Page 1
FEATURESFEATURES
8 pin SOIC Switching Controller with
HICCUP Current Limiting Reduces Diode
Power Dissipation to Less than 1% of Normal
Operation
Soft Start Capacitor allows for smooth Output
Voltage ramp up
On board MOSFET driver
Fastest transient response of any controller
method. ( 0 to 100% Duty Cycle in 100 nS )
1% internal voltage reference
Internal Under Voltage Lockout protects
MOSFET during start-up
APPLICATIONSAPPLICATIONS
Dual supply low voltage processor applications,
such as: P55C,CYRIX M2, POWER PC and
AMD K6
Simple 5V to 3.3V switcher for Pentium with AGP
or Pentium II applications
US3034
8 PIN PWM SWITCHER
CONTROLLER IC
PRELIMINARY DATASHEET
DESCRIPTIONDESCRIPTION
The US3034 IC provides an 8 pin low cost switching
controller with true short circuit protection all in a
compact 8 pin surface mount package, providing a
low cost switching solution for dual supply processor
applications that require switching regulator for the 3.3V
supply such as the applications with AGP on board.
Typically in these applications a dual supply regulator
converts 5V to 3.3V for I/O supply and a jumper programmable supply of 1.25V to 3.5V for CORE supply .
The IC uses an internal regulator generated from the 12V
supply to power the controller as well as the 12V supply
to drive the power MOSFET, allowing a low cost N channel MOSFET to be used. The IC also includes an error
comparator for fast transient response, a precise voltage reference for setting the output voltage as well as a
direct drive of the MOSFET for the minimum part count.
TYPICAL APPLICATIONTYPICAL APPLICATION
C6
R8
R4
R5
R7
R6
Vout
C7
12V
5V
C8
Drv V12 Vfb Vhyst
1 2 3 4
C3
R1
L1
C1
Q2
C2
US3034
5678
GndCS-CS+SS
R3 C5
C4
L2
D1R2
3034app1-1.0
Typical application of US3034
Notes: P55C,Pentium II are trade marks of Intel Corp. K5 & K6 are trade marks of AMD corp. Cyrix 6X86L,M1,M2 are trade marks of
Cyrix Corp. Power PC is trade mark of IBM Corp.
PACKAGE ORDER INFORMATIONPACKAGE ORDER INFORMATION
TA (°C) 8 PIN PLASTIC
SOIC (S)
0 TO 70 US3034CS
Rev. 1.8
1/13/99
4-1
Page 2
US3034
ABSOLUTE MAXIMUM RATINGSABSOLUTE MAXIMUM RATINGS
V12 Supply Voltages ............................................................. 20V
F.B Pin Voltages........................................................ -0.3V to 5V
Storage Temperature Range ................................. -65 TO 150°C
Operating Junction Temperature ............................... 0 TO 150°C
PACKAGE INFORMATIONPACKAGE INFORMATION
8 PIN PLASTIC SOIC (S)
TOP VIEW
1
Drv
2
V12
3
Vfb
4
Vhyst Gnd
θJA =160°C/W
8
SS
7
CS+
6
CS-
5
ELECTRICAL SPECIFICATIONSELECTRICAL SPECIFICATIONS
Unless otherwise specified the following specification applies over V12 =12V, and TA =0 to 70°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
F.B Voltage Initial Accuracy VFB TJ =25°C 1.237 1.250 1.262 V
F.B Voltage Total Variation 1.225 1.250 1.275 V
F.B Voltage Line Regulation 0.2 %
F.B Input Bias Current IFB VFB =1.25V -1 +1 uA
Min On Time VFB is sq wave with 300 ns on 800 nS
time and 2 uS off time
Min Off Time VFB is sq wave with 300 ns off 800 nS
time and 2 uS on time
Vhyst pin output-HI ISOURCE =500uA, VFB =1.5V 11 V
Vhyst pin output-LO ISINK =500uA, VFB =1V 1 V
Supply Current I12SW VFB =1V 10 mA
Maximum Duty Cycle DMAX VFB =1V 100 %
Minimum Duty Cycle DMIN VFB =1.5V 0 %
Gate Drive Rise/Fall Time VGATE Load=IRL3303 70 nS
C.L Threshold Current ICL C.S+ , C.S- from 1.3V to 3.7V 20 uA
C.S Comp Common Mode VCS+ = VCS- 0 4.5 V
Soft Start Current 10 uA
4-2
Rev. 1.8
1/13/99
Page 3
PIN DESCRIPTIONSPIN DESCRIPTIONS
PIN # PIN SYMBOL PIN DESCRIPTION
3 VFB
6 C.S-
7 C.S+
5 Gnd
1 Drv
4 VHYST
2 V12
8 S.S
A resistor divider from this pin to the output of the switching regulator and ground sets the
Core supply voltage.
