General Description
The MAX17067 boost converter incorporates high-
performance (at 1.2MHz), current-mode, fixed-frequency,
pulse-width modulation (PWM) circuitry with a built-in
0.15Ωn-channel MOSFET to provide a highly efficient
regulator with fast response.
High switching frequency (640kHz or 1.2MHz selectable)
allows for easy filtering and faster loop performance. An
external compensation pin provides the user flexibility in
determining loop dynamics, allowing the use of small,
low equivalent-series-resistance (ESR) ceramic output
capacitors. The device can produce an output voltage
as high as 18V.
Soft-start is programmed with an external capacitor, which
sets the input-current ramp rate. The MAX17067 is avail-
able in a space-saving 8-pin μMAX®package. The ultra-
small package and high switching frequency allow the
total solution to be less than 1.1mm high.
Application
LCD Displays
Features
o90% Efficiency
oAdjustable Output from VIN to 18V
o2.4A, 0.15Ω, 22V Power MOSFET
o+2.6V to +4.0V Input Range
oPin-Selectable 640kHz or 1.2MHz Switching
Frequency
oProgrammable Soft-Start
oSmall 8-Pin µMAX Package
oIntegrated Input Voltage Clamp Circuit
MAX17067
Low-Noise Step-Up DC-DC Converter
________________________________________________________________
Maxim Integrated Products
1
IN
LXGND
1
2
3
4
8
7
6
5
SS
FREQFB
COMP
μMAX
TOP VIEW
MAX17067
SHDN
LX
IN
VIN
2.6V TO 4V
GND
FREQ
VOUT
COMP
SHDN
FB
MAX17067
ON/OFF
SS
Typical Operating Circuit
19-3106; Rev 0; 1/08
Pin Configuration
Ordering Information
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.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX17067EUA+ -40°C to +85°C 8 μMAX U8+1
μMAX is a registered trademark of Maxim Integrated Products, Inc.
+
Denotes a lead-free package.
MAX17067
Low-Noise Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 3V, FREQ = 3V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)
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.
LX to GND ..............................................................-0.3V to +22V
SHDN, FREQ to GND ............................................-0.3V to +7.5V
IN to GND (Note 1) ...................................................-0.3V to +6V
SS, COMP, FB to GND ................................-0.3V to (VIN + 0.3V)
RMS LX Pin Current ..............................................................1.2A
Continuous Power Dissipation (TA= +70°C)
8-Pin μMAX (derate 4.1mW/°C above +70°C) ............330mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Supply Range VIN V
OUT < 18V 2.6 4.0 V
Output Voltage 18 V
Input Supply Clamp Voltage Use external limiting resistor; RIN = 100,
VIN = 10V (Note 3) 6.05 6.40 6.60 V
VIN Undervoltage Lockout UVLO VIN rising, typical hysteresis is 50mV, LX
remains off below this level 2.30 2.45 2.57 V
VFB = 1.3V, not switching 0.3 0.6
Quiescent Current IIN VFB = 1.0V, switching 1.5 2.5 mA
SHDN = GND, TA = +25°C 30 60
Shutdown Supply Current IIN SHDN = GND, TA = +85°C 30 μA
ERROR AMPLIFIER
Feedback Voltage VFB Level to produce VCOMP = 1.24V 1.23 1.24 1.25 V
FB Input Bias Current IFB V
FB = 1.24V 50 125 200 nA
Feedback-Voltage Line
Regulation
Level to produce VCOMP = 1.24V,
