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ISL6529EVAL1 Datasheet(PDF) 8 Page - Intersil Corporation |
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ISL6529EVAL1 Datasheet(HTML) 8 Page - Intersil Corporation |
8 / 19 page 8 FN9070.5 April 12, 2005 Undervoltage Protection The FB and FB2 pins are monitored during converter operation by two separate undervoltage (UV) comparators. If the FB voltage drops below 51.5% of the reference voltage (0.41V), a fault signal is generated. The internal fault logic shuts down both regulators simultaneously when the fault signal triggers a restart. Figure 3 illustrates the protection feature responding to a UV event on VOUT1. At time t0, VOUT1 has dropped below 51.5% of the nominal output voltage. Both outputs are quickly shut down and the internal soft-start function begins producing soft-start ramps. The delay interval, t0 to t3, seen by the output is equivalent to three soft-start cycles. After a short delay interval of 10.5ms, the fourth internal soft-start cycle initiates a normal soft-start ramp of the output, at time t3. Both outputs are brought back into regulation by time t4, as long as the UV event has cleared. Had the cause of the UV still been present after the delay interval, the UV protection circuitry becomes active approximately 875ms into the soft-start interval. A fault signal could then be generated and the outputs once again shut down. The resulting hiccup mode style of protection would continue to repeat indefinitely. Output Voltage Selection The output voltage of the PWM converter can be programmed to any level between VIN (i.e. +3.3V) and the internal reference, 0.8V. An external resistor divider is used to scale the output voltage relative to the reference voltage and feed it back to the inverting input of the error amplifier (see Figure 4). CAPACITOR CURRENT CAPACITOR CURRENT 1.5V OUTPUT 1.5V OUTPUT FIGURE 2. TOP SCOPE TRACES ARE VOLTAGE RAMP AND CAPACITOR CURRENT. LOWER TRACES ARE TIME AND VOLTAGE EXPANSION OF UPPER SCOPE TRACES. FIGURE 3. UNDERVOLTAGE PROTECTION RESPONSE 0V 0V TIME VOUT2 (2.5V) t1 t2 t3 t0 t4 (0.5V/DIV) VOUT1 (1.5V) INTERNAL SOFT-START FUNCTION VOUT2 (2.5V) DELAY INTERVAL DELAY INTERVAL ISL6529, ISL6529A |
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