This pin is connected to the minus side of the external current sense resistor. An internal
current source together with an external resistor in series with this pin programs the
current limit threshold voltage. This voltage divided by the external current sense resistor
sets the current limit threshold.
This pin is connected to the plus side of the external current sense resistor. A resistor in
series with this pin and a capacitor connected between this pin and pin 6 provides a high
frequency filtering for the noise spikes of turn on and turn off switching.
This pin is connected to the IC substrate and must be connected to the lowest potential
in the system.
The PWM output of the switching controller. This pin is a totem pole drive that is connected to the gate of the power MOSFET. A resistor may be placed from this pin to the
gate in order to reduce switching noise.
A resistor and a 10pF capacitor is connected from this pin to the VFB1 pin to set the
output ripple voltage for the switching regulator.
This pin supplies the voltage to the PWM drive and hysterises circuitry and it is connected to the 12V supply. A 1 uF, high frequency capacitor must be connected from this
pin to ground to provide the peak current for charging and discharging of the MOSFET.
This pin provides the soft start for the regulator during power up. It also sets a long off
time when the converter goes into current limiting, providing low duty cycle for the catch
diode allowing it to survive during short circuit.
US3034
BLOCK DIAGRAMBLOCK DIAGRAM
V12 Vhyst
2 4 3
Drv
1
Gnd
5
Vfb
5V Reg
UVLO
PWM Control
S.S. / Hiccup
Control
R
1.25V
3R
20uA
Vref
3034blk1-1.1
Figure 1 - Simplified block diagram of the US3034
CS-
6
CS+
7
SS
8
Rev. 1.8
1/13/99
4-3
Page 4
US3034
TYPICAL APPLICATIONTYPICAL APPLICATION
Pentium Core Supply Application (US3034 and US3033 Dual Layout)
Low Cost 4 Bit VID
**
R9
12V
** R9 can be eliminated if dual layout
with US3033 is not
desired.
C8
SS/
V12
Drv V12 Vfb Vhyst
1 2 3 4
CS+/
Drv2
U1
Vfb2
5678
GndCS-/
R8
C6
R7
C3
R1
R3 C5
L2
R6
Vout
L1
5V
C1
Figure2- Typical application of US3034 in a flexible motherboard with the 4 bit VID output voltage selection. This circuit is done
using a dual layout with the US3033 part . The advantage of this circuit is that it uses a single jumper that programs the output voltage
in 16 steps with 0.1V steps from 2V to 3.5V, designed for Intel P55,P54 AMD K5 & K6 as well as Cyrix M1 and M2 applications.
C2
C4
3034app2-1.0
Q2
R4
R5A R5B R5C R5D R5E
D1R2
JP1
1
3
5
7
2
4
6
8
C7
JP1 JP1 JP1 JP1 Output
1-2 3-4 5-6 7-8 Voltage
0 0 0 0 3.5
0 0 0 1 3.4
0 0 1 0 3.3
0 0 1 1 3.2
0 1 0 0 3.1
0 1 0 1 3.0
0 = Jumper block is installed.
1 = Jumper block is not installed.
