General Description
The MAX618 CMOS, PWM, step-up DC-DC converter
generates output voltages up to 28V and accepts inputs
from +3V to +28V. An internal 2A, 0.3Ω switch eliminates
the need for external power MOSFETs while supplying
output currents up to 500mA or more. A PWM control
scheme combined with Idle Mode™ operation at light
loads minimizes noise and ripple while maximizing effi-
ciency over a wide load range. No-load operating current
is 500μA, which allows efficiency up to 93%.
A fast 250kHz switching frequency allows the use of
small surface-mount inductors and capacitors. A shut-
down mode extends battery life when the device is not in
use. Adaptive slope compensation allows the MAX618 to
accommodate a wide range of input and output voltages
with a simple, single compensation capacitor.
The MAX618 is available in a thermally enhanced 16-pin
QSOP package that is the same size as an industry-
standard 8-pin SO but dissipates up to 1W. An evaluation
kit (MAX618EVKIT) is available to help speed designs.
Applications
● Industrial +24V and +28V Systems
● LCD Displays
●Palmtop Computers
Features
●Adjustable Output Voltage Up to +28V
● Up to 93% Efficiency
● Wide Input Voltage Range (+3V to +28V)
●Up to 500mA Output Current at +12V
● 500μA Quiescent Supply Current
● 3μA Shutdown Current
● 250kHz Switching Frequency
●Small 1W, 16-Pin QSOP Package
Idle Mode is a trademark of Maxim Integrated Products, Inc.
+Denotes a lead(Pb)-free/RoHS-compliant package.
PART TEMP. RANGE PIN-PACKAGE
MAX618EEE+ -40°C to +85°C 16 QSOP
PGND
LX
FB
VL
VOUT
UP TO
28V
COMP
IN
SHDN
GND
VIN
3V TO
28V MAX618
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
GND GND
PGND
PGND
PGND
GND
VL
IN
GND
TOP VIEW
MAX618
QSOP
LX
LX
COMP
LX
SHDN
FB
GND
+
MAX618 28V Internal Switch, Step-Up DC-DC Converter
19-1462; Rev 2; 4/15
Typical Application Circuit
Pin Conguration
Ordering Information
EVALUATION KIT AVAILABLE
IN to GND ...............................................................-0.3V to +30V
LX to GND ..............................................................-0.3V to +30V
VL to GND ................................................................-0.3V to +6V
SHDN, COMP, FB to GND ............................-0.3V to (VL + 0.3V)
PGND to GND.....................................................................±0.3V
Continuous Power Dissipation (TA = +70°C) (Note 1)
16-Pin QSOP (derate 15mW/°C above +70°C)...................1W
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Soldering Temperature (reflow) .......................................+260°C
(VIN = +6V, PGND = GND, CVL = 4.7μF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage VIN 3 28 V
Supply Current, No Load IIN VIN = 3V to 28V, VFB = 1.6V, SHDN = VL 500 700 µA
Supply Current, Full Load, VL
Connected to IN IIN V I N = 3V to 5.5V, VFB = 1.4V,
SHDN = VL = IN 5 6.5 mA
Supply Current, Full Load IIN VIN = 3.4V to 28V, VFB = 1.4V,
SHDN = VL, VVL < VIN 2.5 3.5 mA
Shutdown Supply Current IIN VIN = 28V, VFB = 1.6V, SHDN = GND 3 8 µA
VL Output Voltage VVL VIN = 3.5V or 28V, no load 2.9 3.05 3.2 V
VL Load Regulation DVVL ILOAD = 0 to 2mA, VFB = 1.6V 25 40 mV
VL Undervoltage Lockout Rising edge, 1% hysteresis 2.58 2.7 2.8 V
FB Set Voltage VFB 1.47 1.5 1.53 V
FB Input Bias Current IFB VFB = 1.6V 1 50 nA
Line Regulation DVOUT VIN = 3V to 6V,VOUT = 12V 0.01 0.08 %/V
Load Regulation DVOUT VOUT = 12V, ILOAD = 10mA to 500mA 0.2 %
LX Voltage VLX 28 V
LX Switch Current Limit ILXON PWM mode 1.7 2.2 2.7 A
Idle Mode Current Limit
Threshold 0.25 0.35 0.45 A
LX On-Resistance RLXON 0.3 0.6 Ω
LX Leakage Current ILXOFF VLX = 28V 0.02 10 µA
COMP Maximum Output Current ICOMP FB = GND 100 200 µA
COMP Voltage to Switch Current
Transconductance DFB = 0.1V 0.8 1 mmho
SHDN Input Logic Low VIL 0.8 V
SHDN Input Logic High VIH 2.0 V
Shutdown Input Current SHDN = GND or VL 1 µA
Switching Frequency f 200 250 300 kHz
Maximum Duty Cycle DC 90 95 %
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Note 1: With part mounted on 0.9 in.2 of copper.
