General Description
The MAX15032 constant-frequency, pulse-width-modulating (PWM), low-noise boost converter is intended for
low-voltage systems that need a locally generated high
voltage. This device is capable of generating low-noise,
high output voltages, with an output power capability
up to 600mW with a 2.9V input voltage. This device can
be used for a wide variety of applications, such as PIN
or varactor diode biasing and LCD displays. The
MAX15032 operates from +2.7V to +11V.
The constant-frequency (500kHz), current-mode PWM
architecture provides low-noise output voltage that is
easy to filter. A high-voltage internal lateral DMOS
power switch allows this device to boost output voltages up to 36V. The MAX15032 features a shutdown
mode to save power.
The MAX15032 is available in a small thermally
enhanced 3mm x 3mm 8-pin TDFN package and is
specified for operation over the -40°C to +125°C automotive temperature range.
Applications
Avalanche Photodiode Biasing
PIN Diode Bias Supplies
Low-Noise Varactor Diode Bias Supplies
STB Audio IC Supplies
LCD Displays
Features
o Input Voltage Range
+2.7V to +5.5V (Using Internal Charge Pump)
+5.5V to +11V
o Wide Adjustable Output Voltage Range: (V
IN
+ 1V)
to 36V
o Output Power: ≥ 600mW for V
IN
≥ 2.9V
o Internal 0.5Ω (typ), 40V Switch
o Constant PWM Frequency Provides Easy Filtering
in Low-Noise Applications
o 500kHz (typ) Switching Frequency
o 0.5µA (max) Shutdown Current
o Internal Soft-Start
o Small Thermally Enhanced 3mm x 3mm 8-Pin
TDFN Package
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
________________________________________________________________
Maxim Integrated Products
1
Pin Configuration
Ordering Information
MAX15032
INVIN = 2.7V TO 5.5V
V
OUT
36V
SHDN
PGND
LX
FB
CP
CN
GND
R1
D1
L1
R2
C
IN
C
OUT
C
CP
Typical Operating Circuit
19-4232; Rev 0; 8/08
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.
PART
TEMP RANGE
PIN-
TOP
MARK
MAX15032ATA+T
+BKP
+
Denotes a lead-free/RoHS-compliant package.
T = Tape and reel.
*
EP = Exposed pad.
PACKAGE
-40°C to +125°C 8 TDFN-EP*
TOP VIEW
PGND CN IN
CP
865
7
MAX15032
+
1
LX FB SHDNGND
2
TDFN
34
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= +3.3V, V
SHDN
= +3.3V, CIN= 10µF, PGND = GND = 0V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values
are at T
A
= +25°C. See the
Typical Operating Circuit
.) (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.
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
IN to GND ...............................................................-0.3V to +12V
LX to PGND ............................................................-0.3V to +40V
FB to GND ..............................................................-0.3V to +12V
SHDN to GND..............................................-0.3V to (V
IN
+ 0.3V)
CN to GND .............................................................-0.3V to +12V
CP to GND..............................................................-0.3V to +12V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
8-Pin TDFN (derate 24.4mW/°C above +70°C) ......1951.2mW
Junction-to-Case Thermal Resistance (θ
JC
) (Note 1) ........8°C/W
