EXAR SP6656 Advanced High Efficiency 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output
Contents
1. PIN NUMBER PIN NAME DESCRIPTION 1 Pvn Input voltage power pin Inductor charging current passes through this pin 2 Vin Internal supply voltage Control circuitry powered from this pin 3 OVSO Output Voltage Selection Output OVSI 1 pulls this node to GND OVSI 0 this node is open 4 OVSI Output Voltage Select Input See table 1 for definition 5 EN EN 1 device is enabled EN 0 All internal circuitry is disabled and power switches are opened 6 FB External feedback network input connection Connect a resistor from FB to ground and FB to Vur to set the output voltage This pin regulates to the internal bandgap reference voltage of 0 8V 7 Vour Output voltage sense pin Used by the timing circuit to set minimum on and off times GND Internal ground pin Control circuitry returns current to this pin Penn Power ground pin Synchronous rectifier current returns through this pin 10 LX Inductor switching node Inductor tied between this pin and the output capacitor to create regulated output voltage OVSI OVSO Output Voltage Short to GND Vour mon 08 R tR R Table 1 Output Voltage Selection Note Ra Rs iR Vin Vout Pus DRVON _ Lo VOLOW L V T 12. 70 4A V 73 3V Start up from SHDN V 5V 1 7 0 4A V 71 5V Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 7 The SP6656 is a high efficiency synchronous buck regulator with an input voltage range of 2 7V to 5 5V and an output that is adjustable between 1 0V and Vn The SP6656 features a unique on time control loop that runs in discon tinuous conduction mode DCM or continuous conduction mode CCM using synchronous rectification Other features include over tem perature shutdown over current protection an external feedback pin digitally controlled en able and output voltage selection The SP6656 operates with a light load quiescent current of 20uA using a 0 39 PMOS main switch and a 0 3 9 NMOS synchronous switch It operates with excellent efficiency across the entire load range making it an ideal solution for battery powered applications and low current step down conversions The part smoothly tran sitions into a 100 duty cycle under heavy load low input voltage conditions On Time Control Charge Phase The SP6656 uses a precision comparator and a minimum on time to regulate the output voltage and control the inductor current under normal load conditions As the feedback pin drops be low the regulation point the loop comparator output goes high and closes the main switch The minimum on timer is triggered setting a
3. Roc Kon x Vin Iour Roc Rcu where Fip Frp CCM loop frequency Rpc NMOS on resistance 0 3Q typ Ignoring conduction losses simplifies the loop frequency to Vour Kon Vm AND ing the loop comparator and the on timer reduces the switching frequency for load cur rents below half the inductor ripple current This increases light load efficiency The minimum on time insures that the inductor current ripple is a minimum of KowL more than the load Fip Vin Vout Copyright 2005 Sipex Corporation current demands The converter goes in to a standard pulse frequency modulation PFM mode where the switching frequency is propor tional to the load current Low Dropout and Load Transient Operation Using AND logic function the loop comparator also increases the duty ratio past the ideal D Vout Vin up to and including 100 Under a light to heavy load transient the loop compara tor will hold the main switch on longer than the minimum on timer until the output is brought back into regulation Also as the input voltage supply drops down close to the output voltage the main MOSFET resistance loss will dictate a much higher duty ratio to regulate the output Eventually as the input voltage drops low enough the output voltage will follow causing the loop compara tor to hold the converter at 100 duty cycle This mode is critical in extending battery life when the output voltage
