MICROSEMI LX1676

LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
maximizing regulator response.
A true differential input amplifier is
used for remote voltage sensing at the
processor core.
A VID code generator provides an
internal reference that will set the
output voltage. This VID code can be
changed during operation and the
reference will slew the output voltage to
its new setting at a preset rate. During
VID changes on the fly the Power Good
indication will stay valid.
Current through the lower phase 1
MOSFET will be sampled using its
RDS(ON) for current limit and shut
down.
For further protection, an over
voltage circuit will trip at a specified
setting and clamp the output by turning
off the upper MOSFETs and turning on
the lower MOSFETs.
The upper MOSFET drivers will use
a bootstrap capacitor to provide the
upper drive voltage over the input
voltage range of 6 to 24 volts.
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
WWW . Microsemi .C OM
The LX1676 is a highly integrated
VRM power supply controller IC
featuring two PWM switching
regulator stages.
The two constant frequency
voltage-mode PWM phases are
configured as a single biphase high
current output core supply.
In biphase operation, the high
current (>25A) output is generated by
a LoadSHARETM† technique that
balances the currents in the two
phases. Power loss and noise, due to
the ESR of the input capacitors, are
minimized by operating the PWMs
180° out of phase.
A
synchronized
Transient
Correction Loop† provides exceptional control of the output droop and
overshoot during very high di/dt load
changes, the circuit can be configured
for droop only, overshoot only or
both.
This architecture also minimizes
capacitor
requirements
while
APPLICATIONS
ƒ AMD Mobile Athlon™ or
Duron™ Processor Core
Voltage Supply
ƒ Voltage Regulator Modules
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
† Patent numbers US6292378,US6285571,US6356063, US6605931
PRODUCT HIGHLIGHT
T r a n s ie n t C o r r e c tio n L o o p
V in + 5 V
V in 6 to 2 4 V
70nH
LX1676
5 B it V ID
V in 6 to 2 4 V
Vout
LX1676
PACKAGE ORDER INFO
TJ (°C)
0 to 70
PW
Plastic TSSOP
38-Pin
LQ
Plastic MLPQ
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
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
1
38
36
37
35
34
33
ILIM3
EA2LP2
LP1
ILIM1
FBDFOUT
EO1
EA1DACOUT
PWGD
GND
VIN
ROSC
ENA
VID4
VID3
32
31
2
30
3
29
4
28
5
27
Connect Bottom to
Power GND
6
7
26
25
8
24
9
23
10
22
11
12
21
13
14
15
16
17
18
20
19
VS3
I-MAX
VC3
VC1
HO1
VS1
LO1
PGN
LO2
VCCL
I-MIN
PGN3
WWW . Microsemi .C OM
Supply Input Voltage (VCCL, VCC)................................................-0.3V to 6.0V
Battery Input Voltage (VIN) ..............................................................-0.3V to 24V
Current Limit Sense (ILIM1, ILIM3) ................................................-0.3V to 30V
Topside Driver Supply Input Voltage (VC1, VC2, VC3)........ -0.3 toVSx + 6.0V
Topside Driver Return Input Voltage (VS1, VS2)................................-5V to 24V
Differential Sense Input Voltage (FB+, FB-)....................................-0.3V to 6.0V
VID0 – VID4, Input Voltage ...............................................................-0.3V to 6V
High Side Driver Peak (<500ns) Current (HO1/2, I-MAX) ............................+1A
Low Side Driver Peak (<500ns) Sink Current (LO1/2, I-MIN)....................+1.5A
