Rainbow Electronics MAX15026 User Manual
General Description
The MAX15026 synchronous step-down controller operates from a 4.5V to 28V input voltage range and generates an adjustable output voltage from 85% of the input
voltage down to 0.6V while supporting loads up to 25A.
The device allows monotonic startup into a prebiased
bus without discharging the output and features adaptive internal digital soft-start.
The MAX15026 offers the ability to adjust the switching
frequency from 200kHz to 2MHz with an external resistor. The MAX15026’s adaptive synchronous rectification
eliminates the need for an external freewheeling
Schottky diode. The device also utilizes the external
low-side MOSFET’s on-resistance as a current-sense
element, eliminating the need for a current-sense resistor. This protects the DC-DC components from damage
during output overloaded conditions or output shortcircuit faults without requiring a current-sense resistor.
Hiccup-mode current limit reduces power dissipation
during short-circuit conditions. The MAX15026 includes
a power-good output and an enable input with precise
turn-on/turn-off threshold, which can be used for input
supply monitoring and for power sequencing.
Additional protection features include sink-mode current limit and thermal shutdown.
Sink-mode current limit prevents reverse inductor current from reaching dangerous levels when the device is
sinking current from the output.
The MAX15026 is available in a space-saving and thermally enhanced 3mm x 3mm, 14-pin TDFN-EP package. The MAX15026 operates over the -40°C to +85°C
temperature range.
Applications
Set-Top Boxes
LCD TV Secondary Supplies
Switches/Routers
Power Modules
DSP Power Supplies
Points-of-Load Regulators
Features
o 4.5V to 28V or 5V ±10% Input Supply Range
o 0.6V to (0.85 x V
IN
) Adjustable Output
o Adjustable 200kHz to 2MHz Switching Frequency
o Ability to Start into a Prebiased Load
o Lossless, Cycle-by-Cycle Valley Mode Current
Limit with Adjustable, Temperature-Compensated
Threshold
o Sink-Mode Current-Limit Protection
o Adaptive Internal Digital Soft-Start
o ±1% Accurate Voltage Reference
o Internal Boost Diode
o Adaptive Synchronous Rectification Eliminates
External Freewheeling Schottky Diode
o Hiccup-Mode Short-Circuit Protection
o Thermal Shutdown
o Power-Good Output and Enable Input for Power
Sequencing
o ±5% Accurate Enable Input Threshold
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
________________________________________________________________
Maxim Integrated Products
1
Pin Configuration
Ordering Information
19-4108; Rev 0; 5/08
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.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE
PIN-PACKAGE
-40°C to +85°C 14 TDFN-EP*
+
Denotes a lead-free package.
*
EP = Exposed pad.
MAX15026BETD+
TOP VIEW
1
+
V
2
CC
312
EN
4
LIM
5
69
78
MAX15026
*EP
DHIN
14
LX
13
BSTPGOOD
DL
11
DRV
10
GNDCOMP
RTFB
*EP = EXPOSED PAD.
TDFN
(3mm x 3mm)
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= 12V, R
RT
= 27kΩ, R
LIM
= 30kΩ, C
VCC
= 4.7µF, CIN= 1µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at
T
A
= +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.
