US3007
5 BIT PROGRAMMABLE SYNCHRONOUS BUCK PLUS NON SYNCHRONOUS , LDO CONTROLLER AND 200MmA LDO ON BOARD
PRELIMINARY DATASHEET
FEATURES
DESCRIPTION
Provides Single Chip Solution for Vcore,
GTL+ ,Clock Supply & 3.3V Switcher on board
Second Switcher Provides Simple Control for
the On board 3.3V supply
200 mA On board LDO regulator
Designed to meet Intel VRM 8.2 and 8.3
specification for Pentium II
On board DAC programs the output voltage
from 1.3V to 3.5V
Linear regulator controller on board for 1.5V
GTL+ supply
Loss less Short Circuit Protection
Synchronous operation allows maximum
efficiency
Patented architecture allows fixed frequency
operation as well as 100% duty cycle during
dynamic load
Minimum part count
Soft Start
High current totem pole driver for direct
driving of the external Power MOSFET
Power Good function Monitors all Outputs
OVP Circuitry Protects the Switcher Outputs
and generates a Fault output
Thermal Shutdown
APPLICATIONS
Total Power Soloution for Pentium II processor
application
The US3007 controller IC is specifically designed to meet
Intel specification for Pentium II microprocessor applications as well as the next generation of P6 family
processors. The US3007 provides a single chip controller IC for the Vcore , LDO controller for GTL+
and an internal 200mA regulator for clock supply
which are required for the Pentium II applications.
It also contains a switching controller to convert 5V
to 3.3V regulator for an on board applications that
either uses AT type power supply or it is desired
not to rely on the ATX power supply’s 3.3V output.
These devices feature a patented topology that in combination with a few external components as shown in
the typical application circuit ,will provide in excess of
14A of output current for an on- board DC/DC converter
while automatically providing the right output voltage via
the 5 bit internal DAC .The US3007 also features, loss
less current sensing for both switchers by using the
Rds-on of the high side Power MOSFET as the sensing resistor, internal current limiting for the clock
supply, a Power Good window comparator that switches
its open collector output low when any one of the outputs is outside of a pre programmed window. Other features of the device are ; Undervoltage lockout for both
5V and 12V supplies, an external programmable soft
start function , programming the oscillator frequency via
an external resistor, OVP circuitry for both switcher outputs and an internal thermal shutdown.
TYPICAL APPLICATION
5V
SWITCHER2
CONTROL
Vout2
SWITCHER1
CONTROL
Vout1
LINEAR
REGULATOR
Vout4
US3007
LINEAR
CONTROL
Vout3
3007app3-1.0
Notes: Pentium II and Pentium Pro are
trade marks of Intel Corp.
PACKAGE ORDER INFORMATION
Ta (°C)
0 TO 70
Rev. 1.8
12/8/00
Device
US3007CW
Package
28 pin Plastic SOIC WB
4-1
US3007
ABSOLUTE MAXIMUM RATINGS
V5 supply Voltage ........................................... 7V
V12 Supply Voltage ............................................ 20V
Storage Temperature Range ................................. -65 TO 150°C
Operating Junction Temperature Range .......... 0 TO 125°C
PACKAGE INFORMATION
28 PIN WIDE BODY PLASTIC SOIC (W)
TOP VIEW
UGate2 1
28 V12
Phase2 2
27 UGate1
VID4 3
26 Phase1
VID3 4
25 LGate1
VID2 5
24 PGnd
VID1 6
23 OCSet1
VID0 7
22 Vsen1
PGood 8
21 Fb1
OCSet2 9
20 NC
Fb2 10
19 Fb3
V5 11
18 Gate3
SS 12
17 Gnd
Fault / Rt 13
16 Vout4
Fb4 14
15 Vsen2
θJA =80°C/W
ELECTRICAL SPECIFICATIONS
Unless otherwise specified ,these specifications apply over ,V12 = 12V, V5 = 5V and Ta=0 to 70°C. Typical values
refer to Ta =25°C. Low duty cycle pulse testing are used which keeps junction and case temperatures equal to the
ambient temperature.