Junction-to-Ambient Thermal Resistance (θ
JA
)
(Note 1) ........................................................................41°C/W
Operating Temperature Range .........................-40°C to +125°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
SUPPLY VOLTAGE
Supply Voltage Range V
Supply Current I
Undervoltage Lockout V
Undervoltage Lockout Hysteresis V
Shutdown Current I
LOGIC INPUT (SHDN)
SHDN Input Low Level V
SHDN Input High Level V
BOOST CONVERTER
Output Voltage Adjustment
Range
Switching Frequency f
FB Set Point V
FB Input Bias Current I
LX Switch On-Resistance R
Peak Switch Current Limit I
LX Leakage Current VLX = 36V 2 µA
Line Regulation I
IN
IN
UVLO
UVLO-HYS
SHDN
IL
IH
SW
FB
FB
DS_ON
LIM_LX
CCP = 10nF 2.7 5.5
CP connected to IN 5.5 11
VFB = 1.4V (no switching), CCP = 10nF,
= 3.3V
V
IN
VFB = 1.4V (no switching), CP = IN,
V
= 11V
IN
VIN rising 2.375 2.5 2.675 V
V
= 0V 0.5 µA
SHDN
CCP = 10nF,
= 100mA
I
LX
CP connected to
= 100mA
IN, I
LX
= 2mA 0.25 %
LOAD
2.0 V
+ 1 36 V
V
IN
450 500 550 kHz
1.214 1.245 1.276 V
VIN = 2.9V, VCP = 5.5V 0.42 1
V
= 5.5V, VCP = 10V 0.33 1
IN
VIN = VCP = 5.5V 0.42 1
V
= VCP = 11V 0.33 1
IN
1 1.33 1.7 A
12
1.5 3
100 mV
0.8 V
300 nA
V
mA
Ω
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
_______________________________________________________________________________________ 3
Note 2: All devices are 100% production tested at room temperature (TA= +25°C). All parameter limits through the temperature
range are guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)
(VIN= +3.3V, V
SHDN
= +3.3V, CIN= 10µF, PGND = GND = 0V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values
are at T
A
= +25°C. See the
Typical Operating Circuit
.) (Note 2)
EFFICIENCY
vs. LOAD CURRENT
MAX15032 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
181612 144 6 8 102
40
45
50
55
60
65
70
75
80
85
35
020
V
OUT
= 36V
V
IN
= 5V
V
OUT
= 36V
V
IN
= 3.3V
EFFICIENCY
vs. LOAD CURRENT
MAX15032 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
181612 144 6 8 102
40
45
50
55
60
65
70
75
80
85
35
020
V
OUT
= 30V
V
IN
= 5V
V
OUT
= 30V
V
IN
= 3.3V
EFFICIENCY
vs. LOAD CURRENT
MAX15032 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
454030 3510 15 20 255
40
45
50
55
60
65
70
75
80
85
35
050
V
OUT
= 24V
V
IN
= 5V
V
OUT
= 24V
V
IN
= 3.3V
Typical Operating Characteristics
(VIN= 3.3V, L1 = 4.7µH, R1 = 143kΩ, R2 = 6.2kΩ, CIN= 10µF, C
OUT
= 2.2µF, CCP= 10nF, see the
Typical Operating Circuit
.
TA= +25°C, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Load Regulation I
= 0 to 20mA, V
LOAD
= 30V 1 %
OUT
Soft-Start Duration 8ms
Soft-Start Steps (0.25 x I
LIM_LX
) to I
LIM_LX
32 Steps
THERMAL PROTECTION
Thermal Shutdown Rising +160 °C
Thermal-Shutdown Hysteresis 8°C
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN= 3.3V, L1 = 4.7µH, R1 = 143kΩ, R2 = 6.2kΩ, CIN= 10µF, C
OUT
= 2.2µF, CCP= 10nF, see the
Typical Operating Circuit
.
T
A
= +25°C, unless otherwise noted.)
EFFICIENCY
MAXIMUM LOAD CURRENT
vs. LOAD CURRENT
90
85
80
75
70
65
60
EFFICIENCY (%)
55
50
45
40
35
V
= 12V
OUT
= 3.3V
V
IN
050
LOAD CURRENT (mA)
V
= 12V
OUT
= 5V
V
IN
L = 3.3μH
454030 3510 15 20 255
360
L = 4.7μH FOR V