4. logic high for the duration defined by K Tones 2 s Vin Vout where Kon 2 25V usec constant Vin Vn pin voltage Vout Vout pin voltage To accommodate the use of ceramic and other low ESR capacitors an open loop ramp is added to the feedback signal to mimic the inductor current ripple The following waveforms de scribe the ideal ramp operation in both CCM and DCM operation In either CCM or DCM the negative going ramp voltage VgAwp in the functional diagram Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output THEORY OF OPERATION RAMP CCM OPERATION RAMP DCM OPERATION DRVON L1 FB REF FB REF Vos is added to FB and this creates the FB s signal This FB signal is applied to the negative termi nal of the loop comparator To the positive terminal of the loop comparator is applied the REF voltage of 0 8V plus an offset voltage Vos to compensate for the DC level of VgAwp ap plied to the negative terminal The result is an internal ramp with enough negative going offset approximately 50mV to trip the loop com parator whenever FB falls below regulation The output of the loop comparator a rising VOLOW causes a SET if BLANK 0 and OVR_I 0 This starts inductor charging DRVON 1 and starts the minimum on timer The minimum on timer times out and indicates DRVON can be reset if the voltage loop is sat
5. 0V dynamically adjustable output voltage logic level shutdown control and 140 C over temperature shutdown 2 7V to 5 5V Input TYPICAL APPLICATION SCHEMATIC 3 2 x 1 6 x 1 8mm Date 02 02 05 SP6656 Qvo Pyn LX Penp Vout FB SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 1 Storage Temperature Operating Temperature 65 C to 150 C 40 C to 85 C 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 of the specifications below is not implied Exposure to absolute maximum rating conditions for extended periods of time may affect reliability ELECTRICAL CHARACTERISTICS Vin UVin Ven 3 6V Vout Ves lo OMA Tame 40 C to 85 C typical values at 27 C unless otherwise noted PARAMETER MIN TYP MAX UNITS CONDITIONS Input Voltage Operating 2 7 5 5 V Result of lo measurement at Viy PVin 5 5V Range Minimum Output Voltage 1 0 V FB Set Voltage Vr 0 784 0 800 0 816 V 25 C lo 200mA Close Loop L 10uH Cour 22uF Overall Accuracy Measured at Vin 5 5V no load and 40 C to 85 C 5 Vin 3 6V 200mA load Close Loop 0 C to 70 C 4 On Time Constant Kon 1 5 2 25 3 0 V us Cl
6. 500 ILoad mA 1 55 1 53 1 51 Vout V 1 49 1 47 1 0 100 200 300 400 500 ILoad mA Line Load Rejection V 3 3V Line Load Rejection V p 1 5V 500 Tamb 85 C Tamb 25 C dio Tamb 40 C 300 z 200 100 4 3 0 33 36 39 42 Vin V 50 Tamb 85 C Tamb 25 C 40 Tamb 40 C 30 lin uA 3 0 33 3 6 3 9 42 Vin V No Load Battery Current V 23 3V OUT Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output 4 No Load Battery Current V 1 5V OUT Copyright 2005 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS Refer to the typical application schematic Tamp 27 C 3 5 3 5 3 0 3 0 n 2 5 o gt o o e o eo 20 2 20 s Ed g 15 B 15 1 0 1 0 0 5 0 5 0 0 3 6 3 9 4 2 4 5 4 8 5 1 5 4 0 0 3 3 0 3 3 36 39 42 45 48 51 54 Min V Vin V Koy YS Ving Vou473 3V Kon YS Vine Vov SV 3 5 3 5 3 0 3 0 2 5 4 4 4 25 mi o 2 20
7. size From the operations section it has been shown Inductor Current Ripple Irr Kon L For the typical SP6656 application circuit with inductor size of LOWH and Kon of 2V usec the SP6656 currentripple would be about 200mA and Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output THEORY OF OPERATION Output Voltage Selection The OVSI Output Voltage Selection Input pin is internally driving a NMOS Gate which Drain OVSO pin is used to short circuit Rs and then achieve a higher output voltage see table 1 for calculation page 3 External Feedback Pin The FB pin 6 is compared to an internal refer ence voltage of 0 8V to regulate the SP6656 output The output voltage can be externally programmed within the range 1 