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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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XRP7720 датащи(PDF) 21 Page - Exar Corporation |
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XRP7720 датащи(HTML) 21 Page - Exar Corporation |
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21 / 28 page  X XR RP P7 77 72 20 0 Q Qu ua ad d O Ou uttp pu utt U Un niiv ve errs sa all C Cu us stto om miiz za ab blle e P PM MIIC C w wiitth h P PF FM M © 2014 Exar Corporation 21/28 Rev. 1.0.0 OCP A user defined OCP fault level is set with 10mA increments in PA 5.1. PA 5.1 uses calculations to give the user the approximate DC output current entered in the current limit field. However the actual current limit trip value programmed into the part is limited to 280mV as defined in the electrical characteristics. The maximum value the user can program is limited by Rdson of the synchronous Power FET and current monitoring ADC range. For example, using a synchronous FET with Rdson of 30mΩ and wider ADC range the maximum current limit programmed would be: ������������ ������������(����) = 280�������� 30����Ω = 9.33���� The current is sampled approximately 30ns before the low side MOSFET turns off so the actual measured DC output current in this example would be 9.33A plus approximately half the inductor ripple. An OCP Fault is considered to have occurred only if the fault threshold has been tripped in four consecutive switching cycles. When the switching frequency is set to the 4x multiplier the current is sampled every other cycle. As a result it can take as many as 8 switching cycles for an over current event to be detected. When operating in 4x mode an inductor with a soft saturation characteristic is recommended. In addition, OCP fault can be monitored through HW Flags on GPIO0. The OCP warning level is calculated by PA 5.1 as 85% of the OCP fault level. A user can choose one of three options in response to an OCP event: shut down the faulting channel, shut down faulting channel and perform auto-restart of the channel, or restart the chip. The output current reported by the XRP7720 is processed through a 7 sample median filter in order to reduce noise. The OCP limit is compared against unfiltered ADC output. In the case of Shutdown and Auto-restart Channel the user has an option to specify startup timeout (the time in which the fault is validated) and hiccup timeout (the period after which the controller will try to restart the channel) periods in 1 msec increments with a maximum value of 255 msec. Note: The Channel Fault Action response is the same for either the OVP or OCP event. Start-up Time-out Fault A channel will be at Start-up Time-out Fault if it does not come-up in a time period specified in the “Startup Timeout” box. In addition a channel is at Start-up Timeout Fault if its pre- bias configuration voltage is within a defined value too close to the target. LDO5 OCP When current is drawn from the LDO5 that exceeds the LDO5 current limit the controller will be reset. V5EXT SWITCHOVER The V5EXT gives the user an opportunity to supply an external 5 Volt rail to the controller in order to reduce the controller’s power dissipation. The 5 Volt rail can be an independent power rail present in a system or any of 7720 channels regulated to 5 Volts and routed back to the V5EXT pin. It is important to note that voltage to Vcc must be applied all the time even after the switchover, in which |
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