330
300
MAX15032 toc04
270
V
240
L = 3.3μH
210
180
150
120
90
MAXIMUM LOAD CURRENT (mA)
60
30
0
211
OUT
= 12V
vs. INPUT VOLTAGE
= 36V, 30V, AND 24V
OUT
V
= 30V
OUT
INPUT VOLTAGE (V)
MAX15032 toc05
V
= 24V
OUT
V
= 36V
OUT
1097 84 5 63
MINIMUM STARTUP VOLTAGE
vs. LOAD CURRENT
2.80
V
= 30V
OUT
2.75
2.70
2.65
2.60
2.55
2.50
2.45
2.40
MINIMUM STARTUP VOLTAGE (V)
2.35
2.30
020
LOAD CURRENT (mA)
MAX15032 toc06
181612 144 6 8 102
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1.6
VFB = 1.4V
1.4
1.2
1.0
0.8
0.6
SUPPLY CURRENT (mA)
0.4
0.2
0
211
SUPPLY VOLTAGE (V)
EXITING SHUTDOWN
V
= 5V
IN
= 1mA
I
OUT
1093 4 5 76 8
MAX15032 toc10
1.00
0.95
MAX15032 toc07
0.90
0.85
0.80
0.75
0.70
0.65
SUPPLY CURRENT (mA)
0.60
0.55
0.50
V
SHDN
2V/div
V
OUT
10V/div
VFB = 1.4V
-40 125
SUPPLY CURRENT
vs. TEMPERATURE
TEMPERATURE (°C)
ENTERING SHUTDOWN
MAX15032 toc11
V
= 5V
IN
= 1mA
I
OUT
SWITCHING FREQUENCY
vs. TEMPERATURE
550
VIN = 5V
540
1109565 80-10 5 20 35 50-25
MAX15032 toc09
V
OUT
(AC-COUPLED)
50mV/div
V
LX
20V/div
MAX15032 toc08
530
520
510
500
490
480
SWITCHING FREQUENCY (kHz)
470
460
450
1109565 80-10 5 20 35 50-25
V
SHDN
2V/div
V
OUT
10V/div
-40 125
TEMPERATURE (°C)
SWITCHING WAVEFORMS
MAX15032 toc12
I
L
500mA/div
1ms/div
20ms/div
1μs/div
I
OUT
= 20mA
I
L
500mA/div
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VIN= 3.3V, L1 = 4.7µH, R1 = 143kΩ, R2 = 6.2kΩ, CIN= 10µF, C
OUT
= 2.2µF, CCP= 10nF, see the
Typical Operating Circuit
.
T
A
= +25°C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
RISE TIME = 10ns
100ms/div
SWITCH ON-RESISTANCE
vs. TEMPERATURE
1000
VIN = 5V
950
900
850
800
750
700
650
600
550
SWITCH ON-RESISTANCE (mΩ)
500
450
400
-40 125
TEMPERATURE (°C)
MAX15032 toc13
1109565 80-10 5 20 35 50-25
V
OUT
(AC-COUPLED)
200mV/div
I
OUT
5mA/div
MAX15032 toc16
LX LEAKAGE CURRENT (nA)
LINE-TRANSIENT RESPONSE
LX LEAKAGE CURRENT
vs. TEMPERATURE
50
VLX = 36V
45
40
35
30
25
20
15
10
5
0
-40 125
2ms/div
TEMPERATURE (°C)
MAX15032 toc14
I
= 1mA
OUT
V
IN
1V/div
V
OUT
(AC-COUPLED)
50mV/div
MAX15032 toc17
1109565 80-10 5 20 35 50-25
FB VOLTAGE
vs. TEMPERATURE
1.29
1.28
1.27
1.26
1.25
1.24
FB VOLTAGE (V)
1.23
1.22
1.21
-40 125
TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
300
V
= 0V
SHDN
270
240
210
180
150
120
90
60
SHUTDOWN SUPPLY CURRENT (nA)
30
0
-40 125
TEMPERATURE (°C)
MAX15032 toc15
11095-25 -10 5 35 50 6520 80
MAX15032 toc18
1109565 80-10 5 20 35 50-25
OUTPUT VOLTAGE
vs. LOAD CURRENT
30.00
29.95
29.90
29.85
29.80
29.75
29.70
VIN = 3.3V
OUTPUT VOLTAGE (V)
29.65
29.60
29.55
29.50
020
VIN = 5V
LOAD CURRENT (mA)
MAX15032 toc19
181612 144 6 8 102
(V)
V
OUT
42
36
30
24
18
12
6
V
OUT
INDUCTOR VALUE
VIN = 2.7V TO 11V
L OPTIMUM (μH)
vs. OPTIMUM
MAX15032 toc20
4.73.3
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
6 _______________________________________________________________________________________
Pin Description
Functional Diagram
PIN NAME FUNCTION
1LX
2 GND
3FB
4 SHDN
5 IN Input Supply Voltage. Bypass IN to PGND with a 4.7µF minimum ceramic capacitor.
6CN
7CP
8 PGND
—EP
Drain of Internal 40V n-Channel DMOS. Connect inductor/diode to LX. Minimize trace area at LX to
reduce switching noise emission.
