SC2612

SC2612 SEMTECH | Alldatasheet

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Technical content

Features

Applications

August 18, 2004 Typical Application Circuit

Description

The SC2612 is a voltage mode switcher designed for low cost, “point of use” voltage conversion. SC2612 is avail- able with fixed switching frequencies of 600kHz (SC2612A) and 200kHz (SC2612C). The SC2612 has soft start and enable functions and is short circuit protected. The output of the switcher may be set anywhere between 0.8V and 75% of Vin. Short circuit protection is disabled during start-up to allow the output capacitors time to fully charge. /g117Operating frequency of 600kHz or 200kHz /g117Input supply of 3V to 8V /g1170.5A Drive current for up to 10A output /g117Output voltages down to 0.8V /g117Overcurrent protection and soft start /g117MSOP-8 package Q3 R6 SC2612 VCC DH BST FB DLSS/EN COMP GND R10 1.5V OUT 12V IN 3.3V IN C10 /g117Graphics IC Power supplies /g117Embedded, low cost, high efficiency converters

2 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Absolute Maximum Ratings retemaraPl obmySm umixaMs tinU egatloVylppuStupnIV CC 51V egatloVniPtsooBV BST 02V DNGotLD )2( DNGotHD, )2( VDLO V, DHI 02+ot1-V egnaRerutarepmeTtneibmAgnitarepOT A 07ot0C ° erutarepmeTnoitcnuJgnitarepOT J 521C ° erutarepmeTegarotST STG 051ot56-C ° s01)gniredloS(erutarepmeTdaeLT LEAD 003C ° tneibmAotnoitcnuJecnatsiseRlamrehT )3( θJA 311W /C° esaCotnoitcnuJecnatsiseRlamrehT θJC 24W /C° )ledoMydoBnamuH(gnitaRDSED SE2 V k retemaraPl obmySs noitidnoCn iMp yTx aMs tinU egatloVylppuSCCVV CC 0.35 1V tnerruCtnecseiuQCCVI QVCC VCC V,V0.5= BST V0=NE/SS,V0.21=5 0 1A m egatloVylppuSTSBV BST 110 2V tnerruCtnecseiuQTSBI QBST VCC V,V0.5= BST V0=NE/SS,V0.21=5 A m tuokcoLegatloVrednUCCVV U VCC 3.26 .29 .2V tuokcoLegatloVrednUTSBV U BST 0.70 .80 .9V egatloVtuptuOV OS IO V;0= FB V= OS,T A =52C°2 970 088 08V m egatlovpirttnerrucrevOV ITS 4.07 .0V noitalugeRdaoLI O A4otA2.0=1 % noitalugeReniL 5.0±% ycneuqerFrotallicsOf OSC A2162CS0 840 060 27 zHkC2162CS0 610 020 42 elcyCytuDxaMrotallicsO δMAX C2162CS,A2162CS0 8% egatloVnwodtuhSNE/SSV SS 3.08 .0V tnerrucegrahCNE/SSI SS V8.0=ssV5 2 µA tnerruCecruoS/kniSHDkaeP, V5.4=HD-TSBV 3.3=DNG-HD V5.1=DNG-HD 5.0 A Am tnerruCecruoS/kniSLDkaeP, V5.4=LD-TSBV 3.3=DNG-LD V5.1=DNG-LD 5.0 A Am

Electrical Characteristics

Unless specified: VCC = 3V to 12V; V FB = VO; BST = Vcc+5V; TA = 0 to 70°C Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of th e parameters specified in the Electrical Characteristics section is not implied.

3 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Notes: (1) See Gate Resistor selection recommendations (2) 1 square inch of FR4, double sided, 1oz. minimum copper weight. Unless specified: VCC = 3V to 12V; V FB = VO; BST = Vcc+5V; TA = 0 to 70°C retemaraPl obmySs noitidnoCn iMp yTx aMs tinU ecnatcudnocsnarTreifilpmArorrE gm 8.0S m niaGreifilpmArorrEA AE R PMOC nepo=5 4B d tnerruCkniS/ecruoSreifilpmArorrE 06±A µ niaGrotaludoMA M V CC V5=9 1B d emiTdaeD 05s n