PARAMETER
SYM TEST CONDITION
MIN
TYP
MAX
UNITS
Supply UVLO Section
UVLO Threshold-12V
Supply ramping up
10
V
UVLO Hysterises-12V
0.4
V
UVLO Threshold-5V
Supply ramping up
4.3
V
UVLO Hysterises-5V
0.3
V
Supply Current
Operating Supply Current
V12
6
mA
V5
30
Switching Controllers; Vcore (Vout 1) and I/O (Vout 2)
VID Section (Vcore only)
DAC output voltage (note 1)
0.99Vs Vs
1.01Vs V
DAC Output Line Regulation
0.1
%
DAC Output Temp Variation
0.5
%
VID Input LO
0.8
V
VID Input HI
2
V
VID input internal pull-up
resistor to V5
27
kΩ
Vfb2 Voltage
2
V
4-2
Rev. 1.8
12/8/00
US3007
Error Comparator Section
Input bias current
Input Offset Voltage
Delay to Output
Current Limit Section
C.S Threshold Set Current
C.S Comp Offset Voltage
Hiccup Duty Cycle
Output Drivers Section
Rise Time
Fall Time
Dead band Time Between
High side and Synch Drive
(Vcore Switcher Only)
Oscillator Section (internal)
Osc Frequency
2.5V Regulator (Vout 4)
Reference Voltage
Vo4
Reference Voltage
Dropout Voltage
Load Regulation
Line Regulation
Input bias current
Output Current
Current limit
Thermal Shutdown
1.5V Regulator (Vout 3)
Reference Voltage
Vo3
Reference Voltage
Input bias current
Output Drive Current
Power Good Section
Core U.V lower trip point
Core U.V upper trip point
Core U.V Hysterises
Core O.V upper trip point
Core O.V lower trip point
Core O.V Hysterises
I/O U.V lower trip point
I/O U.V upper trip point
FB4 lower trip point
FB4 upper trip point
FB3 lower trip point
FB3 upper trip point
Power Good Output LO
Power Good Output HI
Fault (Overvoltage) Section
Core O.V. upper trip point
Core O.V. lower trip point
Soft Start Section
Pull up resistor to 5V
Rev. 1.8
12/8/00
-2
Vdiff=10mV
2
+2
100
uA
mV
nS
+5
200
Css=0.1 uF
10
uA
mV
%
CL=3000pF
CL=3000pF
70
70
nS
nS
CL=3000pF
200
nS
Rt=Open
200
Khz
Ta=25, Vout4 = FB4
1.260
1.260
0.6
0.5
0.2
V
V
V
%
%
uA
mA
mA
°C
-5
Io = 200 mA
1mA< Io <200 mA
3.1V<VIO<4V, Vo=2.5V
2
200
300
145
Ta=25, GATE3 = FB3
1.260
1.260
2
50
Vsen1 ramping down
Vsen1 ramping up
V
V
uA
mA
Vsen2 ramping down
Vsen2 ramping up
FB4 ramping down
FB4 ramping up
FB3 ramping down
FB3 ramping up
RL=3mA
RL=5K pull up to 5V
0.90Vs
0.92Vs
.02Vs
1.10Vs
1.08Vs
.02Vs
2.4
2.6
0.95
1.05
0.95
1.05
0.4
4.8
V
V
V
V
V
V
V
V
V
V
V
V
V
V
Vsen1 ramping up
Vsen1 ramping down
1.17Vs
1.15Vs
V
V
OCset=0V , Phase=5V
23
KΩ
Vsen1 ramping up
Vsen1 ramping down
4-3
US3007
I/O O.V. upper trip point
Vsen2 ramping up
I/O O.V. lower trip point
Vsen2 ramping down
FAULT Output HI
Io=3mA
Note 1: Vs refers to the set point voltage given in Table 1.
D4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
D3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
D2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
D1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
D0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
Vs
1.30
1.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
2.05
D4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
4.3
4.2
10
D3
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
D2
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
V
V
V
D1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
D0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
Vs
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
Table 1 - Set point voltage vs. VID codes
PIN DESCRIPTIONS
PIN# PIN SYMBOL
7
VID0
6
VID1
5
VID2
4
VID3
3
VID4
8
PGOOD
21
FB1
4-4
Pin Description
LSB input to the DAC that programs the output voltage. This pin is TTL compatible that
realizes a logic “1” as either HI or Open. When left open,his pin is pulled up internally by
a 27kΩ resistor to 5V supply.
Input to the DAC that programs the output voltage. This pin is TTL compatible that realizes a logic “1” as either HI or Open. When left open,his pin is pulled up internally by a
27kΩ resistor to 5V supply.
Input to the DAC that programs the output voltage. This pin is TTL compatible that realizes a logic “1” as either HI or Open. When left open,his pin is pulled up internally by a
27kΩ resistor to 5V supply.
MSB input to the DAC that programs the output voltage. This pin is TTL compatible that
realizes a logic “1” as either HI or Open. When left open,his pin is pulled up internally by
a 27kΩ resistor to 5V supply.
This pin selects a range of output voltages for the DAC.When in the LOW state the range
is 1.3V to 2.05V and when it switches to HI state the range is 2.0V to 3.5V. This pin is
TTL compatible that realizes a logic “1” as either HI or Open. When left open,his pin is
pulled up internally by a 27kΩ resistor to 5V supply.
This pin is an open collector output that switches LO when any of the outputs are outside
of the specified under voltage trip point. It also switches low when Vsen1 pin is more than
10% above the DAC voltage setting.
This pin provides the feedback for the synchronous switching regulator. Typically this pin
can be connected directly to the output of the switching regulator. However, a resistor
divider is recommended to be connected from this pin to vout1 and GND to adjust the
output voltage for any drop in the output voltage that is caused by the trace resistance.
The value of the resistor connected from Vou1 to FB1 must be less than 100Ω.
Rev. 1.8
12/8/00
US3007
PIN# PIN SYMBOL
Pin Description
22
VSEN1
10
FB2
15
VSEN2
23
OCSET1
26
PHASE1
9
OCSET2
2
PHASE2
12
SS
13
FAULT/Rt
18
19
16
14
17
24
GATE3
FB3
VOUT4
FB4
GND
PGND
25
27
1
28
LGATE1
UGATE1
UGATE2
V12
11
V5
20
N.C
This pin is internally connected to the undervoltage and overvoltage comparators sensing
the Vcore status. It must be connected directly to the Vcore supply.