Signal Ground. Connect directly to the local ground plane. Connect GND to PGND at a single point,
typically near the output capacitor return terminal.
Feedback Regulation Point. Connect to the center tap of a resistive divider from the output (V
GND to set the output voltage. The FB voltage regulates to 1.245V (typ).
Active-Low Shutdown Control Input. A logic-low voltage on SHDN shuts down the device and reduces
the supply current to 0.5µA (max). Connect SHDN to IN for always-on operation. Do not connect
SHDN to a voltage higher than V
.
IN
Negative Terminal of the Charge-Pump Flying Capacitor for 2.7V to 5.5V Supply Voltage Operation.
Leave CN unconnected when the input voltage is in the +5.5V to +11V range.
Positive Terminal of the Charge-Pump Flying Capacitor for 2.7V to 5.5V Supply Voltage Operation.
Connect to IN when the input voltage is in the +5.5V to +11V range.
Power Ground. Connect the input and output filter capacitors’ negative terminal to PGND. Connect
externally to GND at a single point, typically at the output capacitor return terminal.
Exposed Pad. Connect EP to a large copper plane at the GND potential to improve thermal
dissipation. Do not use as the main GND connection.
) to
OUT
GND
CN
FB
V
CP
IN
REF
(DOUBLER)
-A
+A
-C
+C
CHARGE
PUMP
UVLO
CLK
OSCILLATOR
500kHz
SHDN
SOFTSTART
V
BIAS AND
REFERENCE
REF
SWITCH
CONTROL
LOGIC
THERMAL
SHUTDOWN
LX
N
PGND
SWITCH
CURRENT
SENSE
MAX15032
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
_______________________________________________________________________________________ 7
Detailed Description
The MAX15032 constant-frequency, current-mode,
pulse-width-modulating (PWM) boost converter is
intended for low-voltage systems that often need a
locally generated high voltage. This device is capable
of generating low-noise, high-output voltage required
for PIN and varactor diode biasing and LCD displays.
The MAX15032 operates either from +2.7V to +5.5V or
from +5.5V to +11V. For +2.7V to +5.5V operation, an
internal charge pump with an external 10nF ceramic
capacitor is used. The MAX15032 also features a shutdown logic input to disable the device and reduce its
standby current to 0.5µA (max).
The MAX15032 operates in discontinuous mode in order
to reduce the switching noise caused by the reverse
recovery charge of the rectifier diode. Other continuous
mode boost converters generate large voltage spikes at
the output when the LX switch turns on because there is
a conduction path between the output, diode, and
switch to ground during the time needed for the diode to
turn off and reverse its bias voltage. To reduce the output noise even further, the LX switch turns off by taking
6.8ns typically to transition from “ON” to “OFF.” As a
consequence, the positive slew rate of the LX node is
reduced and the current from the inductor does not
“force” the output voltage as hard as would be the case
if the LX switch were to turn off more quickly.
Also, the constant-frequency (500kHz) PWM architecture generates an output voltage ripple that is easy to
filter. A 40V lateral DMOS device used as the internal
power switch makes the device ideal for boost converters with output voltages up to 36V.
The MAX15032 can also be used in other topologies
where the PWM switch is grounded, like SEPIC and
flyback.
PWM Controller
The heart of the MAX15032 current-mode PWM controller is a BiCMOS multi-input comparator that simultaneously processes the output-error signal and switch
current signal. The main PWM comparator is direct
summing, lacking a traditional error amplifier and its
associated phase shift. The direct summing configura-
tion approaches ideal cycle-by-cycle control over the
output voltage since there is no conventional error
amplifier in the feedback path.
The device operates in PWM mode using a fixed-frequency, current-mode operation. The current-mode frequency loop regulates the peak inductor current as a
function of the output error signal. The current-mode
PWM controller is intended for discontinuous conduction mode (DCM) operation. No internal slope compensation is added to the current signal.
Shutdown (
SHDN
)
The MAX15032 features an active-low shutdown input
(SHDN). Pull SHDN low to enter shutdown. During shut-
down, the supply current drops to 0.5µA (max).
However, the output remains connected to the input
through the inductor and output rectifier, holding the
output voltage to one diode drop below VINwhen the
MAX15032 shuts down. Connect SHDN to IN for
always-on operation.