0V to 5 0V by tying a resistor from FB to ground and FB to Vour pin7 See the applications section for resistor selection information APPLICATION INFORMATION would be fairly constant for different input and output voltages simplifying the selection of com ponents for the SP6656 power circuit Other inductor values could be selected as shown in Table 2 Components Selection Using a larger value than 10uH in an attempt to reduce output voltageripple would reduce inductor current ripple and may not produce as stable an output ripple Forlarger inductors with the SP6656 which has a peak inductor current of 0 625A most 15uH or 22uH inductors would have t
8. the off time loop control is handed back to the AND logic function on time signal If the output voltage is still low charging begins until the output is in regulation or the current limit has been reached again During startup and over load conditions the converter behaves like a current source at the programmed limit minus half the current ripple The minimum Torr is controlled by the equation Korr Torr MIN OUT Under Voltage Lockout The SP6656 is equipped with a programmable under voltage lockout to protect the input bat tery source from excessive currents when sub stantially discharged When the input supply is below the UVLO threshold both power switches are open to prevent inductor current from flow ing The level of falling input voltage has a typical hysteresis of 120mV to prevent chatter ing due to the impedance of the input source Under Current Detection The synchronous rectifier is comprised of an inductor discharge switch a voltage compara tor and a driver latch During the off time positive inductor current flows into the PGND pin 9 through the low side NMOS switch to LX pin 10 through the inductor and the output capacitor and back to pin 9 The comparator monitors the voltage drop across the discharge NMOS As the inductor current approaches zero the channel voltage sign goes from negative to positive causing the comparator to trigger the driver latch and open the switch to prevent in
9. 50MS s t Hi Res DORE Tek Run 2 50MS s i HiRes IRE i F Ch4 Zoom 1 0X Vert TOS Hor Ch2200m 2 0X Vert 0 01X Horz 1 F i P ROM EN CH 1 Vin TI pea P aN icem Piin i CH2 Voyr 7 5 0V DIV 1 i 0 5V DIV i CH2 Voyr A a 2 0V DIV i s CHA4 ly i SS E a k i 0 5A DIV Lo o o oU moo CHA lw i 44 0 5A DIV Chi 5 00v Ch2 1 00V M2 00ms Chi F 2 90 V Mommsen Chi 5 00 V cha Soon M2 00nis Chi J 290v 4 10 0mVos Vy Start up V 74 2V 1 70 4A V 73 3V Vy Start up V 4 2V I 70 4A V 71 5V Tek 10 0MS s 61 Aca Tek 10 0MS s iem Chi Zoom 2 0X Vert 0 05X Horz Chi Zoom 2 0X Vert 0 05X Horz TD SiimA Wi ro5gs thd 7 12 3mv TE si omv i 100 gt f X Ms Ch4 7 12 4mV Ch4 10 0MY Ch 4 10 0mVcs Load Step V 4 2V 1 70 1A to 0 4A V 73 3V Load Step V 4 2V 1 70 1A to 0 4A V 1 5V Tek Run 10 0MS s H Res 1 Tek Run 2 50MS s i Hi Res Trig i i F Ch2200m 1 0X Vert 0 028 Hor Ch2 Zoom 2 0X Vert 0 01X Horz ert CH 1 Vspon e be J ovog H is i CH 1 Vsupy BEP RR i 5 0V DIV 1 1 d CH 2 Voyr CH 2 Vour 2 0V DIV f 0 5V DIV 4 t CHA lx i CH 4 l x Lo o UL meo 0 5A DIV 44 0 5A DIV 44 t Chi 5 00 V gov 2sogs tha FOV Chi dov TH Sogo wcsons Chi Looy WE 10 0mV os e 10 0mVov Start up from SHDN V SV 1
10. 85 C noni arinean SP6658ER TR 4 trn ere 40 C to 85 C sssssssssss Available in lead free packaging To order add L suffix to part number Example SP6656ER TR standard SP6656ER L TR lead free TR Tape and Reel Pack quantity is 3 000 for DFN ORDERING INFORMATION Package Type RE EE 10 Pin DEN pictor Ate nnI tede 10 Pin DEN Cinav VIA ANALOG EXCELLENCE 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 Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 17