0 1 1 0 2.9
0 1 1 1 2.8
1 0 0 0 2.7
1 0 0 1 2.6
1 0 1 0 2.5
1 0 1 1 2.4
1 1 0 0 2.3
1 1 0 1 2.2
1 1 1 0 2.1
1 1 1 1 2.0
4-4
Rev. 1.8
1/13/99
Page 5
US3034
Pentium Core Supply Application Parts List (US3034 and US3033 Dual Layout)
Low Cost 4 Bit VID
Ref Desig Description Qty Part # Manufacturer
U1 LDO/Switcher IC 1 US3034CS ( 8 pin SOIC) Unisem
Q2 MOSFET 1 IRL3303 (TO220) International
IRL3103S (TO263) (note 1) Rectifier
D1 Schottky Diode 1 MBR1045CT (TO220)
MBRB1545CT (TO263) (note1) Motorola
L2 Inductor 1 Core:T50-18,L=4 uH Micro Metal
Turns: 10T, 18 AWG (core)
L1 Inductor 1 L=2 uH
R1 Resistor 1 22 ohm,5%, SMT 1206 size
R2 Resistor 1 10 ohm, 5%, SMT 1206 size
R3 Resistor 1 324 kohm,1%, SMT 0805 size
R4A * Resistor 1 806 ohm,1%, SMT 0805 size
R4B * Resistor 1 90.9 kohm,1%, SMT 0805 size
R5A Resistor 1 1.24 kohm,1%, SMT 0805 size
R5B Resistor 1 2.49 kohm,1%, SMT 0805 size
R5C Resistor 1 4.99 kohm,1%, SMT 0805 size
R5D Resistor 1 10 kohm,1%, SMT 0805 size
R5E Resistor 1 1.30 kohm,1%, SMT 0805 size
R6 Resistor 1 5 miliohm,5%, 2W
R7 Resistor 1 4.99 kohm,1%, SMT 0805 size
R8 Resistor 1 4.7 kohm,5% for US3034, open for 3033
R9 Resistor 1 open for US3034, 10 ohm for US3033
C1 Capacitor 1 6MV1500GX, 1500uF,6.3V, Elect
C2 Capacitor 1 6MV1500GX, 1500uF,6.3V, Elect Sanyo
C3 Capacitor 1 1 uF,Ceramic, SMT 0805 size
C4 Capacitor 1 470 pF,Ceramic, SMT 0805 size Sanyo
C5 Capacitor 1 10 pF,Ceramic, SMT 0805 size Sanyo
C7 Capacitor 4 6MV1500GX, 1500uF,6.3V, Elect Sanyo
C8 Capacitor 1 0.047 uF for 3034 , 0.1uf for 3033
C6 Capacitor 1 4700pF for US3034, open for US3033
HS1 Heat Sink 1 For MOSFET , 577002 Aavid
HS2 Heat Sink 1 For Schottky Diode , 577002 Aavid
* R4 is a parallel combination of R4A and R4B.
Note 1: For the applications where it is desirable to eliminate the heat sink, the IRL3103S for Q2 and MBR1545CT for D2 in TO263
packages with minimum of 1" square copper pad can be used.
Rev. 1.8
1/13/99
4-5
Page 6
US3034
TYPICAL APPLICATIONTYPICAL APPLICATION
5V to 3.3V for Pentium Application with AGP or Pentium II Application without ATX power supply
Switching mode Operation. (US3034 and US3033 Dual Layout)
R9
12V
5V
C1
L1
C8
CS+/
SS/
Drv2
V12
Drv V12 Vfb Vhyst
1 2 3 4
C3
R1
Q2
C2
U1
Vfb2
5678
GndCS-/
R3 C5
C4
L2
D1R2
3034app3-1.0
R4
R5
R8
C6
R7
R6
Vout
C7
Figure4- The circuit in figure 4 is the application of the US3034 which is done using a dual layout with US3033 in a
switching mode only. This circuit can be used to generate a low cost 5V to 3.3V for either Pentium application with AGP socket or in
Pentium II applications where it is desirable to generate an accurate on board 3.3V supply.
Ref Desig Description Qty Part # Manufacturer
U1 LDO/Switcher IC 1 US3034CS ( 8 pin SOIC) Unisem
Q2 MOSFET 1 IRL3303 (TO220) International
IRL3103S (TO263) (note 1) Rectifier
D1 Schottky Diode 1 MBR1045CT (TO220)
MBRB1545CT (TO263) (note1) Motorola
L2 Inductor 1 Core:T50-18,L=4 uH Micro Metal
Turns: 10T, 18 AWG (core)
L1 Inductor 1 L=2 uH
R1 Resistor 1 22 ohm,5%, SMT 1206 size
R9 Resistor 1 open for US3034, 10 ohm for US3033
R2 Resistor 1 10 ohm, 5%, SMT 1206 size
R3 Resistor 1 249 kohm,1%, SMT 0805 size
R4 Resistor 1 1 kohm,1%, SMT 0805 size
R5 Resistor 1 576 ohm,1%, SMT 0805 size
R6 Resistor 1 5 miliohm,5%, 2W
R7 Resistor 1 4.99 kohm,1%, SMT 0805 size
R8 Resistor 1 4.7 kohm,5% for US3034, open for 3033
C1,2 Capacitor 2 6MV1500GX, 1500uF,6.3V, Elect Sanyo
C3 Capacitor 1 1 uF,Ceramic, SMT 0805 size
C4 Capacitor 1 470 pF,Ceramic, SMT 0805 size Sanyo
C5 Capacitor 1 10 pF,Ceramic, SMT 0805 size Sanyo
C6 Capacitor 1 4700pF for US3034, open for US3033
C7 Capacitor 2 6MV1500GX, 1500uF,6.3V, Elect Sanyo
C8 Capacitor 1 0.047 uF for 3034 , 0.1uf for 3033
HS1 Heat Sink 1 For MOSFET , 577002 Aavid
HS2 Heat Sink 1 For Schottky Diode , 577002 Aavid
Note 1: For the applications where it is desirable to eliminate the heat sink, the IRL3103S for Q2 and MBR1545CT for D2 in TO263
packages with minimum of 1" square copper pad can be used.
