MAXIM MAX618EEE+

19-1462; Rev 1; 12/09
KIT
ATION
EVALU
E
L
B
AVAILA
28V, PWM, Step-Up DC-DC Converter
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 efficiency 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 shutdown 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 16pin QSOP package that is the same size as an industrystandard 8-pin SO but dissipates up to 1W. An
evaluation kit (MAX618EVKIT) is available to help
speed designs.
Features
o Adjustable Output Voltage Up to +28V
o Up to 93% Efficiency
o Wide Input Voltage Range (+3V to +28V)
o Up to 500mA Output Current at +12V
o 500µA Quiescent Supply Current
o 3µA Shutdown Current
o 250kHz Switching Frequency
o Small 1W, 16-Pin QSOP Package
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX618EEE+
-40°C to +85°C
16 QSOP
+Denotes a lead(Pb)-free/RoHS-compliant package.
Applications
Automotive-Powered DC-DC Converters
Industrial +24V and +28V Systems
LCD Displays
Typical Operating Circuit
Palmtop Computers
Pin Configuration
TOP VIEW
GND 1
VIN
3V TO 28V
+
16 GND
LX 2
15 PGND
LX 3
14 PGND
LX 4
MAX618
VOUT
UP TO 28V
MAX618
SHDN
PGND
13 PGND
SHDN 5
12 GND
COMP 6
11 VL
FB 7
10 IN
GND 8
LX
IN
9
VL
COMP
FB
GND
GND
QSOP
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
MAX618
General Description
MAX618
28V, PWM, Step-Up DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
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
Note 1: With part mounted on 0.9 in.2 of copper.
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.)
PARAMETER
SYMBOL
CONDITIONS
VIN
Supply Current, No Load
IIN
VIN = 3V to 28V, VFB = 1.6V, SHDN = VL
Supply Current, Full Load, VL
Connected to IN
IIN
VIN = 3V to 5.5V, VFB = 1.4V, SHDN = VL = IN
Supply Current, Full Load
IIN
VIN = 3.4V to 28V, VFB = 1.4V, SHDN = VL,
VVL < VIN
Shutdown Supply Current
IIN
VIN = 28V, VFB = 1.6V, SHDN = GND
VL Output Voltage
VVL
VIN = 3.5V or 28V, no load
VL Load Regulation
∆VVL
VL Undervoltage Lockout
FB Set Voltage
TYP
MAX
UNITS
28
V
500
700
µA
5
6.5
mA
2.5
3.5
mA
3
8
µA
2.9
3.05
3.2
V
25
40
mV
2.58
2.7
2.8
V
1.47
1.5
1.53
V
ILOAD = 0 to 2mA, VFB = 1.6V
Rising edge, 1% hysteresis
VFB
1
50
nA
Line Regulation
∆VOUT
VIN = 3V to 6V, VOUT = 12V
0.01
0.08
%/V
Load Regulation
∆VOUT
VOUT = 12V, ILOAD = 10mA to 500mA
0.2
FB Input Bias Current
LX Voltage
LX Switch Current Limit
IFB
VFB = 1.6V
VLX
ILXON
PWM mode
Idle Mode Current-Limit
Threshold
%
28
V
1.7
2.2
2.7
A
0.25
0.35
0.45
A
0.3
0.6
Ω
0.02
10
µA
LX On-Resistance
RLXON
LX Leakage Current
ILXOFF
VLX = 28V
COMP Maximum Output Current
ICOMP
FB = GND
100
200
µA
∆FB = 0.1V
0.8
1
mmho
COMP Current vs. FB Voltage
Transconductance
SHDN Input Logic Low
VIL
SHDN Input Logic High
VIH
0.8
V
1
µA
300
kHz
2.0
V
SHDN = GND or VL
Shutdown Input Current
2
MIN
3
Input Voltage
Switching Frequency
f
200
250
Maximum Duty Cycle
DC
90
95
_______________________________________________________________________________________
%
28V, PWM, Step-Up DC-DC Converter
MAX618
ELECTRICAL CHARACTERISTICS
(VIN = +6V, PGND = GND, CVL = 4.7µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
V
VIN = 3V to 28V, VFB = 1.6V, SHDN = VL
800
µA
IIN
VIN = 3V to 5.5, VFB = 1.4V, SHDN = VL = IN
7.5
mA
IIN
VIN = 3.4V to 28V, VFB = 1.4V, SHDN = VL,
VL < VIN
4
mA
Supply Current Shutdown
IIN
VIN = 28V, VFB = 1.6V, SHDN = GND
VL Output Voltage
VVL
VIN = 3.5V or 28V, no load
VL Undervoltage Lockout
VVL
Rising edge, 1% hysteresis
FB Set Voltage
VFB
VIN
Supply Current, No Load
IIN
Supply Current, Full Load,
VL Connected to IN
Supply Current, Full Load
LX Voltage Range
VLXON
LX Switch Current Limit
ILXON
LX On-Resistance
RLXON
Switching Frequency
3
UNITS
28
Input Voltage
10
µA
3.3
V
2.55
2.85
V
1.455
1.545
V
28
V
2.85
1.4
PWM mode
188
f
3
A
0.6
Ω
312
kHz
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25°C.)
