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PDF NB670 Data sheet ( Hoja de datos )
| Número de pieza | NB670 | |
| Descripción | 24V High Current Synchronous Buck Converter | |
| Fabricantes | MPS | |
| Logotipo |  |
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The Future of Analog IC Technology
NB670
24V, High Current
Synchronous Buck Converter With LDO
DESCRIPTION
The NB670 is a fully integrated hig h frequen cy
synchronous rectified step-d own s witch mode
converter with 3.3V f ixed output voltage. It
offers very compact solution to achieve 6 A
continuous output cu rrent and 9A peak output
current ove r a wide in put supply range with
excellent load and line regulation. The NB670
operates at high efficiency over a wide output
current load range. Constant-On-Time (COT )
control mod e provides fast transient respo nse
and eases loop stabilization.
Under voltage lockout is internally set as 4.65 V.
An open drain po wer good signal indicates the
output is within its nominal voltage range.
NB670 also provides a 3.3V LDO, which can be
used to power the external peripheries, such as
the keyboard cont roller in the lapto p compute r.
A 300kHz CLK is also a vailable; its output can
be used to drive an external charge pump,
generating gate d rive voltage for the loa d
switches without redu cing the main converte r’s
efficiency.
Full protection feature s include OCP, OVP,
UVP and thermal shut down.
The converter requires minimum number of
external components and is availa ble in QFN16
(3mmx3mm) package.
TYPICAL APPLICATION
FEATURES
• Wide 5V to 24V Operating Input Range
• 3.3V Fixed Output Voltage
• Built-in 3.3V, 100mA LDO with Switches
• 6A Continuous Output Current
• 9A Peak Output Current
• 300kHZ CLK for External Charge Pump
• Lo w RDS(ON) Internal Power MOSFETs
• Proprietary Switching Loss Reduction
Technique
• Internal Soft Start
• Output Discharge
• 500kHZ Switching Frequency
• OCP, OVP, UVP Protection and Thermal
Shutdown
APPLICATIONS
• Laptop Computer
• Tablet PC
• Net working Systems
• Personal Video Recorders
• Flat Panel Television and Monitors
• Distributed Power Systems
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.
100
95
90
85
80
75
70
65
60
55
50 1
VIN=6V
VIN=8.4V
VIN=12.6V
VIN=19V
10 100 1000 10000
OUTPUT CURRENT (A)
NB670 Rev. 1.01
7/23/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
1
http://www.Datasheet4U.com
1 page  
NB670 ― 24V, HIGH CURRENT SYNCHRONOUS BUCK CONVERTER WITH LDO
PIN FUNCTIONS
PIN #
1 VIN
2
3
4 PG
5
6 LD
7 VO
8, 9
Exposed Pad
15, 16
10 BST
11 VC
12 EN
13 EN
14
Name
PGND
NC
CLK
O
UT
SW
C
LDO
AGND
Description
Supply Voltage. The VIN pin supplies power for internal MOSFET and regulator. The
NB670 operates from a +5V to +24V input rail. An input capacitor is needed to
decouple the input rail. Use wide PCB traces and multiple vias to make the
connection.
Power Ground. Use wide PCB traces and multiple vias to make the connection.
Not connected.
Power good output. The output of this pin is an open drain signal and is high if the
output voltage is higher than 95% of the nominal voltage. There is a delay from Vout
≥ 95% to PGOOD goes high.
300kHZ CLK output to drive the external charge pump
Internal 3.3V LD O o utput. D ecouple with a minimum 4.7µF c eramic c apacitor as
close t o t he pin as p ossible. X7R or X5R gr ade dielectric c eramic c apacitors ar e
recommended for their stable temperature characteristics.
Once the output voltage of the Buck regulator is ready, it will switch over the LDO
output to save the power loss.
Output v oltage s ense. F or t he N B670, the output o f t he Buck regulator is fixed to
3.3V. VOUT pin is u sed to se nse the output voltage of the Buck regulator, connect
this pi n t o the output c apacitor o f t he regulator directly. T his pi n als o acts as th e
input of the 3.3V LDO switch over power input.