11. K Cinav ICA Advanced SP6656 High Efficiency 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output FEATURES Ir 4 E 98 Efficiency Possible e D Eo wie E Offered in small 2 4 x 2 5mm DFN ovso m BD M GND E Ultra low 20uA Quiescent Current ovs E EC Your EN 51 E 625mA Inductor Peak Current Limit E Guaranteed Minimum 400mA Output Current E 2 7V to 5 5V Input Voltage Range Now Available in Lead Free Packaging E Output Adjustable D to 1 0V S UT utput Adjustable Down to 1 E Cell Ph B 100 Duty Ratio Low Dropout Ge i PUER B PDA s Operation E 80uA Light Load Quiescent Current in E DSC s Dropout E MP3 Players B Dynamic Adjustable Output Voltage B ideal for portable designs powered with Li lon battery B USB Devices E Point of Use Power DESCRIPTION The SP6656 is a 400mA synchronous buck regulator that is ideal for portable applications that use a Li lon or 3 cell alkaline NiCD NiMH input The SP6656 s proprietary control loop 20uA light load quiescent current and 0 3 power switches provide excellent efficiency across a wide range of output currents As the input battery supply decreases towards the output voltage the SP6656 seamlessly transitions into 10096 duty ratio operation further extending useful battery life The SP6656 is protected against overload and short circuit conditions with a precise inductor peak current limit Other features include externally programmable output voltage down to 1
12. Power loops on the input and output of the con verter should be laid out with the shortest and widest traces possible The longer and narrower the trace the higher the resistance and inductance it will have The length of traces in series with the capacitors increases its ESR and ESL and reduces their effectiveness at high frequencies Therefore put the 1 uF bypass capacitor as close to the Vr and GND pins of the converter as possible the 10uF Cn close to the Pym pin and the 10uF output capacitor as close to the inductor as possible The external voltage feedback network Rr Ry Rs and feedforward capacitor Cr should be placed very close to the FB pin Any noise traces like the LX pin should be kept away from the voltage feedback network and separated from it by using power ground copper to minimize EMI Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 15 PACKAGE 10 PIN DFN A C 4 D gt lt _ Top View Pin 1 Dot by Marking Side View 2 4x2 5 10 Pin DFN SYMBOL A 0 00 0 05 Bottom View Note Dimensions in mm B C D E 0 80 0 85 0 90 F G H I Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 16 Part Number Operating Temperature Range SP66b6EHR 5 en teenie 40 C to 4
13. a MIN Ton gt Internal Supply ONOVER Min Toy Kow Vin Vout Tonover min Ton e M l rl Pu HP OVRI Vos x g VP EK REF 4 REF VOLOW l En icd E J 6 Le Ra BEER ILIMM l VRamP EB NS S a FB my x RST OVR 1 FZ LX DRVON LN L ee x 7 b 9 REF Zero X uo X One Shot amp Co Pam TSD 5 L 7 f00ns 7 ENL Z BLANK Penn oILIMM E Torr ovSI Kore Vout V oOVR_I gt OVSO GND gt DRVON i m T jira x BLANK BLANK Tg y 7100ns or Tore Koee Vour Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 3 TYPICAL PERFORMANCE CHARACTERISTICS Refer to the typical application schematic Tamp 27 C 100 100 ooo ooo 95 90 95 Ag 85 90 R z g 80 B 85 H E 75 ul amp 80 70 Vi 3 6V 75 Vi 3 9V wees Vi 4 2V 0 1 1 0 10 0 100 0 1000 0 65 eee ay ILoad mA ll l 60 0 1 1 0 10 0 100 0 1000 0 ILoad mA Efficiency vs Load V 3 3V V y 3 6V Efficiency vs Load V y 1 5V 3 45 3 40 3 35 Vout V 3 30 3 25 3 20 T 0 100 200 300 400
14. d mag netic field emissions Capacitor Selection The SP6656 has been designed to work with very low ESR output capacitors listed in Table 2 Component Selection which for the typical appli cation circuit are 10uF ceramic capacitors These capacitors combine small size low ESR and good value Toregulatetheoutput with low ESR capaci tors of 0 01 2 or less an internal ramp voltage Vranmp has been added to the FB signal to reliably trip the loop comparator as described in the Op erations section Output ripple for a buck regulator is determined mostly by output capacitor ESR which for the SP6656 with a constant inductor current ripple can be expressed as Vout ripple