3.3/5
Output Voltage Selection Pin. When FB is connected to GND, the regulator
uses internal feedback to set the output voltage. 3.3/5 = low sets output to
3.3V; 3.3/5 = high sets output to 5V. If an external divider is used at FB,
connect 3.3/5 to ground.
27
15
CLK
Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator.
Optionally, drive with an external clock for external synchronization.
28
16
ONB
Shutdown Input. When ONB = high AND ONA = low, the device turns off
(Table 1).
9, 10, 17,
24, 25
—
N.C.
No Connect. Not internally connected.
EP
—
EP
www.maximintegrated.com
Exposed Pad. Connect to large ground plane for maximum thermal
dissipation.
Maxim Integrated | 7
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
KEEP TRACES
SHORT AND WIDE
1μH
L1
VIN
1V TO 5V
D1
ON-OFF
CONTROL
C1, C2
2 x 150μF
ONA
ONB
LX
CLK
LX
3.3/5
VOUT
5V
C6, C7
2x
150μF
PGND
LX
GND
MAX1709
R1
C3
GND
PGND
SS/LIM
PGND
REF
FB
GND
OUT
C4
0.22μF
R2
2Ω
C5
0.1μF
Figure 1. Standard Operating Circuit
Detailed Description
The MAX1709 step-up converter offers high efficiency
and high integration for high-power applications. It
operates with an input voltage as low as 0.7V and is
suitable for single- to 3-cell battery inputs as well as
2.5V or 3.3V regulated supply inputs. The output voltage is preset to +3.3V or +5.0V or can be adjusted with
external resistors for voltages between +2.5V to +5.5V.
The n-channel switch of the MAX1709EUI+ is rated for
10ARMS and can deliver loads up to 4A, depending on
input and output voltage. The n-channel switch of the
MAX1709ESE has a 6ARMS rating and supplies up to
2.4A output. The MAX1709ESE has a lower RMS switch
rating than the MAX1709EUI+, but has the same peak
switch current limit and so can supply 4A loads intermittently. For flexibility, the current limit and soft-start
rate are independently programmable.
A 600kHz switching frequency allows for a small inductor to be used. The switching frequency is also synchronizable to an external clock ranging from 350kHz
to 1000kHz.
www.maximintegrated.com
ONA, ONB
The logic levels at ONA and ONB turn the MAX1709 on
or off. When ONA = 1 or ONB = 0, the part is on. When
ONA = 0 and ONB = 1, the part is off (Table 1). Logichigh on control can be implemented by tying ONB high
and using ONA for shutdown. Implement inverted single-line on/off control by grounding ONA and toggling
ONB. Implement momentary pushbutton On/Off as
described in the Applications Information section. Both
inputs have approximately 0.15V of hysteresis.
Switching Frequency
The MAX1709 switches at the fixed-frequency internal
oscillator rate (600kHz) or can be synchronized to an
external clock. Connect CLK to OUT for internal clock
operation. Apply a clock signal to CLK to synchronize
to an external clock. The frequency can be changed on
the fly. The MAX1709 will synchronize to a new external
clock rate in two cycles and will take approximately
40µs to revert to its internal clock frequency once the
external clock pulses stop and CLK is driven high.
Table 2 summarizes oscillator operation.
Maxim Integrated | 8
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Table 1. On/Off Logic Control
Table 2. Selecting Switching Frequency
ONA
0
ONB
0
MAX1709
On
0
1
Off
1
0
On
1
1
On
CLK
0
1
External clock
(350kHz−1000kHz)
MODE
Not allowed
PWM
Synchronized PWM
UNDERVOLTAGE LOCKOUT
OUT
MAX1709
IC POWER
PWM
CONTROLLER
2.15V
EN
STARTUP
Q
OSCILLATOR
D
SEE
FIGURE 3.
ONA
ONB
REF
1.260V
EN
ON
RDY
REFERENCE
EN
CLK
FB
3.3/5
GND
DUAL MODE
FB
600kHz
OSCILLATOR
LX
OSC
N
FB
PGND
OUT
Figure 2. Simplified Functional Diagram
Operation
The MAX1709 switches at a constant frequency
(600kHz) and modulates the MOSFET switch pulse
width to control the power transferred per cycle and
regulate the voltage across the load. In low-noise applications, the fundamental and the harmonics generated
by the fixed switching frequency are easily filtered out.