VIN = 8V
90
VIN = 3V
60
50
40
VIN = 3V
70
60
50
40
30
30
20
20
10
10
0
VIN = 5V
80
VIN = 5V
70
VIN = 12V
90
EFFICIENCY (%)
EFFICIENCY (%)
80
100
MAX618 toc01
100
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 28V)
MAX618 toc02
EFFICIENCY vs. OUTPUT CURRENT
(VOUT = 12V)
0
0.1
1
10
100
OUTPUT CURRENT (mA)
1000
0.1
1
10
100
OUTPUT CURRENT (mA)
1000
_______________________________________________________________________________________
3
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25°C.)
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
0.50
550
VIN = 5V
500
VIN = 8V
450
400
0.45
3.5
SHUTDOWN CURRENT (µA)
0.55
600
MAX618 toc06
VIN = 3V
650
SUPPLY CURRENT (µA)
0.60
4.0
MAX618 toc05
700
MAX618 toc04
0.65
SUPPLY CIRRENT (mA)
3.0
2.5
2.0
1.5
1.0
0.5
350
INCLUDES CAPACITOR LEAKAGE CURRENT
0
300
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
-50
-30
-10
10 30 50 70
TEMPERATURE (°C)
90
MAX618 toc09
0
VLX
(10V/div)
VOUT
(100mV/div)
VOUT
(100mV/
div)
3V
2ms/div
IOUT = 200mA, VOUT = 12V
VIN = 5V, VOUT = 12V, IOUT = 500mA
VIN = 5V, VOUT = 12V, IOUT = 200mA
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
SHUTDOWN RESPONSE
LOAD-TRANSIENT RESPONSE
MAX618 toc11
MAX618 toc10
1.6
SHDN
(2V/div)
0
12V
IOUT
(100mA/div)
VOUT
(2V/div)
5V
4
6V
VIN
(5V/div)
2µs/div
2µs/div
0
32
VOUT
(50mV/div)
0
VLX
(10V/div)
VOUT
(200mV/div)
27
LINE-TRANSIENT RESPONSE
IL
(1A/div)
VIN = 5V, VOUT = 12V
12
17
22
SUPPLY VOLTAGE (V)
MAX618 toc08
MAX618 toc07
5ms/div
7
HEAVY-LOAD SWITCHING
WAVEFORMS
MEDIUM-LOAD SWITCHING
WAVEFORMS
IL
(1A/div)
2
110
500µs/div
VIN = 5V, VOUT = 12V, ILOAD = 500mA
VOUT = 12V
1.4
MAX618 toc12
0.40
MAXIMUM OUTPUT CURRENT (A)
MAX618
28V, PWM, Step-Up DC-DC Converter
1.2
1.0
0.8
0.6
0.4
0.2
0
2
3
4
5 6 7 8 9
INPUT VOLTAGE (V)
_______________________________________________________________________________________
10 11 12
28V, PWM, Step-Up DC-DC Converter
PIN
NAME
FUNCTION
1, 8, 9,
12, 16
GND
2, 3, 4
LX
5
SHDN
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 capacitance value shown in Table 2.