This pin provides the feedback for the non-synchronous switching regulator. A resistor
divider is connected from this pin to vout2 and GND that sets the output voltage. The
value of the resistor connected from Vout2 to FB2 must be less than 100Ω.
This pin is connected to the output of the I/O switching regulator. It is an input that
provides sensing for the Under/Over voltage circuitry for the I/O supply as well as the
power for the internal LDO regulator.
This pin is connected to the Drain of the power MOSFET of the Core supply and it
provides the positive sensing for the internal current sensing circuitry. An external resistor programs the C.S threshold depending on the Rds of the power MOSFET. An external
capacitor is placed in parallel with the programming resistor to provide high frequency
noise filtering.
This pin is connected to the Source of the power MOSFET for the Core supply and it
provides the negative sensing for the internal current sensing circuitry.
This pin is connected to the Drain of the power MOSFET of the I/O supply and it provides
the positive sensing for the internal current sensing circuitry. An external resistor programs the C.S threshold depending on the Rds of the power MOSFET. An external
capacitor is placed in parallel with the programming resistor to provide high frequency
noise filtering.
This pin is connected to the Source of the power MOSFET for the I/O supply and it
provides the negative sensing for the internal current sensing circuitry.
This pin provides the soft start for the 2 switching regulators. An internal resistor charges
an external capacitor that is connected from 5V supply to this pin which ramps up the
outputs of the switching regulators, preventing the outputs from overshooting as well as
limiting the input current. The second function of the Soft Start cap is to provide long off
time (HICCUP) for the synchronous MOSFET during current limiting.
This pin has dual function. It acts as an output of the OVP circuitry or it can be used to
program the frequency using an external resistor . When used as a fault detector, if any
of the switcher outputs exceed the OVP trip point, the FAULT pin switches to 12V and
the soft start cap is discharged. If the FAULT pin is to be connected to any external
circuitry, it needs to be buffered as shown in the application circuit.
This pin controls the gate of an external transistor for the 1.5V GTL+ linear regulator.
This pin provides the feedback for the linear regulator that its output drive is GATE3.
This pin is the output of the internal LDO regulator.
This pin provides the feedback for the internal LDO regulator that its output is Vout4.
This pin serves as the ground pin and must be connected directly to the ground plane.
This pin serves as the Power ground pin and must be connected directly to the GND
plane close to the source of the synchronous MOSFET. A high frequency capacitor
(typically 1 uF) must be connected from V12 pin to this pin for noise free operation.
Output driver for the synchronous power MOSFET for the Core supply.
Output driver for the high side power MOSFET for the Core supply.
Output driver for the high side power MOSFET for the I/O supply.
This pin is connected to the 12 V supply and serves as the power Vcc pin for the output
drivers. A high frequency capacitor (typically 1 uF) must be placed close to this pin and
PGND pin and be connected directly from this pin to the GND plane for the noise free
operation.
5V supply voltage. A high frequency capacitor (0.1 to 1 uF) must be placed close to this
pin and connected from this pin to the GND plane for noise free operation.
No connect
Rev. 1.8
12/8/00
4-5
US3007
BLOCK DIAGRAM
4.3V
Enable
V12
Over
Voltage
28
UVLO
V5
11
Vset
Enable
1.17Vset
Vset
7
VID1
6
VID2
5
VID3
4
VID4
3
Vsen1
22
Fb3
19
Gate3
18
Vsen2
15
1.1Vset
Enable
16
14
PGood
8
25
LGate1
26
Phase1
Osc
Soft
Start &
Fault
Logic
Over
Current
0.9Vset
23
OCSet1
2
Phase2
9
OCSet2
13
Fault / Rt
1
UGate2
24
PGnd
17
Gnd
10
Fb2
12
SS
V12
Slope
Comp
1.26V
0.9V
PWM
Control
+
V5
2.0V
Fb4
UGate1
200uA
V12
Vout4
27
V12
Slope
Comp
2.5V
5Bit
DAC
Fb1
PWM
Control
+
VID0
21
V12
Enable
3007blk1-1.4
Figure 1 - Simplified block diagram of the US3007
4-6
Rev. 1.8
12/8/00
TYPICAL APPLICATION
R22
12V
L1
C5
5V
C2
R9
C8
R12
C10
C14
C3
9
OCSet2
R10
Q1
28
V12
23
OCSet1
1 UGate2
UGate1 27
2 Phase2
Phase1 26
R13
Q3
L3
L2
Vout2
3.0V - 3.5V
C1
Vout1
1.8V - 3.5V
C16
R14
C4
Q4
LGate1 25
D1
R1
C13
R15
15 Vsen2
Vsen1 22
10 Fb2
R2
Fb1 21
R17
U1
R3
5V
R16
R21
PGnd 24
R19
11 V5
C15
NC 20
C19
PGood 8
Q2
18 Gate3
PGood
Fault/Rt 13
R5
19 Fb3
Vout3
1.5V
C17
VID0 7
VID1 6
R6
VID2 5
VID3 4
16 Vout4
Vout4
2.5V
C18
Fb4
14
R7
VID4 3
Gnd
17
SS
12
3007app1-1.2
R8
5V
C9
Figure 2 - Typical application of US3007 for an on board DC-DC converter providing power for the Vcore
, GTL+, Clock supply as well as an on board 3.3V I/O supply for the Deschutes and the
next generation processor applications.