Operating Junction Temperature.................................................................. 150°C
Storage Temperature Range...........................................................-65°C to 150°C
Lead Temperature (Soldering 10 seconds) .................................................. 300°C
RoHS Peak Package Solder Reflow Temperature
(40 second maximum exposure) ..................................................... 260°C (+0, -5)
FB+
EO2
PACKAGE PIN OUT
VID2
VID1
VID0
VS2
HO2
VC2
VCC
ABSOLUTE MAXIMUM RATINGS
LQ PACKAGE
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
(Top View)
EA2EO2
FB+
FBDFOUT
EO1
EA1DACOUT
PWGD
GND
VIN
ROSC
ENA
VID4
VID3
VID2
VID1
VID0
VS2
1
38
19
20
LP2
LP1
ILIM1
ILIM3
VS3
I-MAX
VC3
VC1
HO1
VS1
LO1
PGN
LO2
VCCL
I-MIN
PGN3
VCC
VC2
HO2
PW PACKAGE
(Top View)
RoHS / Pb-free 100% Matte Tin Lead Finish
RECOMMENDED OPERATING CONDITIONS
Parameter
Symbol
Min
LX1676
Typ
Max
Units
IC Input Supply Voltage
Battery Input Voltage
Biphase Topside Driver Return Voltage
Transient Correction Phase Driver Return Voltage
Copyright © 2000
Revision: 1.0, 4/12/2005
VCC
VIN
VS1, VS2
VS3
4.5
5.7
0
0
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
5.5
24.0
24.0
5.5
PACKAGE DATA
`
V
V
V
V
Page 2
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
FUNCTIONAL PIN DESCRIPTION
Description
FB+
Differential Amplifier Positive Input – Feedback from output
FB-
Differential Amplifier Negative Input – Feedback from output
DFOUT
EA1-
Differential Amplifier Output
Phase 1 Error Amplifier Negative Input
EO1
Phase 1 Error Amplifier Output
GND
Analog Ground
ROSC
ENA
DACOUT
A resister to ground sets PWM frequency
Enable Input – Logic Low disables all converter phases
DAC Output voltage – 50uA bi-directional current source
VID4
Digital Input for VID code – Has an internal pull-up resister
VID3
Digital Input for VID code – Has an internal pull-up resister
VID2
Digital Input for VID code – Has an internal pull-up resister
VID1
Digital Input for VID code – Has an internal pull-up resister
VID0
Digital Input for VID code – Has an internal pull-up resister
PWGD
WWW . Microsemi .C OM
Name
Power Good Output Pin – Open drain output pin for power good indication. High = Power Good
VCC
IC Supply Voltage. Nominal +5V
VC3
Supply for transient correction phase upper MOSFET driver, bootstrap voltage
PGN3
Power ground pin for Transient Correction Loop driver
I-MIN
Output Driver for lower Transient Correction Loop MOSFET
VS3
Low side of upper driver for Transient Correction Loop – MOSFET Driver power return
I-MAX
Output Driver for upper Transient Correction Loop MOSFET
ILIM3
Transient Correction Loop current sense – A resister sets an upper limit for over current detection and shut down.
LP1
Phase 2 differential amplifier positive input, filtered feedback from phase 1 output
EA2-
Negative Input of phase 2 integrating amplifier
EO2
Output of phase 2 integrating amplifier
LP2
Phase 2 differential amplifier negative input, filtered feedback from phase 2 output
VIN
Battery Voltage Input.
LO2
Driver Output for phase 2 lower MOSFET
VS2
Low side of upper gate driver for phase 2.
Driver Output for phase 2 upper MOSFET
VC2
Supply for phase 2 upper MOSFET driver, bootstrap voltage
PGN
Power ground pin for current sensing of lower MOSFET RDS(ON) for phase 1.
LO1
Driver Output for phase 1 lower MOSFET
ILIM1
Over-Current Limit Set – A resister sets an upper limit for over current detection and shut down.
VS1
Low side of upper gate driver for phase #1.
