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SP7662
Wide Input Voltage Range 12A, 300kHz, Buck Regulator
FEATURES
4.75V to 22V Input Voltage Range using Single Supply 3V to 22V Input Voltage Range using Dual Supply % 0.8V Reference 2A Output Capability Current Limiting using Inductor DCR Built in Low RDS(ON) Power Switches 300 kHz Fixed Frequency Operation Over Temperature Protection Short Circuit Protection with Auto-Restart Wide BW Amp Allows Type II or III Compensation Programmable Soft Start Fast Transient Response HighEfficiency:Greaterthan95% Possible Nonsynchronous Start-Up into a Pre-Charged Output AvailableinRoHSCompliant,LeadFreePackaging: Small 7mm x 4mm DFN U.S. Patent #6,922,04
LX LX LX 26 25 24 BOTTOM VIEW Heatsink Pad 1 Connect to Lx
PowerBlox
SP7662
TM
DFN PACKAGE 7mm x 4mm (Option 2) 1 PGND
2 PGND 3 PGND 4 PGND
LX 23 VCC 2 2 UVIN 21 GND 20 GND 19 VIN 18 BST 17 LX 16 LX 15 LX 14 Heatsink Pad 3 Connect to VINP Pin 29 Heatsink Pad 2 Connect to GND Pin 28 Pin 27
5 GND 6 VFB 7 COMP 8 SS
9 GND 10 ISN 11 ISP 12 SWN 13 VINP
DESCRIPTION
TheSP7662isasynchronousstep-downswitchingregulatoroptimizedforhighefficiency.Thepartisdesigned for use with a single 4.75V to 22V single supply or 3V to 22V input if an external Vcc is provided. The SP7662 providesafullyintegratedbuckregulatorsolutionusingafixed300kHzfrequency,PWMvoltagemodearchitecture. Protection features include UVLO, thermal shutdown, output current limit and short circuit protection. The SP7662 is available in the space saving DFN package.
5 4 3
TYPICAL APPLICATION CIRCUIT
2
VIN 12Vin (9.6V - 16V)
D
VOUT
LX 28 27
C3 22uF
C2 22uF
C 22uF
L, SC508-2R7M 2.7uH, 4. mOhm R3 5.k C4 R9
ISP
3.30V, 0-12A
R4 5.k
3
D
GNDPAD
GND
CZ2
C
2
SWN PAD
VFB 2 3 4 5 6
PGND PGND PGND PGND GND VFB COMP SS GND ISN ISP
LX LX
26 25 24 23 22 2 20 9 8 7 6 5 4 NC
0.uF 6.9k
ISN VFB
RZ3 453
R 0k
C5 C6 00uF 00uF
4
RZ2 4.02k
U SP7662
LX LX VCC UVIN GND GND VIN BST LX
CZ3 2200pF R2 3.6k
0nF
CVCC 4.7uF
CP 00pF CSS 47nF
GND
C
7 8 9 0
CF 00pF
VIN PAD
C9 6.8nF
B
2 3
RBST 5. 22nF CBST
SWN VIN
LX LX
SD0AWS DBST
B
ISN ISP LX
29
Rs Ohm
Cs 2.2nF
LX
Rs2 Ohm
Cs2 2.2nF
Mar -07 Rev AJ
A
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
A
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections ofthespecificationsbelowisnotimplied.Exposuretoabsolutemaximumratingconditionsforextendedperiodsoftimemayaffectreliability. VCC ...................................................................................................7V ViN .................................................................................................25V BST................................................................................................ 30V LX-BST ...............................................................................-0.3V to 7V LX ........................................................................................-V to 30V All other pins .......................................................... -0.3V to VCC + 0.3V Storage Temperature ................................................... -65C to 50C Power Dissipation ........................................Internally Limited via OTP Lead Temperature (Soldering, 0 sec) .......................................300C ESD Rating ........................................................................... 2kV HBM Thermal Resistance JC............................................................ 5C/W
