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PDF MAX15108 Data sheet ( Hoja de datos )
| Número de pieza | MAX15108 | |
| Descripción | Current-Mode Synchronous Step-Down Switching Regulator | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-5917; Rev 0; 6/11
EVAALVUAAILTAIOBNLEKIT
High-Efficiency, 8A, Current-Mode
Synchronous Step-Down Switching Regulator
General Description
The MAX15108 high-efficiency, current-mode, synchro-
nous step-down switching regulator with integrated
power switches delivers up to 8A of output current. The
regulator operates from 2.7V to 5.5V and provides an
output voltage from 0.6V up to 95% of the input voltage,
making the device ideal for distributed power systems,
portable devices, and preregulation applications.
The IC utilizes a current-mode control architecture
with a high gain transconductance error amplifier.
The current-mode control architecture facilitates easy
compensation design and ensures cycle-by-cycle
current limit with fast response to line and load transients.
The regulator offers a selectable skip-mode functionality
to reduce current consumption and achieve a higher effi-
ciency at light output load. The low RDS(ON) integrated
switches ensure high efficiency at heavy loads while
minimizing critical inductance, making the layout design
a much simpler task with respect to discrete solutions.
The IC’s simple layout and footprint assures first-pass
success in new designs.
The regulator features a 1MHz, factory-trimmed fixed-
frequency PWM mode operation. The high switching
frequency, along with the PWM current-mode architecture
allows for a compact, all ceramic capacitor design.
The IC features a capacitor-programmable soft-start
to reduce input inrush current. Internal control circuitry
ensures safe-startup into a prebiased output. Power
sequencing is controlled with the enable input and
power-good output.
The IC is available in a 20-bump (4 x 5 array), 2.5mm x
2mm, WLP package and is fully specified over the -40NC
to +85NC temperature range.
Distributed Power Systems
DDR Memory
Base Stations
Portable Devices
Notebook Power
Server Power
Applications
Features
S Continuous 8A Output Current
S Efficiency Up to 96%
S ±1% Accuracy Over Load, Line, and Temperature
S Operates from a 2.7V to 5.5V Supply
S Adjustable Output from 0.6V to 0.95 x VIN
S Programmable Soft-Start
S Safe Startup into Prebiased Output
S External Reference Input
S 1MHz Switching Frequency
S Stable with Low-ESR Ceramic Output Capacitors
S Skip Mode or Forced PWM Mode
S Enable Input and Power-Good Output for Power-
Supply Sequencing
S Cycle-by-Cycle Overcurrent Protection
S Fully Protected Features Against Overcurrent and
Overtemperature
S Input Undervoltage Lockout
S 20-Bump (4 x 5 Array), 2.5mm x 2mm, WLP
Package
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX15108EWP+ -40NC to +85NC
20 WLP
+Denotes a lead(Pb)-free/RoHS-compliant package.
2.7V TO
5.5V
Typical Operating Circuit
SKIP LX
EN PGND
IN MAX15108
FB
INX
PGOOD
COMP
OUTPUT
SS
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
High-Efficiency, 8A, Current-Mode
Synchronous Step-Down Switching Regulator
Typical Operating Characteristics (continued)
(Circuit of Typical Application Circuit, TA = +25NC, unless otherwise noted.)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
(PWM MODE, VOUT = 1.5V)
1.53
1.52
VIN = 5V
1.51
1.50
VIN = 3.3V
1.49
1.48
1.47
012345678
OUTPUT CURRENT (A)
OUTPUT VOLTAGE ERROR %
vs. SUPPLY VOLTAGE
0.5
0.4 NORMALIZED AT VIN = 3.3V
0.3
0.2
VOUT = 2.5V
VOUT = 1.2V
0.1
0
-0.1
-0.2 VOUT = 0.9V
-0.3 VOUT = 1.5V
-0.4
-0.5
2.7
VOUT = 1.8V
ILOAD = 8A
3.1 3.5 3.9 4.3 4.7 5.1 5.5
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
(SKIP MODE, VOUT = 1.5V)
1.53
1.52 VIN = 5V
1.51
1.50
VIN = 3.3V
1.49
1.48
1.47
012345678
OUTPUT CURRENT (A)
LOAD-TRANSIENT RESPONSE
(VIN = 5V, VOUT = 1.5V)
MAX15108 toc07
40µs/div
VOUT
50mV/div
AC-COUPLED
8A
ILOAD
2A/div
4A
SWITCHING WAVEFORMS
SOFT-START
WA(VIOEUFTOR=M8SA,(IVLOINAD=
5V)
= 8A)MAX15108
toc08
MAX15108 toc11
VEN
2V/div
VOUT
10mV/div
AC-COUPLED
VLX