Rev. 1.8
12/8/00
4-7
US3007
US3007 Application Parts List
Ref Desig
Q1
Q2
Q3
Q4
D1
L1
Description
MOSFET
MOSFET
MOSFET
MOSFET with Schottky
Diode
Inductor
L2
Inductor
Qty
1
1
1
1
1
1
1
1
L3
Inductor
1
C1
C2
C3
C4,13
C5,10
C8
C9,15,19
C14
C16
C17
C18
R1,5,13
,14
R2
R3,6,7,8
R5
R9
R10
R12
R16,17,21
R19
R22
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Ceramic
Capacitor, Ceramic
Capacitor, Ceramic
Capacitor, Ceramic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Resistor
2
1
1
2
2
1
3
2
6
1
1
4
Part #
IRL3103S, TO263 package
RLR024, TO252 package
IRL3103S, TO263 package
IRL3103D1S, TO263 package
MBRB1035, TO263 package
L=1uH, 5052 core with 4 turns of
1.0mm wire
L=4.7uH, 5052 core with 11 turns of
1.0mm wire
L=2.7uH, 5052B core with 7 turns of
1.2mm wire
6MV1500GX, 1500uF,6.3V
10MV470GX, 470uF,10V
10MV1200GX, 1200uF,10V
1000pF, 0603
220pF, 0603
1uF, 0805
1uF, 0603
10MV1200GX, 1200uF,10V
6MV1500GX, 1500uF,6.3V
6MV1000GX, 1000uF,6.3V
6MV150GX, 150uF,6.3V
4.7Ω, 5%, 1206
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
1
4
1
1
1
1
3
1
1
75Ω, 1%, 0603
100Ω, 1%, 0603
19.1Ω, 1%, 0603
1.5kΩ, 5%, 0603
10Ω, 5%, 1206
3.3kΩ, 5%, 0603
2.2kΩ, 1%, 0603
220kΩ, 1%, 0603
10Ω, 5%, 0603
4-8
Manufacture
IR
IR
IR
IR
IR
Micro Metal
Micro Metal
Micro Metal
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
Rev. 1.8
12/8/00
US3007
TYPICAL APPLICATION
(Dual Layout with HIP6019)
R22
12V
L1
C5
5V
C2
R9
C8
R12
C10
C14
C3
9
OCSet2
R10
Q1
28
V12
23
OCSet1
1 UGate2
UGate1 27
2 Phase2
Phase1 26
R13
Q3
L3
L2
Vout2
3.0V - 3.5V
C1
Vout1
1.8V - 3.5V
C16
R14
C4
Q4
LGate1 25
D1
R1
C13
R15
PGnd 24
15 Vsen2
Vsen1 22
10 Fb2
R2
Fb1 21
U1
R11
11 V5/Comp2
R4
C15
NC/Comp1 20
C11
C19
C7
Q2
R17
C12
C6
R3
R16
R21
R18
R19
PGood
PGood 8
18 Gate3
Fault/Rt 13
R5
Vout3
1.5V
19 Fb3
C17
VID0 7
VID1 6
R6
VID2 5
VID3 4
Vout4
2.5V
16 Vout4
C18
Fb4
14
R7
VID4 3
Gnd
17
SS
12
3007app2-1.5
R8
5V
C20
C9
Figure 3 - Typical application of US3007 in a dual layout with HIP6019 for an on board DC-DC converter providing
power for the Vcore , GTL+, Clock supply as well as an on board 3.3V I/O supply for the Deschutes and the
next generation processor applications.
Components that need to be modified to make the dual layout work for US3007 and HIP6019.
Part #
R4
R11
HIP6019 V
O
US3007 O
S
S - Short
O - Open
R18
C6
C7
C9
C11
C12
V
V
V
O
V
V
O
O
O
V
O
O
V - See Unisem or Harris parts list for the value.