HO1
Driver Output for phase 1 upper MOSFET
VC1
VCCL
PACKAGE DATA
HO2
Supply for phase 1 upper MOSFET driver, bootstrap voltage
Voltage bus for the lower MOSFET drivers. Nominal +5V
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 3
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS
Parameter
`
Symbol
Low Side Driver Operating
Current
High Side Driver Operating
Current
Unity Gain Bandwidth
Output Voltage Swing
Unity Gain Bandwidth
Slew Rate
9
1
mA
µA
ENA = VCC, FB+ = FBENA = GND
IQ(VCCL)
ENA = VCC, FB+ = FB-
0.5
1
mA
IQ(VCx)
ENA = VCC, FB+ = FB-
2
4
mA
6
100
mV
nA
dB
V
VOS
IEA1
Common Mode Voltage (VCM) = 1.4V
VICM
CMRR > 50dB
IEA1 = 2mA
IEA1 = -20uA
VOS
ADA
CMRRDA
RIN
VCM
VDFOUT(MAX)
VDFOUT (MIN)
UGBW
SR
-6
-100
60
0.8
70
2.5
4.0
0.15
20
0.5
V
MHz
VCM=1.4V
-6
0.99
0.8V < VCM < 2.5V
Measured at FB+ Input
1
65
30
0
VDFOUT = 0V
IDFOUT = 2mA
IEA1 = -20uA
6
1.01
3
5
4.0
0.2
10
5
mV
V/V
dB
KΩ
V
mA
V
MHz
V/µs
OSCILLATOR
Maximum Clock Frequency
Minimum Clock Frequency
Frequency Stability
fMAX
fMIN
RPWM=10kΩ
RPWM=50kΩ
0.9
180
1
200
4
1.1
220
MHz
KHz
%
PWM OUTPUT
Maximum Duty Cycle
DCMAX
Minimum Pulse Width
Dead Time
tPWM(MIN)
Ramp Amplitude
VRAMP
During Transient Correction Switching
Transient Correction Not Switching
3000pF Load
3000pF Load at 50% of VCCL
VIN = 6V
VIN = 12
VIN = 24 V
100
50
40
50
60
80
0.70
1.40
2.80
200
%
nS
nS
V
PHASE 2 INTEGRATING AMPLIFIER
Input Offset Voltage
DC Open Loop Gain
Output Voltage Swing
Unity Gain Bandwidth
Copyright © 2000
Revision: 1.0, 4/12/2005
VOS
VEO2(MAX)
VEO2(MIN)
UGBW
VCM=1.4V
-6
IEA2 = 2mA
IEA2 = -20uA
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
6
70
4.0
0.15
20
0.5
M V
dB
V
MHz
Page 4
ELECTRICALS
`
5
Units
DIFFERENTIAL AMPLIFIER
Input Offset Voltage
Gain
Common Mode Rejection Ratio
Input Resistance
Input Common Mode Range
Source / Sink Current
`
1
Max
IQ(VCC)
VEO1(MAX)
VEO1(MIN)
UGBW
Output Voltage Swing
`
LX1676
Typ
ERROR AMPLIFIER: PHASE 1
Input Offset Voltage
Input Bias Current
DC Open Loop Gain
Input Common Mode Range
`
Min
REGULATOR
IC Supply Current
`
Test Conditions
WWW . Microsemi .C OM
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.
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS (CONTINUED)
Parameter
`
VOS
ADA
CMRRDA
RB
UGBW
IHOx
Lower MOSFET Driver Current
ILOx
LP1=LP2
-6
0.98
Common Mode Voltage = 0 to 2 V
Units
1
60
180
4
6
1.02
mV
V/V
dB
KΩ
MHz
50
nS
50
nS
VDFOUT Rising 3000pF Load
40
mV
VDFOUT Falling 3000pF Load
40
mV
CL = 3000pF, VCx - VSx = 5V
50
50
nS
VHOx = 20mA, VCx - VSx = 5.0 V
VHOx = -20mA, VCx - VSx = 5.0 V
4.8
VLOx = 20mA, VCCL - VPGN = 5.0 V
VLOx = -20mA, VCCL - VPGN = 5.0 V
VCx - VSx = 5.0 V, Load = 3300pf at
<500nSec
VCCL - PGN = 5.0 V, Load = 3300pf at
<500nSec
4.8
IILIM1
tCSD(ILIM1)
4.9
0.1
4.9
0.1
V
0.2
V
0.2
1
A
1.5
A
44
200
50
400
60
500
µA
nS
40
200
50
400
60
500
µA
nS
TRANSIENT CORRECTION LOOP OVER CURRENT PROTECTION
IILIM3
tCSD(ILIM3)
1.5
0.3
100
V
V
KΩ
0.5
V
ELECTRICALS
ENABLE INPUT / VOLTAGE IDENTIFICATION (VID)
Logic Low Threshold
Hysteresis
Pullup Resistance
`
Max
PHASE 1 OVER CURRENT PROTECTION
Current Sense Bias Current
Current Sense Delay
`
tRISE
tFALL
High Side Driver Current
Current Sense Bias Current
Current Sense Delay
`
LX1676
Typ
OUTPUT DRIVERS
Driver
ƒ
Rise Time
ƒ
Fall Time
High Side Driver Voltage:
[VHOx - VVSx]
ƒ
Drive High
ƒ
Drive Low
Low Side Driver Voltage:
[VLOx – VPGN]
ƒ
Drive High
ƒ
Drive Low
`
Min
TRANSIENT CONTROL LOOP
Voltage Droop Sense
Propagation Delay : FB+ and
FB- to I-MAX
Voltage Overshoot Sense
Propagation Delay : FB+ and
FB- to I-MIN
Voltage Droop Sense Threshold
Voltage Overshoot Sense
Threshold
`
Test Conditions
PHASE 2 DIFFERENTIAL AMPLIFIER
Input Offset Voltage
Gain
Common Mode Rejection Ratio
Input Resistance
Unity Gain Bandwidth
`
Symbol
WWW . Microsemi .C OM
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.