Absolute Maximum Ratings
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
(VIN = +6V, PGND = GND, CVL = 4.7μF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
(Circuit of Figure 1, TA = +25°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage VIN 3 28 V
Supply Current, No Load IIN VIN = 3V to 28V, VFB = 1.6V, SHDN = VL 800 µA
Supply Current, Full Load,
VL Connected to IN IIN VIN = 3V to 5.5, VFB = 1.4V,
SHDN = VL = IN 7.5 mA
Supply Current, Full Load IIN VIN = 3.4V to 28V, VFB = 1.4V,
SHDN = VL, VVL < VIN 4mA
Supply Current Shutdown IIN VIN = 28V, VFB = 1.6V, SHDN = GND 10 µA
VL Output Voltage VVL VIN = 3.5V or 28V, no load 2.85 3.3 V
VL Undervoltage Lockout VVL Rising edge, 1% hysteresis 2.55 2.85 V
FB Set Voltage VFB 1.455 1.545 V
LX Voltage Range VLXON 28 V
LX Switch Current Limit ILXON PWM mode 1.4 3 A
LX On-Resistance RLXON 0.6 Ω
Switching Frequency f 188 312 kHz
100
0
0.1 1 10 100 1000
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 12V)
20
30
10
MAX618 toc01
OUTPUT CURRENT (mA)
EFFICIENCY (%)
40
50
60
70
80
90
VIN = 8V
VIN = 5V
VIN = 3V
100
0
0.1 1 10 100 1000
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 28V)
20
30
10
MAX618 toc02
OUTPUT CURRENT (mA)
EFFICIENCY (%)
40
50
60
70
80
90
VIN = 12V
VIN = 5V
VIN = 3V
320
360
340
400
380
420
440
480
460
500
2 4 5 6 7 8 9 10 113 12
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX618 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
VOUT = 12V
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Electrical Characteristics (continued)
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25°C.)
0.40
0.45
0.55
0.50
0.60
0.65
0 105 15 20 25 30
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX618 toc04
INPUT VOLTAGE (V)
SUPPLY CIRRENT (µA)
300
400
350
500
450
550
600
650
700
-50 -10 10-30 30 50 70 90 110
SUPPLY CURRENT vs. TEMPERATURE
MAX618 toc05
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VIN = 8V
VIN = 5V
VIN = 3V
INCLUDES CAPACITOR LEAKAGE CURRENT
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
2 127 17 22 27 32
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX618 toc06
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (µA)
0
VOUT
(100mV/div)
VLX
(10V/div)
IL
(1A/div)
MEDIUM-LOAD SWITCHING
WAVEFORMS
MAX618 toc07
VIN = 5V, VOUT = 12V, IOUT = 200mA
2µs/div
0
VOUT
(100mV/
div)
VLX
(10V/div)
IL
(1A/div)
HEAVY-LOAD SWITCHING
WAVEFORMS
MAX618 toc08
VIN = 5V, VOUT = 12V, IOUT = 500mA
2µs/div
3V
6V
VOUT
(50mV/div)
VIN
(5V/div)
LINE-TRANSIENT RESPONSE
MAX618 toc09
IOUT = 200mA, VOUT = 12V
2ms/div
0
VOUT
(200mV/div)
IOUT
(100mA/div)
LOAD-TRANSIENT RESPONSE
MAX618 toc10
VIN = 5V, VOUT = 12V
5ms/div
5V
12V
0
SHDN
(2V/div)
VOUT
(2V/div)
SHUTDOWN RESPONSE
MAX618 toc11
VIN = 5V, VOUT = 12V, ILOAD = 500mA
500µs/div
0
0.4
0.2
0.6
1.2
1.4
1.0
0.8
1.6
2 4 5 6 73 8 9 10 11 12
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX618 toc12
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (A)
VOUT = 12V
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Typical Operating Characteristics (continued)
Figure 1. Single-Supply Operation
PIN NAME FUNCTION
1, 8, 9,
12, 16 GND Ground
2, 3, 4 LX Drain of Internal n-channel Switch. Connect the inductor between IN and LX.