C19
O
V
C20
V
O
Table 2 - Dual layout component table
Rev. 1.8
12/8/00
4-9
US3007
US3007 Application Parts List
Dual Layout with HIP6019
Ref Desig
Q1
Q2
Q3
Q4
D1
L1
Description
MOSFET
MOSFET
MOSFET
MOSFET with Schottky
Diode
Inductor
Qty
1
1
1
1
1
1
L2
Inductor
1
L3
Inductor
1
C1
C2
C3
C4,13
C5,10
C6,7,11,12
,20
C8
C9,15,19
C14
C16
C17
C18
R1,13,14
,15
R2
R3,6,7,8
R4,18
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Ceramic
Capacitor, Ceramic
Capacitor, Ceramic
2
1
1
2
2
5
Capacitor, Ceramic
Capacitor, Ceramic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Capacitor, Electrolytic
Resistor
1
3
2
6
1
1
4
Resistor
Resistor
Resistor
1
4
2
R5
R9
R10
R11
R12
R16,17,21
R19
R22
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
1
1
1
1
1
3
1
1
4-10
Part #
IRL3103S, TO263 package
IRLR024, TO252 package
IRL3103S, TO263 package
IRL3103D1S, TO263 package
MBRB1035, TO263 package
L=1uH, 5052 core with 4 turns of
1.0 mm wire
L=4.7uH, 5052 core with 11 turns of
1.0mm wire
L=2.7uH, 5052B core with 7 turns of
1.2mm wire
6MV1500GX, 1500uF,6.3V
10MV470GX, 470uF,10V
10MV1200GX, 1200uF,10V
1000pF, 0603
220pF, 0603
See Table 2, dual layout component
0603 * 5
1uF, 0805
1uF, 0603
10MV1200GX, 1200uF,10V
6MV1500GX, 1500uF,6.3V
6MV1000GX, 1000uF,6.3V
6MV150GX, 150uF,6.3V
4.7Ω, 5%, 1206
Manuf
IR
IR
IR
IR
IR
Micro Metal
Micro Metal
Micro Metal
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
Sanyo
75Ω, 1%, 0603
100Ω, 1%, 0603
See Table 2, dual layout component
0603 * 2
19.1Ω, 1%, 0603
1.5kΩ, 5%, 0603
10Ω, 5%, 1206
0Ω, 0603
3.3kΩ, 5%, 0603
2.2kΩ, 1%, 0603
220kΩ, 1%, 0603
10Ω, 5%, 0603
Rev. 1.8
12/8/00
US3007
Application Information
An example of how to calculate the components for the
application circuit is given below.
Assuming, two set of output conditions that this regulator must meet for Vcore :
a) Vo=2.8V , Io=14.2A, ∆Vo=185mV, ∆Io=14.2A
b) Vo=2V , Io=14.2A, ∆Vo=140mV, ∆Io=14.2A
Also, the on board 3.3V supply must be able to provide
10A load current and maintain less than ±5% total output voltage variation.
The regulator design will be done such that it meets the
worst case requirement of each condition.
Output Capacitor Selection
Vcore
The first step is to select the output capacitor. This is
done primarily by selecting the maximum ESR value
that meets the transient voltage budget of the total ∆Vo
specification. Assuming that the regulators DC initial
accuracy plus the output ripple is 2% of the output voltage, then the maximum ESR of the output capacitor is
calculated as :
ESR ≤
100
= 7 mΩ
14.2
The Sanyo MVGX series is a good choice to achieve
both the price and performance goals. The 6MV1500GX
, 1500uF, 6.3V has an ESR of less than 36 mΩ typ .
Selecting 6 of these capacitors in parallel has an ESR
of ≈6 mΩ which achieves our low ESR goal.
Other type of Electrolytic capacitors from other manufacturers to consider are the Panasonic “FA” series or
the Nichicon “PL” series.
3.3V supply
For the 3.3V supply, since there is not fast transient
requirement, 2 of the 1500uf capacitors is sufficient.
Reducing the Output Capacitors Using Voltage Level
Shifting Technique
The trace resistance or an external resistor from the output
of the switching regulator to the Slot 1 can be used to
the circuit advantage and possibly reduce the number
of output capacitors, by level shifting the DC regulation point when transitioninig from light load to
full load and vice versa. To accomplish this, the output of the regulator is typically set about half the DC
drop that results from light load to full load. For example,
if the total resistance from the output capacitors to the
Slot 1 and back to the GND pin of the 3007 is 5mΩ and
Rev. 1.8
12/8/00
if the total ∆I, the change from light load to full load is
14A, then the output voltage measured at the top of the
resistor divider which is also connected to the output
capacitors in this case, must be set at half of the 70 mV
or 35mV higher than the DAC voltage setting. This intentional voltage level shifting during the load transient
eases the requirement for the output capacitor ESR at
the cost of load regulation. One can show that the new
ESR requirement eases up by half the total trace resistance. For example, if the ESR requirement of the
output capacitors without voltage level shifting must be
7mΩ then after level shifting the new ESR will only need
to be 8.5mΩ if the trace resistance is 5mΩ (7+5/2=9.5).
However, one must be careful that the combined “voltage level shifting” and the transient response is still within
the maximum tolerance of the Intel specification. To insure this, the maximum trace resistance must be less
than:
Rs≤ 2(Vspec - 0.02*Vo - ∆Vo)/∆I
Where :
Rs=Total maximum trace resistance allowed
Vspec=Intel total voltage spec
Vo=Output voltage
∆Vo=Output ripple voltage
∆I=load current step
For example, assuming:
Vspec=±140 mV=±0.1V for 2V output
Vo=2V
∆Vo=assume 10mV=0.01V
∆I=14.2A
Then the Rs is calculated to be:
Rs≤ 2(0.140 - 0.02*2 - 0.01)/14.2=12.6mΩ
However, if a resistor of this value is used, the maximum
power dissipated in the trace (or if an external resistor is
being used) must also be considered. For example if
Rs=12.6 mΩ , the power dissipated is
(Io^2)*Rs=(14.2^2)*12.6=2.54W. This is a lot of power to
be dissipated in a system. So, if the Rs=5mΩ, then the
power dissipated is about 1W which is much more acceptable. If level shifting is not implemented, then the
maximum output capacitor ESR was shown previously
to be 7mΩ which translated to ≈ 6 of the 1500uF,
6MV1500GX type Sanyo capacitors. With Rs=5mΩ, the
maximum ESR becomes 9.5mΩ which is equivalent to
≈ 4 caps. Another important consideration is that if a
trace is being used to implement the resistor, the
power dissipated by the trace increases the case
temperature of the output capacitors which could
seriously effect the life time of the output capacitors.