4 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Block Diagram Pin Configuration Ordering Information Pin Descriptions Note: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free products. srebmuNtraP )1( ycneuqerFe gakcaP RTSMA2162CSz Hk006 8-POSM TRTSMA2162CS )2( zHk006 RTSMC2162CSz Hk002 TRTSMC2162CS )2( zHk002 BST VCC DH GND DL FB SS/EN TOP VIEW (MSOP-8)

8 COMP

#niPe maNniPn oitcnuFniP 1P MOC. reifilpmarorreegatlovnoitcesrehctiwSehtfotuptuO 2N E/SS .etarpmaregatlovtuptuorehctiwsehtslortnoc,nipelbanednatratstfoS 3B F. tupnikcabdeeefnoitcesrehctiwS 4C CV. egatloVtupnIylppuSpihC 5D NG .senilediugtuoyalees,enalpdnuorgotyltceridtcennoc,dnuorGrewoPdnagolanA 6L D. tuptuoevirdTEFediswoLrehctiwS 7H D. tuptuoevirdTEFedishgiHrehctiwS 8T SB. sevirdTEFrofegatlovylppuS DH SS/EN COMP SYNC HRONOU S M OSFET DRIV E DL R S Q LEV EL SHIF T AND HIGH SID E DRIVE UVLO BST OSCILLAT OR 25uA VREF SSOV ER VCC VREF UVLO REF FB SHDN S HOOT -T HRU CONTRO L R S Q GND

5 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Theory of Operation The SC2612 is a step down DC/DC controller designed for minimum cost and size without sacrificing accuracy and protection. Overcurrent protection is implemented by a simple undervoltage detection scheme and is dis- abled until soft start has been completed to eliminate false trips due to output capacitor charging. The SS/EN pin is held low, as are the DH and DL pins, until the undervoltage lockout points are exceeded. Once the VCC and BST pins both rise above their undervoltage lockout points, the SS capacitor begins to charge, controlling the duty cycle of the switcher, and therefore slowly ramping up the switcher output voltage. Once the SS capacitor is charged, the current limit circuitry is enabled. If a short circuit is applied , the output will be pulled down below it’s trip point and shut down. The device may be restarted by either cycling power, or momentarily pulling SS/EN low. Component Selection OUTPUT INDUCTOROUTPUT INDUCTOROUTPUT INDUCTOROUTPUT INDUCTOROUTPUT INDUCTOR - A good starting point for output filter component selection is to choose an inductor value that will give an inductor ripple current of approximately 20% of max. output current. Inductor ripple current is given by:- OSC IN O O RIPPLEL fL V VV I /g215 /g247/g247 /g248 /g246 /g231/g231 /g232 /g230/g45/g215 /g61 So choose inductor value from:- OSCO IN O O fI V VV L /g215 /g247/g247 /g248 /g246 /g231/g231 /g232 /g230/g45/g215/g215 /g61 OUTPUT CAPOUTPUT CAPOUTPUT CAPOUTPUT CAPOUTPUT CAP AAAAACITCITCITCITCITOR(S) OR(S) OR(S) OR(S) OR(S) - The output capacitors should be selected to meet output ripple and transient response criteria. Output ripple voltage is caused by the inductor ripple current flowing in the output capacitor’s ESR (There is also a component due to the inductor ripple current charging and discharging the output capacitor itself, but this component is usually small and can often be ignored). Given a maximum output voltage ripple requirement, ESR is given by:- OSC IN O RIPPLEO ESR fL V VVV R /g215 /g247/g247 /g248 /g246 /g231/g231 /g232 /g230/g45/g215/g215 /g60 Output voltage transient excursions are a function of load current transient levels, input and output voltages and inductor and capacitor values. Capacitance and R ESR values to meet a required tran- sient condition can be calculated from:- release) (load transients positive for VV and n)applicatio (load transients negative for VVV where VV ILC I VR OA OINA AT T T T ESR /g61 /g45/g61 /g215/g215 /g215/g62 /g60 values for positive and negative transients must be cal- culated seperately and the worst case value chosen. For Capacitor values, the calculated value should be doubled to allow for duty cycle limitation and voltage drop issues.