Note 1: Dissipation wattage values are based on still air with no heatsink. Actual maximum power dissipation is a function of heat
extraction technique and may be substantially higher. 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 +30V
BST to GND ............................................................-0.3V to +36V
LX to GND .................................................................-1V to +30V
EN to GND................................................................-0.3V to +6V
PGOOD to GND .....................................................-0.3V to +30V
BST to LX..................................................................-0.3V to +6V
DH to LX ...............................................….-0.3V to (V
BST
+ 0.3V)
DRV to GND .............................................................-0.3V to +6V
DL to GND ................................................-0.3V to (V
DRV
+ 0.3V)
V
CC
to GND...............-0.3V to the lower of +6V and (VIN+ 0.3V)
All Other Pins to GND.................................-0.3V to (V
CC
+ 0.3V)
V
CC
Short Circuit to GND...........................................Continuous
DRV Input Current.............................................................600mA
PGOOD Sink Current ............................................................5mA
Continuous Power Dissipation (T
A
= +70°C) (Note 1)
14-Pin TDFN-EP, Multilayer Board
(derate 24.4mW/°C above +70°C)..............................1951mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
GENERAL
Input Voltage Range V
Quiescent Supply Current V
Shutdown Supply Current I
Enable to Output Delay 480 µs
VCC High to Output Delay EN = V
VCC REGULATOR
Output Voltage V
VCC Regulator Dropout VIN = 4.5V, I
VCC Short-Circuit Output Current VIN = 5V 100 200 300 mA
VCC Undervoltage Lockout V
VCC Undervoltage Lockout
Hysteresis
ERROR AMPLIFIER (FB, COMP)
FB Input Voltage Set-Point V
FB Input Bias Current I
FB to COMP Transconductance g
Amplifier Open-Loop Gain 80 dB
Amplifier Unity-Gain Bandwidth Capacitor from COMP to GND = 50pF 4 MHz
V
COMP-RAMP
COMP Source/Sink Current I
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Minimum Voltage 160 mV
IN
IN_SBY
CC
CC_UVLOVCC
FB
FB
M
COMP
VIN = VCC = V
= 0.9V, no switching 1.75 2.75 mA
FB
EN = GND 290 500 µA
6V < VIN < 28V, I
VIN = 12V, 1mA < I
rising 3.8 4.0 4.2 V
V
= 0.6V -250 +250 nA
FB
I
COMP
V
COMP
DRV
CC
LOAD
= ±20µA 600 1200 1800 µS
= 1.4V 50 80 110 µA
= 25mA
LOAD
< 70mA
LOAD
= 70mA 0.28 V
4.5 28
4.5 5.5
375 µs
5.0 5.25 5.5 V
400 mV
582 592 597 mV
V
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 12V, R
RT
= 27kΩ, R
LIM
= 30kΩ, C
VCC
= 4.7µF, CIN= 1µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at
T
A
= +25°C.) (Note 2)
ENABLE (EN)
EN Input High V
EN Input Low V
EN Input Leakage Current I
OSCILLATOR
Switching Frequency f
1MHz Switching Frequency RRT = 15.7kΩ 0.9 1 1.1 MHz
2MHz Switching Frequency RRT = 7.2kΩ 1.8 2.0 2.4 MHz
Switching Frequency Adjustment
Range (Note 3)
RT Voltage V
PWM Ramp Peak-to-Peak
DRV Undervoltage Lockout
Hysteresis
DH On-Resistance
DL On-Resistance
DH Peak Current C
DL Peak Current C
DH/DL Break-Before-Make Time
SOFT-START
Soft-Start Duration 2048
Reference Voltage Steps 64 Steps
CURRENT LIMIT/HICCUP
Current-Limit Threshold
Adjustment Range
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
EN_H
EN_L
LEAK_ENVEN
SW
RT
V
DRV_UVLOVDRV
V
VEN falling 0.997 1.05 1.103 V
RRT = 27kΩ 540 600 660 kHz
Low, sinking 100mA, V
High, sourcing 100mA, V
Low, sinking 100mA, V
High, sourcing 100mA, V
Time from high side at 1V to low side at
1V
Cycle-by-cycle valley currentlimit threshold adjustment range
valley limit = V
rising 1.14 1.20 1.26 V
EN
= 5.5V -1 +1 µA
200 2000 kHz
1.19 1.205 1.22 V
rising 4.0 4.2 4.4 V
400 mV
= 5V 1 3
BST
= 5V 1.5 4.5
BST
= 5.2V 1 3
DRV
= 5.2V 1.5 4.5
DRV
LOAD
LOAD
= 10nF
= 10nF
LIM
Sinking 1.8
Sourcing 2
Sinking 3
Sourcing 2.4
10 ns
30 300 mV
/10
Switching
Cycles
Ω
Ω
A
A
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 12V, R
RT
= 27kΩ, R
LIM
= 30kΩ, C
VCC
= 4.7µF, CIN= 1µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at
T
A
= +25°C.) (Note 2)
Note 2: All devices are 100% tested at room temperature and guaranteed by design over the specified temperature range.
Note 3: Select R
RT
as: where fSWis in Hertz.
Note 4: T
A
= +25°C.
