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ADM1041AARQZ-REEL Datasheet(PDF) 17 Page - Analog Devices |
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ADM1041AARQZ-REEL Datasheet(HTML) 17 Page - Analog Devices |
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17 / 56 page  ADM1041A Rev. 0 | Page 17 of 56 Mnemonic Description DC_OK The DC_OK function advises the system on the status of the power supply. When it is false, the system is assured of at least 1 ms of operation if ac power is lost for any reason. Other turn-off modes provide more warning time. This pin is an open-drain output. It can be configured as a P-channel pull-up or an N-channel pull-down. It may also be configured as positive or negative (inverted) logic. AC_OK The AC_OK function advises the system whether or not sufficient bulk voltage is present to allow reliable operation. The system may choose to shut down if this pin is false. The power supply normally tries to maintain normal operation as long as possible, although DC_OK goes false when only a millisecond or so of operation time is left. This pin is an open-drain output. It can be configured as a P-channel pull-up or an N- channel pull-down. It may also be configured as positive or negative (inverted) logic. DC_OK on delay The DC_OK output is kept false for typically 100 ms to 900 ms during power-up. DC_OK off delay When the system is to be shut down in response to PSON going low, or in response to an OCP or OTP event, a signal is first sent to the DC_OK output to go false as a warning that power is about to be lost. PEN is signaled false typically 2 ms later (configurable). Debounce Digital Noise Filter All of the inputs to the logic core are first debounced or digitally filtered to improve noise immunity. The debounce period for OV events is in the order of 16 μs, for UV events it is 450 μs, and for PSON it is typically 80 ms (configurable). ACSENSE1 A voltage from the secondary of the power transformer, which can provide an analog of the bulk supply, is rectified and lightly filtered and measured by the ac sense function. At start-up, if this voltage is adequate, this function signals the end-user system that it is okay to start. If a brown-out occurs or ac power is removed, this function can provide early warning that power is about to be lost and allow the system to shut down in an orderly manner. While ACSENSE is low, UVB is enabled, which means undervoltage protection is not initiated. If ac power is so low that the converter cannot continue to operate, other protection circuits on the primary side normally shut down the converter. When an adequate voltage level is resumed, a power-up cycle is initiated. Pulse OK As well as providing ACSENSE, the preceding connection to the transformer is used to gate the operation of the OrFET circuit. If the output of the transformer is good, the OrFET circuit allows gate drive to the OrFET. AC Hysteresis ACSENSE Hysteresis. Configurable voltage on the ACSENSE input allows the ACSENSE upper and lower threshold to be adjusted to suit different amounts of low frequency ripple present on the bulk capacitor. ACSENSE2 An alternate form of ac sense can be accepted by the ADM1041A. This may in the form of an opto-coupled signal from the primary side where the actual level sensing might be done. As with the above, while ac is low and UVB is disabled, AC_OK is false and DC_OK is true. Any brownout protection that might be required on the primary is done on the primary side. Soft-Start At start-up, the voltage reference to the voltage error amplifier is brought up slowly in approximately 127 steps to provide a controlled rate of rise of the output voltage. VDD–OVP An OVP fault on the auxiliary supply to the ADM1041A causes a standard OVP operation (see the OVP function in this table). VDD–UVL A UVL fault on the auxiliary supply to the IC causes a standard UVP operation (see the UVP function in this table). Auto Restart Mode In this mode, the housekeeping circuit attempts to restart the supply after an undervoltage event at about 1 second intervals. No other fault can initiate auto-restart. VREF–MON The internal precision reference is monitored by a separate reference for overvoltage and allows truly redundant OVP. The externally available reference is also monitored for an undervoltage that would indicate a short on the pin. GND–MON The internal ground is constantly monitored against the VS- pin. If the chip ground goes positive with respect to this pin, it indicates that the chip ground is open-circuit either inside the ADM1041A or the external wiring. The ADM1041A would be latched off, similar to an OV event. |
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