2.6V < VIN < 5.5V 0.05 0.15 %/V
Transconductance gmI = 5μA 100 240 440 μS
Voltage Gain AV 3800 V/V
OSCILLATOR
FREQ = GND 500 640 780
Frequency fOSC FREQ = IN 1000 1200 1400 kHz
Maximum Duty Cycle DC FREQ = GND, FREQ = IN 89 92 95 %
n-CHANNEL SWITCH
Current Limit ILIM V
FB = 1V, duty cycle = 68% (Note 4) 1.8 2.4 3.4 A
On-Resistance RON 150 275 m
Leakage Current ILXOFF V
LX = 20V 10 20 μA
Current-Sense Transresistance RCS 0.2 0.3 0.4 V/A
SOFT-START
Reset Switch Resistance 100
Charge Current VSS = 1.2V 2.5 4.5 6.5 μA
MAX17067
Low-Noise Step-Up DC-DC Converter
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 3V, FREQ = 3V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
ELECTRICAL CHARACTERISTICS (continued)
(VIN = SHDN = 3V, FREQ = 3V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CONTROL INPUTS
Input Low Voltage VIL SHDN, FREQ, VIN = 2.6V to 4.0V 0.3 x
VIN V
Input High Voltage VIH SHDN, FREQ, VIN = 2.6V to 4.0V 0.7 x
VIN V
Hysteresis SHDN, FREQ 0.1 x
VIN V
FREQ Pulldown Current IFREQ 3 6 9 μA
SHDN = GND, TA = +25°C -1 +1
SHDN Input Current ISHDN SHDN = GND, TA = +85°C 0 μA
Temperature rising 160
Thermal Shutdown Hysteresis 20
°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Supply Range VIN V
OUT < 18V 2.6 4.0 V
Output Voltage Range 18 V
Input Supply Clamp Voltage Use external limiting resistor;
RIN = 100, VIN = 10V (Note 3) 6.03 6.60 V
VIN Undervoltage Lockout UVLO VIN rising, typical hysteresis is 80mV, LX
remains off below this level 2.30 2.57 V
VFB = 1.3V, not switching 0.6
Quiescent Current IIN VFB = 1.0V, switching 2.5 mA
ERROR AMPLIFIER
Feedback Voltage VFB Level to produce VCOMP = 1.24V 1.227 1.253 V
FB Input Bias Current IFB V
FB = 1.24V 200 nA
Feedback-Voltage Line
Regulation
Level to produce VCOMP = 1.24V,
2.6V < VIN < 4.0V 0.15 %/V
Transconductance gmI = 5μA 100 440 μS
OSCILLATOR
FREQ = GND 450 830
Frequency fOSC FREQ = IN 950 1500 kHz
Maximum Duty Cycle DC FREQ = GND, FREQ = VIN 89 95 %
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA= +25°C, unless otherwise noted.)
MAX17067
Low-Noise Step-Up DC-DC Converter
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VIN = SHDN = 3V, FREQ = 3V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
n-CHANNEL SWITCH
Current Limit ILIM V
FB = 1V, duty cycle = 68% (Note 4) 1.8 3.4 A
On-Resistance RON V
IN = 3V 275
Current-Sense Transresistance RCS 0.19 0.40 V/A
SOFT-START
Reset Switch Resistance 100
Charge Current VSS = 1.2V 2.5 6.5 μA
CONTROL INPUTS
Input Low Voltage VIL SHDN, FREQ, VIN = 2.6V to 4.0V
0.3 x
VIN V
Input High Voltage VIH SHDN, FREQ, VIN = 2.6V to 4.0V 0.7 x
VIN V
Note 1: Limit on IN absolute maximum ratings is for operation without the use of an external resistor for the internal clamp circuit.
See the
IN Supply Clamp Circuit
section for IN voltage limits during clamping circuit operation.
Note 2: Limits are 100% production tested at TA= +25°C. Maximum and minimum limits over temperature are guaranteed by design
and characterization.
Note 3: See the
IN Supply Clamp Circuit
section to properly size the external resistor.
Note 4: Current limit varies with duty-cycle slope compensation. See the
Output-Current Capability
section.