Charge Pump
At low supply voltages (+2.7V to +5.5V), an internal
charge-pump circuit and an external 10nF ceramic
capacitor double the available supply voltage in order
to drive the internal switch efficiently.
In the +5.5V to +11V supply voltage range, the charge
pump must be disabled by connecting CP to IN and
leaving CN unconnected.
Design Procedure
Setting the Output Voltage
Set the MAX15032 output voltage by connecting a
resistive divider from the output to FB to GND (see the
Typical Operating Circuit
). Select R2 (FB to GND resis-
tor) between 6kΩ and 10kΩ. Calculate R1 (V
OUT
to FB
resistor) with the following equation:
where VFB= 1.245V (see the
Electrical Characteristics
table) and V
OUT
can range from (VIN+ 1V) to +36V.
RR
12 1=
⎡
⎛
V
OUT
⎢
⎜
V
⎝
FB
⎣
⎤
⎞
−
⎥
⎟
⎠
⎦
MAX15032
Determining Peak Inductor Current
If the boost converter remains in the discontinuous
mode of operation, then the approximate peak inductor
current, I
LPEAK
(A), is represented by the formula
below:
where TSis the period in µs, V
OUT
is the output voltage in
volts, V
IN_MIN
is the minimum input voltage in volts, I
OUT
is the output current in amperes, L is the inductor value in
µH, and η is the efficiency of the boost converter.
Determining the Inductor Value
Three key inductor parameters must be specified for
operation with the MAX15032: inductance value (L),
inductor saturation current (I
SAT
), and DC resistance
(DCR). In general, the inductor should have a saturation
current rating greater than the maximum switch peak
current-limit value (I
LIM-LX(MAX)
= 1.7A). DC series
resistance (DCR) should be below 0.1Ω for reasonable
efficiency. Due to the high switching frequency of the
MAX15032, inductors with a ferrite core or equivalent
are recommended to minimize core losses. Table 1
shows a list of vendors with 4.7µH inductor parts.
Table 1. Inductor Vendors
Use the following formula to calculate the lower bound
of the inductor value at different output voltages and
output currents. This is the minimum inductance value
for discontinuous mode operation for supplying the full
600mW output power:
where VIN(V), V
OUT
(V), and I
OUT
(A) are typical values, TS(µs) is the period, η is the efficiency, and
I
LIM-LX
is the peak LX current (A).
Calculate the optimum value of L (L
OPTIMUM
) to ensure
the full output power without reaching the boundary
between continuous conduction mode (CCM) and DCM
using the following formula:
where:
For a design in which VIN= 3.3V, V
OUT
= 30V,
I
OUT
= 20mA, η = 0.7, and TS= 2µs, (L
OPTIMUM
=
4.7µH):
L
MAX
= 10.5µH
and
L
MIN
= 3.3µH
For a worst-case scenario in which VIN= 2.9V, V
OUT
=
30V, I
OUT
= 20mA, η = 0.7, I
LIM-LX(MIN)
= 1A, and TS=
1.8µs:
L
MAX
= 9.2µH
and:
L
MIN
= 2.2µH
The choice of 4.7µH is reasonable given the worst-case
scenario above. In general, the higher the inductance,
the lower the switching noise.
Diode Selection
The MAX15032’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommended for most applications because of their fast recovery
time and low forward-voltage drop. Ensure that the
diode’s peak current rating is greater than the inductor
peak current. Also, the diode reverse breakdown voltage must be greater than V
OUT
.
Output Filter Capacitor Selection
For most applications, use a small ceramic surface-mount
output capacitor, 2.2µF or greater. To achieve low output
ripple, a capacitor with low-ESR, low-ESL, and highcapacitance value should be selected. If tantalum or
electrolytic capacitors are used to achieve high capacitance values, always add a small ceramic in parallel to
bypass the high-frequency components of the diode current. The higher ESR and ESL of electrolytic increase both
the output ripple and peak-to-peak transient voltage.