2V/div
ILX
5A/div
VOUT
1V/div
ILX
5A/div
VLX
2V/div
VPGOOD
2V/div
400ns/div
1ms/div
SWITCHING WAVEFORM IN SKIP MODE
(IOUT = 10mA)
MAX15108 toc09
VOUT
10mV/div
AC-COUPLED
ILX
2A/div
VLX
2V/div
20µs/div
_______________________________________________________________________________________ 5
5 Page 
High-Efficiency, 8A, Current-Mode
Synchronous Step-Down Switching Regulator
Programmable Soft-Start (SS)
The IC utilizes a soft-start feature to slowly ramp up the
regulated output voltage to reduce input inrush current
during startup. Connect a capacitor from SS to SGND to
set the startup time. See the Setting the Soft-Start Startup
Time section for capacitor selection details.
Error Amplifier
A high-gain error amplifier provides accuracy for the
voltage feedback loop regulation. Connect a compen-
sation network between COMP and SGND. See the
Compensation Design Guidelines section. The error
amplifier transconductance is 1.4mS. COMP clamp low
is set to 0.93V, just below the PWM ramp compensation
valley, helping COMP to rapidly return to the correct set
point during load and line transients.
PWM Comparator
The PWM comparator compares COMP voltage to the
current-derived ramp waveform (LX current to COMP
voltage transconductance value is 25A/V). To avoid
instability due to subharmonic oscillations when the duty
cycle is around 50% or higher, a compensation ramp
is added to the current-derived ramp waveform. The
compensation ramp slope (0.3V x 1MHz = 0.3V/Fs) is
equivalent to half of the inductor current down-slope in
the worst case (load 2A, current ripple 30% and maxi-
mum duty-cycle operation of 95%). The compensation
ramp valley is set to 1V.
Overcurrent Protection and Hiccup
When the converter output is connected to ground or the
device is overloaded, each high-side MOSFET current-
limit event (14A) turns off the high-side MOSFET and
turns on the low-side MOSFET. A 3-bit counter incre-
ments on each current-limit event. The counter is reset
after three consecutive events of high-side MOSFET
turn-on without reaching the current limit. If the current-
limit condition persists, the counter fills up reaching eight
events. The control logic then discharges SS, stops both
high-side and low-side MOSFETs and waits for a hiccup
period (1024 clock cycles) before attempting a new soft-
start sequence. The hiccup-mode also operates during
soft-start.
Thermal Shutdown Protection
The IC contains an internal thermal sensor that limits the
total power dissipation to protect it in the event of an
extended thermal fault condition. When the die tempera-
ture exceeds +160NC, the thermal sensor shuts down
the device, turning off the DC-DC converter to allow the
die to cool. After the die temperature falls by 25NC, the
device restarts, following the soft-start sequence.
Skip Mode Operation
The IC operates in skip mode when SKIP is connected
to EN. When in skip mode, LX output becomes high
impedance when the inductor current falls below 0.7A.
The inductor current does not become negative. During
a clock cycle, if the inductor current falls below the 0.7A
threshold (during off-time), the low side turns off. At the
next clock cycle, if the output voltage is above the set
point the PWM logic keeps both high-side and low-side
MOSFETs off. If instead the output voltage is below the
set point, the PWM logic drives the high-side on for a
minimum fixed on-time (330ns). In this way, the system
skips cycles, reducing the frequency of operations, and
switches only as needed to service load at the cost of
an increase in output voltage ripple. See the Skip Mode
Frequency and Output Ripple section for details. In
skip mode, power dissipation is reduced and efficiency
improved at light loads because the internal power
MOSFETs do not switch at every clock cycle. Skip mode
must be decided before or at the same time that the part
is enabled. Changing of skip mode operation with the
part operating is not allowed.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet MAX15108.PDF ] | |
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