Irr Resr Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output APPLICATION INFORMATION For the 10uF Ceramic Output Capacitor with 0 003QESR anda 10uH inductor yielding 200mA inductor current ripple I g the Vour ripple would be 0 6mVpp Since 0 6mV is a very small signal level the actual value would probably be as large as 10mV due to noise and layout issues but this illustrates that the SP6656 output ripple can be very low indeed To improve stability a small ceramic capacitor Cp 22pF should be paralleled with the feedback voltage divider RF as shown on the typical application schematic on page 1 An other function of the output capacitance is to hold uptheoutput voltage during the load transien
15. ductor current reversal This circuit along with the on timer puts the converter into PFM Copyright 2005 Sipex Corporation mode and improves light load efficiency when the load current is less than half the inductor ripple current defined by Kon L Thermal Shutdown The converter will open both power switches if the die junction temperature rises above 140 C The die must cool down below 126 C before the regulator is re enabled This feature protects the SP6656 and surrounding circuitry from exces sive power dissipation due to fault conditions Shutdown Enable Control The EN pin of the device is a logic level control pin that shuts down the converter when logic is low or enables the converter when logic is high When the converter is shut down the power switches are opened and all circuit biasing is extinguished leaving only junction leakage cur rents on supply pins 1 and 2 After pin 5 is brought high to enable the converter there is a turn on delay to allow the regulator circuitry to reestablish itself Power conversion begins with the assertion of the internal reference ready signal which occurs approximately 150us after the enable signal is received Inductor Selection The SP6656 uses a specially adapted minimum on time control of regulation utilizing a preci sion comparator and bandgap reference This adaptive minimum on time control has the ad vantage of setting a constant current ripple for a given inductor
16. g 20 4 z t 3 1 5 B 15 1 0 1 0 0 5 0 5 0 0 0 0 96 B9 Xx 45 MBL od c94 30 33 36 39 42 45 48 51 54 Vin V Vin V Korr YS Vins Voy 3 3V Korr YS Vins Voy571 5V 700 0 700 0 600 0 600 0 500 0 500 0 4 eo 400 0 so00 T e Um E riu 5 o E g 300 0 7 300 0 8 hs 200 0 200 0 Vout 3 3V Vout 1 5V 100 0 Measured 100 0 Measured 1 Vout 3 3V Vout 1 5V Calculated Calculated 0 0 0 0 35 4 0 45 5 0 3 4 3 8 42 46 5 0 Vin V Vin V Ripple Frequency vs V 15 70 4A Voy 3 3V Ripple Frequency vs V 1 70 4A V 71 5V Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output 5 Copyright 2005 Sipex Corporation TYPICAL PERFORMANCE CHARACTERISTICS Refer to the typical application schematic Tamp 27 C Plot Overlay 1 Sta paw APU 16 2 81 Fbx data APU 10 3 5 a 0G 07 3 0 i o6 M o g 25 e 9 T gt 705 g L 5 a E 2 0 d lt g ICE k gt o 1 5 e S 2 703 5 lt 1 0 10 2 o 1 0 5 0 0 0 0 0 25 0 50 0 75 1 00 1 25 1 50 Time in Milliseconds Turn on Time 400mA Load Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 6 TYPICAL PERFORMANCE CHARACTERISTICS Refer to the typical application schematic Tawp 27 C Tek Run 2
17. is at or above the minimum usable input voltage The dropout voltage is the minimum Vm Vour below which the output regulation cannot be main tained The dropout voltage of SP6656 is equal to Ir 0 3Q Ry where 0 3Q is the typical Rpscon of the P Channel MOSFET and Ry is the DC resistance of the inductor The SP6656 has been designed to operate in dropout with a light load Iq of only 80uA The on time control circuit seamlessly operates the converter between CCM DCM and low drop out modes without the need for compensation The converter s transient response is quick since there isno compensated error amplifier in the loop Inductor Over Current Protection To reduce the light load