LIM Reference Current I
LIM Reference Current Tempco V
Number of Consecutive CurrentLimit Events to Hiccup
Soft-Start Timeout 4096
Soft-Start Restart Timeout 8192
Hiccup Timeout Out of soft-start 4096
Peak Low-Side Sink Current
Limit
BOOST
Boost Switch Resistance VIN = VCC = 5V, I
POWER-GOOD OUTPUT
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
V
LIM
= 0.3V to 3V (Note 4) 45 50 55 µA
LIM
= 0.3V to 3V 2300 ppm/°C
LIM
7 Events
Sink limit = 1.5V, R
= 30kΩ (Note 4) 75 mV
LIM
= 10mA 3 8 Ω
BST
Switching
Cycles
Switching
Cycles
Switching
Cycles
PGOOD Threshold Rising 88 93 97 % V
PGOOD Threshold Falling 86 90 94 %V
PGOOD Output Leakage I
PGOOD Output Low Voltage V
THERMAL SHUTDOWN
Thermal-Shutdown Threshold Temperature rising +150 °C
Thermal-Shutdown Hysteresis Temperature falling 20 °C
R
=
RT
LEAK_PGD
PGOOD_LIPGOOD
17.3 10
()
f 1x10 )x(f
+
SW
VIN = V
9
×
SW
2
7
−
= 28V, VEN = 5V, VFB = 1V -1 +1 µA
PGOOD
= 2mA, EN = GND 0.4 V
FB
FB
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(VIN= 12V, TA= +25°C, unless otherwise noted.) (See the circuit of Figure 5.)
EFFICIENCY vs. LOAD CURRENT
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
012
V
OUT
V
= 1.2V
OUT
V
= 5V
OUT
V
= 1.8V
OUT
4
LOAD CURRENT (A)
= 3.3V
62
810
MAX15026 toc01
EFFICIENCY (%)
VCC vs. LOAD CURRENT
5.265
5.260
5.255
5.250
(V)
5.245
CC
V
5.240
5.235
5.230
5.225
0 100
LOAD CURRENT (mA)
60
40
8020
MAX15026 toc04
(V)
V
CC
EFFICIENCY vs. LOAD CURRENT
= 12V, VCC = V
(V
100
IN
90
80
70
60
50
40
30
20
10
0
V
V
OUT
4
2012
LOAD CURRENT (A)
V
OUT
= 5V
OUT
= 3.3V
= 1.8V
6
DRV
8
VCC LINE REGULATION
5.3
5mA
5.2
5.1
5.0
4.9
4.8
4.7
4.6
4.5
4.4
4.3
030
50mA
VIN (V)
= 5V)
V
OUT
10
= 1.2V
252015105
0
-0.1
-0.2
MAX15026 toc02
-0.3
-0.4
-0.5
-0.6
-0.7
% OUTPUT FROM NOMINAL
-0.8
-0.9
-1.0
5.248
5.246
MAX15026 toc05
5.244
(V)
5.242
CC
V
5.240
5.238
5.236
-40 85
V
vs. LOAD CURRENT
OUT
LOAD CURRENT (A)
VCC vs. TEMPERATURE
TEMPERATURE (°C)
MAX15026 toc03
106842012
MAX15026 toc06
603510-15
SWITCHING FREQUENCY
vs. RESISTANCE
2500
2000
1500
1000
SWITCHING FREQUENCY (kHz)
500
0
0 100
RESISTANCE (kΩ)
SWITCHING FREQUENCY
vs. TEMPERATURE
2500
2000
MAX15026 toc07
1500
1000
SWITCHING FREQUENCY (kHz)
500
0
80604020
-40 85
TEMPERATURE (°C)
RRT = 7.2k
RRT = 15.7k
RRT = 27k
RRT = 85k
603510-15
Ω
Ω
Ω
Ω
90
80
MAX15026 toc08
70
60
50
40
30
SUPPLY CURRENT (mA)
20
10
0
100 10,000
SUPPLY CURRENT
vs. SWITCHING FREQUENCY
MAX15026 toc09
1000
SWITCHING FREQUENCY (kHz)
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN= 12V, TA= +25°C, unless otherwise noted.) (See the circuit of Figure 5.)