SpecificationsareforTAMB = TJ = 25C, and those denoted by apply over the full operating range, -40C< Tj< 25C. Unless otherwisespecified:4.5VELECTRICAL SPECIFICATIONS
CONDITIONS
PARAMETER
QUIESCENT CURRENT ViN Supply Current (No switching) ViN Supply Current (switching) BST Supply Current (No switching) BST Supply Current (switching) PROTECTION: UVLO
MIN
TYP
.5 8 0.2 3
MAX UNITS
3.0 20 0.4 6 mA mA
VfB= 0.9V
mA mA
VfB= 0.9V
Vcc UVLO Start Threshold 4.00 Vcc UVLO Hysteresis UVIN Start Threshold UVIN Hysteresis UVIN Input Current 00 2.30 200
4.25 200 2.50 300
4.50 300 2.65 400 .0
V mV V
UVIN=3.0V
2XGainConfig.,MeasureVfB; Vcc=5V
mV A
ERROR AMPLIFIER REFERENCE ErrorAmplifierReference 0.792 0.800 0.808 0.784 0.800 0.86 70 -230 50 -50 50 3.2 3.5 -2.0 230 -70 200 3.8 V V
ErrorAmplifier Reference Over Line COMP Sink Current COMP Source Current VfB Input Bias Current COMP Clamp COMP Clamp Temp. Coefficient
VCC LINEAR REGULATOR
VfB=0.9V, COMP=0.9V VfB=0.9V, COMP=0.9V VfB=0.8V
VfB=0.7V, TA=25C
A A
nA V mV/C
VCC Output Voltage
4.7 4.5 250
5.0 4.73 500
5.3
V
Dropout Voltage
750
mV
ViN = 6 to 23V, ILOAD = 0mA to 30mA ViN = 5V, 20mA Vin-Vout = Dropout voltage when Vcc regulated drops by 2%. IVCC = 30mA.
(c) 2007 Sipex Corporation
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
2
SpecificationsareforTAMB = TJ = 25C, and those denoted by apply over the full operating range, -40C< Tj< 25C. Unless otherwisespecified:4.5VELECTRICAL SPECIFICATIONS
PARAMETER
Ramp Amplitude RAMP Offset Ramp offset Temperature Coefficient GHMinimumPulseWidth Maximum Controllable Duty Ratio Maximum Duty Ratio Internal Oscillator Ratio TIMERS: SOFTSTART SSChargeCurrent: SSDischargeCurrent: Short Circuit Threshold Voltage
MIN TYP MAX UNITS
0.80 .7 .00 2.0 -2 50 92 00 255 -6 .0 300 -0 2.0 345 -4.0 3.0 97 80 .20 2.3 V V mV/C ns % % kHZ
CONDITIONS
CONTROL LOOP: PWM COMPARATOR, RAMP & LOOP DELAY PATH

Fault Present, SS=0.2V Valid for 20 cycles
A
mA
PROTECTION: SHORT CIRCUIT, OVERCURRENT & THERMAL 0.20 0.25 220 60 0.30 270 V ms mV

VfB=0.5V Measured ISP - ISN
70 Hiccup Timeout Overcurrent Threshold 54 Voltage ISP, ISN Common Mode 0 Range Thermal Shutdown 35 Temperature Thermal Recovery Temperature Thermal Hysteresis OUTPUT: POWER STAGE
66
3.6
V C C C
Guaranteedbydesign
45 35 0
55
High Side Switch RDSON Synchronous Low Side Switch RDSON Maximum Output Current
2
6.8 6.8
20.5 8.5
m m A
VGS=4.5V; IDrAiN=5A; TAMB=25C VGS=4.5V; IDrAiN=5A; TAMB=25C
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
3
CONTROLLER BLOCK DIAGRAM
VC C
C OMP SS V FB INT 1.6 V
A S Y NC . S TAR TUP C OMP A R A TOR GL HOLD OFF BS T
V FB VCC 10 uA S OFTS TA R T INP UT SS 0.1V
P W M LO O P
VC C Gm ER R OR A MP LIFIE R FA ULT RE S E T DOMINA NT R Q P OS R E F FAULT S QP W M
GH
VPOS
Gm
S Y NC HR O NO US DR I V E R
S WN GL
FA ULT
300 kHZ P GN D C LK C LOC K P ULS E GEN E R A TOR 2.8 V 1.3 V FAULT
R AMP =1V
V CC
R E FE R E NC E C OR E
0.8V R E F OK
PO W E R FA ULT 4.25 V ON 4.05 V OFF 145C O N 135C O FF VC C UV LO
THE R MA L S HUTDOW N
SET DOMINA NT S Q HIC C UP FAULT
0.25V VP OS 5V LINE A R R E GULA TOR V FB INT
S HOR TC IR C UIT DE TE C TION
R
GND 200ms D elay OV E R C UR R E NT DE TE C TION C OU NTE R C LK
V IN 60 mV R E F OK
C LR
140K UV IN 2.50 V ON 2.20 V O FF 50K VIN UV LO
IS P
IS N
T HE R MA L A ND O V E R C UR R E NT P R O T E C T IO N
UV LO C O MP A R AT O R S
Note: The SP7662 uses the Sipex PWM controller SP6133.
