SC2672 SEMTECH | Alldatasheet
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1 www.semtech.com SC2672 Dual Synchronous Voltage Mode Controller POWER MANAGEMENT Description Features
Applications
Revision: July 15, 2004 The SC2672 is a versatile 2 phase, synchronous, volt- age mode PWM controller that may be used in two dis- tinct ways. The SC2672 is ideal for dual voltage inde- pendent applications. The SC2672 features a tempera- ture compensated voltage reference, an undervoltage lockout over current protection and internal level-shifted, high-side drive circuitry. In dual switcher configuration, two feedback paths are provided for independent control of the separate out- puts. The device will provide a regulated output from flexibly configured inputs (3.3V, 5V, 12V), provided 5V is present for V CC. The two switchers are 180° out of phase to minimize input and output ripple. 300kHz operating frequency Soft Start Power Good output provided Undervoltage current limit Phase-shifted switchers minimize ripple High efficiency operation, >90% Programmable output(s) as low as .9V Industrial temperature range SOIC-16 pin package Bias voltage as low as 4.5V Two Independent PWM Controllers Flexible, same or separate V IN Independent control for each channel Independent and separate output UVLO 2 phases operating opposed for ripple reduction (if same V IN used) Graphics cards Peripheral add-in card Power supplies requiring two outputs Typical Application Schematic
2 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT
Electrical Characteristics
RETEMARAPS NOITIDNOCN IMP YTX AMS TINU egatloVtuptuOI O A2= )1( V, TUO V57.2ottes5 6.25 7.25 8.2V egatloVylppuSV CC 35 1V tnerruCylppuSV CC 0.5=0 1A m ecnerefeR 98.9 .1 9. V688.4 19. noitalugeRdaoLI O A51otA3.0= )1( 1% noitalugeReniLecnerefeRV 5< V CC <V 51 5. % noitalugeReniLtuptuOV 5< V NI <V 51 5. % A(niaG LO )V ESNESO Vot O 53B d noitcetorPtiucriCtrohS tuokcolegatlovrednutuptuO0 7% ycneuqerFrotallicsO 0720 030 33z Hk elcyCytuDxaMrotallicsO 09 59% tnerruCkniSHDV 5.2=DNGP-HD7 .1A tnerruCkniSHDV 57.1=DNGP-HD5 8.A tnerruCecruoSHDV 3=HD-HTSB7 .1A tnerruCecruoSHDV 5.2=HD-HTSB5 8.A Unless Specified: VCC = 5 ± 0.25V, VBST = 12 ± 0.6V, GND = PGND = 0V, FB = VO, 0mV < (CS(+) - (CS(-)) < 60mV , TJ = 25°C. Values in bold indicate -40°C ≤ TJ ≤ +125°C retemaraPl obmySs timiLs tinU V CC DNGotV IN 51ot3.0-V DNGotDNGP 1±V DNGotTSB 62ot3.0-V esaCotnoitcnuJecnatsiseRlamrehT θ CJ 04W /C° tneibmAotnoitcnuJecnatsiseRlamrehT θ AJ 021C °W/ gnitarepOe gnaRerutarepmeTtneibmAT A 58+ot04-C ° gnitarepOe gnaRerutarepmeTnoitcnuJT J 521+ot04-C ° egnaRerutarepmeTegarotST GTS 051+ot56-C ° ces01)gniredloS(erutarepmeTdaeLT DAEL 003C ° Absolute Maximum Rating 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 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Electrical Characteristics (Cont.) RETEMARAPS NOITIDNOCN IMP YTX AMS TINU tnerruCkniSLDV 5.2=GNGP-LD7 .1A tnerruCkniSLDV 57.1=DNGP-LD5 8.A tnerruCecruoSLDV 3=LD-LTSB7 .1A tnerruCecruoSLDV 5.2=LD-LTSB5 8.A emiTdaeD 03 05s n tnerruCegrahCtratStfoS )2( 52A µ elbanEtratStfoSe lcycytud%06 .1V dnEtratStfoSe lcycytud%0013 .2V noitisnarTtratStfoS )2( edomsuonorhcnyS3 .3V tuokcoLegatlovrednUtuptuOs lennahchtoB% 66V TUO tnerruCsaiBtupnI2 NI-,1NI- 1 Aµ NOTES: (1) Specification refers to application circuit. (2) The soft start pin sources 25µA to an external capacitor. The converter operates in synchronous mode above the soft start transition threshold and in asynchronous mode below it. (3) Power good is an open collector pulled low when the output voltage is under 75%. Marking Information TOPTOPTOPTOPTOP yyww = Datecode (Example: 9908) xxxx = Semtech Lot # (Example: 90101 ) (SOIC-16) Unless Specified: VCC = 5 ± 0.25V, VBST = 12 ± 0.6V, GND = PGND = 0V, FB = VO, 0mV < (CS(+) - (CS(-)) < 60mV , TJ = 25°C. Values in bold indicate -40°C ≤ TJ ≤ +125°C
4 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Pin Configuration Ordering Information EXPANDED PIN DESCRIPTION Pin 1: (AGND) Analog GND. Return of analog signals and bias of chip Pin 3: (VCC) Bias for chip 3V to 15V. Pin 2, 15: (FB2, FB1) “-” inputs of error amplifiers. Pin 4, 13: (SC2, SC1) Output UVLO programmation. Pin 5, 12: (BST2, BST1) BST signal. Supply for high side driver. Can be connected to a high enough voltage source. Usually connected to bootstrap circuit. Pin 6, 11: (DH2, DH1) DH signal (Drive High). Gate drive for top MOSFETs. Requires a small serie resistor. Pin 7, 10: (DL2, DL1) DL signal (Drive Low). Gate drive for bottom MOSFETs. Requires a small serie resistor. Pin 8: (PGND) Power GND. Return of gate drive currents. Pin 9: (BSTC) Supply for bottom MOSFETs gate drive. Pin 14: (SS/ENA) Soft start pin. Internal current source connected to external capacitor. Inhibits he chip if pulled down. Pin 16: (PGOOD) Power good signal. Open collector signal . Turns to 0 if output voltage is outside the power good window. eciveD )1( egakcaP RTS2762CS 61-CIOS TRTS2762CS )2( Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. Pin Descriptions PGOODAGND TOP VIEW (16 Pin SOIC) FB1FB2 SS/ENAVCC SC1SC2 BST1BST2 DH1DH2 DL1DL2 BSTCPGND
5 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Block Diagram Feedback Network For simple applications with electrolytic output capacitors, the feedback network can be a simple divider from output to feedback pin without phase node injection. For ceramic output capacitors and/or droop control, the network can be: The phase injection improves stability and can provide droop response.
