MAX618EEE+T - Maxim - Pdf.Support

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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, 0.3Ωswitch

eliminates the need for external power MOSFETs while

supplying output currents up to 500mA or more. A

PWM control scheme combined with Idle Mode™ oper-

ation 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 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

Automotive-Powered DC-DC Converters

Industrial +24V and +28V Systems

LCD Displays

Palmtop Computers

Features

oAdjustable Output Voltage Up to +28V

oUp to 93% Efficiency

oWide Input Voltage Range (+3V to +28V)

oUp to 500mA Output Current at +12V

o500µA Quiescent Supply Current

o3µA Shutdown Current

o250kHz Switching Frequency

oSmall 1W, 16-Pin QSOP Package

MAX618

28V, PWM, Step-Up DC-DC Converter

________________________________________________________________

Maxim Integrated Products

GND GND

PGND

GND

TOP VIEW

MAX618

QSOP

COMP

SHDN

GND

PGND

VOUT

UP TO 28V

COMP

SHDN

GND

VIN

3V TO 28V

MAX618

Typical Operating Circuit

Denotes a lead(Pb)-free/RoHS-compliant package.

19-1462; Rev 1; 12/09

Pin Configuration

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products, Inc.

16 QSOP

PIN-PACKAGETEMP. RANGE

-40°C to +85°CMAX618EEE+

PART

EVALUATION KIT

AVAILABLE

MAX618

28V, PWM, Step-Up DC-DC Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.)

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.

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.2of copper.

Shutdown Supply Current IIN 38

μA

VIN = 28V, VFB = 1.6V, SHDN = GND

Maximum Duty Cycle DC 90 95 %

PARAMETER SYMBOL MIN TYP MAX UNITS

VL Output Voltage VVL 2.9 3.05 3.2 V

Supply Current, Full Load IIN 2.5 3.5 mA

Supply Current, Full Load, VL

Connected to IN IIN 5 6.5 mA

VL Load Regulation ΔVVL 25 40 mV

VL Undervoltage Lockout 2.58 2.7 2.8 V

FB Set Voltage VFB 1.47 1.5 1.53 V

FB Input Bias Current IFB 150

Supply Current, No Load

Input Voltage VIN 328

IIN 500 700 μA

Line Regulation ΔVOUT 0.01 0.08 %/V

Load Regulation ΔVOUT 0.2 %

LX Voltage VLX 28 V

LX Switch Current Limit ILXON 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 0.02 10 μA

COMP Maximum Output Current ICOMP 100 200 μA

COMP Current vs. FB Voltage

Transconductance 0.8 1 mmho

SHDN Input Logic Low VIL 0.8 V

SHDN Input Logic High VIH 2.0 V

Shutdown Input Current 1μA

Switching Frequency f200 250 300 kHz

CONDITIONS

VIN = 3V to 6V, VOUT = 12V

VIN = 3.5V or 28V, no load

VOUT = 12V, ILOAD = 10mA to 500mA

VIN = 3.4V to 28V, VFB = 1.4V, SHDN = VL,

VVL < VIN

VIN = 3V to 5.5V, VFB = 1.4V, SHDN = VL = IN

ILOAD = 0 to 2mA, VFB = 1.6V

Rising edge, 1% hysteresis

PWM mode

VFB = 1.6V

VLX = 28V

FB = GND

VIN = 3V to 28V, VFB = 1.6V, SHDN = VL

ΔFB = 0.1V

SHDN = GND or VL

MAX618

28V, PWM, Step-Up DC-DC Converter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VIN = +6V, PGND = GND, CVL = 4.7μF, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

100

0.1 1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(VOUT = 12V)

MAX618 toc01

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 8V

VIN = 5V

VIN = 3V

100

0.1 1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(VOUT = 28V)

MAX618 toc02

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 12V

VIN = 5V

VIN = 3V

Typical Operating Characteristics

(Circuit of Figure 1, TA= +25°C.)

Note 2: Specifications to -40°C are guaranteed by design, not production tested.

PARAMETER SYMBOL MIN TYP MAX UNITS

Supply Current, Full Load IIN 4mA

Supply Current, Full Load,

VL Connected to IN IIN 7.5 mA

Supply Current Shutdown IIN 10 μA

VL Output Voltage VVL 2.85 3.3 V

Supply Current, No Load

Input Voltage VIN 328

IIN 800 μA

VL Undervoltage Lockout VVL 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 1.4 3 A

LX On-Resistance RLXON 0.6 Ω

Switching Frequency f188 312 kHz

CONDITIONS

Rising edge, 1% hysteresis

VIN = 3.4V to 28V, VFB = 1.4V, SHDN = VL,

VL < VIN

VIN = 3V to 5.5, VFB = 1.4V, SHDN = VL = IN

VIN = 28V, VFB = 1.6V, SHDN = GND

PWM mode

VIN = 3.5V or 28V, no load

VIN = 3V to 28V, VFB = 1.6V, SHDN = VL

MAX618

28V, PWM, Step-Up DC-DC Converter

4 _______________________________________________________________________________________

