MAXIM MAX618 User Manual

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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, 0.3switch 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.
Applications
Automotive-Powered DC-DC Converters
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
MAX618
28V, PWM, Step-Up DC-DC Converter
________________________________________________________________ Maxim Integrated Products 1
Typical Operating Circuit
19-1462; Rev 0; 6/99
Pin Configuration
Ordering Information
Idle Mode is a trademark of Maxim Integrated Products.
16 QSOP
PIN-PACKAGETEMP. RANGE
-40°C to +85°CMAX618EEE
PART
EVALUATION KIT
AVAILABLE
V
TOP VIEW
16
15
PGND
14
PGND
13
PGND
12
GND
VL
11
10
IN
9
GND
1
GND GND
LX
2
LX
3
MAX618
4
LX
SHDN
5
COMP
6
FB
7
GND
8
QSOP
3V TO 28V
IN
IN
MAX618
SHDN
VL
COMP
LX
PGND
FB
GND
V
OUT
UP TO 28V
MAX618
28V, PWM, Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
IN
= +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 (T
A
= +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
Lead Temperature (soldering, 10sec) .............................+300°C
Note 1: With part mounted on 0.9 in.
2
of copper.
Shutdown Supply Current I
IN
38
µA
VIN= 28V, VFB= 1.6V, SHDN = GND
Maximum Duty Cycle DC 90 95 %
PARAMETER SYMBOL MIN TYP MAX UNITS
VL Output Voltage V
VL
2.9 3.05 3.2
V
Supply Current, Full Load I
IN
2.5 3.5
mA
Supply Current, Full Load, VL Connected to IN
I
IN
5 6.5
mA
VL Load Regulation ∆V
VL
25 40
mV
VL Undervoltage Lockout
2.58 2.7 2.8
V
FB Set Voltage V
FB
1.47 1.5 1.53
V
FB Input Bias Current I
FB
150
nA
Supply Current, No Load
Input Voltage V
IN
328
V
I
IN
500 700
µA
Line Regulation ∆V
OUT
0.01 0.08
%/V
Load Regulation ∆V
OUT
0.2
%
LX Voltage V
LX
28 V
LX Switch Current Limit I
LXON
1.7 2.2 2.7
A
Idle Mode Current-Limit Threshold
0.25 0.35 0.45
A
LX On-Resistance R
LXON
0.3 0.6
LX Leakage Current I
LXOFF
0.02 10 µA
COMP Maximum Output Current I
COMP
100 200 µA
COMP Current vs. FB Voltage Transconductance
0.8 1 mmho
SHDN Input Logic Low
V
IL
0.8 V
SHDN Input Logic High
V
IH
2.0 V
Shutdown Input Current 1 µA
Switching Frequency f 200 250 300 kHz
CONDITIONS
VIN= 3V to 6V, V
OUT
= 12V
VIN= 3.5V or 28V, no load
V
OUT
= 12V, I
LOAD
= 10mA to 500mA
VIN= 3.4V to 28V, VFB= 1.4V, SHDN = VL, V
VL
< V
IN
V
IN
= 3V to 5.5V, VFB= 1.4V, SHDN = VL = IN
I
LOAD
= 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
FB = 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
0.1 1 10 100 1000
EFFICIENCY vs. OUTPUT CURRENT
(V
OUT
= 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
(V
OUT
= 28V)
20
30
10
MAX618 toc02
OUTPUT CURRENT (mA)
EFFICIENCY (%)
40
50
60
70
80
90
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 I
IN
4
mA
Supply Current, Full Load, VL Connected to IN
I
IN
7.5
mA
Supply Current Shutdown I
IN
10
µA
VL Output Voltage V
VL
2.85 3.3
V
Supply Current, No Load
Input Voltage V
IN
328
V
I
IN
800
µA
VL Undervoltage Lockout V
VL
2.55 2.85
V
FB Set Voltage V
FB
1.455 1.545
V
LX Voltage Range V
LXON
28
V
LX Switch Current Limit I
LXON
1.4 3
A
LX On-Resistance R
LXON
0.6
Switching Frequency f
188 312
kHz
CONDITIONS
Rising edge, 1% hysteresis
VIN= 3.4V to 28V, VFB= 1.4V, SHDN = VL, VL < V
IN
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 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA= +25°C.)
0
V
OUT
(200mV/div)
I
OUT
(100mA/div)
LOAD-TRANSIENT RESPONSE
MAX618 toc10
VIN = 5V, V
OUT
= 12V
5ms/div
5V
12V
0
SHDN
(2V/div)
V
OUT
(2V/div)
SHUTDOWN RESPONSE
MAX618 toc11
VIN = 5V, V
OUT
= 12V, I
LOAD
= 500mA
500µs/div
0
0.4
0.2
0.6
1.2
1.4
1.0
0.8
1.6
2 45673 8 9 101112
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX618 toc12
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (A)
V
OUT
= 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
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)
MEDIUM-LOAD SWITCHING
I
L
(1A/div)
V
LX
(10V/div)
V
OUT
(100mV/div)
VIN = 5V, V
OUT
WAVEFORMS
2µs/div
= 12V, I
OUT
= 200mA
MAX618 toc07
HEAVY-LOAD SWITCHING
WAVEFORMS
I
L
(1A/div)
0
V
LX
(10V/div)
V
OUT
(100mV/
div)
2µs/div
VIN = 5V, V
OUT
= 12V, I
OUT
= 500mA
MAX618 toc08
V
(50mV/div)
0
(5V/div)
LINE-TRANSIENT RESPONSE
OUT
V
IN
I
= 200mA, V
MAX618 toc09
6V
3V
2ms/div
= 12V
_______________ 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 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
MAX618
28V, PWM, Step-Up DC-DC Converter
_______________________________________________________________________________________________________ 5
Pin Description
Figure 1. Single-Supply Operation
Feedback Input. Connect a resistor-divider network to set V
OUT
. 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 V
IN
less one diode drop.
SHDN
5
PIN
Drain of internal N-channel switch. Connect the inductor between IN and LX.LX2, 3, 4
GroundGND
1, 8, 9,
12, 16
FUNCTIONNAME
IN
SHDN
V
L
COMP
L
MAX618
PGND
IND
3V TO 28V
V
IN
C
IND
1µF
4.7µF
C
COMP
V
R1 R2 C
OUT
8V 402k 93.1k150µF12µH 150µF 220pF 0.082µF 12V 715k 100k 100µF15µH 100µH 56pF 0.1µF 28V 574k 32.4k86µF39µH33µF 47pF 0.47µF
LX
FB
GND
LC
ECB1Q503L
C
P
OUT
C
OUT
CPC
V
OUT
UP TO 28V
R1
R2
COMP
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