4-11
US3007
Output Inductor Selection
The output inductance must be selected such that under low line and the maximum output voltage condition,
the inductor current slope times the output capacitor
ESR is ramping up faster than the capacitor voltage is
drooping during a load current step. However if the inductor is too small , the output ripple current and ripple
voltage become too large. One solution to bring the ripple
current down is to increase the switching frequency ,
however that will be at the cost of reduced efficiency and
higher system cost. The following set of formulas are
derived to achieve the optimum performance without
many design iterations.
The maximum output inductance is calculated using the
following equation :
L = ESR * C * ( Vinmin - Vomax ) / ( 2* ∆I )
Where :
Vinmin = Minimum input voltage
For Vo = 2.8 V , ∆I = 14.2 A
L =0.006 * 9000 * ( 4.75 - 2.8) / (2 * 14.2) = 3.7 uH
Assuming that the programmed switching frequency is
set at 200 KHZ , an inductor is designed using the
Micrometals’ powder iron core material. The summary
of the design is outlined below :
The selected core material is Powder Iron , the
selected core is T50-52D from Micro Metal wounded
with 8 Turns of # 16 AWG wire, resulting in 3 uH
inductance with ≈ 3 mΩ of DC resistance.
Assuming L = 3 uH and the switching frequency ; Fsw =
200 KHZ , the inductor ripple current and the output
ripple voltage is calculated using the following set of
equations :
T = 1/Fsw
T ≡ Switching Period
D ≈ ( Vo + Vsync ) / ( Vin - Vsw + Vsync )
D ≡ Duty Cycle
Ton = D * T
Vsw ≡ High side Mosfet ON Voltage = Io * Rds
Rds ≡ Mosfet On Resistance
Toff = T - Ton
Vsync ≡ Synchronous MOSFET ON Voltage=Io * Rds
∆Ir = ( Vo + Vsync ) * Toff /L
∆Ir ≡ Inductor Ripple Current
∆Vo = ∆Ir * ESR
∆Vo ≡Output Ripple Voltage
4-12
In our example for Vo = 2.8V and 14.2 A load , Assuming IRL3103 MOSFET for both switches with maximum
on resistance of19 m Ω, we have :
T = 1 / 200000 = 5 uSec
Vsw =Vsync= 14.2*0.019=0.27 V
D ≈ ( 2.8 + 0.27 ) / ( 5 - 0.27 + 0.27 ) = 0.61
Ton = 0.61 * 5 = 3.1 uSec
Toff = 5 - 3.1 = 1.9 uSec
∆Ir = ( 2.8 + 0.27 ) * 1.9 / 3 = 1.94 A
∆Vo = 1.94 * .006 = .011 V = 11 mV
Power Component Selection
Vcore
Assuming IRL3103 MOSFETs as power components,
we will calculate the maximum power dissipation as follows:
For high side switch the maximum power dissipation
happens at maximum Vo and maximum duty cycle.
Dmax ≈ ( 2.8 + 0.27 ) / ( 4.75 - 0.27 + 0.27 ) = 0.65
Pdh = Dmax * Io^2*Rds(max)
Pdh= 0.65*14.2^2*0.029=3.8 W
Rds(max)=Maximum Rds-on of the MOSFET at 125°C
For synch MOSFET, maximum power dissipation happens at minimum Vo and minimum duty cycle.
Dmin ≈ ( 2 + 0.27 ) / ( 5.25 - 0.27 + 0.27 ) = 0.43
Pds = (1-Dmin)*Io^2*Rds(max)
Pds=(1 - 0.43) * 14.2^2 * 0.029 = 3.33 W
3.3V Supply
Again,for high side switch the maximum power dissipation happens at maximum Vo and maximum duty cycle.
The duty cycle equation for non synchronous replaces
the forward voltage of the diode with the Synch MOSFET
on voltage. In equation below, Vf=0.5V
Dmax ≈ ( 3.3 + 0.5 ) / ( 4.75 - 0.27 + 0.5 ) = 0.76
Pdh = Dmax * Io^2*Rds(max)
Pdh= 0.76*10^2*0.029=2.21 W
Rds(max)=Maximum Rds-on of the MOSFET at 125°C
For diode, the maximum power dissipation happens at
minimum Vo and minimum duty cycle.