5SHDN Shutdown Input. A logic low puts the MAX618 in shutdown mode and reduces supply current to 3µA.
SHDN must not exceed VL. In shutdown, the output falls to VIN less one diode drop.
6 COMP Compensation Input. Bypass to GND with the value of capacitance shown in Table 2.
7FB Feedback Input. Connect a resistor-divider network to set VOUT. FB threshold is 1.5V.
10 IN LDO Regulator Supply Input. IN accepts inputs up to +28V. Bypass to GND with a 1µF ceramic capacitor
as close to pins 10 and 12 as possible.
11 VL Internal 3.1V LDO Regulator Output. Bypass to GND with a 4.7µF capacitor.
13, 14, 15 PGND Power Ground. Source of internal N-channel switch.
COMP 2
+5V INPUT
R3
169kΩ
R4
100kΩ
L1
470
LOW BATTERY INPUT
1.31V
OSC
RON
AT 3Ω
40kHz COMP 1
1.31V
BANDGAP
REFERENCE
AND
BIAS GENERATOR
1 LBR
2 CX
3 LX
4 GND
D1
1N4148
+VS5
IC6
VFB 7
LBD 8 LOW-BATTERY OUTPUT
(LOW IF INPUT < 3V)
CC
R1
499kΩ
R2
47.5kΩ
SHUTDOWN
OPERATE
+15V OUTPUT
20mA
C1
470mF
25V
MAX618
COMP 2
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Pin Description
Detailed Description
The MAX618 pulse-width modulation (PWM) DC-DC
converter with an internal 28V switch operates in a wide
range of DC-DC conversion applications including boost,
SEPIC, and flyback configurations. The MAX618 uses
fixed-frequency PWM operation and Maxim’s proprietary
Idle Mode control to optimize efficiency over a wide range
of loads. It also features a shutdown mode to minimize
quiescent current when not in operation.
PWM Control Scheme and
Idle Mode Operation
The MAX618 combines continuous-conduction PWM
operation at medium to high loads and Idle Mode opera-
tion at light loads to provide high efficiency over a wide
range of load conditions. The MAX618 control scheme
actively monitors the output current and automatically
switches between PWM and Idle Mode to optimize
efficiency and load regulation. Figure 2 shows a functional
diagram of the MAX618’s control scheme.
The MAX618 normally operates in low-noise, continuous-
conduction PWM mode, switching at 250kHz. In PWM
mode, the internal MOSFET switch turns on with each
clock pulse. It remains on until either the error comparator
trips or the inductor current reaches the 2A switch-current
limit. The error comparator compares the feedback-error
signal, current-sense signal, and slope-compensation
signal in one circuit block. When the switch turns off,
energy transfers from the inductor to the output capacitor.
Output current is limited by the 2A MOSFET current limit
Figure 2. Functional Diagram
SHDN
MAX618
IDLE MODE
CURRENT LIMIT
PWM
CURRENT LIMIT
ERROR
COMPARATOR
250kHz
OSCILLATOR
SLOPE
COMPENSATION
LINEAR
REGULATOR
CURRENT-
SENSE
CIRCUIT
PGND IN
LX OUT
R
14R
VL
FB
COMP
IN
VL
NMOS
REFERENCE
INTEGRATOR
GND
SHUTDOWN
PWM
LOGIC
THERMAL
SHUTDOWN
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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and the MAX618’s package power-dissipation limit. See
the Maximum Output Current section for details.
In Idle Mode, the MAX618 improves light-load
efficiency by reducing inductor current and skipping cycles
to reduce the losses in the internal switch, diode, and
inductor. In this mode, a switching cycle initiates only
when the error comparator senses that the output voltage
is about to drop out of regulation. When this occurs, the
NMOS switch turns on and remains on until the inductor
current exceeds the nominal 350mA Idle Mode current
limit.