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
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PIN DESCRIPTION
SP7662
DFN PACKAGE 7mm x 4mm (Option 2) LX 26 LX 25 LX 24 LX 23 VCC 22 UVIN 21 GND 20 GND 19 VIN 18 BST 17 LX 16 LX 15 LX 14 Heatsink Pad 3 Connect to VINP Pin 29 Heatsink Pad 2 Connect to GND Pin 28 Pin 27 1 PGND 2 PGND 3 PGND 4 PGND 5 GND 6 VFB 7 COMP 8 SS 9 GND 10 ISN 11 ISP 12 SWN 13 VINP
BOTTOM VIEW Heatsink Pad 1 Connect to Lx
Pin Pin # Name Description -4 PGND Groundconnectionforthesynchronousrectifier. GroundPin.ThecontrolcircuitryoftheICandlowerpowerdriverarereferencedtothis 5, 9, GND 9, 20 pin. Return separately from other ground traces to the (-) terminal of COut. Feedback Voltage and Short Circuit Detection pin. It is the inverting input of the Error Amplifier and serves as the output voltage feedback point for the Buck Converter. The output voltage is sensed and can be adjusted through an external resistor divider. Whenever VFB drops 0.25V below the positive reference, a short circuit fault is detected and the IC enters hiccup mode.
6
VFB
7
8 0 2 3
4-6, 23-26
OutputoftheErrorAmplifier.Itisinternallyconnectedtotheinvertinginputofthe COMP PWMcomparator.Anoptimalfiltercombinationischosenandconnectedtothis pin and either ground or VFB to stabilize the voltage mode loop. SoftStart.ConnectanexternalcapacitorbetweenSSandGNDtosetthesoftstart SS rate based on the 0A source current. The SS pin is held low via a mA (min) current during all fault conditions. ISN Current sense negative input. Rail-to-rail input for overcurrent detection. ISP SWN VINP LX BST VIN UVIN VCC Current sense positive input. Rail-to-rail input for overcurrent detection. LowersupplyrailfortheGHhigh-sidegatedriver.Connectthispintotheswitching node as close as possible to pins 23- 27. Do not connect this pin to pins 4 - 6. Input connection to the high side N-channel MOSFET. Connect an inductor between this pin and VOut. High side driver supply pin. Connect BST to the external boost diode and capacitor as shown in the Typical Application Circuit on page . The high side driver is connected between BST pin and SWN pin. ViN connection for internal LDO and PWM Controller. UVLO input for ViN voltage. Connect a resistor divider between ViN and UVIN tosetminimumoperatingvoltage.Useresistorvaluesbelow20ktooverride internal resistor divider. Output of internal regulator. May be exterinally biased if Vin < 5V.
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator (c) 2007 Sipex Corporation
7 8 2 22
Mar -07 Rev AJ
5
THEORY OF OPERATION General Overview The SP7662 is a fixed frequency, voltage mode, synchronous PWM regulator optimizedforhighefficiency.Theparthas beenspecificallydesignedforsinglesupply operation from a 5V to 22V input. The heart of the SP7662 is a wide bandwidth transconductanceamplifierdesignedtoaccommodate Type II and Type III compensation schemes. A precision 0.8V reference, present on the positive terminal of the error amplifier, permits the programming of the output voltage down to 0.8V via the VFB pin.Theoutputoftheerroramplifier,COMP, is compared to a .V peak-to-peak ramp, which is responsible for trailing edge PWM control. This voltage ramp and PWM control logic are governed by the internal oscillator that accurately sets the PWM frequency to 300kHz. The SP7662 contains two unique control features that are very powerful in distributed applications. First, nonsynchronous driver control is enabled during startup, to prohibit the low side switch from pulling down the output until the high side switch has attempted to turn on. Second, a 00% duty cycle timeout ensures that the low side switch is periodically enhanced during extended periods at 00% duty cycle. This guarantees the synchronized refreshing of the BST capacitor during very large duty ratios. The SP7662 also contains a number of valuable protection features. Programmable VIN UVLO allows the user to set the exact value at which the conversion voltage can safely begin down-conversion, and an internal VCC UVLO which ensures that the controller itself has enough voltage to properly operate. Other protection features include thermal shutdown and short-circuit detection. In the event that either a thermal, short-circuit, or UVLO fault is detected, the SP7662 is forced into an idle state where the output drivers areheldoffforafiniteperiodbeforearestart is attempted.