Assuming the contribution from the ESR and capacitor
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
8 _______________________________________________________________________________________
I
LPEAK
×× ×
=
TV V I
S OUT IN MIN OUT
−2( )
_
η
L
×
PART NUMBER
VENDOR PHONE FAX
TDK 408-437-9585 408-437-9591
TOKO 847-297-0070 847-699-7864 636CY-4R7M+P3
Coilcraft 800-322-2645 847-639-1469 MOS6020-472MLC
LH
[]
μη=
MIN
TI V V
×× ×
S OUT OUT IN MIN
()
2
I
×
LIM LX
2
OF 4.7µH
INDUCTOR
SLF7045T4R7M2R0-PF
−
_
−
LH
[]
L
OPTIMUM
VVV Ts
IN MIN OUT IN MIN
LH
[]
μη=
MAX
__
MAX
=
.μ225
2
2
−
()
IV
××
OUT OUT
××
2
discharge equals 50% (proportions could vary), calculate the output capacitance and ESR required for a specified ripple using the following equations:
For very low output-ripple applications, the output of the
boost converter can be followed by an RC filter to further reduce the ripple. Figure 1 shows a 10Ω, 2.2µF filter used to reduce the switching output ripple to
1mV
P-P
with a 20mA output and a ripple voltage of
400µV
P-P
with a 2mA load. The output voltage regulation resistive divider must remain connected to the
diode/output capacitor node.
X7R ceramic capacitors are stable over -40°C to
+125°C temperature range. Where the automotive temperature range is required, use X7R ceramic capacitors. X5R dielectric can be used for -40°C to +85°C
applications.
Input Capacitor Selection
Bypass IN (the input voltage pin) to PGND with a minimum 4.7µF ceramic capacitor. Depending on the supply source impedance, higher values might be needed.
Make sure that the input capacitor is close enough to
the IC to provide adequate decoupling at IN as well. If
the layout cannot achieve this, add another 0.1µF
ceramic capacitor between IN and PGND in the imme-
diate vicinity of the IC. Bulk aluminum electrolytic
capacitors might be needed to avoid chattering at low
input voltages. In the case of aluminum electrolytic
capacitors, calculate the capacitor value and ESR of
the input capacitor using the following equations:
Applications Information
Layout Considerations
Careful PCB layout is critical to achieve clean and stable operation. Protect sensitive analog grounds by
using a star ground configuration. Connect GND and
PGND together close to the device at the return terminal
of the output bypass capacitor. Do not connect them
together anywhere else. Keep all PCB traces as short
as possible to reduce stray capacitance, trace resistance, and radiated noise. Ensure that the feedback
connection to FB is short and direct. Route high-speed
switching nodes away from the sensitive analog areas.
Avoid any coupling from LX to FB node by keeping the
FB node away from the LX routing. In addition, decoupling LX and FB with a small 22pF capacitor from FB to
GND can be used. Use an internal PCB layer for GND
as an EMI shield to keep radiated noise away from the
device, feedback dividers, and bypass capacitors.
MAX15032
500kHz, 36V Output, 600mW PWM
Step-Up DC-DC Converter
_______________________________________________________________________________________ 9
Figure 1. Typical Operating Circuit with RC Filter
CF
[]
μ=
OUT
0505Δ
V
OUT
Ω
⎡
IL
−
T
⎢
S
⎢
⎣
×
.
=
Δ
I
OUT
I
OUT
.()
×
[]
ESR m
×
LPEAK OPTIMUM
−
VV
OUT IN MIN
V
OUT
_
⎤
⎥
⎥
⎦
CF
[]
μ
=
IN
VI
×
OUT OUT
η
VV
×××
IN MIN IN
ESR m
.()
0505Δ
___
[]
=
Ω
⎡
IL V
LPEAK OPTIMUM OUT
−
T
⎢
S
VVV
⎢
IN MIN OUT IN MIN
⎣
.
η
×××
ΔΔ
VV
IN IN MIN
×
VI
OUT OUT
××
−
_
⎤
⎥
⎥
⎦
C
IN
10μF
INVIN = 2.9V TO 5.5V
SHDN
PGND
L1
4.7μH
MAX15032
GND
CP
CN
R
C
OUT
2.2μF
10Ω
F
V
OUT
30V
C
F
2.2μF
C
CP
10nF
D1
1A/40V
R1
143kΩ
R2
6.2kΩ
LX
FB
MAX15032
500kHz, 36V Output, 600mW 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.
10
____________________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.
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages
.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
8 TDFN T833-2
21-0137
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