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LM3880Q Datasheet(PDF) 9 Page - Texas Instruments |
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LM3880Q Datasheet(HTML) 9 Page - Texas Instruments |
9 / 20 page EN FLAG1 FLAG2 FLAG3 td2 td1 td3 120 ms td4 td5 td6 LM3880, LM3880Q www.ti.com SNVS451H – AUGUST 2006 – REVISED JULY 2011 If the enable signal remains high for the entire power-up sequence, then the part will operate as shown in the standard timing diagrams. However, if the enable signal is de-asserted before the power-up sequence is completed the part will enter a controlled shutdown. This allows the system to walk through a controlled power cycling, preventing any latch conditions from occuring. This state only occurs if the enable pin is de-asserted after the completion of timer 1, but before the entire power-up sequence is completed. When this event occurs, the falling edge of enable pin resets the current timer and will allow the remaining power-up cycle to complete before beginning the power down sequence. The power down sequence starts approximately 120ms after the final power-up flag. This allows output voltages in the system to stabilize before everything is shutdown. An example of this operation can be seen below: Figure 7. Incomplete Sequence All the internal timers are generated by a master clock that has an extremely low tempco. This allows for tight accuracy across temperature and a consistent ratio between the individual timers. There is a slight additional delay of approximately 400 µs to timers 1 and 4 which is a result of the EPROM refresh. This refresh time is in addition to the programmed delay time and will be almost insignificant to all but the shortest of timer delays. CUSTOM SEQUENCER The LM3880 Power Sequencer is based on a CMOS process utilizing an EPROM that has the capability to be custom programmed at the factory. Approximately 500,000,000 different options are available allowing even the most complex system to be simply sequenced. Because of the vast options that are possible, customization is limited to orders of a certain quantity. Please contact National Semiconductor for more information. The variables that can be programmed include the six delay timers and the reverse sequence order. For the timers, each can be individually selected from one of the timer selector columns in the table shown below. However, all six time delays must be from the same column. Timer Options 1 Timer Options 2 Timer Options 3 Timer Options 4 0 0 0 0 2 4 6 8 4 8 12 16 6 12 18 24 8 16 24 32 10 20 30 40 12 24 36 48 14 28 42 56 16 32 48 64 18 36 54 72 20 40 60 80 22 44 66 88 24 48 72 96 26 52 78 104 28 56 84 112 30 60 90 120 Copyright © 2006–2011, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3880 LM3880Q |
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