Mar -07 Rev AJ
Soft Start "Soft Start" is achieved when a power converter ramps up the output voltage while controlling the magnitude of the input supply source current. In a modern step down converter, ramping up the positive terminal oftheerroramplifiercontrolssoftstart.Asa result,excesssourcecurrentcanbedefined as the current required to charge the output capacitor. IViN = COut * (VOut / TSOft-StArt) The SP7662 provides the user with the option to program the soft start rate by tying a capacitor from the SS pin to GND.The selection of this capacitor is based on the 0A pull up current present at the SS pin and the 0.8V reference voltage. Therefore, theexcesssourcecanberedefinedas: IViN = COut * [VOut *0A / (CSS * 0.8V)]
Under Voltage Lock Out (UVLO) The SP7662 has two separate UVLO comparators to monitor the bias (Vcc) and Input (ViN) voltages independently. The Vcc UVLO is internally set to 4.25V. The ViN UVLO is programmable through UViN pin. When UVIN pin is greater than 2.5V the SP7662 is permitted to start up pending the removal of all other faults. A pair of internal resistors isconnectedtoUVINasshowninthefigure below. SP7662
VIN
R6 UVIN
140K
R7 GND
2.5V ON 2.2V OFF 50K
+
Internal and external bias of UVIN
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
6
THEORY OF OPERATION Therefore without external biasing the ViN start threshold is 9.5V. A small capacitor mayberequiredbetweenUVINandGNDto filteroutnoise.ForapplicationswithViN of 5V or 3.3V, connect UVIN directly to ViN. To program the ViN start threshold, use a pair of external resistors as shown. If external resistors are an order of magnitude smaller than internal resistors, then the ViN start thresholdisgivenby: ViN(start) = 2.5 * (R6+R7)/R7 For example, if it is required to have a ViN startthresholdof7V,thenletR7=5Kand using the ViN start threshold equation we get R6=9.09K. Thermal and Short-Circuit Protection Because the SP7662 is designed to drive large output current, there is a chance that the power converter will become too hot. Therefore, an internal thermal shutdown (45C) has been included to prevent the IC from malfunctioning at extreme temperatures. A short-circuit detection comparator has also been included in the SP7662 to protect against an accidental short at the output of the power converter. This comparator constantly monitors the positive and negative terminals of the error amplifier, and if the VfB pin falls more than 250mV (typical) below the positive reference, a short-circuit fault is set. Because the SS pin overrides the internal 0.8V reference during soft start, the SP7662 is capable of detecting short-circuit faults throughout the duration of soft start as well as in regular operation. Over-Current Protection The Over-current protection feature can onlybeusedonoutputvoltages3.3volts. It is limited by the common mode rating of the op-amp used to sense the voltage across the inductor. Over-current is deMar -07 Rev AJ
tected by monitoring a differential voltage across the output inductor as shown in the nextfigure.
SP7662
SWN L=2.7uH,DCR=4.1m
VOUT
R3 5.11K
R4 5.11K
ISP ISN CSP 6.8nF CS 0.uF
Over-current detection circuit Inputs to an over-current detection comparator, set to trigger at 60 mV nominal, are connected to the inductor as shown. Since the average voltage sensed by the comparator is equal to the product of inductor current and inductor DC resistance (DCR), then IMAx = 60mV / DCR. Solving this equationforthespecificinductorincircuit1,IMAx = 4.6A. When IMAx is reached, a 220 ms time-out is initiated, during which top and bottom drivers are turned off. Following the time-out, a restart is attempted. If the fault condition persists, then the time-out is repeated (referred to as hiccup). Increasing the Current Limit If it is desired to set IMAx > {60mV / DCR} (in this case larger than 4.6A), then a resistor R9 should be added as shown in the next figure.R9formsaresistordividerandreduces the voltage seen by the comparator. (IMAx * DCR) Since:60mV = R9 {R3 + R4 + R9}
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
7
THEORY OF OPERATION SolvingforR9weget: R9 = [60mV * (R3 + R4)] [(IMAx * DCR) - 60mV] Asanexample:ifdesiredIMAx is 7A, then R9 = 63.4K. R8 = R4 * [VOut - 60mV + (IMAX * DCR)] 60mV - (IMAX * DCR) Asanexample:forIMAx of 2A and VOut of 3.3V,calculatedR8is1.5M.