dropout Iq the SP6656 over current system is only enabled when I gt 400mA The inductor over current protection circuitry is programmed to limit the peak induc tor current to 0 625A This is done during the on time by comparing the source to drain volt age drop of the PMOS passing the inductor Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output THEORY OF OPERATION current with a second voltage drop representing the maximum allowable inductor current As the two voltages become equal the over current comparator triggers a minimum off time one shot The off time one shot forces the loop into the discharge phase for a minimum Torr time causing the inductor current to decrease At the end of
18. isfied If Vour is still below the regulation point RESET is held low until Vour is above Copyright 2005 Sipex Corporation regulation Once RESET occurs Tox minimum is reset and the Topp one shot is triggered to blank the loop comparator from starting a new charge cycle for a minimum period This blank ing period occurs during the noisy LX transition to discharge where spurious comparator states may occur For Torr gt Tprawx the loop is in a discharge or wait state until the loop comparator starts the next charge cycle by DRVON going high If an over current occurs during charge the loop is interrupted and DRVON is RESET The off time one shot pulse width is widened to Torr Korr Vout which holds the loop in discharge for that time At the end of the off time the loop is released and controlled by VOLOW In this manner maximum inductor current is controlled onacycle by cycle basis Anassertion of UVLO undervoltage lockout or TSD thermal shut down holds the loop in no charge until the fault has ended On Time Control Discharge Phase The discharge phase follows with the high side PMOS switch opening and the low side NMOS switch closing to provide a discharge path for the inductor current The decreasing inductor current and the load current cause the output voltage to drop Under normal load conditions when the inductor current is below the pro grammed limit the off time will continue until the output voltage fa
19. itor Type Manufacturer uF Q max A 45 C LxW mm Ht mm V Website 10 TDK C2012X5R0J106M 0 003 1 00 2 0x1 2 1 25 6 3 X5R Ceramic tdk com 10 Murata GRM21BR60J106KE01 0 003 1 00 2 0x1 2 1 25 6 3 POSCAP murata com 47 TDK C2012X5R0J475M 0 005 1 00 20x1 2 125 6 3 X5R Ceramic tdk com 47 Murata GRM21BR60J475KE01 0 005 1 00 2 0x1 2 1 25 6 3 POSCAP murata com Note Components highlighted in bold are those used on the SP6656 Evaluation Board Table 2 Component Selection Output Voltage Ripple Frequency An important consideration in a power supply application is the frequency value of the output ripple Given the control technique ofthe SP6656 as described in the operations section the frequency of the output ripple will vary when in light to moderate load in the discontinuous or PFM mode For moderate to heavy loads greater than about 100mA inductor current ripple for the typical 10uH inductor application on 100mA is half the 200mA inductor current ripple the output ripple frequency will be fairly constant From the operations section this maximum loop frequency in continuous conduction mode is 1 Your Vin Vour Kon VIN Data for loop frequency as measured from output voltage ripple frequency can be found in the typical performance curves Fi p Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Layout Consideration