VOUT

(100mV/div)

VLX

(10V/div)

(1A/div)

MEDIUM-LOAD SWITCHING

WAVEFORMS

MAX618 toc07

VIN = 5V, VOUT = 12V, IOUT = 200mA

2μs/div

VOUT

(100mV/

div)

VLX

(10V/div)

(1A/div)

HEAVY-LOAD SWITCHING

WAVEFORMS

MAX618 toc08

VIN = 5V, VOUT = 12V, IOUT = 500mA

2μs/div

VOUT

(50mV/div)

VIN

(5V/div)

LINE-TRANSIENT RESPONSE

MAX618 toc09

IOUT = 200mA, VOUT = 12V

2ms/div

Typical Operating Characteristics (continued)

(Circuit of Figure 1, TA= +25°C.)

VOUT

(200mV/div)

IOUT

(100mA/div)

LOAD-TRANSIENT RESPONSE

MAX618 toc10

VIN = 5V, VOUT = 12V

5ms/div

12V

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 4567389101112

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

MAX618 toc12

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (A)

VOUT = 12V

0.40

0.45

0.55

0.50

0.60

0.65

0105 15202530

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE

MAX618 toc04

INPUT VOLTAGE (V)

SUPPLY CIRRENT (mA)

300

400

350

500

450

550

600

650

700

-50 -10 10-30 30507090110

SUPPLY CURRENT vs. TEMPERATURE

MAX618 toc05

TEMPERATURE (°C)

SUPPLY CURRENT (μA)

VIN = 8V

VIN = 5V

VIN = 3V

INCLUDES CAPACITOR LEAKAGE CURRENT

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

2127 17222732

SHUTDOWN CURRENT

vs. SUPPLY VOLTAGE

MAX618 toc06

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (μA)

_______________ 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 pro-

prietary 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 oper-

ation at light loads to provide high efficiency over a

wide range of load conditions. The MAX618 control

scheme actively monitors the output current and auto-

matically 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, continu-

ous-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

MAX618

28V, PWM, Step-Up DC-DC Converter

_______________________________________________________________________________________________________ 5

Pin Description

PGND

ECB1Q503L

1μF

4.7μF

COUT

CIND

VOUT

SHDN

GND

COMP

UP TO 28V

3V TO 28V

VIN

CCOMP

MAX618

VOUT R1 R2 CIND LC

OUT CPCCOMP

8V 402kΩ 93.1kΩ150μF12μH 150μF 220pF 0.082μF

12V 715kΩ 100kΩ100μF15μH 100μH 56pF 0.1μF

28V 574kΩ 32.4kΩ86μF39μH33μF 47pF 0.47μF

Figure 1. Single-Supply Operation

Feedback Input. Connect a resistor-divider network to set VOUT. FB threshold is 1.5V.FB7

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.

IN10

Internal 3.1V LDO Regulator Output. Bypass to GND with a 4.7μF capacitor.VL11

Power Ground, source of internal N-channel switchPGND13, 14, 15

Compensation Input. Bypass to GND with the capacitance value shown in Table 2.COMP6

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.

SHDN

Drain of internal N-channel switch. Connect the inductor between IN and LX.LX2, 3, 4

GroundGND

1, 8, 9,

12, 16

FUNCTIONNAME

MAX618

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 efficien-

cy 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 volt-

age 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 par-

allel: 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 inte-

grator capacitor (CCOMP), and the pole capacitor (CP)

from FB to GND. CPcancels 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 regula-

tor 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.

28V, PWM, Step-Up DC-DC Converter

6 _______________________________________________________________________________________

SHDN

MAX618

IDLE MODE

CURRENT LIMIT

PWM

CURRENT LIMIT

ERROR

COMPARATOR

250kHz

OSCILLATOR

SLOPE

COMPENSATION

LINEAR

REGULATOR

CURRENT-

SENSE

CIRCUIT

PGND IN

LX OUT

14R

COMP

NMOS

REFERENCE

INTEGRATOR

GND

SHUTDOWN

PWM

LOGIC

THERMAL

SHUTDOWN

Figure 2. Functional Diagram

MAX618

28V, PWM, Step-Up DC-DC Converter

_______________________________________________________________________________________ 7

45678910111213141516171819202122232425262728

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

4 0.18 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

8 0.19 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

9 0.20 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

VOUT

VIN

Table 1. PWM/Idle-Mode Transition Load Current (IOUT in Amps) vs. Input and Output Voltage

MAX618

28V, PWM, Step-Up DC-DC Converter

8 _______________________________________________________________________________________

GND

COUT

PGND

COMP

CCOMP

SHDN

UP TO 28V

VIND

UP TO 28V

CIND

IN OUT

MAX618

2.7V TO 5.5V

4.7μF

1μF

CIND

COUT

PGND

GND

COMP

CCOMP

SHDN

UP TO 28V

VIND

UP TO 28V

OUT

MAX618

3V TO 28V

4.7μF

1μF

Figure 3. Dual-Supply Operation (VIN = 2.7V to 5.5V) Figure 4. Dual-Supply Operation (VIN = 3V to 28V)

Table 2. Input Configurations

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 power-

ing VL and VIN directly from the logic supply as shown

in Figure 3.

