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IS31LT3932-GRLS2-TR Datasheet(PDF) 7 Page - Integrated Silicon Solution, Inc |
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IS31LT3932-GRLS2-TR Datasheet(HTML) 7 Page - Integrated Silicon Solution, Inc |
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7 / 12 page  IS31LT3932 Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 8/14/2013 7 resistors of 1% should be used. A small, 1nF capacitor, C7, is used to filter high frequency noise. Working Frequency The working frequency is set by connecting a resistor between the FSET pin and ground. The relationship between the frequency and resistance is: ) ( 250 1 50 Ω × × = k R V V k f CT FB Output open circuit protection Open circuit protection is realized by connecting a resistor network to the FB pin. By sensing the voltage of the auxiliary winding, which is proportional to the output voltage, the IS31LT3932 detects when there is an open circuit condition on the secondary and stop the switching action. The threshold voltage for the FB pin is 1.25V. Figure 14 OVP Output short circuit protection If the output of the circuit is suddenly shorted, the voltage of the secondary winding is quickly reduced. This in-turn reduces the reflected voltage in the auxiliary winding, so VCC of the device drops rapidly. If the VCC voltage drops below the UVLO, the device will stop switching, thus indirectly achieving output short circuit protection. Figure 15 Output short circuit protect UVLO protection The device will not operate if the VCC voltage is below the under-voltage lockout threshold. Until the VCC voltage get startup threshold, the device start again. CS over current and maximum duty cycle protection If the CS pin is shorted to ground, the device can no longer detect the peak current of the inductor, and thus will quickly cause damage to the power MOS, inductor, or other circuit components. The maximum duty cycle of the gate is limited to 62.5% internally to prevent a shorted CS pin from going into current runaway. when the duty cycle greater than 62.5% the gate will turn off 80ms. In addition to the duty cycle limit protection, there is also an inductor over current protection. If a fault condition exists wherein the inductor current continues to increase cycle per cycle, this would eventually cause the inductor into an over current condition. However, if the Vcs pin rises to 0.7V, the NMOS will immediately be shut off by the driving the gate low for a period of 40ms, after which the device will attempt a restart. Load regulation Frequency control is controlled by the FB pin voltage, when the FB pin voltage in the range of 0.5~1.25V, the control voltage is proportional to the frequency and FB, when the FB voltage is less than 0.5V, the frequency remained unchanged. Because the auxiliary winding voltage and the output voltage is the transformer turns ratio relationship, the FB pin detection auxiliary winding voltage, so, FB voltage follower output voltage changes, namely control frequency following the change of output voltage, in order to achieve constant output current. Transformer design VCC GATE VCC GATE |
Similar Part No. - IS31LT3932-GRLS2-TR |
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Similar Description - IS31LT3932-GRLS2-TR |
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