SP7662
SWN L=2.7uH,DCR=4.1m
SP7662
VOUT
SWN
L=2.7uH,DCR=4.1m
VOUT
R3 5.11K R9 63.4K
R4 5.11K
R3 5.11K
R4 5.11K
ISP ISN CSP 6.8nF
ISP ISN
CS 0.uF
CSP 6.8nF
CS 0.uF
R8 1.5M
Over-current detection circuit for Imax > 60mV / DCR Decreasing the Current Limit If it is required to set IMAx < {60mV / DCR, a resistor is added as shown in the following figure. R8 increases the net voltage detected by the current-sense comparator. Voltage at the positive and negative terminal ofcomparatorisgivenby: VSP = VOut + (IMAx * DCR) VSN = VOut * {R8 / (R4 +R8)} Sincethecomparatoristriggeredat60mV: VSP-VSN = 60 mV Combining the above equations and solvingforR8:
Over-current detection circuit for Imax < {60mV / DCR} Handling of Faults Upon the detection of power (UVLO), thermal, or short-circuit faults, the SP7662 is forced into an idle state where the SS and COMP pins are pulled low and both switches are held off. In the event of UVLO fault, the SP7662 remains in this idle state until the UVLO fault is removed. Upon the detection of a thermal or short-circuit fault, an internal 200ms timer is activated. In the event of a short-circuit fault, a restart is attempted immediately after the 200ms timeout expires. Whereas, when a thermal fault is detected the 200ms delay continuously recycles and a restart cannot be attempted until the thermal fault is removed and the timer expires.
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
8
APPLICATIONS INFORMATION Error Amplifier and Voltage Loop The heart of the SP7662 voltage error loop is a high performance, wide bandwidth transconductance amplifier. Because of theamplifier'scurrentlimited(+/-150A) transconductance, there are many ways to compensate the voltage loop or to control the COMP pin externally. If a simple, single-pole, single-zero response is desired, then compensation can be as simple as an RC circuit toGround.Ifamorecomplexcompensation isrequired,thentheamplifierhasenough bandwidth (45 at 4 MHz), and enough gain (60dB) to run Type III compensation schemes with adequate gain and phase margins at crossover frequencies greater than 50kHz. The common mode output of the error amplifieris0.9Vto2.2V.Therefore,thePWM voltage ramp has been set between .V and 2.2V to ensure proper 0% to 00% duty cycle capability. The voltage loop also includes two other very important features. One is a nonsynchronous startup mode. Basically, the synchronousrectifiercannotturnonunless the high side switch has attempted to turn on or the SS pin has exceeded .7V. This feature prevents the controller from "dragging down" the output voltage during startup or in fault modes.
VBST GH Voltage VSWN V(VCC) GL Voltage 0V V(VIN) SWN Voltage -0V -V(Diode) V V(VIN)+V(VCC) BST Voltage V(VCC) TIME
Mar -07 Rev AJ
The second feature is a 00% duty cycle timeout that ensures synchronized refreshing of the BST capacitor at very high duty ratios. In the event that the high side NFET is on for 20 continuous clock cycles, a reset isgiventothePWMflipflophalfwaythrough the 2stcycle.ThisforcesGLtoriseforthe cycle, in turn refreshing the BST capacitor. The boost capacitor is used to generate a high voltage drive supply for the high side switch, which is Vcc above ViN. Power MOSFETs The SP7662 contains a pair of integrated low resistance N-channel switches designed to drive up to 2A of output current. Care should be taken to de-rate the output current based on the thermal conditions in the systemsuchasambienttemperature,airflow and heat sinking. Maximum output current could be limited by thermal limitations of a particular application by taking advantage of the integrated-over-temperature protective scheme employed in the SP7662. The SP7662 incorporates a built-in overtemperature protection to prevent internal overheating. Setting Output Voltages The SP7662 can be set to different output voltages. The relationship in the following formula is based on a voltage divider from the output to the feedback pin VfB, which is set to an internal reference voltage of 0.80V. Standard1%metalfilmresistorsofsurface mount size 0603 are recommended. VOut = 0.80V [R / R2 + ] =>
R2 = R / [ ( VOut / 0.80V ) - ]
Where R1=10Kand forVOut = 0.80V setting, simply remove R2 from the board. Furthermore, one could select the value of the R and R2 combination to meet the exact output voltage setting by restricting the R resistance range such that 10K < R1 < 100Kforoverallsystemloopstability.