Dmin ≈ ( 3.3 + 0.5 ) / ( 5.25 - 0.27 + 0.5 ) = 0.69
Pdd = (1-Dmin)*Io*Vf=(1 - 0.69) * 10 * 0.5 = 1.55 W
Switcher Current Limit Protection
The US3007 uses the MOSFET Rds-on as the sensing
resistor to sense the MOSFET current and compares to
a programmed voltage which is set externally via a resistor (Rcs) placed between the drain of the MOSFET
and the “CS+” terminal of the IC as shown in the application circuit.
Rev. 1.8
12/8/00
US3007
For example, if the desired current limit point is set to
be 22A for the synchronous and 16A for the non synchronous , and from our previous selection, the maximum MOSFET Rds-on =19mW, then the current sense
resistor Rcs is calculated as :
Vcore
Vcs=IcL*Rds=22*0.019=0.418V
Rcs=Vcs/Ib=(0.418V)/(200uA)=2.1kΩ
Where: Ib=200uA is the internal current setting of the
US3007
3.3V supply
Vcs=IcL*Rds=16*0.019=0.3V
Rcs=Vcs/Ib=(0.3V)/(200uA)=1.50kΩ
1.5V, GTL+ Supply LDO Power MOSFET Selection
The first step in selectiong the power MOSFET for the
1.5V linear regulator is to select its maximum Rds-on of
the pass transistor based on the input to output Dropout
voltage and the maximum load current.
Rds(max)=(Vin - Vo)/IL
For Vo=1.5V, and Vin=3.3V , IL=2A
Rds-max=(3.3 - 1.5)/2= 0.9Ω
Note that since the MOSFETs Rds-on increases with
temperature, this number must be divided by ≈ 1.5,
inorder to find the Rds-on max at room temperature. The
Motorola MTP3055VL has a maximum of 0.18Ω Rds-on
at room temperature, which meets our requirement.
To select the heatsink for the LDO Mosfet the first step
is to calculate the maximum power dissipation of the
device and then follow the same procedure as for the
switcher.
Pd = ( Vin - Vo ) * IL
Where :
Pd = Power Dissipation of the Linear Regulator
IL = Linear Regulator Load Current
For the 1.5V and 2A load:
Pd = (3.3 - 1.5)*2=3.6 W
Assuming Tj-max=125°C
Ts = Tj - Pd * (θjc + θcs)
Ts = 125 - 3.6 * (1.8 + 0.05) = 118 °C
With the maximum heat sink temperature calculated in
the previous step, the Heat Sink to Air thermal resistance (θsa) is calculated as follows :
Assuming Ta=35 °C
∆T = Ts - Ta = 118 - 35 = 83 °C Temperature Rise
Above Ambient
θsa = ∆T/Pd
θsa = 83 / 3.6 = 23 °C/W
Rev. 1.8
12/8/00
The same heat sink as the one selected for the switcher
MOSFETs is also suitable for the 1.5V regulator.
2.5V, Clock Supply
The US3007 provides a complete 2.5V regulator with a
minimum of 200mA current capability. The internal regulator has short circuit protection with internal thermal
shutdown.
1.5V and 2.5V Supply Resistor Divider Selection
Since the internal voltage reference for the linear regulators is set at 1.26V for US3007, there is a need to use
external resistor dividers to step up the voltage. The resistor dividers are selected using the following equations:
Vo=(1+Rt/Rb)*Vref
Where:
Rt=Top resistor divider
Rb=Bottom resistor divider
Vref=1.26V typical
For 1.5V supply :
Assuming Rb=1kΩ
Rt=Rb*[(Vo/Vref) - 1]
Rt=1*[(1.5/1.26) - 1]=191Ω
For 2.5V supply :
Assuming Rb=1.02kΩ
Rt=Rb*[(Vo/Vref) - 1]
Rt=1.02*[(2.5/1.26) - 1]=1kΩ
Switcher Output Voltage Adjust
Vcore
As it was discussed earlier,the trace resistance from
the output of the switching regulator to the Slot 1 can be
used to the circuit advantage and possibly reduce the
number of output capacitors, by level shifting the DC
regulation point when transitioninig from light load to full
load and vice versa. To account for the DC drop, the
output of the regulator is typically set about half the DC
drop that results from light load to full load. For example,
if the total resistance from the output capacitors to the
Slot 1 and back to the GND pin of the 3007 is 5mΩ and
if the total ∆I, the change from light load to full load is
14A, then the output voltage measured at the top of the
resistor divider which is also connected to the output
capacitors in this case, must be set at half of the 70 mV
or 35mV higher than the DAC voltage setting. To do this,
the top resistor of the resistor divider(R17 in the application circuit) is set at 100Ω, and the R19 is calculated.
For example, if DAC voltage setting is for 2.8V and the
desired output under light load is 2.835V, then R19 is
calculated using the following formula :
4-13
US3007
R19= 100*{Vdac /(Vo - 1.004*Vdac)} [Ω]
R19= 100*{2.8 /(2.835 - 1.004*2.800)} = 11.76 kΩ
Select 11.8 kΩ , 1%
Note: The value of the top resistor must not exceed
100Ω. The bottom resistor can then be adjusted to raise
the output voltage.
