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PDF MPQ28261 Data sheet ( Hoja de datos )
| Número de pieza | MPQ28261 | |
| Descripción | 21V 3A 500kHz Synchronous Step-Down Coverter | |
| Fabricantes | MPS | |
| Logotipo |  |
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MPQ28261
Step-Down
The Future of Analog IC Technology
DESCRIPTION
The MPQ2 8261 is a synchronous, rectif ied,
step-down, switch-mode converter with built-in
120mΩ high-side MOSF ET and 20m Ω low-side
MOSFET. It offers a very compact solution to
achieve a continuous 3 A output cu rrent over a
wide input supply range, with excellent load and
line regulation. Its synchronous mode operatio n
increases it s efficien cy over its ou tput current
load range, and uses a fixed 500kHz switching
frequency.
Current mode operation provides a fast
transient response and
improves loop
stabilization. Full prote ction featur es include
over-current protection and thermal shut down.
The MPQ2 8261 has an external SS pin to
program the soft-start time and power-good
signal output.
The MPQ28261 requires a minimal number of
readily-available standard external components
and is available in a space saving 3mmx4 mm
14-pin QFN package.
TYPICAL APPLICATION
21V, 3A, 500kHz Synchronous
Coverter
FEATURES
• Wide 4.5V-to-21V Operating Input Range
• 3A Maximum Continuous Output Current
• Integrated 120mΩ High-Side and 20mΩ
Low-Side Power MOSFETs
• 1% Reference Voltage Accuracy
• Up to 85% Efficiency (for Drops of 12V to
1.2V)
• Fixed 500kHz Switching Frequency
• External Soft-Start
• PG Output
• OCP and Thermal Shutdown
• Output Adjustable from 0.603V to 18V
• Available in a 3mm x 4mm 14-pin QFN
Package.
APPLICATIONS
• DSL Modems
• Cable Modems
• Set-Top Boxes
• Telecom
All MPS parts are lead-free and adhere to the RoHS directive. For MPS green
status, please visit MPS website under Products, Quality Assurance page.
“MPS” and “The Future of Analog IC Technology” are registered trademarks of
Monolithic Power Systems, Inc.
4.5V-21V
VIN
C1
22uF
ON/OFF
VCC
R10
100K
1 IN
BST 6
MPQ28261
9 PG
SW 2,3,4,5
C4
0.1uF
11 VCC
FB 8
C3
0.1uF L1
2.8uH
R1
Rt 10K
24K
7 EN
SS 10
GND AGND
12,13 14
C7
47nF
R2
10K
VOUT
1.2V/3A
C2
47uF
Efficiency vs. Load Current
VOUT=1.2V
100
90
80
70 VIN=4.5V
60
50 VIN=12V
40
30 VIN=21V
20
10
0
0 0.5 1 1.5 2 2.5 3 3.5
LOAD CURRENT (A)
MPQ28261 Rev. 1.12
www.MonolithicPower.com
10/10/2013
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
1
http://www.Datasheet4U.com
1 page  
MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER
PIN FUNCTIONS
QFN14
(3x4mm)
Pin #
Name
1 IN
2,3,4,5 SW
6 BST
7 EN
8 FB
9 PG
10 SS
11 VCC
12,13,
Exposed
Pad
GND
14 AGND
Description
Supply Voltage. Supplies power for the internal MOSFET and regulator. The MPQ28261
operates from a 4.5V-to-21V input rail. Requires a low-ESR and low-inductance
capacitor (C1) to decouple the input rail. Place the input capacitor close to this pin and
connect it with wide PCB traces and multiple vias.
Switch Output. Connect to the inductor and bootstrap capacitor. The internal high-side
MOSFET drives these pins up to the VIN voltage during the PWM duty-cycle on-time. The
inductor current drives the SW pins negative during the off-time. The on-resistance of the
low-side switch and the internal Schottky diode fixes the negative voltage. Connect using
wide PCB traces and multiple vias.
Bootstrap. Use a capacitor connected betwe en S W an d BST pins to fo rm a floating
supply across the high-side switch driver.
Enable. Con nected internally to a 1MΩ pull -down resistor. EN=1 to e nable th e
MPQ28261. Pull EN low to disable the part.
Feedback. Connect to the tap of an external resistor divider from the output to GND to
set the output voltage. The frequency fold-back comparator lowers the oscillator
frequency when the FB voltage is below 100mV to prevent current-limit runaway during a
short circuit fault condition. Place the resistor divider as close to FB pin as possible.
Avoid vias on the FB traces.
Power-Good Output. Active high. Pin output goes to open drain of an internal switch.
Power-good low-to-high threshold is 90% of regulation value. There is delay from FB ≥
90% to PG high during start up, which is about 1/4 of SS time. Power-good high-to-low
threshold is 80% of regulation value.
Soft-Start. Conne ct an ex ternal capacitor to p rogram the soft-st art time of th e switch -
mode regul ator. The soft-start pin connects to an i nternal reference source a nd to the
non-inverting input of an error am plifier. W hen the soft-start peri od begin s, a n interna l
10µA cu rrent sou rce be gins charging the c apacitor. The soft-sta rt voltage co ntinues to
rise until the voltage exceeds the reference voltage of 0.6V.
Bias Supply. Typical level of around 5.1V. Decouple with a 0.1μF-up-to-0.22μF capacitor.
Provides most of the power to the device’s internal circuits. Powered by VIN, and
operates in the full VIN range. When VIN exceeds 5.1V, VCC operates at maximum
output. When VIN falls below 5.1V, VCC decreases.
System Ground. Reference ground for the regulated output voltage. Requires special
care for PCB layout. Connect exposed pad to GND plane for optimal thermal
performance.
Signal Ground. AGND is not internally connected to System Ground—connect to System
Ground on PCB.
MPQ28261 Rev. 1.12
www.MonolithicPower.com
10/10/2013
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
5
5 Page 
MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER
FUNCTIONAL BLOCK DIAGRAM
IN
VCC
VCC
Regulator
PG PG Comparator
Oscillator
EN Reference
1MEG
FB
1pF
50pF 400 k
Error Amplifier
Current Sense
Amplifier
Boost
Regulator
HS
Driver
Current Limit
Comparator
Comparator
On Time
Control Logic
Control
VCC
LS
Driver
RSEN
BST
SW
GND
SS
Figure 1: Functional Block Diagram
MPQ28261 Rev. 1.12
www.MonolithicPower.com
10/10/2013
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
11
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| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet MPQ28261.PDF ] | |
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