(c) 2007 Sipex Corporation
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
9
APPLICATIONS INFORMATION Inductor Selection There are many factors to consider in selecting the inductor including core material, inductance vs. frequency, current handling capability,efficiency,sizeandEMI.Inatypical SP7662 circuit, the inductor is chosen primarily for value, saturation current and DC resistance. Increasing the inductor value will decrease output voltage ripple, but degrade transient response. Low inductor values provide the smallest size, but cause large ripple currents,poorefficiencyandrequiremore output capacitance to smooth out the larger ripple current. The inductor must be able to handle the peak current at the switching frequency without saturating, and the copper resistance in the winding should be kept as low as possible to minimize resistive power loss. A good compromise between size, loss and cost is to set the inductor ripple current to be within 20% to 40% of the maximum output current. The switching frequency and the inductor operating point determine the inductor value asfollows: L =
.
and provide low core loss at the high switching frequency. Low cost powderediron cores have a gradual saturation characteristic but can introduce considerable AC core loss, especially when the inductor value is relatively low and the ripple current is high. Ferrite materials, although more expensive, have an abrupt saturation characteristic with the inductance dropping sharply when the peak design current is exceeded. Nevertheless, they are preferred at high switching frequencies because they present very low core loss while the designer is only required to prevent saturation. In general, ferrite or molypermalloy materials are a better choice for all but the most cost sensitive applications. Optimizing Efficiency The power dissipated in the inductor is equal to the sum of the core and copper losses. To minimize copper losses, the winding resistance needs to be minimized, but this usually comes at the expense of a larger inductor.Corelosseshaveamoresignificant contribution at low output current where the copper losses are at a minimum, and can typically be neglected at higher output currents where the copper losses dominate. Core loss information is usually available from the magnetics vendor. Proper inductor selection can affect the resulting power supplyefficiencybymorethan15%! The copper loss in the inductor can be calculatedusingthefollowingequation: PL(Cu) = I L(rMS) * rwiNDiNg where IL(rMS) is the RMS inductor current thatcanbecalculatedasfollows: IL(rMS) = IOut(MAx) *
2
ViN(MAx) * s * Kr * IOut(MAx)
VOut * (ViN(MAx) - VOut)
where:
s = switching frequency
Kr = ratio of the AC inductor ripple current to the maximum output current Thepeak-to-peakinductorripplecurrentis: IPP =
.V
Out
ViN(MAx) * s *L
* (ViN(MAx) - VOut)
Once the required inductor value is selected, the proper selection of core material is based onpeakinductorcurrentandefficiencyrequirements. The core must be large enough not to saturate at the peak inductor current IPP IPeAk = IOut(MAx) + 2
( )
+ 3
.
IPP IOut(MAx)
2
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
0
APPLICATIONS INFORMATION Output Capacitor Selection The required ESR (Equivalent Series Resistance) and capacitance drive the selection of the type and quantity of the output capacitors. The ESR must be small enough that both the resistive voltage deviation due to a step change in the load current and the output ripple voltage do not exceed the tolerance limits expected on the output voltage. During an output load transient, the output capacitor must supply all the additional current demanded by the load until the SP7662 adjusts the inductor current to the new value. In order to maintain VOut,the capacitance must be large enough so that the output voltage is held up while the inductor current ramps to the value corresponding to the new load current. Additionally, the ESR in the output capacitor causes a step in the output voltage equal to the current. Because of the fast transient response and inherent 00% to 0% duty cycle capability provided by the SP7662 when exposed to output load transients, the output capacitor is typically chosen for ESR, not for capacitance value. The ESR of the output capacitor, combined with the inductor ripple current, is typically the main contributor to output voltage ripple. The maximum allowable ESR required to maintain a specifiedoutputvoltageripplecan be calculated by: ReSr VOut IPk-Pk VOut =
