TPS51216 DDR3 400-kHz Application Circuit, Tracking Discharge, Figure 33

For one or two memory ICs in which only 5-10A are needed at most, is Q3 required? Can it be removed, and also have Vin = 5V instead of 8V to 20V? This would make the low side use only a single MOSFET instead of two, and feed 5V into the high side drain. Thanks.