Refer to Table 1 for an estimate of load currents at which
the MAX618 transitions between PWM and Idle Mode.
Compensation Scheme
Although the higher loop gain of voltage-controlled
architectures tends to provide tighter load regulation,
current-controlled architectures are generally easier to
compensate over wide input and output voltage ranges.
The MAX618 uses both control schemes in parallel:
the dominant, low-frequency components of the error
signal are tightly regulated with a voltage-control loop,
while a current-control loop improves stability at higher
frequencies. Compensation is achieved through the
selection of the output capacitor (COUT), the integrator
capacitor (CCOMP), and the pole capacitor (CP) from
FB to GND. CP cancels the zero formed by COUT and
its ESR. Refer to the Capacitor Selection section for
guidance on selecting these capacitors.
VL Low-Dropout Regulator
The MAX618 contains a 3.1V low-dropout linear regulator
to power internal circuitry. The regulator’s input is IN and
its output is VL. The IN to VL dropout voltage is 100mV,
so that when IN is less than 3.2V, VL is typically 100mV
below IN. The MAX618 still operates when the LDO is in
dropout, as long as VL remains above the 2.7V undervolt-
age lockout. Bypass VL with a 4.7μF ceramic capacitor
placed as close to the VL and GND pins as possible.
VL can be overdriven by an external supply between
2.7V and 5.5V. In systems with +3.3V or +5V logic power
supplies available, improve efficiency by powering VL and
VIN directly from the logic supply as shown in Figure 3.
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Table 1. PWM/Idle-Mode Transition Load Current (IOUT in Amps) vs. Input and Output Voltage
VIN
VOUT
45678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
3 0.20 0.20 0.18 0.15 0.12 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.04 0.04 0.03 0.03 0.03 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02
40.18 0.21 0.20 0.17 0.15 0.13 0.12 0.10 0.09 0.08 0.07 0.07 0.06 0.05 0.05 0.04 0.04 0.04 0.03 0.03 0.03 0.03 0.03 0.03
5 0.16 0.20 0.21 0.19 0.17 0.16 0.14 0.13 0.11 0.10 0.09 0.09 0.08 0.07 0.07 0.06 0.06 0.05 0.05 0.04 0.04 0.04 0.04
6 0.15 0.20 0.21 0.20 0.19 0.18 0.16 0.15 0.13 0.12 0.11 0.10 0.10 0.09 0.08 0.08 0.07 0.07 0.06 0.06 0.05 0.05
7 0.17 0.19 0.21 0.21 0.20 0.19 0.17 0.16 0.15 0.14 0.13 0.12 0.11 0.10 0.10 0.09 0.08 0.08 0.07 0.07 0.07
80.19 0.18 0.20 0.21 0.20 0.20 0.19 0.17 0.16 0.15 0.14 0.13 0.13 0.12 0.11 0.10 0.10 0.09 0.09 0.08
90.20 0.17 0.20 0.21 0.21 0.20 0.19 0.18 0.18 0.17 0.16 0.15 0.14 0.13 0.12 0.12 0.11 0.10 0.10
10 0.21 0.16 0.19 0.20 0.21 0.21 0.20 0.19 0.18 0.17 0.17 0.16 0.15 0.14 0.13 0.13 0.12 0.11
11 0.22 0.15 0.19 0.20 0.21 0.21 0.20 0.20 0.19 0.18 0.17 0.17 0.16 0.15 0.14 0.14 0.13
12 0.23 0.15 0.18 0.20 0.21 0.21 0.21 0.20 0.20 0.19 0.18 0.18 0.17 0.16 0.15 0.15
13 0.24 0.16 0.17 0.19 0.20 0.21 0.21 0.20 0.20 0.19 0.19 0.18 0.17 0.17 0.16
14 0.25 0.17 0.17 0.19 0.20 0.21 0.21 0.21 0.20 0.20 0.19 0.19 0.18 0.17
15 0.25 0.18 0.16 0.18 0.20 0.20 0.21 0.21 0.21 0.20 0.20 0.19 0.19
16 0.26 0.19 0.16 0.18 0.19 0.20 0.21 0.21 0.21 0.20 0.20 0.20
17 0.26 0.20 0.15 0.17 0.19 0.20 0.20 0.21 0.21 0.21 0.20
18 0.27 0.20 0.15 0.17 0.19 0.20 0.20 0.21 0.21 0.21
19 0.27 0.21 0.16 0.17 0.18 0.19 0.20 0.21 0.21
20 0.27 0.21 0.17 0.16 0.18 0.19 0.20 0.20
21 0.28 0.22 0.17 0.16 0.18 0.19 0.20
22 0.28 0.22 0.18 0.15 0.17 0.19
23 0.28 0.23 0.18 0.15 0.17
24 0.28 0.23 0.19 0.15
25 0.29 0.24 0.19
26 0.29 0.24
27 0.29
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Operating Congurations
The MAX618 can be connected in one of three configura-
tions described in Table 2 and shown in Figures 1, 3, and
4. The VL linear regulator allows operation from a single
supply between +3V and +28V as shown in Figure 1.