6 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C COMPENSACOMPENSACOMPENSACOMPENSACOMPENSA TION COMPONENTSTION COMPONENTSTION COMPONENTSTION COMPONENTSTION COMPONENTS - Once the filter com- ponents have been determined, the compensation com- ponents can be calculated. The goal of compensation is to modify the frequency response characteristics of the error amplifier to ensure that the closed loop feedback system has the highest gain and bandwidth possible while maintaining stability. A simplified stability criteria states that the open loop gain of the converter should fall through 0dB at 20dB/ decade at a frequency no higher than 20-25% of the switching frequency. This objective is most simply met by generating asymp- totic bode plots of the small signal response of the vari- ous sections of the converter. L VOUT Co SC2612 AND FETS FB OUT COMP Ra MODULATORREF + EA RbResr Zp Zf Zs It is convenient to split the converter into two sections, the Error amp and compensation components being one section and the Modulator, output filter and divider be- ing the other. First calculate the DC Filter+Modulator+Divider gain The DC filter gain is always 0dB, the Modulator gain is 19dB at 5V in and is proportional to Vin, so modulator gain at any input voltage is. /g247 /g248 /g246/g231 /g232 /g230/g215/g43/g61 52019 IN MOD VLogG the divider gain is given by /g247/g247 /g248 /g246 /g231/g231 /g232 /g230 /g43/g215/g61 820 RR RLogGDIV So the total Filter+Modulator+Divider DC Gain is /g247/g247 /g248 /g246 /g231/g231 /g232 /g230 /g43/g215/g43/g247 /g248 /g246/g231 /g232 /g230/g215/g43/g61 BA BIN FMD RR RLogVLogG 2052019 Calculate the filter double pole frequency (Fp(lc)) LCo )lc(Fp /g112 /g61 and calculate ESR Zero frequency (Fz(esr)) srReCo)esr(Fz /g215/g215/g112/g612 Choose an open loop crossover frequency (Fco) no higher than 20% of the switching frequency (Fs). The proximity of Fz(esr) to the crossover frequency Fco determines the type of compensation required, if Fz(esr)>Fco/4, use type 3 compensation, otherwise use type 2. Type 1 compensation is not appropriate and is not discussed here. Type 2 Example As an example of type 2 compensation, we will use the Evaluation board schematic. 3.3uH VOUT 3000uF SC2612 AND FETS FB OUT COMP 6.98k MODULATORREF + EA 8.06k22mOhm Cs Cp Rs Vin=5V The total Filter+Modulator+Divider DC Gain is dB... .LogLogGFMD 613068986 068205 52019 /g61/g247 /g248 /g246/g231 /g232 /g230 /g43/g215/g43/g247 /g248 /g246/g231 /g232 /g230/g215/g43/g61 This is drawn as the line A-B in Fig2 kHz. .LCo )lc(Fp 61 10300010332 /g187 /g215/g215/g215/g112 /g61 /g112 /g61 /g45/g45 This is point B in Fig2. kHz.)esr(Fz 4210221030002 36 /g61/g215/g215/g215/g215/g112/g61 /g45/g45 This is point C in Fig2., the line joining B-C slopes at - 40dB/decade, the line joining C-D slopes at -20dB/de- cade. For 600kHz switching frequency, crossover is designed for 100kHz. Since Fz(esr)<<Fco/4 Type 2 compensation is appropri- ate.

7 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Having plotted the line ABCD, and confirmed the type of compensation necessary, compensation component val- ues can be determined. At Fco, the line ABCD shows a gain of -27.5dB and a slope of -20dB/decade. In order for the total open loop gain to be 0dB with a -20dB/decade slope at this frequency, the compensated error amp gain at Fco must be +27.5dB with a 0dB slope. This is the line FG on the plot below. Since open loop DC gain should be as high as possible to minimize errors, a zero is placed at F and to minimize high frequency gain and switching interference a pole is placed at G. The zero at F should be no higher than Fco/4 and the pole at G no lower than 4*Fco. The equations to set the gain and the pole and zero locations are: dB) (in Fco at gain A where gmRs A /g61/g61 2010 RsFzCs /g215/g215/g112/g61 12 RsFpCp /g215/g215/g112/g61 12 For this example, this results in the following values. /g87/g187/g87/g61/g61 kk..Rs 3062980 10 20 527 nF.Cs 220103010256 33 /g61/g215/g215/g215/g215/g187 ) rolloffEA to duey (unecessar pFCp 141030104006 33 /g61/g215/g215/g215/g215/g187 Fco Fz(esr) Fp(lc) -60 -40 -20 100 Frequency (Hz) Gain (dB) A B C D E F G H Fp1Fz1 Filter+modulator +divider gain Compensated Error Amp gain Total open loop gain Fig2: Type 2 Error Amplifier Compensation