Figure 2 shows the simplified functional diagram for the
MAX1709. Figure 3 shows the simplified PWM controller functional diagram. The MAX1709 enters synchronized current-mode PWM when a clock signal
(350kHz < f CLK < 1000kHz) is applied to CLK. For
wireless or noise-sensitive applications, this ensures
that switching harmonics are predictable and kept outside the IF frequency band(s). High-frequency operation permits low-magnitude output ripple voltage and
minimum inductor and filter capacitor size. Switching
losses will increase at the higher frequencies (see
Power Dissipation).
Setting the Output Voltage
The MAX1709 features Dual-Mode™ operation. When
FB is connected to ground, the MAX1709 generates a
fixed output voltage of either +3.3V or +5V, depending
on the logic applied to the 3.3/5 input (Figure 1). The
output can be configured for other voltages, using two
external resistors as shown in Figure 4. To set the output voltage externally, choose an R3 value that is large
enough to minimize load at the output but small enough
to minimize errors due to leakage and the time constant
to FB. A value of R3 ≤ 50kΩ is required.
⎛V
⎞
R4 = R3 ⎜⎜ OUT − 1⎟⎟
⎝ VFB
⎠
where VFB = 1.24V.
Soft-Start/Current-Limit Adjustment
(SS/LIM)
The soft-start pin allows the soft-start time to be adjusted by connecting a capacitor from SS/LIM to ground.
Select capacitor C3 (connected to SS/LIM pin) as:
C3 (in µF) = 3.2 tSS
where tSS is the time (in seconds) it takes the switch
current limit to reach full value.
To improve efficiency or reduce inductor size at
reduced load currents, the current limit can be reduced
Dual Mode is a trademark of Maxim Integrated Products, Inc.
www.maximintegrated.com
Maxim Integrated | 9
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Table 3. Component Selection Guide
PRODUCTION
INDUCTORS
Surface mount
CAPACITORS
Coilcraft DO3316P-102HC
Panasonic EEFUE0J151R
Motorola MBRD1035CTL
Coiltronics UP2B-1R0
Sanyo 6TPC100M
STM-Microelectronics
STPS8L30B
at a different frequency, scale the inductor value with
the inverse of frequency (L1 = 1µH 600kHz / fSYNC).
The PWM design tolerates inductor values within ±25%
of this calculated value, so choose the closest standard
inductor value. For example, use 1.5µH for 350kHz and
0.68µH for 1MHz.
Table 4. Component Suppliers
SUPPLIER
PHONE
FAX
Coilcraft
847-639-6400
847-639-1489
Coiltronics
561-241-7876
561-241-9339
Motorola
602-303-5454
602-994-6430
Panasonic
714-373-7939
714-373-7183
STMMicroelectronics
617-259-0300
617-259-9442
from its nominal value (see Electrical Characteristics). A
resistor (R1 in Figure 1) between SS/LIM and ground
reduces the current limit as follows:
R1 = 312.5kΩ ×
DIODES
I1
(R1 ≤ 312.5kΩ)
ILIM
where I1 is the desired current limit in amperes, and
I LIM is the current limit value from the Electrical
Characteristics.
