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AS2316N Datasheet(PDF) 8 Page - List of Unclassifed Manufacturers |
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AS2316N Datasheet(HTML) 8 Page - List of Unclassifed Manufacturers |
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8 / 10 page  AS23xx Secondary Side Housekeeping Circuit ASTEC Semiconductor 98 Theory of Operation the outputs of the PSU. Usually, just one or the other output is used depending on the PSU’s cost and system definition. Both methods are in- tended to protect the customer’s system, and the customer, as the first priority. 1.2 Undervoltage Faults: POK and FAULT An undervoltage condition is sometimes not con- sidered a catastrophic or dangerous condition, but always one which the customer should be warned about. The POK signal is a logic line to the customer’s system that is specified in most PC type power supply systems. The AS23xx will pull the POK signal low when a UV fault is detected. A UV fault may or may not require the system to shut down, so an undervoltage blank- ing pin is provided (UVB). Grounding this pin will prevent UV faults from propogating to the FAULT pin. CBD does not react to UV faults. 1.3 Input Undervoltage: AC and HYST In addition, there is a special undervoltage detec- tion input for sensing the input voltage to the power supply, designated as the AC pin. This pin will cause the POK pin to go low if there is insufficient voltage to run the PSU outputs. Since power supplies must maintain high voltage isola- tion between the primary and secondary sides of the system, the AC pin is usually tied to a divided down and filtered representation of the second- ary side switching waveform. Hysteresis for this function, to provide immunity from line ripple, is configured by the PSU designer and is imple- mented with the HYST pin, which is an open collector output of the AC comparator. Section 2 - PSU Start-up Sequences 2.0 System Start-up Sequence When the power supply starts up, the AS23xx must not erroneously report a FAULT. In addi- tion, most PC type power supply specifications The AS23xx performs housekeeping functions for power supplies, especially switching power supplies for personal computers. The chip re- sides on the secondary side of the power supply (PSU), and it performs three primary functions: 1) monitors the output voltages and reports faults 2) sequences the start-up of the PSU 3) sequences the shutdown of the PSU Section 1 - Output Voltages and Faults 1.0 Output Voltage Monitoring The AS23xx monitors the standard voltage out- puts for PC type power supplies. It has inputs for +12 V, +5 V, +3.3 V, -5 V and -12 V. These inputs are tied directly to the outputs of the PSU, and therefore do not require external dividers to set the error thresholds. These pins are monitored for both overvoltage (OV) and undervoltage (UV) conditions. The spec’s for these thresholds are listed in the data sheet. 1.1 Overvoltage Faults: FAULT and CBD An overvoltage condition in a power supply is considered to be a catastrophic and dangerous condition which must result in a safe, complete and near-instantaneous shutdown of the sys- tem. Overvoltages most often result from a break in the system feedback and control cir- cuitry or from a short between outputs. When the AS23xx detects an overvoltage, the fault is latched internally, and the FAULT and CBD pins go high. The FAULT pin is an open collector NPN output which is intended to drive an optocoupler LED for feedback to the primary side controller of the PSU. The CBD pin is an NPN Darlington output which is intended to drive an SCR crowbar circuit which will short circuit |
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Similar Description - AS2316N |
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