ISL6506BIBZ Datasheet, PDF (7/8 Pages) Intersil Corporation – Multiple Linear Power Controller with ACPI Control Interface

ISL6506BIBZ
Transistor Selection/Considerations
The ISL6506BIBZ usually requires one P-Channel and two
N-Channel MOSFETs. All three of these MOSFETs are
utilized as ON/OFF switching elements.
One important criteria for selection of transistors for all the
switching elements is package selection for efficient removal
of heat. The power dissipated in a switch element while on is
shown in Equation 2:
P_LOSS = I_o2 × r_DS(ON)
(EQ. 2)
Select a package and heatsink that maintains the junction
temperature below the rating with the maximum expected
ambient temperature.
Q1, Q3
These N-Channel MOSFETs are used to switch the 3.3V and
5V inputs provided by the ATX supply into the 3.3V_AUX and
5V_DUAL outputs while in active (S0, S1) state. The main
criteria for the selection of these transistors is output voltage
budgeting. The maximum r_DS(ON) allowed at highest junction
temperature can be expressed using Equation 3:
r_DS(ON)max
=
V_{-----I--N----m-----i-n-----–----}V_{----O-----U----T----m----i--n-}
I_OUTmax
(EQ. 3)
where:
V_INmin = minimum input voltage
V_OUTmin = minimum output voltage allowed
I_OUTmax = maximum output current
Q2
This is a P-Channel MOSFET used to switch the 5V_SB
output of the ATX supply into the 5V_DUAL output during
sleep states. The selection criteria of this device, as with the
N-Channel MOSFETs, is proper voltage budgeting. The
maximum r_DS(ON), however, has to be achieved with only
4.5V of gate-to-source voltage, so a true logic level
MOSFET needs to be selected.
7
FN7814.0
June 8, 2011