Datasheet

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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, 0.3Ω 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™ 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

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

MAX618

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

________________________________________________________________

Maxim Integrated Products

GND GND

PGND

GND

TOP VIEW

MAX618

QSOP

COMP

SHDN

GND

PGND

OUT

UP TO 28V

COMP

SHDN

GND

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

Summary of content (14 pages)

PAGE 1
9-1462; 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.
PAGE 2
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.
PAGE 3
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.
PAGE 4
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.
PAGE 5
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.
PAGE 6
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.
PAGE 7
_______________________________________________________________________________________ 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.
PAGE 8
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.
PAGE 9
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).
PAGE 10
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.
PAGE 11
______________________________________________________________________________________ 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.
PAGE 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.
PAGE 13
______________________________________________________________________________________ 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
PAGE 14
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.