The circuit in Figure 3 allows a logic supply to power
the MAX618 while using a separate source for DC-DC
conversion power (inductor voltage). The logic supply
(between 2.7V and 5.5V) connects to VL and IN. VL = IN;
voltages of 3.3V or more improve efficiency by providing
greater gate drive for the internal MOSFET.
The circuit in Figure 4 allows separate supplies to power
IN and the inductor voltage. It differs from the connection
in Figure 3 in that the MAX618 chip supply is not limited
to 5.5V.
Figure 3. Dual-Supply Operation (VIN = 2.7V to 5.5V) Figure 4. Dual-Supply Operation (VIN = 3V to 28V)
Table 2. Input Configurations
CIRCUIT CONNECTION VIN RANGE INDUCTOR
VOLTAGE BENEFITS/COMMENTS
Figure 1 Input voltage
connects to IN
and inductor.
3V to VOUT
(up to 28V) VIN
• Single supply operation.
• SHDN must be connected to or pulled up to VL. On/off control
requires an open-drain or open-collector connection to SHDN.
Figure 3
IN and VL
connect together.
Inductor voltage
supplied by a
separate source.
2.7V to 5.5V 0V to VOUT
(up to 28V)
• Increased efciency.
• SHDN can be driven by logic powered from the supply
connected to IN and VL, or can be connected to or pulled up
to VL.
• Input power source (inductor voltage) is separate from the
MAX618’s bias (VIN = VL) and can be less than or greater
than VIN.
Figure 4
IN and inductor
voltage supplied
by separate
sources.
3V to 28V 0V to VOUT
(up to 28V)
• Input power source (inductor voltage) is separate from the
MAX618’s bias (VIN) and can be less than or greater than VIN.
• SHDN must be connected to or pulled up to VL. On/off control
requires an open-drain or open-collector connection to SHDN.
GND
LX
COUT
L
PGND
R2
R1
CP
VL
COMP
CCOMP
IN
SHDN
UP TO 28V
VIND
UP TO 28V
CIND
IN OUT
MAX618
2.7V TO 5.5V
4.7µF
1µF
FB
LX
CIND
COUT
L
PGND
GND
R1
VL
COMP
CCOMP
IN
SHDN
UP TO 28V
VIND
UP TO 28V
OUT
MAX618
IN
3V TO 28V
4.7µF
1µF
R2
CP
FB
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Shutdown Mode
In shutdown mode (SHDN = 0), the MAX618’s feedback
and control circuit, reference, and internal biasing circuitry
turn off and reduce the IN supply current to 3μA (10μA
max). When in shutdown, a current path remains from
the input to the output through the external inductor and
diode. Consequently, the output falls to VIN less one
diode drop in shutdown.
SHDN may not exceed VL. For always-on operation,
connect SHDN to VL. To add on/off control to the circuit
of Figure 1 or 4, pull SHDN to VL with a resistor (10kΩ
to 100kΩ) and drive SHDN with an open-drain logic gate
or switch as shown in Figure 5. Alternatively, the circuit of
Figure 3 allows direct SHDN drive by any logic-level gate
powered from the same supply that powers VL and IN, as
shown in Figure 6.
Design Procedure
The MAX618 operates in a number of DC-DC converter
configurations including step-up, SEPIC, and flyback. The
following design discussion is limited to step-up converters.
Setting the Output Voltage
Two external resistors (R1 and R2) set the output voltage.
