Configuration Handbook - Kamami.pl

APEX 20KE Power SequencingUse these guidelines to ensure a successful power-up and configuration:■■V CCINT is powered before V CCIO —These guidelines should befollowed for applications where the sequence of the power suppliesis unknown. It is highly recommended that you follow theseguidelines to ensure successful configuration of your APEX 20KEdevice.V CCINT is powered after V CCIO —These guidelines should be followedif V CCIO is powered before V CCINT .V CCINT is Powered Before V CCIOIf V CCINT is powered before V CCIO , the nCONFIG signal must be held lowfor the entire time that the two supplies are powering up to their specifiedoperating ranges. The recommendations in this section should also befollowed for applications where the sequence of the power supplies isunknown (e.g., hot-socketing applications). These guidelines should befollowed for all configuration schemes using a configuration device or anexternal host, such as a microprocessor.fFor more details on APEX 20KE and configuration device voltage supplyspecifications, refer to the APEX 20K Programmable Logic Device FamilyData Sheet and the Configuration Devices for Altera FPGAs Data Sheet orEnhanced Configuration Devices (EPC4, EPC8 & EPC16) Data Sheet,respectively.Use one of the following methods to hold nCONFIG low:■■■Use a power-monitoring circuit on the board. This circuit will drivenCONFIG low when V CCINT and V CCIO are out of range, and thenrelease nCONFIG. nCONFIG can then be externally pulled up whenV CCINT returns to a normal operating level. National Semiconductoroffers a small power-on reset circuit (part number LP3470) for apower monitor.Many voltage regulators offer a power-good signal that can be usedto hold nCONFIG low during power-up. If there are multipleregulators, use the power-good signal on the regulator that powersup last. If the power sequence is unknown, the power-good signalscan be ANDed in a discrete device.A microcontroller or intelligent host can externally drive nCONFIGlow while both the V CCINT and V CCIO supplies are being powered.7–68 Altera CorporationConfiguration Handbook, Volume 1 August 2005