7
FB
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
Ground
Drain of internal N-channel switch. Connect the inductor between IN and LX.
Power Ground, source of internal N-channel switch
_______________ Detailed Description
L
3V TO 28V
VIN
CIND
ECB1Q503L
LX
IN
COUT
1µF
VOUT
UP TO 28V
MAX618
SHDN
R1
PGND
VL
PWM Control Scheme and
Idle Mode Operation
FB
4.7µF
CP
R2
GND
COMP
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.
CCOMP
VOUT
R1
R2
CIND
L
COUT
CP
CCOMP
8V
12V
28V
402kΩ
715kΩ
574kΩ
93.1kΩ
100kΩ
32.4kΩ
150µF
100µF
86µF
12µH
15µH
39µH
150µF
100µH
33µF
220pF
56pF
47pF
0.082µF
0.1µF
0.47µF
Figure 1. Single-Supply Operation
The MAX618 combines continuous-conduction PWM
operation at medium to high loads and Idle Mode operation 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 slopecompensation signal in one circuit block. When the
switch turns off, energy transfers from the inductor to
_______________________________________________________________________________________________________
5
MAX618
Pin Description
MAX618
28V, PWM, Step-Up DC-DC Converter
IDLE MODE
CURRENT LIMIT
MAX618
PWM
CURRENT LIMIT
CURRENTSENSE
CIRCUIT
PGND
IN
VL
ERROR
COMPARATOR
PWM
LOGIC
NMOS
R
250kHz
OSCILLATOR
GND
SLOPE
COMPENSATION
LX
FB
14R
REFERENCE
INTEGRATOR
SHDN
THERMAL
SHUTDOWN
SHUTDOWN
OUT
COMP
LINEAR
REGULATOR
IN
VL
Figure 2. Functional Diagram
the output capacitor. Output current is limited by the 2A
MOSFET current limit 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
6
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 undervoltage lockout. Bypass VL with a 4.7µF
ceramic capacitor placed as close to the VL and GND
pins as possible.
_______________________________________________________________________________________
_______________________________________________________________________________________
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
4
5
6
7
0.20 0.20 0.18 0.15
0.18 0.21 0.20
0.16 0.20
0.15
8
0.12
0.17
0.21
0.20
0.17
9
0.10
0.15
0.19
0.21
0.19
0.19
10
0.09
0.13
0.17
0.20
0.21
0.18
0.20
11
0.08
0.12
0.16
0.19
0.21
0.20
0.17
0.21
12
0.07
0.10
0.14
0.18
0.20
0.21
0.20
0.16
0.22
13
0.06
0.09
0.13
0.16
0.19
0.20
0.21
0.19
0.15
0.23
14
0.05
0.08
0.11
0.15
0.17
0.20
0.21
0.20
0.19
0.15
0.24
15
0.04
0.07
0.10
0.13
0.16
0.19
0.20
0.21
0.20
0.18
0.16
0.25
16
0.04
0.07
0.09
0.12
0.15
0.17
0.19
0.21
0.21
0.20
0.17
0.17
0.25
VOUT
17
0.04
0.06
0.09
0.11
0.14
0.16
0.18
0.20
0.21
0.21
0.19
0.17
0.18
0.26
18
0.03
0.05
0.08
0.10
0.13
0.15
0.18
0.19
0.20
0.21
0.20
0.19
0.16
0.19
0.26
19
0.03
0.05
0.07
0.10
0.12
0.14
0.17
0.18
0.20
0.21
0.21
0.20
0.18
0.16
0.20
0.27
20
0.03
0.04
0.07
0.09
0.11
0.13
0.16
0.17
0.19
0.20
0.21
0.21
0.20
0.18
0.15
0.20
0.27
21
0.03
0.04
0.06
0.08
0.10
0.13
0.15
0.17
0.18
0.20
0.20
0.21
0.20
0.19
0.17
0.15
0.21
0.27
22
0.03
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.17
0.19
0.20
0.21
0.21
0.20
0.19
0.17
0.16