First, select a value for R2 between 10kΩ and 200kΩ.
Calculate R1 with:
OUT
12
FB
V
RR 1
V
= −
where VFB is 1.5V.
Determining the Inductor Value
The MAX618’s high switching frequency allows the use of
a small value inductor. The recommended inductor value
is proportional to the output voltage and is given by the
following:
OUT
5
V
L
7 10
=×
After solving for the above equation, round down as
necessary to select a standard inductor value.
When selecting an inductor, choose one rated to 250kHz,
with a saturation current exceeding the peak inductor
current, and with a DC resistance under 200mΩ. Ferrite
core or equivalent inductors are generally appropriate
(see MAX618 EV kit data sheet). Calculate the peak
inductor current with the following equation:
( )
OUT IN
OUT IN
LX(PEAK) OUT IN OUT
VV
VV
I I 2µs
V LV
−
= +
Note that the peak inductor current is internally limited
to 2A.
Diode Selection
The MAX618’s high switching frequency demands a high-
speed rectifier. Schottky diodes are preferred for most
applications because of their fast recovery time and low
forward voltage. Make sure that the diode’s peak current
rating exceeds the 2A peak switch current, and that its
breakdown voltage exceeds the output voltage.
Figure 5. Adding On/Off Control to Circuit of Figure 1 or 4 Figure 6. Adding On/Off Control to Circuit of Figure 3
MAX618
VL
100kΩ
ON/OFF
CONTROL
OPEN-DRAIN
LOGIC
SHDN
MAX618
IN
VL
SYSTEM LOGIC
ON/OFF
CONTROL SHDN
SYSTEM
LOGIC SUPPLY
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Maximum Output Current
The MAX618’s 2.2A LX current limit determines the output
power that can be supplied for most applications. In some
cases, particularly when the input voltage is low, output
power is sometimes restricted by package dissipation
limits. The MAX618 is protected by a thermal shutdown
circuit that turns off the switch when the die temperature
exceeds +150°C. When the device cools by 10°C, the
switch is enabled again. Table 3 details output current
with a variety of input and output voltages. Each listing in
Table 3 is either the limit set by an LX current limit or by
package dissipation at +85°C ambient, whichever is lower.
The values in Table 3 assume a 40mΩ inductor resistance.
Capacitor Selection
Input Capacitors
The input bypass capacitor (CIND) reduces the input
ripple created by the boost configuration. High-impedance
sources require high CIND values. However, 68μF is
generally adequate for input currents up to 2A. Low-ESR
capacitors are recommended because they will decrease
the ripple created on the input and improve efficiency.
Capacitors with ESR below 0.3Ω are generally appropriate.
In addition to the input bypass capacitor, bypass IN with a
1μF ceramic capacitor placed as close to the IN and GND
pins as possible. Bypass VL with a 4.7μF ceramic capaci-
tor placed as close to the VL and GND pins as possible.
Output Capacitor
Use Table 4 to find the minimum output capacitance
necessary to ensure stable operation. In addition, choose
an output capacitor with low ESR to reduce the output
ripple. The dominant component of output ripple is the
product of the peak-to-peak inductor ripple current and
the ESR of the output capacitor. ESR below 50mΩ
generates acceptable levels of output ripple for most
applications.
Integrator Capacitor
The compensation capacitor (C
COMP
) sets the dominant
pole in the MAX618’s transfer function. The proper com-
pensation capacitance depends upon output capacitance.
Table 5 shows the capacitance value needed for the
output capacitances specified in Table 4. However, if a
different output capacitor is used (e.g., a standard value),
then recalculate the value of capacitance needed for the
integrator capacitor with the following formula:
COMP OUT
COMP OUT
C (Table 5) C
CC (Table 4)
×
=
Pole Compensation Capacitor
The pole capacitor (C
P
) cancels the unwanted zero intro-
duced by C
OUT
’s ESR, and thereby ensures stability in
PWM operation. The exact value of the pole capacitor is
not critical, but it should be near the value calculated by
the following equation:
ESR OUT 1 2
P12
R C (R R )
CRR
×+
=×
where R
ESR
is C
OUT
’s ESR.
Layout Considerations
Proper PC board layout is essential due to high current
levels and fast switching waveforms that radiate noise.