4-6
Rev. 1.8
1/13/99
Page 7
TYPICAL APPLICATIONTYPICAL APPLICATION
5V to 3.3V with lossles short cicuit protection(output UVLO detection).
US3034
C8
5678
GndCS-CS+SS
R7
US3034
12V
Drv V12 Vfb Vhyst
1 2 3 4
C3
R1
R3 C5
R6
C6
L2
Vout
L1
5V
C1
Figure 5- The circuit in figure 5 is designed to provide lossles output short detection by detecting the dc voltage across the inductor
and shutting down the MOSFET and entering HICCUP mode. Note that the current limit point is a function of the inductor resistance
and in this application with approximately 8 mil ohm resistance the peak C.L is set at 10A. See application note on how to set the
current limiting threshold.
Q2
C2
C4
R4
D1R2
R5
3034app5-1.1
Ref Desig Description Qty Part # Manufacturer
U1 Switcher IC 1 US3034CS ( 8 pin SOIC) Unisem
Q2 MOSFET 1 IRL3303 (TO263) International
D1 Schottky Diode 1 PBYR735(Axial Thr Hole pkg)
PBYR1035B(SMT, TO263 pkg) Motorola
L2 Inductor 1 Core:T50-18,L=4 uH Micro Metal
Turns: 7T, 18 AWG (core)
L1 Inductor 1 L=1 uH
R1,2 Resistor 2 10 ohm,5%, SMT
R3 Resistor 1 182 kohm,1%, SMT
R4 Resistor 1 1 kohm,1%, SMT
R5 Resistor 1 576ohm,1%, SMT
R7 Resistor 1 3.83 kohm,1%, SMT
R6 Resistor 1 1 kohm,1% , SMT
C1 Capacitor 1 470uF, Elect
C2 Capacitor 1 6MV1000GX, 1000uF,6.3V, Elect Sanyo
C3 Capacitor 1 1 uF,Ceramic, SMT
C5 Capacitor 1 10 pF,Ceramic, SMT Sanyo
C6 Capacitor 1 0.1 uF
C7 Capacitor 2 6MV1000GX, 1000uF,6.3V, Elect Sanyo
C8 Capacitor 1 0.047 uF
C7
Rectifier
Rev. 1.8
1/13/99
4-7
Page 8
US3034
APPLICATION INFORMATIONAPPLICATION INFORMATION
Introduction
The US3034 device is an application specific product
designed to provide an on board switching supply for the
new generation of microprocessors requiring separate
Core and I/O supplies where the load current demand
from the I/O supply requires this regulator to also be a
switching regulator such as the motherboard applications with AGP slot or the Pentium II with on board 5V to
3.3V converter. The US3034 provides an easy and low
cost switching regulator solution for Vcore and 3.3V
supplies with true short circuit protection.
Switching Controller Operation
The operation of the switching controller is as follows :
after the power is applied, the output drive pin, "Drv" goes
to 100% duty cycle and the the current in the inductor
charges the output capacitor causing the output voltage
to increase. When output reaches a pre-programmed
set point the feedback pin "Vfb" exceeds 1.25V causing
the output drive to switch low and the "Vhyst" pin to
switch high which jumps the feedback pin higher than
1.25V resulting in a fixed output ripple which is given by
the following equation :
dVo=(Rt/Rh)x11
Where:
Rt=Resistor connected from Vout to the Vfb pin of
US3034
Rh=Resistor connected from Vfb pin to Vhyst pin.
For example, if Rt=1k and Rh=422k, then the output
ripple is :
dVo=(1/422)x11=26mV
The advantage of fixed output ripple is that when the
output voltage changes from 2V to 3.5V, the ripple voltage remains the same which is important in meeting the
Intel maximum tolerance specification.
