MIC3808/3809 Micrel MIC3808/3809 Push-Pull PWM Controller General Description Features The MIC3808 and MIC3809 are a family of complementary Dual output drive stages in push-pull configuration output push-pull PWM control ICs that feature high speed and Leading edge current-sense blanking low power consumption. The MIC3808/9 are ideal for telecom 130A typical start-up current level (36V to 75V) isolated step down dc/dc conversion 1mA typical run current applications where high output current, small size, and high Operation to 1MHz efficiency are required. Internal soft start On-chip error amplifier with 4MHz gain bandwidth The dual-ended push-pull architecture of the MIC3808/9 product allows more efficient utilization of the transformer than single- On-chip V clamping ended topologies, allowing smaller size dc/dc solutions. DD Output drive stages capable of 500mA peak source Additionally, the out-of-phase push-pull topology allows a current, 1A peak sink current higher effective duty cycle, reducing input and output ripple as well as stress on the external components. The dead-time Applications between the two outputs is adjustable between 60ns to High efficiency brick power supply modules 200ns, limiting the duty cycle of each output stage to less than Half bridge converters 50%. Full bridge converters The MIC3808/9 are built on a low-power, high-speed BiCMOS Push-pull converters process. The 130A start-up current and 1mA run-current Voltage-fed push-pull converters reduce the size of the start-up circuitry and allow high Telecom equipment and power supplies efficiency even at light loads. The high-speed internal 4MHz Networking power supplies error amplifier allows MIC3808/9 operation up to 1MHz. Industrial power supplies The MIC3808 has a turn-on threshold of 12.5V whereas the 42V automotive power supplies MIC3809 has a lower turn-on threshold of 4.3V. Both devices Base stations are available in SOP-8 and MSOP-8 package options with an operating range of 40C to +85C. Data sheets and support documentation can be found on Micrels web site at: www.micrel.com. Typical Application V OUT 12V 100W V IN 36V to 75V Start-Up Circuitry MIC3808 RC VDD GND OUTA COMP OUTB FB CS Slope Comp Reference & Isolation Micrel, Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 MIC3808/3809 Micrel Ordering Information Part Number Turn On Turn Off Standard Lead-Free Threshold Threshold Temperature Range Package MIC3808BM MIC3808YM 12.5V 8.3V 40C to +85C 8-Pin SOIC MIC3809BM MIC3809YM 4.3V 4.1V 40C to +85C 8-Pin SOIC MIC3808BMM MIC3808YMM 12.5V 8.3V 40C to +85C 8-Pin MSOP MIC3809BMM MIC3809YMM 4.3V 4.1V 40C to +85C 8-Pin MSOP Pin Configuration COMP 1 8 VDD FB 2 7 OUTA CS 3 6 OUTB RC 4 5 GND SOIC-8 (M) MSOP-8 (MM) Pin Description Pin Number Pin Name Pin Function 1 COMP COMP is the output of the error amplifier and the input of the PWM com- parator. The error amplifier in the MIC3808 is a true low-output impedance, 4MHz operational amplifier. As such, the COMP pin can both source and sink current. However, the error amplifier is internally current limited, so that zero duty cycle can be externally forced by pulling COMP to GND. The MIC3808 family features built-in full cycle soft start. Soft start is imple- mented as a clamp on the maximum COMP voltage. 2 FB The inverting input to the error amplifier. For best stability, keep FB lead length as short as possible and FB stray capacitance as small as possible. 3 CS The input to the PWM, peak current, and overcurrent comparators. The overcurrent comparator is only intended for fault sensing. Exceeding the overcurrent threshold will cause a soft start cycle. An internal MOSFET discharges the current sense filter capacitor to improve dynamic perfor- mance of the power converter. and 4 RC The oscillator programming pin. The MIC3808s oscillator tracks V DD GND internally, so that variations in power supply rails minimally affect frequency stability. Only two components are required to program the and RC), and a capacitor (tied to the RC oscillator, a resistor (tied to the V DD and GND). The approximate oscillator frequency is determined by the simple 1.41 formula: F = OSCILLATOR RC where frequency is in Hertz, resistance in Ohms, and capacitance in Farads. The recommended range of timing resistors is between 7k and 200k and range of timing capacitors is between 100pF and 1000pF. Timing resistors less than 7k should be avoided. For best performance, keep the timing capacitor lead to GND as short as possible, the timing resistor lead from V DD as short as possible, and the leads between timing components and RC as short as possible. Separate ground and V traces to the external timing DD network are encouraged. MIC3808/3809 2 April 2005