MIC5164 Datasheet, PDF (12/23 Pages) Micrel Semiconductor – Dual Regulator Controller for DDR3 GDDR3/4/5 Memory and High-Speed Bus Termination

Micrel, Inc.
MOSFET Gate Threshold
N-Channel MOSFETs require an enhancement voltage
greater than its source voltage. Typical N-Channel
MOSFETs have a gate-source threshold (V_GS) of 1.8V or
higher. Since the source of the high side N-Channel
MOSFET is connected to V_TT, the MIC5164 VCC pin
requires a voltage greater than the V_GS voltage. For
example, our SSTL_2 termination circuit has a V_TT
MIC5164
voltage of 1.25V. For N-Channel MOSFET that has a
V_GS rating of 2.5V, the V_CC voltage can be as min as
3.75V. For N-Channel MOSFET that has a 4.5V V_GS, the
minimum V_CC required is 5.75V. It is recommended that
the V_CC voltage has enough margin to be able to fully
enhance the MOSFETs for large signal transient
response. In addition, low gate thresholds MOSFETs are
recommended to reduce the V_CC requirements.
Figure 5. DDR2 Termination (Four MOSFETs Support Up To 7A)
Figure 6. SSTL-2 Application (Two MOSFETs Support Up To 3.5A)
June 2010
12
M9999-061510