20. llel with RI The formula for RF witha given Re RI and output voltage is Rr Vour 0 8V 1 x RD FB 2 Dual V selectable First pick the lowest voltage that will be used and utilize the same method as above Rp Vour Low 0 8V 1 X Rp Riz 300k Then use the following equation to determine Rs OVSO 0 8 x Rf R Rs 24 R Rs VourT_HIGH 0 8 Rs IRZ Rs ee Ry Rs Ry Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation 13 APPLICATION INFORMATION INDUCTORS SURFACE MOUNT Inductor Specification Inductance Manufacturer Part No Series RQ Igar A Size Inductor Type Manufacturer uH LxW mm Ht mm Website 10 Murata LQH32CN100K11 0 300 0 45 3 2 x 1 6 1 8 Unshielded Ferrite Core murata com 10 TDK RLF5018T 100MR94 0 056 0 94 5 6 x 5 2 2 0 Shielded Ferrite Core tdk com 10 Coilcraft LPO6013 103K 0 300 0 70 6 0 x 5 4 1 3 Unshielded Ferrite Core coilcraft com 22 Murata LQH32CN220K21 0 710 0 25 3 2 x 1 6 1 8 Unshielded Ferrite Core murata com 22 TDK RLF5018T 220MR63 0 130 0 63 5 6 x 5 2 2 0 Shielded Ferrite Core tdk com 22 Coilcraft LPO6013 103 0 520 0 45 6 0 x 5 4 1 3 Unshielded Ferrite Core coilcraft com CAPACITORS SURFACE MOUNT Capacitor Specification Capacitance Manufacturer Part No ESR RippleCurrent Size Voltage Capac
21. lls below the regulation threshold which initiates anew charge cycle via the loop comparator The inductor current floats in continuous con duction mode During this mode the inductor peak current is below the programmed limit and the valley currentis above zero This is to satisfy load currents that are greater than half the mini mum current ripple The current ripple Irr is defined by the equation Ibe SON Vin Vour lour Ren LR Vin Vout where Date 02 02 05 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output THEORY OF OPERATION L Inductor value Iour Load current Rcg PMOS on resistance 0 3Q typ If the Iour Rcy term is negligible compared with Vm Vout the above equation simplifies to Kon L For most applications the inductor currentripple controlled by the SP6656 is constant regardless of input and output voltage Because the output voltage ripple is equal to Vout ripple Irr Resr where ILp Resr ESR of the output capacitor the output ripple of the SP6656 regulator is independent of the input and output voltages For battery powered applications where the battery voltage changes significantly the SP6656 provides constant output voltage ripple through out the battery lifetime This greatly simplifies the LC filter design The maximum loop frequency in CCM is de fined by the equation _ Vin Vour Vour lour
22. o be larger physical sizes limiting their use in small por table applications Smaller values like 10uH would more easily meet the 0 625A limit and come in small case sizes and the increased Copyright 2005 Sipex Corporation inductor current ripple of almost 200mA would produce very stable regulation and fast load transient response at the expense of slightly reduced efficiency Other inductor parameters are important the in ductor current rating and the DC resistance When the current through the inductor reaches the level of Isar the inductance drops to 70 of the nominal value This nonlinear change can cause stability problems or excessive fluctuation in in ductor current ripple To avoid this the inductor should be selected with saturation current at least equal to the maximum output current of the con verter plus half the inductor current ripple To provide the best performance in dynamic condi tions such as start up and load transients inductors should be chosen with saturation current close to the SP6656 inductor current limit of 0 625A DC resistance another important inductor charac teristic directly affects the efficiency of the con verter so inductors with minimum DC resistance should be chosen for high efficiency designs Recommended inductors with low DC resistance are listed in Table 2 Preferred inductors for on board power supplies with the SP6656 are mag netically shielded types to minimize radiate
