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CS1600 Scheda tecnica(PDF) 10 Page - Cirrus Logic |
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CS1600 Scheda tecnica(HTML) 10 Page - Cirrus Logic |
10 / 18 page CS1600 10 DS904A7 4.3.3 Overpower Protection The nominal output power is estimated internally by the CS1600 from the following equation where Po = rated output power of the system η = efficiency of the boost converter = estimated as 100% by the internal PFC algorithm Vin(min) = minimum RMS line voltage for operation Vlink = PFC output voltage fmax = maximum switching frequency LB = boost inductor used in the application Operation estimated to be at power levels higher than that calculated by Eq. 3 above is tracked by the IC as an overpower condition. During this phase, the PFC output voltage, Vlink, is reduced and will continue to decrease as the power draw increases. When Vlink reaches its undervoltage threshold, it goes into the start-up mode as explained in section 4.1.1. At this point, the overpower protection timer is activated. If this condition continues to exist for 112 ms, the gate drive is disabled for a period of about 3 seconds. This “hiccup” mode of operation continues until the fault is removed. If a value of the boost inductor other than that obtained from Eq. 3 above is used, the total output power capability as well as the thresholds for the different operating conditions will scale accordingly. 4.3.4 Open/short circuit protection The CS1600 protects the system in case the feedforward resistor tied to the IAC pin or the feedback resistor tied to the FB pin is open or shorted to ground. A fault seen on the resistor going into the FB pin would imply no current being fed into the pin, which would trigger the Vlink undervoltage algorithm as described in Section 4.3.1. A fault detected on the IAC pin would trigger the brownout condition discussed in Section 4.3.5 below. 4.3.5 Brownout Protection Brownout occurs when the current representing the rectified input voltage, nominally 100% of the reference current used for the output voltage, drops to 49% of its nominal value. Detection of brownout for a period of 56 ms disables the gate drive. The device continues to monitor the input voltage while in this condition. The CS1600 exits the brownout mode when the input current scales up to, and stays above 56.4% of its nominal value for a period of 56 ms. To minimize false detects, the brownout detection circuit increases the brownout detection time by a factor of 1.6 mS/V for every volt differential between the minimum operating voltage and the brownout threshold, following half of a line cycle of exceeding the brownout threshold. The following diagram illustrates the brownout sequence whereby the CS1600 enters standby, and upon recovery from brownout, enters normal operation.. Figure 15. Brownout 4.3.6 Over-temperature Protection Over-temperature protection is activated and PFC switching is disabled when the die temperature of the device exceeds 125°C. There is a hysteresis of about 30°C before resumption of normal operation. 4.4 Standby (STBY) Function The standby (STBY) pin may be used as a means to force the CS1600 into a non-operating, low-power state. The STBY input should be driven by an open-collector/open-drain device. Internal to the pin, there is a pull-up resistor connected to the VDD pin as shown in Figure 16. A filter capacitance of about 1000 pF is recommended while this pin is being used. Figure 16. STBY Pin Connection Po αη V in min () () × 2 × V link V in min () 2 × () – 2f max L B V link × × × --------------------------------------------------------- × = [Eq.3] α V link 400V -------------- 90V V in min () -------------------- × 2 V link V link 400V -------------- 90V × 2 × – V link V in min () 2 × – --------------------------------------------------------------------- × = 56 ms 56 ms Start Timer Enter Standby Exit Standby Upper Lower Brownout Thresholds Start Timer TBrownout <1 nF 600 k Ω See Text CAP STBY GND CS1600 |
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