MAX17067 toc01
50
1 100010010
EFFICIENCY vs. L0AD CURRENT
(VIN = 3.3V, VOUT = 9V)
70
90
80
100
60
LOAD CURRENT (mA)
EFFICIENCY (%)
fOSC = 1.2MHz
L = 3.3μH
fOSC = 640kHz
L = 4.7μH
-0.5
1 100010010
STEP-UP CONVERTER
LOAD REGULATION
0
1.0
0.5
MAX17067 toc02
LOAD CURRENT (mA)
REGULATION (%)
L = 3.3μH
INPUT VOLTAGE (V)
500
2.5 5.54.53.5 5.04.03.0
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
800
600
1200
1000
1400
900
700
1300
1100
MAX17067 toc03
SWITCHING FREQUENCY (kHz)
FREQ = IN
FREQ = GND
MAX17067
Low-Noise Step-Up DC-DC Converter
_______________________________________________________________________________________
5
0
0.5
2.5
2.0
1.5
1.0
3.5
3.0
4.0
2.5 2.9 3.1 3.32.7 3.5 3.7 3.9
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX17067 toc04
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
NONSWITCHING
SWITCHING
0V
0A
VOUT
5V/div
INDUCTOR
CURRENT
1A/div
SOFT-START
(RLOAD = 18Ω)
MAX17067 toc05
2ms/div
LOAD-TRANSIENT RESPONSE
(ILOAD = 10mA TO 200mA)
MAX17067 toc06
100μs/div
L = 3.3μH
RCOMP = 39kΩ
CCOMP1 = 620pF
IOUT
200mA/div
10mA
VOUT
500mA/div
AC-COUPLED
0V
INDUCTOR
CURRENT
500mA/div
0A
IOUT
1A/div
0.1A
9V
0V
0A
INDUCTOR
CURRENT
1A/div
VOUT
200mV/div
AC-COUPLED
10μs/div
PULSED LOAD-TRANSIENT RESPONSE
(ILOAD = 40mA TO 1.1A)
MAX17067 toc07
L = 3.3μH
RCOMP = 39kΩ
CCOMP1 = 620pF
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.3V, fOSC = 640kHz, TA= +25°C, unless otherwise noted.)
LX
5V/div
INDUCTOR
CURRENT
1A/div
0V
0A
1μs/div
SWITCHING WAVEFORMS
(ILOAD = 500mA)
MAX17067 toc08
MAX17067
Low-Noise Step-Up DC-DC Converter
6 _______________________________________________________________________________________
Pin Description
Switch Pin. Connect the inductor/catch diode to LX and minimize the trace area for lowest EMI.LX5
Supply Pin. Bypass IN with at least a 1μF ceramic capacitor directly to GND.IN6
Frequency Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high,
the frequency is 1.2MHz. This input has a 5μA pulldown current.
FREQ7
Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. Leave open for no soft-start. The soft-
start capacitor is charged with a constant current of 4μA. Full current limit is reached after t = 2.5 x105CSS.
The soft-start capacitor is discharged to ground when SHDN is low. When SHDN goes high, the soft-start
capacitor is charged to 0.5V, after which soft-start begins.
SS8
GroundGND4
Active-Low Shutdown Control Input. Drive SHDN low to turn off the MAX17067. SHDN
3
PIN
Feedback Pin. Reference voltage is 1.24V nominal. Connect an external resistor-divider tap to FB and
minimize the trace area. Set VOUT according to: VOUT = 1.24V (1 + R1 / R2). See Figure 1.
FB2
Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the
Loop
Compensation
section for component selection guidelines.
COMP1
FUNCTIONNAME
Detailed Description
The MAX17067 is a highly efficient power supply that
employs a current-mode, fixed-frequency PWM architec-
ture for fast-transient response and low-noise operation.
The device regulates the output voltage through a com-
bination of an error amplifier, two comparators, and sev-
eral signal generators (Figure 2). The error amplifier
compares the signal at FB to 1.24V and varies the
COMP output. The voltage at COMP determines the cur-
rent trip point each time the internal MOSFET turns on.
As the load varies, the error amplifier sources or sinks
current to the COMP output accordingly to produce the
inductor peak current necessary to service the load. To
maintain stability at high duty cycle, a slope-compensa-
tion signal is summed with the current-sense signal.
At light loads, this architecture allows the ICs to “skip”
cycles to prevent overcharging the output voltage. In
this region of operation, the inductor ramps up to a fixed
peak value, discharges to the output, and waits until
another pulse is needed again.
