전자부품 데이터시트 검색엔진 |
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SS9176 데이터시트(PDF) 7 Page - Silicon Standard Corp. |
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SS9176 데이터시트(HTML) 7 Page - Silicon Standard Corp. |
7 / 12 page www.SiliconStandard.com 7 of 12 SS9175/6 OPERATION The SS9175/6 series controllers integrate two sets of synchronous MOSFET driver circuits with current sharing capability. The following descriptions highlight the advantages of the SS917x designs. Soft-start A 25uA start-up current is provided by the SS/EN pin for the start-up sequence. During this start-up sequence, the SS917x is disabled when the SS/EN pin is less than 1.0V. From 1.0V to 3.0V, PWM output duty cycle is gradually and smoothly increased to its desired value. During this time, the current sharing circuit is disabled for smooth soft start. After 3.0V, the current sharing circuit is enabled and the whole circuit operates normally. Oscillator operation The SS9175/6 series have three versions with different oscillation frequencies. The oscillation frequency is fixed at 300 kHz, 600 kHz or 1 MHz. The voltage amplitude of the internal saw tooth oscillator is from 1.2V to 2.8V. Error amplifier The error amplifier’s inverting input is connected to the IN pin, and the output is connected to the COMP pin. The COMP output is available for external compensation, allowing designers to control the feedback-loop frequency-response. Non-inverting input is not wired out to a pin, but it is internally biased to a fixed 0.7V ± 1% voltage. Over-current protection The over-current protection (OCP) is implemented by adding a resistor from the MOSFET supply voltage to the CL+ pin, which sinks a 100uA current source. An internal comparator senses the voltage difference between CL+ and CL- pin. If the CL- pin voltage is lower than the CL+ pin voltage, meaning there is a larger current flowing through the high-side MOSFET, the comparator will trigger the OCP protection. The OCP function also has a 50% fold-back circuit to limit the MOSFET current within the desired over-current value. Output driver The high-side driver uses an external bootstrap circuit to provide the required boost supply voltage. The external bootstrap circuit uses the BSTC output voltage for providing the diode voltage. For the low-side driver, the supply voltage is coming from the BSTC output voltage, which is roughly 6V if VCC is larger than 6.5V.The output stage is designed to ensure zero cross-conduction current. Current Sharing The dual-phase controller has current-sharing capability to match both channels to within 5%. APPLICATION INFORMATION Rev.2.02 12/29/2003 PRELIMINARY |
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