23. ose Loop Li 10uH Cour 22uF Min Ton Kon Vin Vout Off Time Constant Kore 1 6 2 4 3 2 V us Inductor current limit tripped VFB 0 5V Min Toge Korr Vour Measured at Vout 1V Off Time Blanking 100 ns Turn On Time 200 400 us 400mA Load PMOS Switch Resistance 0 3 0 6 Q Ipmos 200mA NMOS Switch Resistance 0 3 0 6 Q Inmos 200mA Inductor Current Limit 500 625 750 mA VFB 0 5V Power Efficiency 96 96 Vout 2 5V lo 200mA 92 Vout 3 3V lo 400mA Minimum Guaranteed Load 400 500 mA Current Vin Quiescent Current 20 30 uA Vout 3 3V V 3 6V and Vn 5 5V Vin Shutdown Current 1 500 nA EN 0V Vout Quiescent Current 2 5 uA Vout 3 3V Vout Shutdown Current 1 500 nA EN 0V UVLO Undervoltage Lockout 2 55 2 70 2 85 V EN Vin Threshold Vin falling UVLO hysteresis 40 mV OVSO Output Voltage TBD V OVSOLeakage Current TBD uA Over Temperature 140 C Rising Trip Point Over Temperature Hysteresis 14 C EN Leakage Current 1 500 nA EN Input Threshold Voltage 0 60 0 90 V High to Low Transition 1 25 1 8 V Low to High Transition FB Leakage Current 1 100 nA FB 1V LX Leakage 3 5 uA EN OV Vn 3 6V LX OV LX Vn 0 2V OVSI Leakage Current 1 500 nA OVSI Input Threshold Voltage 0 60 0 90 V High to Low Transition 1 25 1 8 Low to High Transition Date 02 02 05 2 SP6656 400mA Synchronous Buck Regulator with Dynamically Adjustable Voltage Output Copyright 2005 Sipex Corporation PIN DESCRIPTION
24. s Proper layout of the power and control circuits is necessary in a switching power supply to obtain good output regulation with stability and a mini mum of output noise The SP6656 application circuit can be made very small and reside close to the IC for best performance and solution size as long as some layout techniques are taken into consideration To avoid excessive interference between the SP6656 high frequency converter and the other active components on the board some tules should be followed Refer to the typical application schematic on page 1 and the sample PCB layout shown in the following figures to illustrate how to layout a SP6656 power supply Avoid injecting noise into the sensitive part of circuit via the ground plane Input and output capacitors conduct high frequency current through the ground plane Separate the control and power grounds and connect them together at a single point Power ground plane is shown in the figure titled PCB top sample layout and connects the Copyright 2005 Sipex Corporation APPLICATION INFORMATION ground of the Cour capacitor to the ground of the Cry capacitor and then to the PGND pin 10 The control ground plane connects from pin 9 GND to ground of the Cyn capacitor and the Ry ground return of the feedback resistor These two separate control and power ground planes come together in the figure titled PCB top sample layout where SP6656 pin 9 GND is connected to pin 10 PGND
25. ts and prevent excessive overshoot and undershoot The typical performance characteristics curves show very good load step transient response for the SP6656 with the recommended output capaci tance of IOuF ceramic The input capacitor will reduce the peak current drawn from the battery improve efficiency and significantly reduce high frequency noises in duced by a switching power supply The typical input capacitor for the SP6656 is 1OuF ceramic These capacitors will provide good high frequency bypassing and their low ESR will reduce resistive losses for higher efficiency An RC filteris recom mended for the Viv pin 2 to effectively reduce the noise for the ICs analog supply rail which powers sensitive circuits This time constant needs to be at least 5 times greater than the switching period which is calculated as 1 FLP during the CCM mode The typical application schematic uses the values of Rym 10 and Cyr 1 uF to meet these requirements Copyright 2005 Sipex Corporation APPLICATION INFORMATION The output voltage is programmed by the external divider as shown in the typical application circuit on Page 1 Depending on the topology used 1 or 2 voltages V is set as follows OUT 1 Single Vur First pick a value for RIthat is no largerthan 300K Vour vo Too large a value of RI will reduce the AC voltage seen by the loop comparator since the internal FB pin capacitance can form a low pass filter with RF in para
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