POWER GOOD
Low Output Voltage
Copyright © 2000
Revision: 1.0, 4/12/2005
VPWGD
IPWGD = -3mA
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS (CONTINUED)
Parameter
`
Test Conditions
Min
LX1676
Typ
Max
Units
UVLO
VCC
ƒ
ƒ
VIN
ƒ
ƒ
`
Symbol
Threshold
Hysteresis
VCC Rising
Threshold
Hysteresis
VIN Rising
4.2
0.3
V
5.5
0.3
OVER VOLTAGE PROTECTION
Over Voltage Threshold
` UNDER VOLTAGE PROTECTION
Under Voltage Threshold
` DAC
-
1 ≤ VDACOUT ≤1.4
0.925 ≤ VDACOUT < 1
Initial DACOUT Accuracy
High Side Driver Current
IHOx
Lower MOSFET Driver Current
ILOx
2.35
V
0.800
V
1
2
1.4 < VDACOUT ≤ 2
VCx - VSx = 5.0 V, Load = 3300pf at
<500nSec
VCCL - PGN = 5.0 V, Load = 3300pf at
<500nSec
VID Logic High Threshold
VID Hysteresis
0.5
%
1
A
1.5
A
1.3
0.3
2
WWW . Microsemi .C OM
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.
V
V
VOLTAGE IDENTIFICATION (VID) CODE
Copyright © 2000
Revision: 1.0, 4/12/2005
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
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
ELECTRICALS
VID[4:0]
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
Page 6
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
SIMPLIFIED BLOCK DIAGRAM
EA1 -
EO1
WWW . Microsemi .C OM
DFOUT
VCCL
I-MAX
VC1
-
0°
-
HO1
R
-
VS1
+
+
FB -
+
Phase 1
Error Amp
Diff Amp
Q
S
I-MIN
FB +
LO1
I-MIN
DACOUT
PGOOD
50µA
PGN
Q
R
+
180°
VC2
S
DAC
POR
DACOUT
- 30mV
VID1
ILIM
DACOUT
UV
S R S
+
0.85
VID3
VID4
VS2
_
_
OV
+
2.35
LO2
Fault
S
gm
Bandgap
S
VCC
VIN
PWGD
S
UVLO
+
VID2
HO2
I-MAX
-
EA2 -
PGOOD
100K
90K
DACOUT
VIN
ROSC
0°
180°
PGN
35mV
offset
35mV
offset
Phase 2
Differential
Amp
+
_
VCCL
_IMIN
90K
+
VS3
LP2
90K
Bandgap
BLOCK DIAGRAM
VCC
VIN
90K
LP1
IMAX
+
_
AMP
FRQ
OSC
EO2
Phase 2
Integrating
Amp
+
VID0
ENA
GND
ILIM
ILIM3 ILIM1
Copyright © 2000
Revision: 1.0, 4/12/2005
ILIM
PGN3
I-Min
VS3 I-Max
VC3
ENA
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
APPLICATION CIRCUITS
WWW . Microsemi .C OM
CR3
UPS5817
+5VP
C13
47µf
6.3v
CR1
SK32
Q3
IRF7811W
L3 70µH
R2 61.9K
C12
0.22µF
C2
4700pF
CORE FB-
R3 61.9K
C7 10µF
25V
VBAT
Q2
NDS7002A
7
8
9
R10 45.3K 10
PWRGD
EN
VS3
ILIM3
31
+5VP
30
I-MAX
LP1
ILIM
LP2
EA2-
FB+
32
DFOUT
VC1
EO1
HO1
EA1-
VS1
DACOUT
LO1
PGN
LX1676
PWRGD
GND
VIN
LO2
VCCL
ROSC
I-MIN
ENA
PGN3
11
12
13
14
15
16
17
18
C4
UPS5817
29
VC3
VBAT
28
27
Q5
IRF7811W
C15
0.22µF
26
C19
10µF
25V
C20
10µF
25V
C21
10µF
25V
C105
10µF
L1 3.3µH
25
VCORE
24
23
C25
C11 4.7µF
6.3V
Q7
IRF7822
Q6
IRF7822
CR8 N/U
22
VCORE
RTN
21
20
C10 4.7µF
6.3V
VCC
Q1
NDS7002A
33
VC2
6
34
HO2
5
C4
4700pF
35
VS2
C5
0.22µF
36
VID0
R9 10K
4
R5 4.02K
VID1
3
R4 4.02K
VID2
R7 100K
+5VP
VID3
2
FB-
VID4
1
R6 4.02K
37
EO2
38
Q4
IRF7811W
C3
4700pF
C1 4700pF
R1 2K
CORE FB-
CR2
SK32
19
R21 10 Ohm
+5VP
C8 4.7µF
6.3V
C9 4.7µF
6.3V
R13 100K
R14 100K
VBAT
R15 100K
Q8
IRF7811W
R16 100K
C22
10µF
25V
C23
10µF
25V
C24
10µF
25V
C104
10µF
C17
0.22µF
R17 100K
L2 3.3µH
2.5V
VID(4)
VID(3)
VID(2)
+5VP
CR5
UPS5817
Q9
IRF7822
Q10
IRF7822
CR7 N/U
VID(1)
VID(0)
VBAT
C18
10µF
25V
+5VP
C103
47µF
6.3V
