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LX1676 Schematic ( PDF Datasheet ) - Microsemi Corporation

Teilenummer LX1676
Beschreibung Mobile AMD Athlon VRM Controller
Hersteller Microsemi Corporation
Logo Microsemi Corporation Logo 




Gesamt 16 Seiten
LX1676 Datasheet, Funktion
LX1676
TM ® Mobile AMD AthlonVRM Controller
PRODUCTION DATA SHEET
DESCRIPTION
The LX1676 is a highly integrated maximizing regulator response.
VRM power supply controller IC A true differential input amplifier is
featuring two PWM switching used for remote voltage sensing at the
www.rDeagtauSlhaeteot4rUs.tnaegt es.
processor core.
The two constant frequency A VID code generator provides an
voltage-mode PWM phases are internal reference that will set the
configured as a single biphase high output voltage. This VID code can be
current output core supply.
changed during operation and the
In biphase operation, the high reference will slew the output voltage to
current (>25A) output is generated by its new setting at a preset rate. During
a LoadSHARETM† technique that VID changes on the fly the Power Good
balances the currents in the two indication will stay valid.
phases. Power loss and noise, due to Current through the lower phase 1
the ESR of the input capacitors, are MOSFET will be sampled using its
minimized by operating the PWMs RDS(ON) for current limit and shut
180° out of phase.
down.
A synchronized Transient For further protection, an over
Correction Loop† provides except- voltage circuit will trip at a specified
ional control of the output droop and setting and clamp the output by turning
overshoot during very high di/dt load off the upper MOSFETs and turning on
changes, the circuit can be configured the lower MOSFETs.
for droop only, overshoot only or The upper MOSFET drivers will use
both.
a bootstrap capacitor to provide the
This architecture also minimizes upper drive voltage over the input
capacitor requirements while voltage range of 6 to 24 volts.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Patent numbers US6292378,US6285571,US6356063, US6605931
V in + 5 V
PRODUCT HIGHLIGHT
T ra n s ie n t C o rre c tio n L o o p
V in 6 to 2 4 V
70nH
5 B it V ID
LX1676
V in 6 to 2 4 V
KEY FEATURES
ƒ High Current Biphase
Operation
ƒ Outputs As Low As 0.925V
ƒ † Biphase LoadSHARETM
ƒ † Transient Correction Loop
Reduces Required
Capacitance
ƒ Differential Amplifier For
Remote Voltage Sensing
ƒ Integrated High Current
MOSFET Drivers
ƒ 200KHz to 1MHz Frequency
Operation
ƒ Programmable Slew Rate
Control For Start-Up Sequence
and VID change
ƒ VID Changes On The Fly
ƒ Power Good Indicator
ƒ Short Circuit Protection
ƒ Output Over Voltage and
Under Voltage Protection
ƒ No current-sense resistors
APPLICATIONS
ƒ AMD Mobile Athlonor
DuronProcessor Core
Voltage Supply
ƒ Voltage Regulator Modules
Vout
TJ (°C)
0 to 70
PACKAGE ORDER INFO
Plastic TSSOP
PW 38-Pin
Plastic MLPQ
LQ 38-Pin
RoHS Compliant / Pb-free Transition DC: 0518 RoHS Compliant / Pb-free Transition DC: 0512
LX1676CPW
LX1676CLQ
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1676CLQ-TR)
Copyright © 2000
Revision: 1.0, 4/12/2005
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1