0.21
0.28
23
0.02
0.03
0.05
0.07
0.09
0.11
0.13
0.15
0.17
0.18
0.19
0.20
0.21
0.21
0.20
0.19
0.17
0.17
0.22
0.28
24
0.02
0.03
0.05
0.07
0.08
0.10
0.12
0.14
0.16
0.18
0.19
0.20
0.21
0.21
0.20
0.20
0.18
0.16
0.17
0.22
0.28
25
0.02
0.03
0.04
0.06
0.08
0.10
0.12
0.13
0.15
0.17
0.18
0.19
0.20
0.21
0.21
0.20
0.19
0.18
0.16
0.18
0.23
0.28
26
0.02
0.03
0.04
0.06
0.07
0.09
0.11
0.13
0.14
0.16
0.17
0.19
0.20
0.20
0.21
0.21
0.20
0.19
0.18
0.15
0.18
0.23
0.29
27
0.02
0.03
0.04
0.05
0.07
0.09
0.10
0.12
0.14
0.15
0.17
0.18
0.19
0.20
0.21
0.21
0.21
0.20
0.19
0.17
0.15
0.19
0.24
0.29
28
0.02
0.03
0.04
0.05
0.07
0.08
0.10
0.11
0.13
0.15
0.16
0.17
0.19
0.20
0.20
0.21
0.21
0.20
0.20
0.19
0.17
0.15
0.19
0.24
0.29
MAX618
VIN
Table 1. PWM/Idle-Mode Transition Load Current (IOUT in Amps) vs. Input and Output Voltage
28V, PWM, Step-Up DC-DC Converter
7
MAX618
28V, PWM, Step-Up DC-DC Converter
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.
Operating Configurations
The MAX618 can be connected in one of three configurations 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.
Table 2. Input Configurations
CIRCUIT
CONNECTION
VIN
RANGE
Figure 1
Input voltage connects
to IN and inductor.
3V to VOUT
(up to 28V)
IN and VL connect
together. Inductor voltage supplied by a
separate source.
Figure 3
INDUCTOR
VOLTAGE
2.7V to 5.5V
BENEFITS/COMMENTS
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.
0 to VOUT
(up to 28V)
• Increased efficiency.
• 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.
• Input power source (inductor voltage) is separate from the
IN and inductor voltage supplied by separate sources.
Figure 4
VIND
UP TO 28V
0 to VOUT
(up to 28V)
3V to 28V
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.
VIND
UP TO 28V
L
CIND
IN
2.7V TO 5.5V
L
CIND
OUT
UP TO 28V
IN
IN
3V TO 28V
1µF
COUT
MAX618
R1
SHDN
LX
1µF
COUT
MAX618
OUT
UP TO 28V
IN
LX
SHDN
PGND
R1
PGND
VL
VL
4.7µF
COMP
CCOMP
4.7µF
FB
CP
R2
GND
Figure 3. Dual-Supply Operation (VIN = 2.7V to 5.5V)
8
FB
COMP
CP
CCOMP
R2
GND
Figure 4. Dual-Supply Operation (VIN = 3V to 28V)
_______________________________________________________________________________________
28V, PWM, Step-Up DC-DC Converter
OPEN-DRAIN
LOGIC
MAX618
MAX618
MAX618
IN
VL
SYSTEM
LOGIC SUPPLY
100k
VL
SHDN
ON/OFF
CONTROL
SYSTEM LOGIC
Figure 5. Adding On/Off Control to Circuit of Figure 1 or 4
SHDN
ON/OFF
CONTROL
Figure 6. Adding On/Off Control to Circuit of Figure 3
Shutdown Mode
Determining the Inductor Value
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.
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:
__________________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:
⎛V
⎞
R1 = R2 ⎜ OUT − 1⎟
V
⎝ FB
⎠
where VFB is 1.5V.
L=
VOUT
7 ⋅ 10 5
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:
V
⎛ V ⎞ ⎛ ( VOUT − VI N ) ⎞
ILX(PEAK) = IOUT OUT + 2µ s ⎜ IN ⎟ ⎜
⎟
⎝ L ⎠⎝
VIN
VOUT
⎠
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.