NOTE:
Q7 & Q10 Optional
APPLICATIONS
C25 Several Capacitors Under Processor Socket
Figure 2– Typical VRM Application
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 8
LX1676
TM
®
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
THEORY OF OPERATION
POWER UP AND INITIALIZATION
At power up, the LX1676 monitors the supply voltage to
VCC and Vin, Before both supplies reach their undervoltage lock-out (UVLO) thresholds, a power on reset
condition will prevent soft-start from beginning, the
oscillator is disabled and all MOSFETs are kept off.
SOFT-START
Once the supplies are above the UVLO threshold and the
Enable pin is brought high, the soft-start capacitor begins to
be charged up by the reference DAC through the DACOUT
pin. The capacitor voltage at the DACOUT pin rises as a
linear ramp. The DACOUT pin is connected to the error
amplifier’s non-inverting input which controls the output
voltage. The output voltage will follow the DACOUT pin
voltage.
Phase 3 (hysteretic phase) is disabled during soft-start.
Copyright © 2000
Revision: 1.0, 4/12/2005
OVER-CURRENT PROTECTION (PHASE 1)
The phase 1 current limit uses the RDS(ON) of the
lower MOSFET, together with a resistor (RSET) to set the
actual current limit point. The current limit comparator
senses the current 400 nS after the lower MOSFET is
switched on. A current source supplies a current (ISET),
of 50µA which flows into RSET and determines the
current limit trip point. The value of RSET is selected to
set the current limit for the application.
Phase 1 RSET is calculated by:
R SET =
ILimit • RDS(ON)
50 µA
The current limit comparator will trip when the drop
across RSET equals the drop across the lower MOSFET
RDS(ON)., at this time the comparator outputs a signal to
set the I limit latch and removes the enable command. The
Over-Current sensing is done on phase 1 only because
phase 2 current is always being forced to equal the phase
1 current, therefore the current trip point is set at half of the
desired current limit. For an output current limit setting of
30 amps, the current trip point for phase 1 is set at 15
amps.
When the phase 1 over current latch is set all three
phases are disabled, all MOSFETs are turned off.
Vin
50 uA
Q1
RSET
+
_
+
_
Vout
_
Iout
RDS(ON)
+
Current Limit
Comparator
Q2
Q2
Current
Flow
400nSec Delay
Figure 3 – Phase 1 Current Limit
The delay before current limit is activated will result in
current pulses exceeding the calculated values during the
delay period if a short circuit is applied during that time.
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APPLICATIONS
OVER-CURRENT PROTECTION
There are two separate current limit circuits in the
LX1676. One looks at the phase 1 lower MOSFET drain
current and the second looks at the phase 3 upper MOSFET
drain current. Both circuits have a 400 nS delay before a
current limit command is issued to the current limit latch,
once set the current limit latch will hold all three phases off
until it is reset.
