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FAN100 Datasheet(PDF) 7 Page - Fairchild Semiconductor |
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FAN100 Datasheet(HTML) 7 Page - Fairchild Semiconductor |
7 / 21 page AN-6067 APPLICATION NOTE © 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.1 • 1/26/10 7 Frequency Hopping Operation A frequency hopping function is built in to further improve EMI system performance. The frequency hopping period is no longer than 3ms and the PWM switching frequency range is 42kHz +/- 2.6kHz. +/- 2.6KHz 44.6KHz Frequency Hopping Period 3mS → 39.4KHz Figure 15. Gate Signal with Frequency Hopping CV / CC Regulation Battery chargers are typically designed for two modes of operation, constant-voltage charging and constant-current charging. The basic charging characteristic is shown in Figure 16. When the battery voltage is low, the charger operates on a constant current charging. This is the main method for charging batteries and most of the charging energy is transferred into the batteries. When the battery voltage reaches its end-of-charge voltage, the current begins to taper-off. The charger then enters the constant voltage method of charging. Finally, the charging current continues to taper-off until reaching zero. Vo(V) Io(mA) CV Regulation Charging Sequence Figure 16. Basic Charging V-I Characteristic As mentioned in the CV regulation region section, the V COMV modulates MOSFET’s on-time and PWM frequency to provide enough power to the output load. As shown in Figure 17, as the output load increases, V COMV gradually rises until the system shifts into the CC regulation region. At the same time, V COMV increases to 4.5V and the MOSEFT’s on time is controlled by V COMI. However, when power system operates in the CC regulation region at a fixed 42kHz frequency, the MOSFET’s on-time is determined by VCOMI to modulate the output current. CV Regulation CC Regulation Charging Sequence 4.5V Deep Green Mode COMV V COMI V decreasing output impedance Figure 17. CV/CC Regulation Charging Sequence Temperature Compensation The PSR controller has built-in temperature compensation circuitry to provide constant reliable voltage regulation even at a different ambient temperature. This internal positive temperature coefficient (PTC) compensation current is used to compensate for the temperature due to the forward- voltage drop of the diode output. Without temperature compensation, the output voltage is distinctly higher in high temperatures than in lower temperature condition, as shown in Figure 18. o V o I high temp. room temp. after compensation at high temp. Figure 18. Output V-I Curve with Temperature Compensation As shown in Figure 19, the accuracy value of R1 and R2 determines the voltage regulation amount. The suggested deviation for R1 and R2 is a +/-1% tolerance. Auxiliary Winding Vs Temperature Compensation PTC PSR Controller / SH Vref Figure 19. Temperature Compensation |
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