SEMTECH SC2612E

SC2612E 500kHz Step-Down DC/DC Converter POWER MANAGEMENT Description Features The SC2612E is a voltage mode switcher designed for � Operating frequency of 500kHz low cost, “point of use” voltage conversion. SC2612E is � Input supply of 4.5V to 15V available with fixed switching frequencies of 500kHz. � 0.5A Drive current for up to 10A output � Output voltages down to 0.8V The SC2612E has soft start and enable functions and is � Overcurrent protection and soft start short circuit protected. The output of the switcher may � SO-8 package 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. Applications � Graphics IC Power supplies � Embedded, low cost, high efficiency converters Typical Application Circuit 12V IN 5V IN R1 C10 C1 C2 U2 2 6 VCC BST Q2 R2 7 5 COMP DH L1 R3 8 3 SS/EN DL 1.5V OUT C5 4 1 GND FB Q3 R6 C7 C3 SC2612E C9 R9 R10 1 Revision: October 12, 2004 www.semtech.com SC2612E POWER MANAGEMENT Absolute Maximum Ratings Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Pl arameter Sm ymbo Ms aximu Unit VV CC Supply Voltage CC 1V 8 BV oost Pin Voltage BST 2V 0 (1) (1) DL to GND , DH to GND VDLO, VDHI -V 1 to +20 DH to GND Negative Pulse (tpulseFco/4, use type 3 compensation, otherwise use This objective is most simply met by generating asymp- type 2. Type 1 compensation is not appropriate and is totic bode plots of the small signal response of the vari- not discussed here. ous sections of the converter. Type 2 Example As an example of type 2 compensation, we will use the SC2612E AND FETS Evaluation board schematic. REF + MODULATOR EA FB - L OUT VOUT SC2612E AND FETS Vin=5V Ra COMP REF MODULATOR + Zf EA Co FB - 3.3uH Zp OUT Zs Resr VOUT Rb 6.98k COMP 3000uF Cs Cp 22mOhm 8.06k Rs 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. The total Filter+Modulator+Divider DC Gain is First calculate the DC Filter+Modulator+Divider gain 5 8.06 � � � � The DC filter gain is always 0dB, the Modulator gain is G �19�20�Log �20�Log �13.6dB � � � � FMD 5 6.98�8.06 � � � � 19dB at 5V in and is proportional to Vin, so modulator This is drawn as the line A-B in Fig2 gain at any input voltage is. 1 1 V � � IN Fp(lc)� � �1.6kHz G �19�20�Log � � MOD �6 �6 2� LCo 5 2� 3.3�10 �3000�10 � � the divider gain is given by This is point B in Fig2. 1 � R � 8 G � 20 � Log � � Fz(esr) � � 2.4kHz DIV �6 �3 � � R � R 2��3000�10 �22�10 � 5 8 � This is point C in Fig2., the line joining B-C slopes at - So the total Filter+Modulator+Divider DC Gain is 40dB/decade, the line joining C-D slopes at -20dB/de- V � R � � � IN B cade. � � G �19�20�Log� ��20�Log FMD � � 5 R � R � � � A B � For 500kHz switching frequency, crossover is designed for 100kHz. Since Fz(esr)<