LX
IN
VIN
2.6V TO 4.0V
GND
FREQ
VOUT
COMP
SS
SHDN
FB
R1
R2
L
0.027μF
MAX17067 COUT
C1
10μF
6.3V
RCOMP
CCOMP
CCOMP2
D1
MBRS130LT1
CIN
640kHz
1.2MHz
ON/OFF
VIN
Figure 1. Typical Application Circuit
MAX17067
Low-Noise Step-Up DC-DC Converter
_______________________________________________________________________________________ 7
IN Supply Clamp Circuit
The MAX17067 features an internal clamp to allow appli-
cations where there is overvoltage stress on the supply
line. In many cases, high-voltage spikes happen on pro-
duction lines and are difficult to protect against. The
MAX17067’s internal clamp circuit can solve this prob-
lem. The internal clamp circuit limits the voltage at the IN
pin to 6.4V (typ) to protect the IN pin from a continuous
or transient overvoltage stress condition on the supply
line. To use the clamp circuit, put a series resistor (RIN)
between supply and IN, and a decoupling capacitor
(1μF typical) from IN to GND. To properly size the exter-
nal resistor, several factors should be considered:
• The maximum current for the clamp is 40mA, and the
clamp voltage at the IN pin is 6.05V (min). Therefore,
the external resistor is:
• Power dissipation in the clamp is in addition to the
total power loss.
• The external resistor causes a DC voltage drop in
the IN supply line. The voltage at the IN pin has to
be properly maintained when clamping is used. The
worst-case quiescent current of the IN pin is 2.5mA;
therefore, the worst-case voltage drop is 2.5mA
multiplied by RIN.
Output-Current Capability
The output-current capability of the MAX17067 is a
function of current limit, input voltage, operating fre-
quency, and inductor value. Because of the slope com-
pensation used to stabilize the feedback loop, the duty
cycle affects the current limit. The output-current capa-
bility is governed by the following equation:
IOUT(MAX) = [ILIM x (1.26 - 0.4 x Duty) -
0.5 x Duty x VIN/(fOSC x L)] x ηx VIN/VOUT
where:
ILIM = current limit specified at 68% (see the
Electrical
Characteristics
):
Duty = duty cycle = (VOUT - VIN + VDIODE)/
(VOUT - ILIM x RON + VDIODE)
VDIODE = catch diode forward voltage at ILIM
η= conversion efficiency, 85% nominal
RV
IN IN
≥
()
⎡
⎣⎤
⎦
-605 004..Ω
GND
LX
IN
FREQ
FB
COMP
4μA
5μA
N
ERROR
COMPARATOR
ERROR
AMPLIFIER
SKIP
COMPARATOR
SS
CLOCK
SKIP
BIAS
SHDN
MAX17067
ΣCURRENT
SENSE
CONTROL
AND DRIVER
LOGIC
SOFT-
START
SLOPE
COMPEN-
SATION
OSCILLATOR
∞
1.24V
Figure 2. Functional Diagram
MAX17067MAX17067
Low-Noise Step-Up DC-DC Converter
8 _______________________________________________________________________________________
Soft-Start
The MAX17067 can be programmed for soft-start upon
power-up with an external capacitor. When the shut-
down pin is taken high, the soft-start capacitor (CSS) is
immediately charged to 0.5V. Then the capacitor is
charged at a constant current of 4.5μA (typ). During
this time, the SS voltage directly controls the peak
inductor current, allowing 0A at VSS = 0.5V to the full
current limit at VSS = 1.5V. The maximum load current
is available after the soft-start cycle is completed.
When the shutdown pin is taken low, the soft-start
capacitor is discharged to ground.
Frequency Selection
The MAX17067’s frequency can be user selected to oper-
ate at either 640kHz or 1.2MHz. Connect FREQ to GND
for 640kHz operation. For a 1.2MHz switching frequen-
cy, connect FREQ to IN. This allows the use of small,
minimum-height external components while maintaining
low output noise. FREQ has an internal pulldown, allow-
ing the user the option of leaving FREQ unconnected
for 640kHz operation.
Shutdown
The MAX17067 is shut down to reduce the supply cur-
rent to 30μA when SHDN is low. In this mode, the inter-
nal reference, error amplifier, comparators, and biasing
circuitry turn off while the n-channel MOSFET is turned
off. The boost converter’s output is connected to IN by
the external inductor and catch diode.