_______________________________________________________________________________________
9
MAX618
28V, PWM, Step-Up DC-DC Converter
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 capacitor 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 (CCOMP) sets the dominant pole in the MAX618’s transfer function. The proper
compensation 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:
10
C COMP =
C COMP (Table 5)⋅ C OUT
C OUT (Table 4)
Pole Compensation Capacitor
The pole capacitor (CP) cancels the unwanted zero
introduced by COUT’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:
R ESR ⋅ C OUT (R1 + R2)
R1 ⋅ R2
CP =
where RESR is COUT’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.
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns,
go to www.maxim-ic.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
DOCUMENT NO.
16 QSOP
EF16+8F
21-0055
______________________________________________________________________________________
______________________________________________________________________________________
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
VIN
4
5
6
7
0.77 0.59 0.49 0.41
0.96 0.76 0.64
1.09 0.89
1.18
8
0.34
0.56
0.76
0.99
1.26
9
0.29
0.49
0.67
0.85
1.07
1.32
10
0.25
0.43
0.60
0.76
0.93
1.13
1.37
11
0.22
0.38
0.54
0.68
0.83
1.00
1.19
1.41
12
0.20
0.34
0.50
0.63
0.76
0.90
1.06
1.24
1.44
13
0.18
0.31
0.45
0.58
0.70
0.82
0.96
1.11
1.28
1.47
14
0.17
0.28
0.41
0.54
0.65
0.76
0.88
1.01
1.15
1.31
1.49
15
0.15
0.26
0.37
0.50
0.60
0.71
0.81
0.93
1.05
1.19
1.34
1.52
16
0.14
0.24
0.34
0.46
0.57
0.66
0.76
0.86
0.97
1.10
1.23
1.37
1.53
VOUT
17
0.13
0.22
0.32
0.42
0.53
0.62
0.71
0.81
0.91
1.02
1.13
1.26
1.40
1.55
18
0.12
0.21
0.30
0.39
0.50
0.59
0.67
0.76
0.85
0.95
1.05
1.16
1.29
1.42
1.57
19
0.12
0.19
0.28
0.37
0.46
0.56
0.64
0.72
0.80
0.89
0.99
1.09
1.19
1.31
1.44
1.58
20
0.11
0.18
0.26
0.34
0.43
0.53
0.61
0.68
0.76
0.84
0.93
1.02
1.12
1.22
1.33
1.46
1.59
21
0.10
0.17
0.25
0.32
0.41
0.50
0.58
0.65
0.72
0.80
0.88
0.96
1.05
1.14
1.25
1.36
1.47
1.60
22
0.10
0.16
0.23
0.31
0.38
0.47
0.55
0.62
0.69
0.76
0.83
0.91
0.99
1.08
1.17
1.27
1.37
1.49
1.61
23
0.09
0.16
0.22
0.29
0.36
0.44
0.53
0.59
0.66
0.73
0.80
0.87
0.94
1.02
1.11
1.20
1.29
1.39
1.50
1.62
24
0.09
0.15
0.21
0.28
0.35
0.42
0.50
0.57
0.63
0.70
0.76
0.83
0.90
0.97
1.05
1.13
1.22
1.31
1.41
1.51
1.63
25
0.08
0.14
0.20
0.26
0.33
0.40
0.47
0.55
0.61
0.67
0.73
0.79
0.86
0.93
1.00
1.07
1.15
1.24
1.33
1.42
1.53
1.64
26
0.08
0.14
0.19
0.25
0.31
0.38
0.45
0.52
0.58
0.64
0.70
0.76
0.82
0.89
0.95
1.02
1.10
1.18
1.26
1.35
1.44
1.54
1.64
27
0.08
0.13
0.18
0.24
0.30
0.36
0.43
0.50
0.56
0.62
0.67
0.73
0.79
0.85
0.91
0.98
1.05
1.12
1.20
1.28
1.36
1.45
1.55
1.65
28
0.07
0.12
0.18
0.23
0.29
0.35
0.41
0.47
0.54
0.60
0.65
0.71
0.76
0.82
0.88
0.94
1.00
1.07
1.14
1.22
1.29
1.38
1.46
1.56
1.66
MAX618
Table 3. Typical Output Current vs. Input and Output Voltages
28V, PWM, Step-Up DC-DC Converter
11
12
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