Keep the VOUT sensing trace far away from the SW node. Vias should also be
avoided on the VOUT sensing trace.
Switch Output. Connect this pin to the inductor and bootstrap capacitor. This pin is
driven up to the VIN voltage by the high-side switch during the on-time of the PWM
duty cycle. The inductor current drives the SW pin negative during the off-time. The
on-resistance of the low-side switch and the internal diode fixes the negative
voltage. Use wide and short PCB traces to make the connection. Try to minimize the
area of the SW pattern.
Bootstrap. A c apacitor c onnected between S W a nd BST pins is required t o f orm a
floating supply across the high-side switch driver.
Internal 5V LDO output. The driver and control circuits are powered from this
voltage. Decouple with a minimum 1µF ceramic capacitor as close to the pin as
possible. X7R or X5R grade dielectric ceramic capacitors are recommended for their
stable temperature characteristics.
100mA LDO and VCC enable pin. ENLDO is in ternally pulled up to high. Leave this
pin open to enable the LDO. Drive it low to turn off all the regulators .
Buck regulator and charge pump clock enable pin. EN is a digital input that turns the
Buck r egulator a nd C LK on or off. W hen t he p ower s upply of t he c ontrol c ircuit is
ready, drive EN high t o t urn on t he Buck regulator and c harge pump c lock, dr ive it
low to turn them off.
Analog ground. The internal reference is referred to AGND.
NB670 Rev. 1.01
7/23/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
5
5 Page 
NB670 ― 24V, HIGH CURRENT SYNCHRONOUS BUCK CONVERTER WITH LDO
VNOISE
VS LOPE 2
V FB
V REF
Figure 3—Light Load Operation
As the output current in creases from the lig ht
load condit ion, the time period within which the
current mo dulator reg ulates becomes sho rter.
The HS -FET is turne d ON mo re frequently.
Hence, t he s witching freque ncy increases
correspondingly. The o utput cu rrent rea ches th e
critical le vel when the current modulator time is
zero. The critical le vel of the outp ut cu rrent is
determined as follows:
IOUT
=
(VIN −×VOUT) VOUT
2L×× FSW × VIN
(1)
It turns into PWM mode once the output curren t
exceeds the critical level. After that, the switching
frequency stays fairly c onstant over the output
current range.
Jitter and FB Ramp Slope
Jitter occurs in both PWM and skip modes when
noise in the V FB ripple propagate s a delay to th e
HS-FET d river, as sho wn in Figures 4 and 5 .
Jitter c an affect s ystem s tability, with nois e
immunity propor tional to the steep ness of V FB’s
downward slope. Ho wever, V FB rip ple does not
directly affect noise immunity.
VNOISE
V S L O PE1
VFB
VREF
HS D river
J itter
Figure 4—Jitter in PWM Mode
HS D river
Jitter
Figure 5—Jitter in Skip Mode
Selecting the Output Capacitors
The t raditional constan t-on-time co ntrol scheme
is intrinsica lly unstable if output capacitor’s ESR
is not large enough as an effective current-sense
resistor. Ce ramic capacitors usually can not be
used as output capacitor.
Figure 6 sho ws an e quivalent c ircuit in PW M
mode with the HS-FET off. To realize the stability,
the ESR value should be chosen as follow:
RESR
≥
TSTW
0.7 ×π
+
COUT
TSW is the switching period.
ON
2
(2)
L
SW
VOUT
R
FB
R
VOUT
ESR
CAP
Figure 6—Simplified Circuit in PWM Mode
The NB670 has built
in internal ramp
compensation to ma ke sure the system is stabl e
even without the help of output cap acitor’s ESR;
and thus the pure ce ramic capacitor solution can
be applicant. The pu re ceramic capacitor solution
can signif icantly reduce the output ripple, tot al
BOM cost and the board area.
Configuring the EN Control
The NB670 has t wo e nable pins t o control th e
on/off of the internal regulators.
ENLDO is used to en able or disable the whole
NB670 Rev. 1.01
7/23/2013
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet NB670.PDF ] | |
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