Inductors with a ferrite core or equivalent are recommended; powder iron cores are not recommended for
use at high switching frequencies. Ensure the inductor’s saturation rating (the current at which the core
begins to saturate and inductance falls) exceeds the
internal current limit. Note that this current may be
reduced through SS/LIM if less than the MAX1709’s full
load current is needed (see Electrical Characteristics
for ratings). For highest efficiency, use a coil with low
DC resistance, preferably under 10mΩ. To minimize
radiated noise, use a toroid, pot core, or shielded
inductor. See Tables 3 and 4 for a list of recommended
components and component suppliers. To calculate the
maximum output current (in amperes), use the following
equation:
⎛
⎛V
+ VD − VIN ⎞ ⎞
IOUT(MAX) = D' ⎜ ILIM − D' ⎜ OUT
⎟⎟
2 × ƒ × L1
⎝
⎠⎠
⎝
Design Procedure
Inductor Selection (L1)
The MAX1709’s high switching frequency allows the
use of a small-size inductor. Use a 1.0µH inductor for
600kHz operation. If the MAX1709 will be synchronized
where:
VIN = input voltage
VIN
FB
REF
SLOPE
COMP
LX
R
Q
N
VOUT
LX
S
MAX1709
R4
SS/LIM
12.5
(LIMITED TO 100mV)
OSCILLATOR
Figure 3. Simplified PWM Controller Functional Diagram
www.maximintegrated.com
FB
11mΩ
PGND
KEEP SHORT
R3
Figure 4. Adjustable Output Voltage
Maxim Integrated | 10
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Output Filter Capacitors (C6, C7)
270k
ON/OFF
μC
MAX1709
ONB
VDD
I/O
ONA
I/O
270k
0.1μF
Figure 5. Momentary Pushbutton On-Off Switch
VD = forward voltage drop of the Schottky diode at ILIM
current
VOUT = output voltage
D' = (VIN) / (VOUT + VD), assuming switch voltage drop
is negligible
f = switching frequency
L1 = inductor value
ILIM = minimum value of switch current limit from Electrical Characteristics or set by RSET/LIM.
Diode Selection (D1)
The MAX1709’s high switching frequency demands a
high-speed rectifier. Schottky diodes, such as the
MBRD1035CTL or STPS8L30B (Table 3), are recommended. The diode’s current rating must exceed the
maximum load current, and its breakdown voltage must
exceed VOUT. The diode must be placed within 10mm
of the LX switching node and the output filter capacitor.
The diode also must be able to dissipate the power calculated by the following equation:
PDIODE = IOUT VD
where IOUT is the average load current and VD is the
diode forward voltage at the peak switch current.
Capacitor Selection
Input Bypass Capacitors (C1, C2)
Two 150µF, low-ESR tantalum input capacitors will
reduce peak currents and reflected noise due to inductor current ripple. Lower ESR allows for lower input ripple current, but combined ESR values up to 50mΩ are
acceptable. Smaller ceramic capacitors may also be
used for light loads or in applications that can tolerate
higher input current ripple.
www.maximintegrated.com
The output filter capacitor ESR must be kept under
15mΩ for stable operation. Two parallel 150µF polymer
capacitors (Panasonic EEFUE0J151R) typically exhibit
5mΩ of ESR. This translates to approximately 35mV of
output ripple at 7A switch current. Bypass the
MAX1709 IC supply input (OUT) with a 0.1µF ceramic
capacitor to GND and connect a 2Ω series resistor to
OUT (R2, as shown in Figure 1).
Power Dissipation
The MAX1709 output current may be more limited by
package power dissipation than by the current rating of
the on-chip switch. For pulsed loads, output currents of
4 Amps or more can be supplied with either the
MAX1709EUI+ or MAX1709ESE, but the RMS (or thermal) limit of the MAX1709ESE is lower (6ARMS) than
that of the MAX1709EUI+ (10ARMS). Continuous output
current depends on the input and output voltage, operating temperature, and external components.
The major components of the MAX1709 dissipated
power (PD, i.e., power dissipated as heat in the IC and
NOT delivered to the load) are:
1) Internal switch conduction losses - PSW
2) Internal switch transition losses - PTRAN
3) Internal capacitive losses - PCAP
These are losses that directly dissipate heat in the
MAX1709, but keep in mind that other losses, such as
those in the external diode and inductor, increase input
power by reducing overall efficiency, and so indirectly
contribute to MAX1709 heating.
Approximate equations for the loss terms are as follows. Values in {} are example values for a 3.3V input,
4V output, 4A design.