VIN
4
173
5
128
151
6
100
118
132
7
80
96
107
117
8
65
80
90
97
104
9
54
68
77
83
89
94
10
46
59
67
72
77
82
86
11
40
51
59
64
68
72
76
79
12
35
45
52
57
61
64
67
70
73
Table 4. Minimum COUT for Stability (µF)
13
31
39
46
51
55
58
61
63
66
68
14
28
35
41
46
50
52
55
57
59
62
64
15
25
32
37
42
45
48
50
52
54
56
58
60
16
23
29
34
38
42
44
46
48
50
51
53
55
56
VOUT
17
21
27
31
35
39
41
42
44
46
47
49
50
52
53
18
19
24
29
32
35
38
39
41
43
44
45
47
48
49
50
19
18
23
26
30
33
35
37
38
40
41
42
43
44
46
47
48
20
17
21
25
28
30
33
34
36
37
38
39
40
42
43
44
45
46
21
15
20
23
26
28
31
32
34
35
36
37
38
39
40
41
42
43
43
22
15
18
21
24
26
29
30
32
33
34
35
36
37
37
38
39
40
41
42
23
14
17
20
23
25
27
29
30
31
32
33
34
35
35
36
37
38
38
39
40
24
13
16
19
21
23
25
27
28
29
30
31
32
33
33
34
35
36
36
37
38
38
25
12
15
18
20
22
24
25
27
28
29
29
30
31
32
32
33
34
34
35
36
36
37
26
12
15
17
19
21
22
24
25
26
27
28
29
29
30
31
31
32
33
33
34
34
35
35
27
11
14
16
18
20
21
23
24
25
26
27
27
28
29
29
30
30
31
32
32
33
33
34
34
28
10
13
15
17
19
20
21
23
24
25
25
26
27
27
28
28
29
29
30
31
31
32
32
33
33
MAX618
28V, PWM, Step-Up DC-DC Converter
______________________________________________________________________________________
______________________________________________________________________________________
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
VIN
4
40
5
46
42
6
54
45
43
7
64
51
45
44
8
73
58
49
45
45
9
83
66
54
48
45
46
10
94
74
60
52
47
45
46
11
105
82
67
57
50
47
46
47
12
118
91
75
62
54
49
47
46
47
13
130
100
81
68
58
52
48
46
46
48
14
143
109
88
74
63
56
51
48
46
47
48
15
157
119
96
80
68
60
54
50
48
47
47
49
16
172
130
103
86
74
64
57
52
49
47
47
47
49
VOUT
17
187
141
111
92
79
68
61
55
51
49
47
47
47
49
18
203
152
120
99
85
73
64
58
54
50
48
47
47
48
49
19
219
164
128
105
90
78
68
61
56
52
50
48
47
47
48
50
20
236
176
137
112
95
83
73
65
59
55
52
49
48
47
47
48
50
21
253
188
147
119
101
88
77
69
62
57
54
51
49
48
47
47
48
50
22
271
201
156
127
107
93
82
72
65
60
56
53
50
49
48
47
47
48
50
23
290
214
166
134
113
98
86
77
69
63
58
55
52
50
48
48
47
48
49
50
24
309
228
176
142
119
103
91
81
72
66
61
57
53
51
49
48
48
47
48
49
50
25
329
242
187
150
125
108
95
85
76
69
63
59
55
53
51
49
48
48
47
48
49
51
26
349
257
197
159
132
113
99
89
80
72
66
61
57
54
52
50
49
48
48
48
48
49
51
27
370
272
209
167
139
119
104
93
84
75
69
64
59
56
53
51
50
49
48
48
48
48
49
51
28
391
287
220
176
146
124
109
97
88
79
72
66
62
58
55
53
51
49
48
48
48
48
48
49
51
MAX618
Table 5. Minimum CCOMP for Stability (nF)
28V, PWM, Step-Up DC-DC Converter
13
MAX618
28V, PWM, Step-Up DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/99
1
12/09
DESCRIPTION
Initial release
PAGES
CHANGED
—
Updated part to lead-free, added soldering temperatures (reflow), and corrected error in
equation
1, 2, 10
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
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