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PDF XRP6142 Data sheet ( Hoja de datos )
| Número de pieza | XRP6142 | |
| Descripción | Synchronous Step-Down Controller | |
| Fabricantes | Exar | |
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March 2010
XRP6142
Synchronous Step-Down Controller with DDR
Memory Termination
Rev. 1.0.0
GENERAL DESCRIPTION
The XRP6142 is a synchronous step down
switching controller for over 15 Amps point-of-
loads converters and optimized to generate
and support DDR I, II and III memory
voltages requirements.
Optimized to operate from standard 3.3V and
5V rails, the XRP6142 supports conversions
down to 0.5V from an input voltage as low as
1V and can reach efficiencies of up to 96%.
Based on a constant on-time control scheme
and operating at a constant switching
frequency over the whole input voltage range,
it provides excellent load transient response
while requiring no external compensation
components. Three selectable on-time options
allow for further switching frequency, solution
footprint and efficiency optimization.
Dedicated support for DDR I, II and II
memories is also provided. The XRP6142
easily generates VDDQ (VDD) or VTT voltages
while an on board buffer provides the buffered
VTT reference voltage.
Under-voltage Lock out, short-circuit and
over-current and over-temperature protection
insure safe operations under abnormal
operating conditions.
The XRP6142 is available in a compact RoHS
compliant “green”/halogen free 16-pin QFN
package.
APPLICATIONS
• High-Power Point-of-Loads Converters
• Audio-Video Equipments
• FPGA and DSP Power Supplies
• DDR Memory Based Embedded Systems
FEATURES
• Over 15A Point-of-Load Capable
− Down to 0.5V Output Voltage Conversion
− Up to 96% Efficiency
• Wide 1.0V-5.5V Input Voltage Range
Conversions
− Single Input 3.3V and 5V rails Operations
• Constant On-Time Operations
− Constant Frequency Operations
− No External Compensation
• DDR I, II & III Termination Support
− VDDQ/VDD or VTT Voltages Generation
− Buffered VTT Ref. Voltage Generation
• Soft-Start and Enable Functions
• UVLO, Short Circuit and Over Current
Protection
• RoHS Compliant “Green”/Halogen Free
3mm x 3mm 16-Pin QFN Package
TYPICAL APPLICATION DIAGRAM
VIN
CIN
3V-5.5V
VCC
EN
VIN GH
BST
SW
XRP6142
VREF
ILIM
REFIN
PGND
GL
CSGND
FB
AGND
Thermal
Pad
VDDQ/2
VTTREF
RLIM
Operation as DDR Supply
VDDQ
QT
L1
VOUT
ACNTL
VIN VOUT
VTT
CFF R1
COUT
R3
SP2996B
REF EN
QB R2
R4
GND
VREF
Figure. 1: XRP6142 as a Step-Down Converter or a DDR Supply
Exar Corporation
48720 Kato Road, Fremont CA 94538, USA
www.exar.com
Tel. +1 510 668-7000 – Fax. +1 510 668-7001
1 page  
XRP6142
Synchronous Step-Down Controller with DDR
Memory Termination
ORDERING INFORMATION
Part Number
Temperature
Range
Marking Package
Packing
Quantity
XRP6142EL0-5-F
XRP6142ELTR0-5-F
XRP6142EL1-0-F
XRP6142ELTR1-0-F
XRP6142EL2-0-F
XRP6142ELTR2-0-F
XRP6142EVB
6142E
-40°C≤TJ≤+125°C YYWW05
X
16-pin QFN
Bulk
6142E
-40°C≤TJ≤+125°C YYWW05
X
16-pin QFN 3K/Tape & Reel
6142E
-40°C≤TJ≤+125°C YYWW10
X
16-pin QFN
Bulk
6142E
-40°C≤TJ≤+125°C YYWW10
X
16-pin QFN 3K/Tape & Reel
6142E
-40°C≤TJ≤+125°C YYWW20
X
16-pin QFN
Bulk
6142E
-40°C≤TJ≤+125°C YYWW20
X
16-pin QFN 3K/Tape & Reel
XRP6142 Evaluation Board – XRP6142EL2-0-F based
Note 1
RoHS Compliant
Halogen Free
RoHS Compliant
Halogen Free
RoHS Compliant
Halogen Free
RoHS Compliant
Halogen Free
RoHS Compliant
Halogen Free
RoHS Compliant
Halogen Free
Note 2
0.5µs on time
0.5µs on time
1.0µs on time
1.0µs on time
2.0µs on time
2.0µs on time
“YY” = Year – “WW” = Work Week – “X” = Lot Number
© 2010 Exar Corporation
Page 5 of 17
Rev. 1.0.0
5 Page 
XRP6142
Synchronous Step-Down Controller with DDR
Memory Termination
( )CIN
=
I OUT ,MAX × VOUT ×
fs × 0.02VIN
VIN − VOUT
× VIN 2
SYNCHRONOUS FET (LOW-SIDE FET)
Select the synchronous FET for voltage rating
BVDSS, on resistance rating RDS(ON) and gate
drive rating VGS. As a rule of thumb, voltage
rating should be at least twice the converter
input voltage. FETs with voltage rating of up to
30V should provide satisfactory performance.