The Over-Current Protection is disabled during positive
VID changes.
To reset the current limit latch either the enable command
(ENA) must be cycled low then back high or the input
power must cycle off and then back on.
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GENERAL DESCRIPTION
The LX1676 is a voltage-mode pulse-width modulation
controller integrated circuit. The PWM frequency is
programmable from 200kHz to 1MHz. The device has
external compensation, for more flexibility of the loop
response. The LX1676 also makes use of a true differential
input amplifier for remote voltage sensing at the actual
processor core. This is a very important feature now that
the core voltages are in the 1 to 2 volt range. The reference
for the biphase PWM output is a 5 bit VID code DAC. The
VID code DAC can generate a reference voltage of 0.925 to
2.000 volts. The output of the DAC is a bi-directional
current source and is connected to the DACOUT pin.
Connecting a capacitor from this pin to ground will
generate a linear ramp, which will determine the rate of
change of the output voltage. The rate of change can be set
so that the current required to charge the total output
capacitance is below the maximum current limit trip point.
This will allow VID changes on the fly without tripping the
over current sensor.
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
THEORY OF OPERATION (CONTINUED)
50 uA
ILIM3
+_
RSET
+
Current Limit
Comparator
+
RDS(ON)
Q1
_
ƒ
ƒ
ƒ
ƒ
Enable (ENA) pin being pulled low
Over-current condition on either phase 1 or phase 3
Over Voltage output > 2.35V
Under Voltage output < 0.85V
In all cases except Over Voltage all MOSFET drivers
will be latched off. For an Over Voltage fault the lower
MOSFETs for phase 1 and 2 will be held on to discharge
the bulk capacitance on the output till a lower limit of .85
volts is reached then all MOSFETS will be turned off.
To reset a fault it necessary to cycle the ENA pin low
then back high or remove and reapply the input voltage
VIN.
The Under Voltage monitor is not enabled until the
output voltage has ramped up to the level commanded by
the DACOUT pin and the PWGD output in high.
Vin
_
FAULT LOGIC
There are a number of possible states that will cause a
fault condition that will disable the output MOSFET
drivers. A fault condition will be caused by the following:
Vout
VS3
400nS Delay
Q2
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OVER-CURRENT PROTECTION (PHASE 3)
The hysteretic phase has its own current limit protection
because with it’s very fast response time with a 100 nH
inductor the upper MOSFET cannot be allowed to stay on
during an output short circuit condition. The phase 3 overcurrent sensing uses the RDS(ON) of the upper MOSFET
with a resistor RSET to determine the over current limit
point. A current source draws 50uA through RSET which
determines the required drop across the MOSFET
RDS(ON) to initiate a current limit condition.
PWM FREQUENCY
An external resistor sets the PWM frequency from the
ROSC pin to ground.
Figure 4 – Phase 3 Current Limit
Phase 3 RSET is calculated by:
The equation for ROSC is:
ILimit • RDSon
Rset =
50uA
ROSC =
OVER VOLTAGE PROTECTION
An over voltage protection circuit monitors the output
voltage and will latch all three phases off if an over voltage
condition (greater than 2.35 V) is detected.
Both
MOSFETs for phase 3 will be held off and the lower
MOSFETs for phase 1 and 2 will be held on to discharge
the output capacitor till the output voltage drops below .85
volt, at .85 volts all MOSFETs will be turned off.
1
(
K•f
) + 100e − 9
where ROSC is in KΩ, f is in Hz, K=105e-12
APPLICATIONS
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 10
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
THEORY OF OPERATION (CONTINUED)
Phase 1
Low Pass Filter
Phase 1 Diff
Amp
+
-
-
Differential
Amp
EA -
LP2
_
gm
180°
Phase 2
Integrating
Amp
Ramp .75 V to 3 V
Both PWMs
+
Phase 2
Comparator
HO1
LO1
PWM
+
DC Bias
Phase 1
Comparator
+
DC Bias
+
+
_
PWM
DACOUT
DC Bias
0°
-
Differential Feedbach From Vout
LP1
Phase 1 Error
Amp
HO2
Vout
LO2
EO2
APPLICATIONS
Phase 2
Low Pass Filter
Figure 5 – LoadSHARE Control Loop
Copyright © 2000
Revision: 1.0, 4/12/2005
WWW . Microsemi .C OM
The second feedback loop will use the output of the
phase 1 LPF as a reference signal for an error amplifier
that will compare this reference to the output of the phase 2
LPF. This error signal will be amplified and used to
control the PWM circuit of phase 2. Therefore, the duty
cycle of phase 2 will be set so that the equivalent voltage
potential will be forced across the phase 2 inductor as
compared to the phase 1 inductor. This will force the
current in the phase 2 inductor to follow and equal the
phase 1 inductor current.
