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IR3856WMPBF Schematic ( PDF Datasheet ) - International Rectifier

Teilenummer IR3856WMPBF
Beschreibung SYNCHRONOUS BUCK REGULATOR
Hersteller International Rectifier
Logo International Rectifier Logo 




Gesamt 30 Seiten
IR3856WMPBF Datasheet, Funktion
PD-97506
IR3856WMPbF
SupIRBuckTM
HIGHLY EFFICIENT
INTEGRATED 6A, SYNCHRONOUS BUCK REGULATOR
Features
Greater than 95% Maximum Efficiency
Wide Input Voltage Range 1.5V to 16V
Wide Output Voltage Range 0.7V to 0.9*Vin
Continuous 6A Load Capability
Integrated Bootstrap-diode
High Bandwidth E/A for excellent transient
performance
Programmable Switching Frequency up to 1.5MHz
Programmable Over Current Protection
PGood output
Hiccup Current Limit
Precision Reference Voltage (0.7V, +/-1%)
Programmable Soft-Start
Enable Input with Voltage Monitoring Capability
Enhanced Pre-Bias Start-up
Seq input for Tracking applications
-40oC to 125oC operating junction temperature
Thermal Protection
4mm x 5mm Power QFN Package
Halogen Free, Lead Free and RoHS compliant
Applications
Server Applications
Storage Applications
Embedded Telecom Systems
Distributed Point of Load Power Architectures
Description
The IR3856W SupIRBuckTM is an easy-to-use,
fully integrated and highly efficient DC/DC
synchronous Buck regulator. The MOSFETs co-
packaged with the on-chip PWM controller make
IR3856W a space-efficient solution, providing
accurate power delivery for low output voltage
applications.
IR3856W is a versatile regulator which offers
programmability of start up time, switching
frequency and current limit while operating in
wide input and output voltage range.
The switching frequency is programmable from
250kHz to 1.5MHz for an optimum solution.
It also features important protection functions,
such as Pre-Bias startup, hiccup current limit and
thermal shutdown to give required system level
security in the event of fault conditions.
Netcom Applications
Computing Peripheral Voltage Regulators
General DC-DC Converters
Rev 9.0
Fig. 1. Typical application diagram
1
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IR3856WMPBF Datasheet, Funktion
PD-97506
IR3856WMPbF
Electrical Specifications (continued)
Unless otherwise specified, these specifications apply over 4.5V< PVcc=Vcc<5.5V, Vin=12V
0oC<Tj< 125oC. Typical values are specified at Ta = 25oC.
Parameter
Oscillator
Rt Voltage
Frequency
Symbol
FS
Ramp Amplitude
Ramp Offset
Min Pulse Width
Fixed Off Time
Max Duty Cycle
Vramp
Ramp (os)
Dmin(ctrl)
Dmax
Error Amplifier
Input Offset Voltage
Input Bias Current
Input Bias Current
Sink Current
Source Current
Slew Rate
Gain-Bandwidth Product
DC Gain
Maximum Voltage
Minimum Voltage
Common Mode Voltage
Soft Start/SD
Soft Start Current
Soft Start Clamp Voltage
Shutdown Output
Threshold
Over Current Protection
OCSET Current
Vos
IFb(E/A)
IVp(E/A)
Isink(E/A)
Isource(E/A)
SR
GBWP
Gain
Vmax(E/A)
Vmin(E/A)
ISS
Vss(clamp)
SD
IOCSET
OC Comp Offset Voltage
SS off time
Bootstrap Diode
Forward Voltage
Deadband time
VOFFSET
SS_Hiccup
Test Condition
Rt=59K
Rt=28.7K
Rt=9.31K, Note4
Note4
Note4
Note4
Note4
Fs=250kHz
Vfb-Vseq,
Vseq=0.8V
Note4
Note4
Note4
Vcc=4.5V
Note4
Source
Fs=250kHz
Fs=500kHz
Fs=1500kHz
Note4
I(Boot)=30mA
Note4
Min TYP MAX
0.665
225
450
1350
92
0.7
250
500
1500
1.8
0.6
50
130
0.735
275
550
1650
200
-10
-1
-1
0.40
8
7
20
100
3.4
0
0
0.85
10
12
30
110
3.5
120
+10
+1
+1
1.2
13
20
40
120
3.75
220
1
14 20
2.7 3.0
26
3.3
0.3
20.8
23.6
43 48.8
136 154
-10 0
4096
26.4
54.6
172
+10
180 260
5 10
470
30
Units
V
kHz
Vp-p
V
ns
%
mV
μA
mA
V/μs
MHz
dB
V
mV
V
μA
V
μA
mV
Cycles
mV
ns
Rev 9.0
6
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IR3856WMPBF pdf, datenblatt
Circuit Description
THEORY OF OPERATION
Introduction
The IR3856W uses a PWM voltage mode control
scheme with external compensation to provide
good noise immunity and maximum flexibility in
selecting inductor values and capacitor types.
The switching frequency is programmable from
250kHz to 1.2MHz and provides the capability of
optimizing the design in terms of size and
performance.
IR3856W provides precisely regulated output
voltage programmed via two external resistors
from 0.7V to 0.9*Vin.
The IR3856W operates with an external bias
supply from 4.5V to 5.5V, allowing an extended
operating input voltage range from 1.5V to 21V.
The device utilizes the on-resistance of the low
side MOSFET as current sense element, this
method enhances the converter’s efficiency and
reduces cost by eliminating the need for external
current sense resistor.
IR3856W includes two low Rds(on) MOSFETs
using IR’s HEXFET technology. These are
specifically designed for high efficiency
applications.
Under-Voltage Lockout and POR
The under-voltage lockout circuit monitors the
input supply Vcc and the Enable input. It assures
that the MOSFET driver outputs remain in the off
state whenever either of these two signals drop
below the set thresholds. Normal operation
resumes once Vcc and Enable rise above their
thresholds.
The POR (Power On Ready) signal is generated
when all these signals reach the valid logic level
(see system block diagram). When the POR is
asserted the soft start sequence starts (see soft
start section).
Enable
The Enable features another level of flexibility for
start up. The Enable has precise threshold which
is internally monitored by Under-Voltage Lockout
(UVLO) circuit. Therefore, the IR3856W will turn
on only when the voltage at the Enable pin
exceeds this threshold, typically, 1.2V.
Rev 9.0
PD-97506
IR3856WMPbF
If the input to the Enable pin is derived from the
bus voltage by a suitably programmed resistive
divider, it can be ensured that the IR3856W does
not turn on until the bus voltage reaches the
desired level. Only after the bus voltage reaches
or exceeds this level will the voltage at Enable
pin exceed its threshold, thus enabling the
IR3856W. Therefore, in addition to being a logic
input pin to enable the IR3856W, the Enable
feature, with its precise threshold, also allows the
user to implement an Under-Voltage Lockout for
the bus voltage Vin. This is desirable particularly
for high output voltage applications, where we
might want the IR3856W to be disabled at least
until Vin exceeds the desired output voltage level.
Fig. 3a. Normal Start up, Device turns on
when the Bus voltage reaches 10.2V
Figure 3b. shows the recommended start-up
sequence for the non-sequenced operation of
IR3856W.
Fig. 3b. Recommended startup sequence,
Non-Sequenced operation
Figure 3c. shows the recommended startup
sequence for sequenced operation of IR3856W
12
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