Use the MAX618 evaluation kit or equivalent PC layout to
perform initial prototyping. Breadboards, wire-wrap, and
proto-boards are not recommended when prototyping
switching regulators.
It is important to connect the GND pin, the input bypass
capacitor ground lead, and the output filter capacitor
ground lead to a single point to minimize ground noise
and improve regulation. Also, minimize lead lengths to
reduce stray capacitance, trace resistance, and radiated
noise, with preference given to the feedback circuit, the
ground circuit, and LX. Place the feedback resistors as
close to the FB pin as possible. Place a 1μF input bypass
capacitor as close as possible to IN and GND.
Refer to the MAX618 evaluation kit for an example of
proper board layout.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
16 QSOP EF16+8F 21-0055
MAX618 28V Internal Switch, Step-Up DC-DC Converter
www.maximintegrated.com Maxim Integrated
│
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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.
Chip Information
PROCESS: BiCMOS
Table 3. Typical Output Current vs. Input and Output Voltages
VIN
VOUT
45678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
3 0.77 0.59 0.49 0.41 0.34 0.29 0.25 0.22 0.20 0.18 0.17 0.15 0.14 0.13 0.12 0.12 0.11 0.10 0.10 0.09 0.09 0.08 0.08 0.08 0.07
4 0.96 0.76 0.64 0.56 0.49 0.43 0.38 0.34 0.31 0.28 0.26 0.24 0.22 0.21 0.19 0.18 0.17 0.16 0.16 0.15 0.14 0.14 0.13 0.12
51.09 0.89 0.76 0.67 0.60 0.54 0.50 0.45 0.41 0.37 0.34 0.32 0.30 0.28 0.26 0.25 0.23 0.22 0.21 0.20 0.19 0.18 0.18
6 1.18 0.99 0.85 0.76 0.68 0.63 0.58 0.54 0.50 0.46 0.42 0.39 0.37 0.34 0.32 0.31 0.29 0.28 0.26 0.25 0.24 0.23
7 1.26 1.07 0.93 0.83 0.76 0.70 0.65 0.60 0.57 0.53 0.50 0.46 0.43 0.41 0.38 0.36 0.35 0.33 0.31 0.30 0.29
8 1.32 1.13 1.00 0.90 0.82 0.76 0.71 0.66 0.62 0.59 0.56 0.53 0.50 0.47 0.44 0.42 0.40 0.38 0.36 0.35
91.37 1.19 1.06 0.96 0.88 0.81 0.76 0.71 0.67 0.64 0.61 0.58 0.55 0.53 0.50 0.47 0.45 0.43 0.41
10 1.41 1.24 1.11 1.01 0.93 0.86 0.81 0.76 0.72 0.68 0.65 0.62 0.59 0.57 0.55 0.52 0.50 0.47
11 1.44 1.28 1.15 1.05 0.97 0.91 0.85 0.80 0.76 0.72 0.69 0.66 0.63 0.61 0.58 0.56 0.54
12 1.47 1.31 1.19 1.10 1.02 0.95 0.89 0.84 0.80 0.76 0.73 0.70 0.67 0.64 0.62 0.60
13 1.49 1.34 1.23 1.13 1.05 0.99 0.93 0.88 0.83 0.80 0.76 0.73 0.70 0.67 0.65
14 1.52 1.37 1.26 1.16 1.09 1.02 0.96 0.91 0.87 0.83 0.79 0.76 0.73 0.71
15 1.53 1.40 1.29 1.19 1.12 1.05 0.99 0.94 0.90 0.86 0.82 0.79 0.76
16 1.55 1.42 1.31 1.22 1.14 1.08 1.02 0.97 0.93 0.89 0.85 0.82
17 1.57 1.44 1.33 1.25 1.17 1.11 1.05 1.00 0.95 0.91 0.88
18 1.58 1.46 1.36 1.27 1.20 1.13 1.07 1.02 0.98 0.94
19 1.59 1.47 1.37 1.29 1.22 1.15 1.10 1.05 1.00
20 1.60 1.49 1.39 1.31 1.24 1.18 1.12 1.07
21 1.61 1.50 1.41 1.33 1.26 1.20 1.14
22 1.62 1.51 1.42 1.35 1.28 1.22
23 1.63 1.53 1.44 1.36 1.29
24 1.64 1.54 1.45 1.38
25 1.64 1.55 1.46
26 1.65 1.56
27 1.66
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Table 4. Minimum COUT for Stability (μF)
VIN
VOUT
45678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