3.3V supply
The loop gain for the non synchronous switching regulator is intentionally set low to take advantage of the level
shifting technique to reduce the number of output capacitors. Typically there is a 1% drop in the output voltage from light load (discontinous conduction mode) to
full load (continous conduction mode) in the 3.3V supply. To account for this, the output voltage is set at 3.5V
typically. The same procedure as for the synchronous is
applied to the non synch with the exception that the
internal voltage reference of this regulator is internally
set at 2V. The following is the set of equations to use for
the output voltage setting for the non-synchronous assuming the Vo=3.5V and the top resistor,( R2 in the application circuit ) is; R2=75Ω. The bottom resistor, R3 is
calculated as follows:
R3= R2*{2 /(Vo - 2)} [Ω]
R3= 75*{2 /(3.5 - 2)} = 100Ω , 1%
Note: The value of the top resistor , R2 must not
exceed 100Ω.
Soft Start Capacitor Selection
The soft start capacitor must be selected such that during the start up when the output capacitors are charging
up, the peak inductor current does not reach the current
limit treshold. A minimum of 1uF capacitor insures this
for most applications. An internal 10uA current source
charges the soft start capacitor which slowly ramps up
the inverting input of the PWM comparator Vfb3. This
insures the output voltage to ramp at the same rate as
the soft start cap thereby limiting the input current. For
example, with 1uF and the 10uA internal current source
the ramp up rate is (∆V/ ∆t)=I/C = 1V/100mS. Assuming that the output capacitance is 9000uF, the maximum start up current will be:
I=9000uF*(1V/100mS)=0.09A
Input Filter
It is highly recommended to place an inductor between
the system 5V supply and the input capacitors of the
switching regulator to isolate the 5V supply from the
switching noise that occurs during the turn on and off of
the switching components. Typically an inductor in the
range of 1 to 3 uH will be sufficient in this type of application.
4-14
External Shutdown
The best way to shutdown the US3007 is to pull down
on the soft start pin using an external small signal transistor such as 2N3904 or 2N7002 small signal MOSFET.
This allows slow ramp up of the output, the same as the
power up.
Layout Considerations
Switching regulators require careful attention to the layout of the components, specifically power components
since they switch large currents. These switching components can create large amount of voltage spikes and
high frequency harmonics if some of the critical components are far away from each other and are connected
with inductive traces. The following is a guideline of how
to place the critical components and the connections
between them in order to minimize the above issues.
Start the layout by first placing the power components:
1) Place the input capacitors C3 and C14 and the high
side mosfets ,Q1 and Q3 as close to their respective
input caps as possible
2) Place the synchronous mosfet,Q4 and the Q3 as
close to each other as possible with the intention that
the source of Q3 and drain of the Q4 has the shortest
length. Repeat this for the Q1 and D1 for the non synchronous.
3) Place the snubber R15 & C13 between Q4 & Q3.
Repeat this for R1 and C4 with respect to the Q1 and D1
for the non synchronous.
4) Place the output inductor ,L3 and the output capacitors ,C16 between the mosfet and the load with output
capacitors distributed along the slot 1 and close to it.
Repeat this for L2 with respect to the C1 for the non
synchronous.
5) Place the bypass capacitors, C8 and C19 right next
to 12V and 5V pins. C8 next to the 12V, pin 28 and C19
next to the 5V, pin 11.
6) Place the US3007 such that the pwm output drives,
pins 27 and 25 are relatively short distance from gates
of Q3 and Q4. The non-synch MOSFET must also be
situated such that the distance from its gate to the pin 1
of the US3007 is also relatively short.
7) Place all resistor dividers close to their respective
feedback pins.
8) Place the 2.5V output capacitor, C18 close to the
pin16 of the IC and the 1.5V output capacitor, C17 close
to the Q2 MOSFET.
Rev. 1.8
12/8/00
US3007
Note: It is better to place the 1.5V linear regulator components close to the 3007 and then run a trace from the
output of the regulator to the load. However, if this is not
possible then the trace from the linear drive output pin,
pin 18 must be run away from any high frequency
data signals.
It is critical, to place high frequency ceramic capacitors close to the clock chip and termination
resistors to provide local bypassing.
9) Place R12 and C10 close to pin 23 and R9 and C5
close to pin 9.
10) Place C9 close to pin 12
Component connections:
Note : It is extremely important that no data bus
should be passing through the switching regulator
section specifically close to the fast transition nodes
such as PWM drives or the inductor voltage.
Using the 4 layer board, dedicate on layer to GND, another layer as the power layer for the 5V, 3.3V, Vcore,
1.5V and if it is possible for the 2.5V.
Connect all grounds to the ground plane using direct vias to the ground plane.
Use large low inductance/low impedance plane to connect the following connections either using component
side or the solder side.
a) C14 to Q3 Drain and C3 to Q1 drain
b) Q3 Source to Q4 Drain and Q1 Source to D1 cathode
c) Q4 drain to L3 and D1 cathode to L2
d) L3 to the output capacitors, C16 and L2 to the output
capacitors, C1
e) C16 to the load, slot 1
f) Input filter L1 to the C16 and C3
g) C1 to Q2 drain
h) C17 to the Q2 source
I) A minimum of 0.2 inch width trace from the C18 capacitor to pin 16
Connect the rest of the components using the shortest
connection possible
Rev. 1.8
12/8/00
4-15