Operating Configurations

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 pro-

viding 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.

CIRCUIT

Figure 1 Input voltage connects

to IN and inductor.

CONNECTION VIN

RANGE

3V to VOUT

(up to 28V) VIN

INDUCTOR

VOLTAGE BENEFITS/COMMENTS

• 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

Figure 4 0 to VOUT

(up to 28V)

0 to VOUT

(up to 28V)

• Increased efficiency.

• SHDN can be driven by logic powered from the supply con-

nected 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

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.

IN and inductor volt-

age supplied by sepa-

rate sources.

IN and VL connect

together. Inductor volt-

age supplied by a

separate source.

2.7V to 5.5V

3V to 28V

Shutdown Mode

In shutdown mode (SHDN = 0), the MAX618’s feed-

back 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 exter-

nal 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 volt-

age. First, select a value for R2 between 10kΩand

200kΩ. Calculate R1 with:

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:

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 gener-

ally appropriate (see MAX618 EV kit data sheet).

Calculate the peak inductor current with the following

equation:

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 cur-

rent, and that its breakdown voltage exceeds the out-

put voltage.

V2s V

LX(PEAK) OUT OUT

IN OUT I

⎛

⎝

⎜⎞

⎠

⎟−

μNN

OUT

()

⎛

⎝

⎜⎞

⎠

⎟

LVOUT

=⋅710

RRV

OUT

12 1=−

⎛

⎝

⎜⎞

⎠

⎟

MAX618

28V, PWM, Step-Up DC-DC Converter

_______________________________________________________________________________________ 9

MAX618

100k

ON/OFF

CONTROL

OPEN-DRAIN

LOGIC

SHDN

MAX618

SYSTEM LOGIC ON/OFF

CONTROL

SHDN

SYSTEM

LOGIC SUPPLY

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

28V, PWM, Step-Up DC-DC Converter

10 ______________________________________________________________________________________

Maximum Output Current

The MAX618’s 2.2A LX current limit determines the

output power that can be supplied for most applica-

tions. In some cases, particularly when the input volt-

age 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 40mΩinductor resistance.

Capacitor Selection

Input Capacitors

The input bypass capacitor, CIND, reduces the input

ripple created by the boost configuration. High-imped-

ance 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 0.3Ωare gener-

ally 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 cur-

rent and the ESR of the output capacitor. ESR below

50mΩgenerates acceptable levels of output ripple for

most applications.

Integrator Capacitor

The compensation capacitor (CCOMP) sets the domi-

nant 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 capaci-

tance needed for the integrator capacitor with the fol-

lowing formula:

Pole Compensation Capacitor

The pole capacitor (CP) cancels the unwanted zero

introduced by COUT’s ESR, and thereby ensures stabil-

ity 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:

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 proto-

typing 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 resis-

tance, 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 possi-

ble 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.

CRC(R1R2)

R1 R2

PESR OUT

⋅⋅

CC Table C

C Table

COMP COMP OUT

OUT

=⋅()

()

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

16 QSOP EF16+8F 21-0055

MAX618

28V, PWM, Step-Up DC-DC Converter

______________________________________________________________________________________ 11

45678910111213141516171819202122232425262728

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

5 1.09 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

9 1.37 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

VIN

VOUT

Table 3. Typical Output Current vs. Input and Output Voltages

MAX618

28V, PWM, Step-Up DC-DC Converter

12 ______________________________________________________________________________________

45678910111213141516171819202122232425262728

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

4 151 118 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

6 117 97 83 72 64 57 51 46 42 38 35 32 30 28 26 24 23 21 20 19 18 17

7 104 89 77 68 61 55 50 45 42 39 35 33 30 28 26 25 23 22 21 20 19

8 9482726458524844413835333129272524222120

9 86766761555046423937343230292725242321

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

VIN

VOUT

Table 4. Minimum COUT for Stability (μF)

MAX618

28V, PWM, Step-Up DC-DC Converter

______________________________________________________________________________________ 13

45678910111213141516171819202122232425262728

3 40 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

5 43 45 49 54 60 67 75 81 88 96 103 111 120 128 137 147 156 166 176 187 197 209 220

6 44 45 48 52 57 62 68 74 80 86 92 99 105 112 119 127 134 142 150 159 167 176

7 45454750545863687479859095101107113119125132139146

8 464547495256606468737883889398103108113119124

9 4646474851545761646873778286919599104109

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

VOUT

VIN

Table 5. Minimum CCOMP for Stability (nF)

MAX618

28V, PWM, Step-Up DC-DC Converter

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.

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 6/99 Initial release —

1 12/09

Updated part to lead-free, added soldering temperatures (reflow), and corrected error in

equation 1, 2, 10