A conservative efficiency estimate for the MAX1709
boosting from 3.3V to 5V at 4A is 81%. Total estimated
power loss is then:
{4.7W}
PLOSS = (POUT / 0.81) - POUT
The total loss consists of:
Diode Loss = D’ x ISW x VD
{2.5W}
Inductor Loss (resistive loss + dynamic loss
estimate)
{0.58W}
External Capacitive Loss = (1 - D’) x ISW2 x
RCAP-ESR (ESR est. = 10mΩ)
{0.27W}
MAX1709 Internal Loss, PD(MAX1709)
{1.35W}
Maxim Integrated | 11
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Approximate equations for the MAX1709 internal loss
terms are as follows. Values in {} are example values for
a 3.3V input, 4V output, 4A design:
PD(MAX1709) = PSW + PTRAN + PCAP
{1.35W}
where:
PSW = (1 - D’) x ISW2 x RSW
{1.08W}
PTRAN = (VOUT + VD) x ISW x
tSW x f / 3
{0.18W}
PCAP = (CDIO + CDSW + CGSW) x
(VOUT + VD)2 f
{0.09W}
where:
D’ = duty factor of the n-channel switch =
VIN / (VOUT + VD)
(Note: D’ = 1 means the switch is always off)
{0.6}
ISW, the approximate peak switch current =
IOUT / (D’ x eff),
{8.23A}
(with eff. estimated at 81%)
RSW = Internal n-channel switch
resistance
(estimate for elevated die temperature)
VD = forward voltage of the external
rectifier
tSW = the transition time of the
n-channel switch
f = the switching rate of the MAX1709
CDIO = rectifier capacitance
{0.04W)
{0.5V}
{20ns}
{600kHz}
The MAX1709ESE and MAX1709EUI+ both utilize PC
board area for heatsinking. Package dissipation ratings
in the Absolute Maximum Ratings section assume 1in2
of 1oz copper.
The MAX1709EUI+ has superior power-dissipating ability
due to an exposed metal pad on the underside of the
package. The thermal resistance from the die to the
exposed pad is a very low 1.2°C/W. The MAX1709ESE’s
ability to dissipate power will especially depend on the
PC board design. Typical thermal resistance for 1in2 of
copper is 34°C/W. For tighter layouts, 0.5in2 typically
exhibits 40°C/W. Adding multiple vias under the
MAX1709EUI+ to conduct heat to the bottom of the board
will also help dissipate power.
Due to high inductor current levels and fast switching
waveforms, proper PC board layout is essential. Protect
sensitive analog grounds by using a star ground configuration. Connect PGND, the input bypass capacitor
ground lead, and the output filter capacitor ground lead
to a single point (star ground configuration). In addition,
minimize trace lengths to reduce stray capacitance and
trace resistance, especially from the LX pins to the
catch diode (D1) and output capacitors (C6 and C7) to
PGND pins. If an external resistor-divider is used to set
the output voltage (Figure 4), the trace from FB to the
resistors must be extremely short and must be shielded
from switching signals, such as CLK or LX. Refer to a
layout example in the MAX1709EVKIT data sheet.
{1nF}
CDSW = internal n-channel drain
capacitance
{2.5nF}
CGSW = internal n-channel gate
capacitance
{1.5nF}
Applications Information
Using a Momentary On/Off Switch
A momentary pushbutton switch can be used to turn
the MAX1709 on and off. As shown in Figure 5, when
ONA is pulled low and ONB is pulled high, the part is
off. When the momentary switch is pressed, ONB is
pulled low and the regulator turns on. The switch
should be on long enough for the microcontroller to exit
reset. The controller issues a logic high to ONA, which
guarantees that the part will stay on regardless of the
subsequent switch state. To turn the regulator off, press
the switch long enough for the controller to read the
switch status and pull ONA low. When the switch is
released, ONB pulls high and the regulator turns off.
www.maximintegrated.com
Layout Considerations
Chip Information
TRANSISTOR COUNT: 1112
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND PATTERN
NO.
16 SOIC (N)
S16+8
21-0041
90-0097
28 TSSOP-EP
U28E+4
21-0108
90-0146
Maxim Integrated | 12
4A, Low-Noise, High-Frequency,
Step-Up DC-DC Converter
MAX1709
Revision History
REVISION
NUMBER
REVISION
DATE
3
2/15
DESCRIPTION
Updated the Benefits and Features section
PAGES
CHANGED
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2015 Maxim Integrated Products, Inc. | 13