LIM REFERENCE CURRENT
vs. TEMPERATURE
MAX15026 toc10
TEMPERATURE (°C)
LIM REFERENCE CURRENT (µA)
603510-15
10
20
30
40
50
60
70
0
-40 85
SINK AND SOURCE CURRENT-LIMIT
THRESHOLDS vs. RESISTANCE (R
ILIM
)
MAX15026 toc11
RESISTANCE (kΩ)
CURRENT-LIMIT THRESHOLDS (V)
605040302010
-0.3
-0.2
-0.1
0
0.1
0.2
-0.4
070
SINK CURRENT-LIMIT
SOURCE CURRENT-LIMIT
LOAD TRANSIENT ON OUT
MAX15026 toc12
400µs/div
AC-COUPLED
V
OUT
200mV/div
I
OUT
10A
1A
STARTUP AND DISABLE FROM EN
(R
LOAD
= 1.5Ω)
MAX15026 toc13
4ms/div
V
OUT
1V/div
V
IN
5V/div
PGOOD
5V/div
STARTUP RISE TIME
MAX15026 toc14
1ms/div
V
IN
5V/div
V
OUT
1V/div
POWER-DOWN FALL TIME
MAX15026 toc15
4ms/div
V
IN
5V/div
V
OUT
1V/div
STARTUP WITH PREBIASED
OUTPUT (1.5V)
MAX15026 toc16
1ms/div
V
IN
5V/div
V
OUT
1V/div
0.5V OUTPUT PREBIAS
STARTUP WITH PREBIASED
OUTPUT (1.5V)
MAX15026 toc17
2ms/div
V
IN
5V/div
V
OUT
1V/div
2V OUTPUT PREBIAS
OUTPUT SHORT-CIRCUIT BEHAVIOR MONITOR
OUTPUT VOLTAGE AND CURRENT
MAX15026 toc18
4ms/div
500mV/div
0
V
OUT
I
OUT
20A/div
0
MAX15026
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
_______________________________________________________________________________________ 7
Pin Description
PIN NAME FUNCTION
1IN
2V
3 PGOOD Open-Drain Power-Good Output. Connect PGOOD with an external resistor to any supply voltage.
4EN
5 LIM
6 COMP
7FB
8RT
9 GND Ground
10 DRV
11 DL Low-Side Gate-Driver Output. DL swings from DRV to GND. DL is low during UVLO.
12 BST
CC
Regulator Input. Bypass IN to GND with a 1µF minimum ceramic capacitor. Connect IN to V
operating in the 5V ±10% range.
5.25V Linear Regulator Output. Bypass VCC to GND with a minimum of 4.7µF low-ESR ceramic
capacitor to ensure stability up to the regulated rated current when V
DRV. Bypass V
minimum ceramic capacitor.
Active-High Enable Input. Pull EN to GND to disable the output. Connect EN to V
operation. EN can be used for power sequencing and as a UVLO adjustment input.
Current-Limit Adjustment. Connect a resistor from LIM to GND to adjust current-limit threshold from
30mV (R
Compensation Input. Connect compensation network from COMP to FB or from COMP to GND. See
the Compensation section.
Feedback Input. Connect FB to a resistive divider between output and GND to adjust the output
voltage between 0.6V and (0.85 x Input Voltage). See the Setting the Output Voltage section.
Oscillator Timing Resistor Input. Connect a resistor from RT to GND to set the oscillator frequency
from 200kHz to 2MHz. See the Setting the Switching Frequency section.
Drive Supply Voltage. DRV is internally connected to the anode terminal of the internal boost diode.
Bypass DRV to GND with a 2.2µF minimum ceramic capacitor (see the Typical Application Circuits).
Boost Flying Capacitor. Connect a ceramic capacitor with a minimum value of 100nF between BST
and LX.
LIM
to GND when VCC supplies the device core quiescent current with a 2.2µF
CC
= 6kΩ) to 300mV (R
= 60kΩ). See the Setting the Valley Current Limit section.
LIM
supplies the drive current at
CC
for always-on
CC
CC
when
External Inductor Connection. Connect LX to the switching side of the inductor. LX serves as the
13 LX
14 DH High-Side Gate-Driver Output. DH swings from LX to BST. DH is low during UVLO.
—EP
lower supply rail for the high-side gate driver and as a sensing input of the drain to source voltage
drop of the synchronous MOSFET.
Exposed Paddle. Internally connected to GND. Connect EP to a large copper plane at GND potential
to improve thermal dissipation. Do not use EP as the only GND ground connection.
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