8 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Layout Guidelines Careful attention to layout requirements are necessary for successful implementation of the SC2612 PWM con- troller. High currents switching at high frequency are present in the application and their effect on ground plane voltage differentials must be understood and minimized. 1). The high power parts of the circuit should be laid out first. A ground plane should be used, the number and position of ground plane interruptions should be such as to not unnecessarily compromise ground plane integrity. Isolated or semi-isolated areas of the ground plane may be deliberately introduced to constrain ground currents to particular areas, for example the input capacitor and bottom FET ground. 2). The loop formed by the Input Capacitor(s) (Cin), the Top FET (Q1) and the Bottom FET (Q2) must be kept as small as possible. This loop contains all the high current, fast transition switching. Connections should be as wide and as short as possible to minimize loop inductance. Minimizing this loop area will a) reduce EMI, b) lower ground injection currents, resulting in electrically “cleaner” grounds for the rest of the system and c) minimize source ringing, resulting in more reliable gate switching signals. 3). The connection between the junction of Q1, Q2 and the output inductor should be a wide trace or copper region. It should be as short as practical. Since this con- nection has fast voltage transitions, keeping this con- nection short will minimize EMI. The connection between the output inductor and the output capacitors should be a wide trace or copper area, there are no fast voltage or current transitions in this connection and length is not so important, however adding unnecessary impedance will reduce efficiency. L 12V IN Cout 10uFU1 SC2612 VCC DH BST FB DLSS/EN COMP GND Vin Vout GND 0.1uF Cin

9 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Layout Guidelines (Cont.) 4) The Output Capacitor(s) (Cout) should be located as close to the load as possible, fast transient load cur- rents are supplied by Cout only, and connections between Cout and the load must be short, wide copper areas to minimize inductance and resistance. 5) The SC2612 is best placed over a quiet ground plane area, avoid pulse currents in the Cin, Q1, Q2 loop flowing in this area. PGNDH and PGNDL should be returned to the ground plane close to the package. The AGND pin should be connected to the ground side of (one of) the output capacitor(s). If this is not possible, the AGND pin may be connected to the ground path between the Out- put Capacitor(s) and the Cin, Q1, Q2 loop. Under no cir- cumstances should AGND be returned to a ground in- side the Cin, Q1, Q2 loop. 6) Vcc for the SC2612 should be supplied from the 5V supply through a 10 Ω resistor, the Vcc pin should be decoupled directly to AGND by a 0.1 µF ceramic capaci- tor, trace lengths should be as short as possible. Vout Vin Currents in Power Section

10 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Typical Characteristics VIN = 5V 12V 70% 75% 80% 85% 90% 95% 100% 02468 1 0 Output Current (A) Efficiency (%) VBST = 12V for VIN = 5V VBST = 18V for VIN = 12V Typical Efficiency 20% 40% 60% 80% 100% SS/EN Voltage (V) Duty Cycle (%) (No Feedback) SS/EN Control of duty cycle 1.490 1.492 1.494 1.496 1.498 1.500 456789 1 0 1 1 1 2 VIN (V) VO (V) IO = 2.00A; VBST = 18V Typical Line Regulation VIN = 12V -2.0% -1.5% -1.0% -0.5% 0.0% 02468 1 0 IO (A) VO (V) VBST = 12V for VIN = 5V VBST = 18V for VIN = 12V Typical Load Regulation

11 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C 0.1uF GND C10 1500uF 1500uF Si4410DY 1.5V OUT C11 EMPTY 10uF L1 1uH 2.2 GND Si4410DY 12V IN 2.2 GND J6 U1 SC2612 6 2 VCC DH BST FB DL SS/EN COMP GND EN J11 C1 0.1uF EMPTY 220pF 30k 6.98k 8.06k 3.3V - 12V IN 150 0uF GND 1500uF 1500uF 3.3V - 5 V IN Evaluation Board Schematic & Layout

12 2003 Semtech Corp. www.semtech.com POWER MANAGEMENT SC2612A/C Outline Drawing - MSOP-8 Land Pattern - MSOP-8 Contact Information Semtech Corporation Power Management Products Division

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