6 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Evaluation Board Schematic Two Independent Channels
7 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Main Loop(s) The SC2672 is a dual, voltage mode synchronous Buck controller, the two separate channels are identical and share only IC supply pins (Vcc and GND), output driver ground (PGND) and pre-driver supply voltage (BSTC). They also share a common oscillator generating a sawtooth waveform for channel 1 and an dephased sawtooth for channel 2. Channel 2 has both inputs of the error amplifier uncommitted and available externally. a) Two independent channels with either common or different input voltages and different output volt- ages. The two channels each have their own volt- age feedback path from their own output. In this mode, positive inputs of error amplifier 2 are con- nected externally to Vref. If the application uses a common input voltage, the sawtooth phase shift between the channels provides some measure of input ripple current cancellation. Applications Information - Theory of Operation Power Good The controller provides a power good signal. This is an open collector output, which is pulled low if the output voltage is outside of the power good window. Soft Start/Enable The Soft Start/Enable (SS/ENA) pin serves several func- tions. If held below the Soft Start Enable threshold, both channels are inhibited. DH1 and DH2 will be low, turning off the top FETs. Between the Soft Start Enable thresh- old and the Soft Start End threshold, the duty cycle is allowed to increase. At the Soft Start End threshold, maximum duty cycle is reached. In practical applications the error amplifier will be controlling the duty cycle be- fore the Soft Start End threshold is reached. To avoid boost problems during startup in current share mode, both channels start up in asynchronous mode, and the bottom FET body diode is used for recirculating current during the FET off time. When the SS/ENA pin reaches the Soft Start Transition threshold, the channels begin operating in synchronous mode for improved efficiency. The soft start pin sources approximately 25uA and soft start timing can be set by selection of an appropriate soft start capacitor value.
8 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Power and signal traces must be kept separated for noise considerations. Feedback, current sense traces and ana- log ground should not cross any traces or planes carrying high switching currents, such as the input loop or the phase node. The input loop, consisting of the input capacitors and both MOSFETs must be kept as small as possible. All of the high switching currents occur in this loop. The en- closed loop area must be kept small to minimize induc- tance and radiated and conducted emissions. Designing for minimum trace length is not always the best approach, often a more optimum layout can be achieved by keep- ing loop area constraints in mind. It is important to keep gate lengths short, the IC must be close to the power switches. This is more difficult in a dual channel device than a single and requires that the two power paths run on either side of a centrally located controller. Grounding requirements are always conflicting in a buck converter, especially at high power, and the trick is to achieve the best compromise. Power ground (PGND) should be returned to the bottom MOSFET source to pro- vide the best gate current return path. Analog ground (GND) should be returned to the ground side of the out- put capacitors so that the analog circuitry in the control- ler has an electrically quiet reference and to provide the greatest feedback accuracy. The problem is that the dif- ferential voltage capability of the two IC grounds is lim- ited to about 1V for proper operation and so the physical separation between the two grounds must also be mini- mized. If the grounds are too far apart, fast current tran- sitions in the connection can generate voltage spikes exceeding the 1V capability, resulting in unstable and er- ratic behavior. The feedback divider must be close to the IC and be returned to analog ground. Current sense traces must be run parallel and close to each other and to analog ground. The IC must have a ceramic decoupling capacitor across its supply pins, mounted as close to the device as pos- sible. The small ceramic, noise-filtering capacitors on the current sense lines should also be placed as close to the IC as possible. Layout Guidelines
9 2004 Semtech Corp. www.semtech.com SC2672 POWER MANAGEMENT Semtech Corporation Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804 Contact Information Outline Drawing - SO-16 Land Pattern - SO-16