Drive voltage of 4.5V is sufficient for
applications with minimum input voltage of
4.5V. For applications with a lower input
voltage a FET with 2.5V gate drive should be
selected. Switching losses of the Synchronous
FET are negligible in comparison to its
conduction losses. RDS(ON) is calculated based
on conduction losses from:
( )RDS (ON ) ≤
PConduction
1 − D × IOUT 2
It is common practice to allocate 50% of the
total FET losses to the synchronous FET. As an
example, consider a 10W buck converter with
a target efficiency of 90%. Therefore, the
target total power loss is 1.1W. Assume that
the only significant non-FET loss is the
inductor loss estimated at 0.1W. Thus the
maximum conduction loss of the synchronous
FET should not exceed 0.5W. By using this
value in the above equation RDS(ON) can be
calculated and a suitable FET selected.
SWITCHING FET (HIGH-SIDE FET)
Select the switching FET for voltage rating
BVDSS, on-resistance rating RDS(ON), gate drive
rating VGS, rise time tr and fall time tf. BVDSS
and VGS selection guidelines are the same as
Synchronous FET. The switching FET incurs
switching (i.e., transitional) as well as
conduction losses. RDS(ON) is calculated based
on conduction losses from:
RDS (ON )
≤
PConduction
D × IOUT 2
It is common practice to allocate 50% of the
total high-side FET losses to conduction.
Proceeding with the example from previous
section the total target loss is 0.5W, and thus
target conduction loss equals 0.25W. By using
this value in the above equation RDS(ON) can be
calculated. Rise and fall time can be
approximated from:
tr
+tf
=
PSwitching
VIN × Iout ×
fs
Since the allotted switching loss budget is
0.25W, tr and tf can be calculated from the
above equation.
For a detailed explanation of FET losses and
FET selection procedure refer to EXAR
application note ANP-20.
R-C SNUBBER (OPTIONAL)
An R-C snubber placed across the synchronous
FET eliminates the ringing and reduces the
amplitude of overshoot at SW node. Use
surface-mount components and place them
close to the FET drain-source. Calculate the
value of snubber capacitor Csnb from:
Csnb = 3× Coss
Coss is the output capacitance of the
synchronous FET corresponding to VIN.
Calculate the value of the snubber resistor
Rsnb from:
Rsnb =
2 ×VOUT
I OUT
DDR MEMORY POWER APPLICATIONS
XRP6142 can be used to generate the required
VDDQ (VDD) or VTT Reference voltages for DDR I,
II and III memories and provides a 40mA
buffered VTT Reference voltage. When used in
conjunction with Exar’s SP2996 DDR Memory
Termination, the XRP6142 provides a complete
DDR power management solution. A cost-
effective DDR2 solution is shown on page 15.
XRP6142 provides the VDDQ and VTTREF
voltages. SP2996 provides the VTT voltage.
Please note that the current output of VDDQ
can be increased up to 10A by using a larger
QT/QB MOSFET and scaling the L1 and C3
accordingly.
© 2010 Exar Corporation
Page 11 of 17
Rev. 1.0.0
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet XRP6142.PDF ] | |
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