s = Switching Frequency
D = Duty Cycle COut = Output Capacitance Value
Input Capacitor Selection
(
IPP * ( - D)
s * COut
)
2
+ (IPP *ReSr)
2
The input capacitor should be selected for ripple current rating, capacitance and voltage rating. The input capacitor must meet the ripple current requirement imposed by the switching current. In continuous conduction mode, the source current of the high-side MOSFET is approximately a square wave of duty cycle VOut/ViN. More accurately, the current wave form is trapezoidal,givenafiniteturn-onandturn-off, switch transition slope. Most of this current is supplied by the input bypass capacitors. The RMS current handling capability of the input capacitors is determined at maximum output current and under the assumption that the peak-to-peak inductor ripplecurrentislow,itisgivenby:
ICiN(rMS) = IOut(MAx) * D(1 - D)
The worst case occurs when the duty cycle D is 50% and gives an RMS current value equal to IOUT/2. Select input capacitors with adequate ripple current rating to ensure reliable operation. The power dissipated in the input capacitoris: PCiN = I CiN(rMS) * reSr(CiN) Thiscanbecomeasignificantpartofpower losses in a converter and hurt the overall energy transfer efficiency. The input voltage ripple primarily depends on the input
2
where:
VOut = Peak-to-Peak Output Voltage Ripple IPk-Pk = Peak-to-Peak Inductor Ripple Current The total output ripple is a combination of the ESR and the output capacitance value andcanbecalculatedasfollows:
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
APPLICATIONS INFORMATION capacitor ESR and capacitance. Ignoring the inductor ripple current, the input voltage ripplecanbedeterminedby: ViN = Loop Compensation Design The open loop gain of the whole system can be divided into the gain of the error amplifier,PWMmodulator,buckconverteroutput stage, and feedback resistor divider. In order to cross over at the desired frequency cut-off (FCO),thegainoftheerroramplifiermust compensate for the attenuation caused by the rest of the loop at this frequency. The goal of loop compensation is to manipulate loop frequency response such that its crossover gain at 0db, results in a slope of -20db/decade. The first step of compensation design is to pick the loop crossover frequency. High crossover frequency is desirable for fast transient response, but often jeopardizes the power supply stability. Crossover frequency should be higher than the ESR zero but less than /5 of the switching frequency or
IOut(MAx)*reSr(CiN) + IOut(MAx)*VOut*(ViN - VOut) V2iN * s * CiN
The capacitor type suitable for the output capacitors can also be used for the input capacitors. However, exercise extra caution when tantalum capacitors are used. Tantalum capacitors are known for catastrophic failure when exposed to surge current, and input capacitors are prone to such surge current when power supplies are connected "live" to low impedance power sources. Although tantalum capacitors have been successfully employed at the input, it is generally not recommended.
Type III Voltage Loop Compensation GAMP (s) Gain Block VREF (Volts) (SRz2Cz2+1)(SR1Cz3+1) SR1Cz2(SRz3Cz3+1)(SRz2Cp1+1) Notes: RESR = Output Capacitor Equivalent Series Resistance. RDC = Output Inductor DC Resistance. VRAMP_PP = SP7662 Internal Ramp Amplitude Peak-to-Peak Voltage. Condition: Cz2 >> Cp1 & R1 >> Rz3 Output Load Resistance >> RESR & RDC
PWM Stage GPWM Gain Block VIN VRAMP_PP
Output Stage GOUT (s) Gain Block (SRESRCOUT+ 1) [S^2LCOUT+S(RESR+RDC) COUT+1]
VOUT (Volts)
Voltage Feedback GFBK Gain Block R2 VFBK (Volts) (R1 + R2) or VREF VOUT
SP7662 Voltage Mode Control Loop with Loop Dynamic
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
2
APPLICATIONS INFORMATION 60kHz. The ESR zero is contributed by the ESR associated with the output capacitors andcanbedeterminedby:
P(LC) =
.
2* L * COut
Z(ESR) =
2* COut * ReSr
The next step is to calculate the complex conjugate poles contributed by the LC outputfilter,
Gain (dB)
When the output capacitors are of a Ceramic Type, the SP7662 Evaluation Board requires a Type III compensation circuit to give a phase boost of 80 in order to counteract the effects of an underdamped resonance of the output filteratthedoublepolefrequency.
Condition: C22 >> CP1, R1 >> RZ3
Error Amplifier Gain Bandwidth Product
20 Log (RZ2/R1)
1/6.28 (RZ2) (CP1)
1/6.28 (RZ3) (CZ3)
1/6.28 (R1) (CZ3)
1/6.28(R22) (CZ2)
1/6.28 (R1) (CZ2)
Frequency (Hz)
Bode Plot of Type III Error Amplifier Compensation.