LX1676 Datasheet, Funktion
LX1676
TM ® Mobile AMD AthlonVRM Controller
PRODUCTION DATA SHEET
ELECTRICAL CHARACTERISTICS (CONTINUED)
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C TA 70°C except where
otherwise noted and the following test conditions: VCC = 5V, VCCL = 5V, VIN = 12V, Switching Frequency = 500KHz.
Parameter
` UVLO
VCC
ƒ
ƒ
Threshold
Hysteresis
VIN
ƒ Threshold
ƒ Hysteresis
` OVER VOLTAGE PROTECTION
Over Voltage Threshold
` UNDER VOLTAGE PROTECTION
Under Voltage Threshold
` DAC
Initial DACOUT Accuracy
High Side Driver Current
Lower MOSFET Driver Current
VID Logic High Threshold
VID Hysteresis
Symbol
Test Conditions
VCC Rising
VIN Rising
-
1 VDACOUT 1.4
0.925 VDACOUT < 1
1.4 < VDACOUT 2
IHOx
VCx - VSx = 5.0 V, Load = 3300pf at
<500nSec
ILOx
VCCL - PGN = 5.0 V, Load = 3300pf at
<500nSec
LX1676
Units
Min Typ Max
4.2
0.3
5.5
0.3
2.35
0.800
1
2
1
1.5
0.5 1.3
0.3
2
V
V
V
%
A
A
V
V
VOLTAGE IDENTIFICATION (VID) CODE
VID[4:0]
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
VOUT (V)
2.000
1.950
1.900
1.850
1.800
1.750
1.700
1.650
1.600
1.550
1.500
1.450
1.400
1.350
1.300
Shutdown
VID[4:0]
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
VOUT (V)
1.275
1.250
1.225
1.200
1.175
1.150
1.125
1.100
1.075
1.050
1.025
1.000
0.975
0.950
0.925
Shutdown
Copyright © 2000
Revision: 1.0, 4/12/2005
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6

6 Page









LX1676 pdf, datenblatt
LX1676
TM ® Mobile AMD AthlonVRM Controller
PRODUCTION DATA SHEET
THEORY OF OPERATION (CONTINUED)
LOOP GAIN AUTOMATIC COMPENSATION
The PWM ramp shown in Figure 5 is automatically
adjusted to keep its amplitude fixed ratio to Vin over the
range of 6 to 24 V input.
This maintains a constant loop gain that is set by the
feedback networks around the error amplifiers independent
of PWM input voltage.
TRANSIENT CORRECTION LOOP
Phase 3 is a Transient Correction Loop that can sum a
large amount of current into the output node when required
by an out of range condition. The differential feedback
summing amplifier is connected directly to the output
terminals and has sufficient bandwidth to follow any fast
changes in output voltage. The feedback error voltage is
compared to the commanded reference voltage (DACOUT)
by two high speed comparators, I-Max and I-Min. The
other inputs of these comparators are offset from the
DACOUT as shown in Fig 6. If the error in output voltage
exceeds the offset in either direction the appropriate
MOSFET will be turned on to force current into or out of
the output node to correct the voltage error. The very low
value inductor (100nH) allows large amounts of current to
be forced into or out of the output node very quickly.
When the Transient Correction Loop is switching it
forces the appropriate upper or lower MOSFETs in phases
1 and 2 to stay on (100% or 0% duty cycle) until the error
is corrected.
The two drivers for the Transient Correction Loop have
outputs (I-Max) and (I-Min) that may be used to drive a
half bridge to correct for both low and high output voltage
conditions. This permits pulling the output low if an
overshoot occurs due to a rapid reduction in load current.
With a conventional Buck regulator rapid changes in the
negative direction are not possible due to the low voltage
available as a forcing function.
The two outputs (I-MAX and I-MIN) are completely
independent. A single MOSFET and diode can be used to
correct for voltage droop only or voltage overshoot only
when driven by the appropriate output. If the I-MAX driver
is not used the VC3 and VS3 pins must be connected to +5
volts.
Under normal operation the Transient Correction phase
is only active for a very brief time during high di/dt loads
on the output.
DACOUT
Differential Feedback
From Output
FB -
VC3
+
35mV
I-Max
Comparator
VCCL
I-Max
VS3
+5
Vout
70nH
FB +
35mV
+
I-Min
Comparator
I-Min
PGN3
Figure 6 – Phase 3 Transient Correction Loop
Copyright © 2000
Revision: 1.0, 4/12/2005
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 12

12 Page





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