Thermal-Overload Protection
Thermal-overload protection prevents excessive power
dissipation from overheating the MAX17067. When the
junction temperature exceeds TJ= +160°C, a thermal
sensor immediately activates the fault protection, which
shuts down the MAX17067, allowing the device to cool
down. Once the device cools down by approximately
20°C, it returns to normal operation.
Applications Information
Boost DC-DC converters using the MAX17067 can be
designed by performing simple calculations for a first
iteration. All designs should be prototyped and tested
prior to production. Table 1 provides a list of compo-
nents for a range of standard applications. Table 2 lists
component suppliers.
External component value choice is primarily dictated
by the output voltage and the maximum load current,
as well as maximum and minimum input voltages.
Begin by selecting an inductor value. Once L is known,
choose the diode and capacitors.
Inductor Selection
The minimum inductance value, peak current rating, and
series resistance are factors to consider when selecting
the inductor. These factors influence the converter’s effi-
ciency, maximum output load capability, transient-
response time, and output voltage ripple. Physical size
and cost are also important factors to be considered.
Table 2. Component Suppliers
847-639-6400
561-241-7876
847-956-0666
PHONE
847-639-1469Coilcraft
561-241-9339Coiltronics
847-956-0702Sumida USA
FAXSUPPLIER
803-946-0690
408-986-0424
619-661-6835
847-297-0070
803-626-3123AVX
408-986-1442KEMET
619-661-1055SANYO
847-699-1194TOKO
408-573-4150 408-573-4159Taiyo Yuden
Inductors
Capacitors
PHONE FAXSUPPLIER
516-435-1110
310-322-3331
516-543-7100
602-303-5454
847-843-7500
516-864-7630Zetex
847-843-2798Nihon
516-435-1824
Central
Semiconductor
310-322-3332
International
Rectifier
602-994-6430Motorola
Diodes
Table 1. Component Selection
VIN (V) VOUT (V) fOSC (Hz) L (μH) COUT (μF) RCOMP (k ) CCOMP (pF) CCOMP2
(pF)
IOUT(MAX)
(mA)
3.3 9 1.2M 3.3 10 121 620 10 250
3.3 9 640k 4.7 10 82 1000 10 250
MAX17067
Low-Noise Step-Up DC-DC Converter
_______________________________________________________________________________________ 9
The maximum output current, input voltage, output volt-
age, and switching frequency determine the inductor
value. Very high inductance values minimize the cur-
rent ripple and therefore reduce the peak current,
which decreases core losses in the inductor and I2R
losses in the entire power path. However, large induc-
tor values also require more energy storage and more
turns of wire, which increase physical size and can
increase I2R losses in the inductor. Low inductance val-
ues decrease the physical size but increase the current
ripple and peak current. Finding the best inductor
involves choosing the best compromise between circuit
efficiency, inductor size, and cost.
The equations used here include a constant LIR, which
is the ratio of the inductor peak-to-peak ripple current to
the average DC inductor current at the full load current.
The best trade-off between inductor size and circuit
efficiency for step-up regulators generally has an LIR
between 0.3 and 0.5. However, depending on the AC
characteristics of the inductor core material and the
ratio of inductor resistance to other power path resis-
tances, the best LIR can shift up or down. If the induc-
tor resistance is relatively high, more ripple can be
accepted to reduce the number of turns required and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can decrease losses throughout the power
path. If extremely thin high-resistance inductors are
used, as is common for LCD-panel applications, the
best LIR can increase to between 0.5 and 1.0.
Once a physical inductor is chosen, higher and lower
values of the inductor should be evaluated for efficiency
improvements in typical operating regions.
Calculate the approximate inductor value using the typ-
ical input voltage (VIN), the maximum output current
(IMAIN(MAX)), the expected efficiency (ηTYP) taken from
an appropriate curve in the
Typical Operating
Characteristics
, and an estimate of LIR based on the
above discussion:
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input cur-
rent at the minimum input voltage VIN(MIN) using con-
servation of energy and the expected efficiency at that
operating point (ηMIN) taken from an appropriate curve
in the
Typical Operating Characteristics
:
Calculate the ripple current at that operating point and
the peak current required for the inductor:
The inductor’s saturation current rating and the
MAX17067s’ LX current limit (ILIM) should exceed IPEAK
and the inductor’s DC current rating should exceed
IIN(DC,MAX). For good efficiency, choose an inductor with
less than 0.1Ωseries resistance.