With the LoadSHARETM topology it is possible to
imbalance the phases so that one phase will supply more
current than the other under unique situations. The LX1676
will normally be used with the same supply voltages on
phase 1 and 2 PWM inputs and will have equal currents in
both phases.
THEORY OF OPERATION FOR A BI-PHASE,
LOADSHARETM CONFIGURATION
The basic principle used in LoadSHARETM in a multiple
phase buck converter topology is that if multiple, identical,
inductors have the same identical voltage impressed across
their leads, they must then have the same identical current
passing through them. The current that we would like to
balance between inductors is mainly the DC component
along with as much as possible the transient current. All
inductors in a multiphase buck converter topology have
their output side tied together at the output filter capacitors.
Therefore this side of all the inductors has the same
identical voltage.
If the input side of the inductors can be forced to have
the same equivalent DC potential on this lead, then they
will have the same DC current flowing. To achieve this
requirement, phase 1 will be the control phase that sets the
output operating voltage, under normal PWM operation.
To force the current of phase 2 to be equal to the current of
phase 1; a second feedback loop is used. Phase 2 has a low
pass filter connected from the input side of each inductor.
This side of the inductors has a square wave signal that is
proportional to its duty cycle. The output of each LPF is a
DC
(+ some AC) signal that is proportional to the
magnitude and duty cycle of its respective inductor signal.
Microsemi
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Page 11
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
THEORY OF OPERATION (CONTINUED)
DACOUT
+5
VC3
+
Differential Feedback
From Output
FB -
35mV
I-Max
I-Max
Comparator
Vout
VCCL
VS3
70nH
+
-
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.
-
TRANSIENT CORRECTION LOOP
-
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.
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.
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LOOP GAIN AUTOMATIC COMPENSATION
FB +
+
35mV
I-Min
I-Min
Comparator
PGN3
Figure 6 – Phase 3 Transient Correction Loop
APPLICATIONS
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
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
APPLICATION NOTE
The allowed ESR can be found by:
VRIPPLE = ESR × I RIPPLE
(
VIN − VOUT
L
×
D
fs
∆I is the inductor ripple current, L is the output inductor
value and ESR is the Effective Series Resistance of the
output capacitor.
∆I should typically be in the range of 20% to 40% of the
maximum output current. Higher inductance results in
lower output voltage ripple, allowing slightly higher ESR to
satisfy the transient specification. Higher inductance also
slows the inductor current slew rate in response to the loadcurrent step change, ∆I, resulting in more output-capacitor
voltage droop. When using electrolytic capacitors, the
capacitor voltage droop is usually negligible, due to the
large capacitance
The inductor-current rise and fall times are:
TRISE = L×
∆I
(V
IN
− VOUT
)
and
TFALL = L×
∆I
∆I
×
D
fs
I RMS = I L d(0.5 − d) for d < 0.5
OUTPUT CAPACITOR
The output capacitor is sized to meet ripple and transient
performance specifications. Effective Series Resistance
(ESR) is a critical parameter. When a step load current
occurs, the output voltage will have a step that equals the
product of the ESR and the current step, ∆I. In an advanced
Copyright © 2000
Revision: 1.0, 4/12/2005
Where IL is the inductor current and d is the duty cycle.
The maximum RMS value of 0.25IL will occur when d =
25% or 75%.
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APPLICATIONS
VIN − VOUT
Where IRIPPLE is the inductor ripple current, ∆I is the
maximum load current step change, and VEX is the
allowed output voltage excursion in the transient.
Electrolytic capacitors can be used for the output
capacitor, but are less stable with age than tantalum
capacitors. As they age, their ESR degrades, reducing the
system performance and increasing the risk of failure. It is
recommended that multiple parallel capacitors be used, so
that, as ESR increase with age, overall performance will
still meet the processor’s requirements.
