Specifications

39
Fig. 4.2: A schematic r ep resentation the reverse polarity protection circuit.
was extended an estimated three weeks to two months. The ability to switch the circuit’s
behavior from an open circuit to a diode also allows both ports to be powered at the same
time. When the power on the auxiliary port is 4.5V or above, the battery pack will cu tout
and the auxiliary port will supply all power needs. If power on the auxiliary falls below
4.2V, the battery pack will be switched back in with no power glitches.
Low-Power LDOs
The LDO regulator chosen here is TI’s TPS715XX [37]. It comes in a regulated
3.3/5.0VDC output at 50mA. The regulator’s quiescent current is 3.2µA. Reasons for
this selection are that it matched performance requirements, low cost, and was already in
Acclima’s sto ck.
3.3V Swit cher
After extensive r eview, TI’s TPS62110 [38] synchronous buck switcher was selected to
perform this function. It is rated to be 95% efficient within the operating ranges of this
device and has a quiescent cur rent of 2µA.