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PDF MAX8855A Data sheet ( Hoja de datos )
| Número de pieza | MAX8855A | |
| Descripción | 2MHz Step-Down Regulators | |
| Fabricantes | Maxim Integrated | |
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19-0726; Rev 4; 10/11
EVAALVUAAILTAIOBNLEKIT Dual, 5A, 2MHz Step-Down Regulators
General Description
The MAX8855/MAX8855A high-efficiency, dual step-down
regulators are capable of delivering up to 5A at each out-
put. The devices operate from a 2.25V to 3.6V supply, and
provide output voltages from 0.6V to 0.9 x VIN, making them
ideal for on-board point-of-load applications. Total output
error is less than ±1% over load, line, and temperature.
The MAX8855/MAX8855A operate in PWM mode with a
switching frequency ranging from 0.5MHz to 2MHz, set
by an external resistor. It can also be synchronized to
an external clock in the same frequency range. Two
internal switching regulators operate 180° out-of-phase
to reduce the input ripple current, and consequently
reduce the required input capacitance. The high
operating frequency minimizes the size of external
components. High efficiency, internal dual-nMOS
design keeps the board cool under heavy loads. The
voltage-mode control architecture and the high-band-
width (> 15MHz typ) voltage-error amplifier allow a type
III compensation scheme to be utilized to achieve fast
response under both line and load transients, and also
allow for ceramic output capacitors.
Programmable soft-start reduces input inrush current.
Two enable inputs allow the turning on/off of each out-
put individually, resulting in great flexibility for system-
level designs. A reference input is provided to facilitate
output-voltage tracking applications. The MAX8855/
MAX8855A are available in a 32-pin TQFN (5mm x 5mm)
package with 0.8mm max height.
Applications
ASIC/CPU/DSP Power Supplies
DDR Power Supplies
Set-Top Box Power Supplies
Printer Power Supplies
Network Power Supplies
Features
o 27mΩ On-Resistance Internal MOSFETs
o Dual, 5A, PWM Step-Down Regulators
o Fully Protected Against Overcurrent,
Short Circuit, and Overtemperature
o ±1% Output Accuracy Over Load, Line,
and Temperature
o Operates from 2.25V to 3.6V Supply
o REFIN on One Channel for Tracking or
External Reference
o Integrated Boost Diodes
o Adjustable Output from 0.6V to 0.9 x VIN
o Soft-Start Reduces Inrush Supply Current
o 0.5MHz to 2MHz Adjustable Switching,
or FSYNC Input
o All-Ceramic-Capacitor Design
o 180° Out-of-Phase Operation Reduces Input
Ripple Current
o Individual Enable Inputs and PWRGD Outputs
o Safe-Start into Prebiased Output
o Available in 5mm x 5mm Thin QFN Package
o Sink/Source Current in DDR Applications
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX8855ETJ+
-40°C to +85°C 32 TQFN-EP*
MAX8855AETJ+
-40°C to +85°C 32 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Typical Operating Circuit
OUTPUT1
1.2V / 5A
INPUT1
2.25V TO 3.6V
IN1 IN2
BST1 BST2
LX1 LX2
INPUT2
2.25V TO 3.6V
OUTPUT2
1.5V / 5A
PGND1 PGND2
MAX8855/
MAX8855A
FB1 FB2
Pin Configuration appears at end of data sheet.
TYPE III
COMPENSATION
ON
OFF
COMP1 COMP2
PWRGD1 PWRGD2
EN1 EN2
GND
TYPE III
COMPENSATION
ON
OFF
________________________________________________________________ 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.
Free Datasheet http://www.datasheet-pdf.com/
1 page  
Dual, 5A, 2MHz Step-Down Regulators
Typical Operating Characteristics (continued)
(VIN1 = VIN2 = 3.3V, MAX8855/MAX8855A, circuit of Figure 6, TA = +25°C, unless otherwise noted.)
1100
1080
1060
1040
1020
1000
980
960
940
920
900
-40
SWITCHING FREQUENCY
vs. TEMPERATURE
-15 10 35 60
AMBIENT TEMPERATURE (°C)
85
610
608
606
604
602
600
598
596
594
592
590
-40
FEEDBACK VOLTAGE
vs. TEMPERATURE
-15 10 35 60
AMBIENT TEMPERATURE (°C)
85
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
10
IIN1 + IIN2 + IVDL + IVDD
9
8
7
6
5
4
3
2
1
0
2.35
2.60 2.85 3.10 3.35
SUPPLY VOLTAGE (V)
3.60
VOUT_
LOAD TRANSIENT
MAX8855/MAX8855A toc07
1.8V OUTPUT
100mV/div
3.0A
IOUT_ 1.5A
1.5A 1A/div
20µs/div
SWITCHING WAVEFORMS
MAX8855/MAX8855A toc08
VLX1 2V/div
SOFT-START AND SHUTDOWN
MAX8855/MAX8855A toc09
VEN2 5V/div
IL1
2A/div
VOUT2
1V/div
VLX2
2V/div
VPWRGD2
2V/div
IIN2
IL2 2A/div
1A/div
400ns/div
3A LOAD
400µs/div
_______________________________________________________________________________________ 5
Free Datasheet http://www.datasheet-pdf.com/
5 Page 
Dual, 5A, 2MHz Step-Down Regulators
reference with soft-start time set independently by the
SS1 capacitor (see Figure 3a).
For ratiometric tracking applications, connect REFIN to
the center of a voltage-divider from the output of regula-
tor 2 to GND (see Figure 3b). In this application, the EN_
inputs are connected to each other and driven as a sin-
gle enable input. Regulator 2 starts up with a normal soft-
start (CSS2 sets the time), and regulator 1 output
ratiometrically tracks the regulator 2 output voltage. The
voltage-divider resistors set the VOUT1/VOUT2 ratio (see
the Setting the Output Voltage section). In Figure 3b,
VOUT1 regulates to half of VOUT2. Note that a capaci-
tance of 1000pF should be connected to SS1 for stability.
Figure 3c shows the output sequencing application
using an external reference.
EN
OUT2
OUT1
PWRGD2
PWRGD1
10kΩ
10kΩ
PWRGD1 EN1
VDD EN2
PWRGD2 SS2
SS1 REFIN
EN
OUT2
10kΩ
10kΩ
Figure 3b. Startup and Sequencing Options—Ratiometric Tracking Startup and Shutdown Waveforms VOUT1 Track VOUT2
EN1
OUT1
10kΩ
PWRGD1
10kΩ
OUT2
PWRGD2
PWRGD1 EN1
VDD EN2
EN1
PWRGD2
SS2
SS1 REFIN
REFIN
Figure 3c. Startup and Sequencing Options—Sequencing Startup and Shutdown Waveforms with External Reference
______________________________________________________________________________________ 11
Free Datasheet http://www.datasheet-pdf.com/
11 Page | ||
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