There is frequently strong pressure to use the least
expensive components possible, however, this could lead
to degraded long-term reliability, especially in the case of
filter capacitors. Microsemi’s demonstration boards use
the CDE Polymer AL-EL (ESRE) filter capacitors, which
are aluminum electrolytic, and have demonstrated
reliability. The OS-CON series from Sanyo generally
provides the very best performance in terms of long term
ESR stability and general reliability, but at a substantial
cost penalty. The CDE Polymer AL-EL (ESRE) filter
series provides excellent ESR performance at a reasonable
cost. Beware of off-brand, very low-cost filter capacitors,
which have been shown to degrade in both ESR and
general electrolytic characteristics over time.
INPUT CAPACITOR
The input capacitor and the input inductor, if used, are
to filter the pulsating current generated by the buck
converter to reduce interference to other circuits connected
to the same 5V rail. In addition, the input capacitor
provides local de-coupling for the buck converter. The
capacitor should be rated to handle the RMS input current
requirement. The RMS input current is:
VOUT
.
The inductance value can be calculated by:
L=
)
ESR × I RIPPLE + ∆I < VEX
where
∆I =
microprocessor power supply, the output capacitor is
usually selected from ESR instead of capacitance or RMS
current capability. A capacitor that satisfies the ESR
requirements usually has a larger capacitance and current
capability than strictly needed
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OUTPUT INDUCTOR
The output inductor should be selected to meet the
requirements of the output voltage ripple in steady-state
operation and the inductor current slew-rate during
transient. The peak-to-peak output voltage ripple is:
LX1676
TM
®
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
APPLICATION NOTE (CONTINUED)
PROGRAMMING THE OUTPUT VOLTAGE
Output voltage is determined by the internal 5 bit DAC.
The DAC inputs are the Voltage Identification (VID) 0-4
lines, the VID table lists the available output voltages for
the corresponding VID codes.
There are no external resistor dividers to program output
voltage and only the steps listed are available.
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SOFT-START CAPACITOR
An external soft-start capacitor is connected to the
DACOUT pin and will be charged, or discharged, at a
linear rate by the internal 50uA bi-directional current source
after the UVLO circuit has been satisfied. Whenever the
VID code is changed during normal operation the soft-start
capacitor will determine the rate of change at the output.
APPLICATIONS
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 14
LX1676
®
TM
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
38-Pin Thin Small Shrink Outline (TSSOP)
Dim
A
B
C
D
E
F
G
H
L
M
P
*LC
1
19
P
20
38
F
E
D
B
G
LQ
M
A
H
L
C
MILLIMETERS
MIN
MAX
0.85
0.95
0.19
0.25
0.09
0.20
9.60
9.80
4.30
4.50
0.50 BSC
0.05
0.15
–
1.10
0.50
0.75
0°
8°
6.25
6.50
–
0.10
INCHES
MIN
MAX
0.033
0.037
0.19
0.009
0.003
0.008
0.378
0.390
0.169
0.176
0.0196 BSC
0.002
0.005
–
0.043
0.020
0.030
0°
8°
0.246
0.256
–
0.004
MILLIMETERS
MIN
MAX
0.80
1.00
0
0.05
0.20 REF
0.18
0.30
5.00 BSC
3.00
3.25
7.00 BSC
5.00
5.25
0.50 BSC
0.30
0.50
INCHES
MIN
MAX
0.031
0.039
0
0.002
0.008 REF
0.007
0.011
0.196 BSC
0.118
0.127
0.275 BSC
0.196
0.206
0.019 BSC
0.012
0.020
WWW . Microsemi .C OM
PW
38-Pin Plastic MLPQ (5x7mm EP)
D
L
Dim
A
A1
A3
b
D
D2
E
E2
e
L
D2
E
E2
3
2
1
e
Note:
A1
Copyright © 2000
Revision: 1.0, 4/12/2005
b
A3
Microsemi
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Page 15
MECHANICALS
1. Dimensions do not include mold flash or protrusions; these
shall not exceed 0.155mm(.006”) on any side.
Lead
A
dimension shall not include solder coverage.
LX1676
TM
®
Mobile AMD Athlon™ VRM Controller
P RODUCTION D ATA S HEET
NOTES
WWW . Microsemi .C OM
NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
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 16