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LP2998 - OK for DDR3 VTT termination?
We use the LP2998 on an existing product for VTT termination on a DDR2 interface running at 1.8V and would like to reuse the part for a new design which uses DDR3 memory at 1.5V with a termination voltage of 0.75V
The datasheet for this part is a bit muddled in that the Electrical characteristics section suggests that it's fine to run the PVin and VDDQ pins at 1.5V, but other parts of the datasheet which are descriptive - e.g. page 9 about AVIN and PVIN are clear that PVIN should always be used with 1.8V or 2.5V.
It looks like the text just hasn't been updated to cover the new operating conditions, but can you please confirm that it's fine to use this part for DDR3 VTT termination with Avin = 3.3V, PVIN, VDDQ = 1.5V and thus Vref and VTT = 0.75V?
You can use the LP2998 in DDR3 applications. The reason the datasheet is muddled is because the part came out before DDR3, and all references to DD3 were added later.
However, in the DDR3 configuration the amount of current the LP2998 can sink and source is less than for the DD2 configuration.
Basically the part's ability to sink and source current reduces as PVIN is lowered. To stay within the DDR3 limits requires that the current supplied for termination be less than +-0.4A on average.
If PVin is increased to 1.8 or 2.5V the amount of current the part can be sourced increases.
Let me know if you have any further questions,
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