Considering the application circuit in Figure 4, the maxi-
mum load current (IMAIN(MAX)) is 250mA with a 9V output
and a typical input voltage of 3.3V. Choosing an LIR of 0.7
and estimating efficiency of 85% at this operating point:
Using the application’s minimum input voltage (3V) and
estimating efficiency of 80% at that operating point:
The ripple current and the peak current are:
IA
AA
PEAK =+≈094 051
2119...
IVVV
HV MHz A
RIPPLE =×−
×× ≈
393
33 9 12 051
()
..
.
μ
IAV
VA
IN DC MAX(, )
.
..=×
×≈
025 9
308 094
LV
V
VV
AMHz
=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜⎞
⎠
⎟
33
9
933
025 12
08
2
..
..
. 55
07 33
..
⎛
⎝
⎜⎞
⎠
⎟≈μH
II I
PEAK IN DC MAX RIPPLE
=+
(, ) 2
IVVV
LV f
RIPPLE
IN MIN MAIN IN MIN
MAIN OSC
=×−
××
() ()
()
IIV
V
IN DC MAX
MAIN MAX MAIN
IN MIN MIN
(, )
()
()
=×
×η
LV
V
VV
I f LIR
IN
MAIN
MAIN IN
MAIN MAX OSC
TYP
=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜⎞
⎠
⎟⎛
⎝
⎜⎞
⎠
⎟
2
()
η
MAX17067
Low-Noise Step-Up DC-DC Converter
10 ______________________________________________________________________________________
Diode Selection
The output diode should be rated to handle the output
voltage and the peak switch current. Make sure that the
diode’s peak current rating is at least IPK and that its
breakdown voltage exceeds VOUT. Schottky diodes are
recommended.
Input and Output Capacitor Selection
Low-ESR capacitors are recommended for input
bypassing and output filtering. Low-ESR tantalum
capacitors are a good compromise between cost and
performance. Ceramic capacitors are also a good
choice. Avoid standard aluminum electrolytic capaci-
tors. A simple equation to estimate input and output-
capacitor values for a given voltage ripple is as follows:
where VRIPPLE is the peak-to-peak ripple voltage on the
capacitor.
Output Voltage
The MAX17067 operates with an adjustable output from
VIN to 20V. Connect a resistor voltage-divider to FB
(see the
Typical Operating Circuit
) from the output to
GND. Select the resistor values as follows:
where VFB, the boost-regulator feedback set point, is
1.24V. Since the input bias current into FB is typically
zero, R2 can have a value up to 100kΩwithout sacrificing
accuracy. Connect the resistor-divider as close to the IC
as possible.
Loop Compensation
The voltage feedback loop needs proper compensation
to prevent excessive output ripple and poor efficiency
caused by instability. This is done by connecting a resis-
tor (RCOMP) and capacitor (CCOMP) in series from
COMP to GND, and another capacitor (CCOMP2) from
COMP to GND. RCOMP is chosen to set the high-fre-
quency integrator gain for fast-transient response, while
CCOMP is chosen to set the integrator zero to maintain
loop stability. The second capacitor, CCOMP2, is chosen
to cancel the zero introduced by output-capacitance
ESR. For optimal performance, choose the components
using the following equations:
RCOMP =(274Ω/A2x VIN xVOUT x COUT/(L x IOUT)
CCOMP ≅(0.36 x 10-3 A/Ω) x L/VIN
CCOMP2 ≅(0.0036 A/Ω) x RESR x L x IOUT/(VIN xVOUT)
For the ceramic output capacitor, where ESR is small,
CCOMP2 is optional. Table 1 shows experimentally verified
external component values for several applications.
The best gauge of correct loop compensation is by
inspecting the transient response of the MAX17067.
Adjust RCOMP and CCOMP as necessary to obtain opti-
mal transient performance.
