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AP2002S Datasheet(PDF) 6 Page - Anachip Corp |
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AP2002S Datasheet(HTML) 6 Page - Anachip Corp |
6 / 7 page AP2002 Synchronous PWM Controller Anachip Corp. www.anachip.com.tw Rev. 0.2 Apr 14, 2004 6/7 Function Description (Continued) Hiccup Mode During power up, the SS/ SHDN pin is internally pulled low until VCC reaches the under-voltage lockout level of 4.2V. Once VCC has reached 4.2V, the SS/ SHDN pin is released and begins to source 10uA of current to the external soft-start capacitor. As the soft-start voltage rises, the output of the internal error amplifier is clamped to this voltage. When the error signal reaches the level of the internal triangular oscillator, which swings from 1V to 2V at a fixed frequency of 200KHz, switching occurs. As the error signal crosses over the oscillator signal, the duty cycle of the PWM signal continues to increase until the output comes into regulation. If an over-current condition has not occurred the soft-start voltage will continue to rise and level off at about 2.2V. An over-current condition occurs when the high-side drive is turned on, but the PHASE node does not reach the voltage level set at the OCSET pin. The PHASE node is sampled only once per cycle during the vally of the triangular oscillator. Once an over-current occurs, the high-side drive is turned off and the low-side drive turns on and the SS/ SHDN pin begins to sink 2uA. The soft-start voltage will begin to decrease as the 2uA of current discharge the external capacitor. When the soft-start voltage reaches 0.8V, the SS/ SHDN pin will begin to source 10uA and begin to charge the external capacitor causing the soft-start voltage to rise again. Again, when the soft-start voltage reaches the level of the internal oscillator, switching will occur. If the over-current condition is no longer present, normal operation will continue. If the over-current condition is still present, the SS/ SHDN pin will again begin to sink 2uA. This cycle will continue indefinitely until the over-current condition is removed. In conclusion, above is shown a typical “12V Application Circuit” which has a BSTH voltage derived by bootstrapping input voltage to the PHASE node through diode D1. This circuit is very useful in cases where only input power of 5V(or 12V) is available. In order to prevent substrate glitching, a small-signal diode should be placed in close proximity to the chip with cathode connected to PHASE and anode connected to PGND. Marking Information ( Top View ) SOP-14L 1 8 7 AC AP2002 YY WW X X Logo ID code: internal Year: "01" = 2001 "02" = 2002 Xth week: 01~52 14 Part No. Blank: normal L: Lead Free Package |
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