3 173 128 100 80 65 54 46 40 35 31 28 25 23 21 19 18 17 15 15 14 13 12 12 11 10
4151 118 96 80 68 59 51 45 39 35 32 29 27 24 23 21 20 18 17 16 15 15 14 13
5 132 107 90 77 67 59 52 46 41 37 34 31 29 26 25 23 21 20 19 18 17 16 15
6117 97 83 72 64 57 51 46 42 38 35 32 30 28 26 24 23 21 20 19 18 17
7104 89 77 68 61 55 50 45 42 39 35 33 30 28 26 25 23 22 21 20 19
894 82 72 64 58 52 48 44 41 38 35 33 31 29 27 25 24 22 21 20
986 76 67 61 55 50 46 42 39 37 34 32 30 29 27 25 24 23 21
10 79 70 63 57 52 48 44 41 38 36 34 32 30 28 27 25 24 23
11 73 66 59 54 50 46 43 40 37 35 33 31 29 28 26 25 24
12 68 62 56 51 47 44 41 38 36 34 32 30 29 27 26 25
13 64 58 53 49 45 42 39 37 35 33 31 29 28 27 25
14 60 55 50 47 43 40 38 36 34 32 30 29 27 26
15 56 52 48 44 42 39 37 35 33 31 29 28 27
16 53 49 46 43 40 37 35 33 32 30 29 27
17 50 47 44 41 38 36 34 32 31 29 28
18 48 45 42 39 37 35 33 31 30 28
19 46 43 40 38 36 34 32 30 29
20 43 41 38 36 34 33 31 29
21 42 39 37 35 33 32 30
22 40 38 36 34 32 31
23 38 36 34 33 31
24 37 35 33 32
25 35 34 32
26 34 33
27 33
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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Table 5. Minimum CCOMP for Stability (nF)
VIN
VOUT
45678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
340 46 54 64 73 83 94 105 118 130 143 157 172 187 203 219 236 253 271 290 309 329 349 370 391
4 42 45 51 58 66 74 82 91 100 109 119 130 141 152 164 176 188 201 214 228 242 257 272 287
543 45 49 54 60 67 75 81 88 96 103 111 120 128 137 147 156 166 176 187 197 209 220
644 45 48 52 57 62 68 74 80 86 92 99 105 112 119 127 134 142 150 159 167 176
745 45 47 50 54 58 63 68 74 79 85 90 95 101 107 113 119 125 132 139 146
846 45 47 49 52 56 60 64 68 73 78 83 88 93 98 103 108 113 119 124
9 46 46 47 48 51 54 57 61 64 68 73 77 82 86 91 95 99 104 109
10 47 46 46 48 50 52 55 58 61 65 69 72 77 81 85 89 93 97
11 47 46 46 48 49 51 54 56 59 62 65 69 72 76 80 84 88
12 48 47 47 47 49 50 52 55 57 60 63 66 69 72 75 79
13 48 47 47 47 48 50 52 54 56 58 61 63 66 69 72
14 49 47 47 47 48 49 51 53 55 57 59 61 64 66
15 49 47 47 47 48 49 50 52 53 55 57 59 62
16 49 48 47 47 48 49 50 51 53 54 56 58
17 49 48 47 47 48 48 49 51 52 53 55
18 50 48 47 47 48 48 49 50 51 53
19 50 48 47 47 48 48 49 50 51
20 50 48 48 47 48 48 49 49
21 50 49 48 47 48 48 48
22 50 49 48 48 48 48
23 50 49 48 48 48
24 51 49 48 48
25 51 49 48
26 51 49
27 51
MAX618 28V Internal Switch, Step-Up DC-DC Converter
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REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
06/09 Initial release —
112/09 Updated part to lead-free, added soldering temperatures (reow), and
corrected error in equation 1, 2, 10
24/15 No /V ordering information; removed Automotive reference from Applications
section 1
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 specications 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.
MAX618 28V Internal Switch, Step-Up DC-DC Converter
© 2015 Maxim Integrated Products, Inc.
│
15
Revision History
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.