CP1
RZ3
CZ3
CZ2 VFB RSET
RZ2
VOUT
R1 68.1k, 1%
+ + - 0.8V
COMP CF1
RSET =
54.48 (k) (VOUT -0.8)
Type III Error Amplifier Compensation Circuit
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
3
APPLICATIONS INFORMATION
VOUT 3.30V, 0-12A
LX
2.7uH, 4.1 m R3 5.11K D1 NP C4 R9
ISP
R4 5.11K 0.1uF 60k
ISN
28
27
R11 10,1% C5 100uF RZ3 499,1% R1 10k,1% C6 100uF C7 NP
1 2
SWN PAD
GND PAD
PGND PGND PGND PGND GND VFB COMP SS GND ISN ISP SWN VINP
LX LX
26 25 24 23 22 21 20 19 18 17 16 15 14
CZ2 22nF CP1
RZ2 2K,1% 100pF
3 4 5 6 7
U1 SP7662
LX LX VCC UVIN GND GND VIN BST LX LX LX
CVCC 4.7uF
R12 0 Ohms
GND
CZ3 2200pF R7 NP C8 NP
CF1 100pF
CSS
47nF
8 9
R2 3.2k,1%
R6 NP
R8
NP
10 11
RBST
C9
6.8nF
12 13
0 Ohms 22nF CBST SD101AWS DBST
ISN ISP LX
29
VIN PAD
Rs1 1
Cs1 2.2nF
Rs2 1
Cs2 2.2nF
VIN
5-22Vin
C3 22uF
C2 22uF
C1 22uF
GND
Evaluation Board Schematic Parts shown for 5V-22V input, 3.3V Output
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
4
TYPICAL PERFORMANCE CHARACTERISTICS
00 95 90
Efficiency (%)
Efficiency vs Load at 22Vin
00 95 90
Efficiency (%)
Efficiency vs. Load at 12VIN
85 80 75 70 65 60 55 50 0 2 4 6 8 0 2 Vout=5.0V Vout=2.5V Vout=.5V Vout=3.3V Vout=.8V Vout=.2V
85 80 75 70 65 60 55 50 0 2 4 6 8 0 2
Vout=5.0V Vout=3.3V Vout=2.5V Vout=.8V Vout=.5V Vout=.2V Vout=0.8V
Output Load (A)
Output Load (A)
00
Efficiency vs Load at 3.3Vin
00
Efficiency vs Load at 5.0Vin
90
Efficiency (%)
Efficiency (%)
90
80
Vout=2.5V
80
Vout=3.3V
70
Vout=1 .8V Vout=1 .5V
70
Vout=2.5V Vout=1 .8V
60
Vout=1 .2V Vout=0.8V
60
Vout=1 .5V Vout=1 .2V Vout=0.8V
50 0 2 4 6 8 0 2
50 0 2 4 6 8 0 2
Output Load (A)
Output Load (A)
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
5
TYPICAL PERFORMANCE CHARACTERISTICS
Vout Ripple
Vout Ripple
Output Ripple, No Load
Output Ripple, Iout=12A
Vin
Vout
Vin
Vout Soft start
Soft start
Iout 5A/div
Iout 5A/div Start up Response, Iout=6A
Start up Response, No Load
Vin
Vout Soft start
Vout Transient
Iout 10A/di Start up response, Iout=12A
Mar -07 Rev AJ
Iout 5A/div Load Step Response, Iout=6A -12A
(c) 2007 Sipex Corporation
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
6
TYPICAL PERFORMANCE CHARACTERISTICS
Vout Transient
Vout Soft start
Iout 5A/div
Iout 0A/div
Load Step Response, Iout=0A -2A
Output Short Circuit
Vout Vin SoftStart Vout (V)
3.38 3.36 3.34
Vout vs Load at 12Vin
Iout 5A/div
Vout=3.3V 3.32 0 2 4 6 8 0 2
Output Load (A)
OCP Hiccup Response
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
7
PACKAGE: 26 PIN DFN
Mar -07 Rev AJ
SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator
(c) 2007 Sipex Corporation
8
ORDERING INFORMATION
Part Number
Junction Temperature
Package
SP7662ER/TR..................................-40C to +25C............ .................................26 Pin 7 X 4 DFN (Option 2) SP7662ER-L/TR.............................-40C to +25C..........................(Lead Free) 26 Pin 7 X 4 DFN (Option 2)
/TR = Tape and Reel Pack quantity is 3,000 26 pin DFN.
Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL:(408)934-7500 FAX:(408)935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Mar -07 Rev AJ SP7662 Wide Input Voltage Range 2A, 300kHz Buck Regulator (c) 2007 Sipex Corporation
9

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