Soft Start
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 0.1uF capacitor insures
this for most applications. During start up the soft start
capacitor is charged up to approximately 6V keeping
the output shutdown before an internal 10uA current
source start discharging the soft start capacitor which
slowly ramps up the inverting input of the PWM comparator, Vfb. This insures the output to ramp up at the
same rate as the soft start cap thereby limiting the input
current. For example, with 0.1uF and the 10uA internal
current source the ramp up rate is (∆V/ ∆t)=I/Css = 10/
0.1=100V/Sec or 0.1V/mSec. Assuming that the output
capacitance is 6000uF, the peak input current will be:
Iin(pk)=Css*(∆V/ ∆t)=6000uF*(0.1V/mSec)=0.6A
The soft start capacitor also provides a delay in the turn
on of the output which is given by:
Td=CSS*K
Where K=30 ms/uF
For example for CSS=0.1uF,
Td=0.1* 30=3 ms
Switcher Current Limit Protection
The US3034 uses an external current sensing resistor
and compares the voltage drop across it to a programmed
voltage which is set externally via a resistor (RcL) placed
between the “CS-” terminal of the IC and Vout. Once the
voltage across the sense resistor exceeds the threshold, the soft start capacitor pulls up to 12V, pulling up
the inverting pin of the error comparator higher than non
inverting which causes the external MOSFET to shut
off. At this point the C.S comparator changes its state
and pulls the soft start capacitor to Vcc which is 12V
and shutting the PWM drive. After the output drive is
turned off, an internal 10uA current source slowly discharge the soft start capacitor to approximately 5.7V,
before the output starts to turn back on causing a long
delay before the MOSFET turns back on. This delay
causes the catch diode to cool off between the current
limit cycles allowing the converter to survive a short circuit condition. An example is given below as how to
select the current limiting components. Assuming the
desired current limit point is set to be 20A and the current sense resistor Rs=5mΩ, then the current limit pro-
gramming resistor,RcL is calculated as :
Vcs=IcL*Rs=20*0.005=0.1V
RcL=Vcs/Ib=(0.1V)/(20uA)=5kΩ
Where: Ib=20uA is the internal current source of the
US3034
The peak power dissipated in the C.S. resistor is :
Ppk=(IcL^2)*Rs=20^2*0.005=2W
However, the average power dissipated is much lower
than 2W due to the long off time caused by the hiccup
circuit of 3034. The average power is in fact the short
circuit period divided by the short circuit period plus the
off time or "hiccup" period. For example, if the short circuit lasts for TSC=100uSec before the 3034 enters hiccup, the average power is calculated as :
Pave=0.5*Ppk*DSC
Where:
DSC=TSC/THCP
THCP=CSS*M
Where M=200 ms/uF & CSS, is the soft start capacitor
For example for CSS=0.1uF & TSC=500uSec=0.5mS
THCP=0.1* 200=20 ms
Pave=0.5*2*(0.5/20)=25 mW
Without "hiccup" technique, the power dissipation
of the resistor is 2W.
4-8
Rev. 1.8
1/13/99
Page 9
Switcher Output Voltage Setting
The output voltage can be set using the following
equations.
Assuming , Vo=3.38V and the selected output ripple
is ≈ 1.3%(44mV) of the output voltage, a set of
equations are derived that selects the resistor divider
and the hysterises resistor.
Assuming, Rt=1kΩ , 1%
Rh=(11*Rt)/∆Vo
Where:
Rt=Top resistor of the resistor divider
Rh=Hysterises resistor connected between pins 3 and
4 of the US3034
∆Vo=Selected output ripple (typically 1% to 2% of
output voltage)
Assuming, ∆Vo=44mV
Rh=(11*1000)/0.044=250 kΩ
Select Rh=249 kΩ , 1%
The bottom resistor of the divider is then calculated
using the following equations:
Rb=Rt/X
Where:
Rb=Bottom resistor of the divider
X=[(Vo + (∆Vo/2))/Vref] - 1
Vref=1.25 V typ.
X=[(3.38+ (0.044/2))/1.25] - 1 = 1.72
Rb=1000/1.72=580 Ω
Select Rb=576 Ω , 1%
US3034
Frequency Calculation
The US3034 frequency of operation is calculated using
the following formula:
Fs=[(Vo*(1-D)*ESR)]/(L*∆Vo) (MHz)
Where:
Vo=Output voltage (V)
D=Duty cycle
ESR=Output capacitor ESR (V)
L=Output inductance (uH)
∆Vo=Output ripple voltage (V)
For our example:
D≈(Vo + Vf)/Vin
Where, Vf=Forward voltage drop of the Schotky diode
D=(3.38 + 0.5)/5=0.78
The ESR=18mΩ for 2 of the Sanyo 1500uF,
6MV1500GX caps. If L=3.5uH then, Fs is calculated
as follows:
Fs=[(3.38*(1-0.78)*0.018)]/(3.5*0.044)= 0.087 Mhz =
87 kHz
Rev. 1.8
1/13/99
4-9
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