Soft-Start Capacitor
The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate CSS to be:
where:
COUT = total output capacitance including any bypass
capacitor on the output bus
VOUT = maximum output voltage
IINRUSH = peak inrush current allowed
IOUT = maximum output current during power-up stage
VIN = minimum input voltage
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:
tMAX = 2.5 x 105CSS
C 21 10 C V V V
V I I V
SS 6OUT
IN OUT
IN INRUSH OUT OUT
OUT
2
>× × −×
×−×
⎛
⎝
⎜⎞
⎠
⎟
−
RRV
V
OUT
FB
12 1=−
⎛
⎝
⎜⎞
⎠
⎟
C
0.5 L I
V V
PK2
RIPPLE OUT
≥××
⎛
⎝⎞
⎠
×
MAX17067
Low-Noise Step-Up DC-DC Converter
______________________________________________________________________________________ 11
Application Circuits
1-Cell to 3.3V SEPIC Power Supply
Figure 3 shows the MAX17067 in a single-ended primary
inductance converter (SEPIC) topology. This topology is
useful when the input voltage can be either higher or
lower than the output voltage, such as when converting
a single lithium-ion (Li+) cell to a 3.3V output. L1A and
L1B are two windings on a single inductor. The coupling
capacitor between these two windings must be a low-
ESR type to achieve maximum efficiency, and must also
be able to handle high ripple currents. Ceramic capaci-
tors are best for this application. The circuit in Figure 3
provides 400mA output current at 3.3V output when
operating with an input voltage from +2.6V to +4.0V.
AMLCD Application
Figure 4 shows a power supply for active matrix (TFT-
LCD) flat-panel displays. Output-voltage transient per-
formance is a function of the load characteristic. Add or
remove output capacitance (and recalculate compen-
sation-network component values) as necessary to
meet transient performance. Regulation performance
for secondary outputs (VGOFF and VGON) depends on
the load characteristics of all three outputs.
LX
FB
C6
OPEN
C15
27nF R2
44.2kΩ
R1
274kΩ
FREQ
IN
VIN
2.6V TO 4.0V
VOUT
+9V/250mA
COMP
SHDN
SS
D1
GND
U1
MAX17067
C5
620pF
R5
121kΩ
C1
10μF
10V R3
10ΩC4
1μFR6
100kΩ
L1
3.3μH
6
4
5
2
1
3
7
8
C14
4.7μFC13
1μF
C12
1μF
D4 D2
1
3
2
2
1
C9
0.1μF
C11
0.1μF
VGOFF
-9V
VGON
+27V
3
C7
10μF
25V
D3 2
1
C10
0.1μF
3
Figure 4. Multiple-Output, Low-Profile (1.2mm max) TFT-LCD Power Supply
LX
IN
VIN
2.6V TO 4.0V
GND
L1 = CTX8-1P
COUT = TPSD226025R0200
C2
10μF
FREQ
VOUT
3.3V
CC
SS
SHDN
FB
D1
R1
1MΩ
R2
605kΩ
L1A
5.3μH
0.027μF
MAX17067 COUT
22μF
20V
C1
10μF
10V
RCOMP
CCOMP
CCOMP2
L1B
5.3μH
Figure 3. MAX17067 in a SEPIC Configuration
MAX17067
Layout Procedure
Good PCB layout and routing are required in high-fre-
quency switching power supplies to achieve good regu-
lation, high efficiency, and stability. It is strongly
recommended that the evaluation kit PCB layouts be fol-
lowed as closely as possible. Place power components
as close together as possible, keeping their traces short,
direct, and wide. Avoid interconnecting the ground pins
of the power components using vias through an internal
ground plane. Instead, keep the power components
close together and route them in a star ground configura-
tion using component-side copper, then connect the star
ground to internal ground using multiple vias.
Low-Noise Step-Up DC-DC Converter
12 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 3657
MAX17067
Low-Noise Step-Up DC-DC Converter
MAX17067
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.
13
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036
J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2 A1
c
eb
A
L
FRONT VIEW SIDE VIEW
E H
0.6±0.1
0.6±0.1
Ø0.50±0.1
1
TOP VIEW
D
8
A2 0.030
BOTTOM VIEW
1
6°
S
b
L
H
E
D
e
c
0°
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
AMIN
0.002 0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6°0°
0.13 0.18
MAX
MIN
MILLIMETERS
- 1.10
0.05 0.15
α
α
DIM
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
