ISL6506B Intersil Corporation, ISL6506B Datasheet - Page 7

• Manufacturer Part Number: ISL6506B
• Description: Multiple Linear Power Controller
• Manufacturer: Intersil Corporation

Component Selection Guidelines
Output Capacitors Selection
The output capacitors should be selected to allow the output
voltage to meet the dynamic regulation requirements of
active state operation (S0/S1). The load transient for the
various microprocessor system’s components may require
high quality capacitors to supply the high slew rate (di/dt)
current demands. Thus, it is recommended that the output
capacitors be selected for transient load regulation, paying
attention to their parasitic components (ESR, ESL).
Also, during the transition between active and sleep states
on the 5V
which none of the power pass elements are conducting.
During this time the output capacitors have to supply all the
output current. The output voltage drop during this brief
period of time can be easily approximated with the following
formula:
∆V
ESR
I
C
t
The output voltage drop is heavily dependent on the ESR
(equivalent series resistance) of the output capacitor bank,
the choice of capacitors should be such as to maintain the
output voltage above the lowest allowable regulation level.
Input Capacitors Selection
The input capacitors for an ISL6506/A application must have
a sufficiently low ESR so as not to allow the input voltage to
dip excessively when energy is transferred to the output
capacitors. If the ATX supply does not meet the
specifications, certain imbalances between the ATX’s
outputs and the ISL6506/A’s regulation levels could have as
a result a brisk transfer of energy from the input capacitors to
the supplied outputs. At the transition between active and
sleep states, such phenomena could be responsible for the
5V
regulation. The solution to such a potential problem is using
larger input capacitors with a lower total combined ESR.
∆
OUT
t
V
OUT
= active-to-sleep/sleep-to-active transition time (10µs typ.)
SB
OUT
OUT
OUT
= output current during transition
voltage drooping excessively and affecting the output
= output capacitor bank capacitance
=
= output voltage drop
DUAL
= output capacitor bank ESR
I
OUT
×
output, there is a short interval of time during



ESR
OUT
+
--------------- -
C
OUT
7
t
t



, where
ISL6506, ISL6506A, ISL6506B
Transistor Selection/Considerations
The ISL6506/A 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
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
and 5V
criteria for the selection of these transistors is output voltage
budgeting. The maximum r
junction temperature can be expressed with the following
equation:
V
V
I
Q2
This is a P-Channel MOSFET used to switch the 5V
output of the ATX supply into the 5V
sleep states. The selection criteria of this device, as with the
N-Channel MOSFETs, is proper voltage budgeting. The
maximum r
4.5V of gate-to-source voltage, so a true logic level
MOSFET needs to be selected.
r
OUTmax
P
DS ON
INmin
OUTmin
LOSS
(
DUAL
)max
= minimum input voltage
=
= maximum output current
= minimum output voltage allowed
I
2
o
DS(ON)
×
=
outputs while in active (S0, S1) state. The main
r
DS on
V
-------------------------------------------------- -
INmin
(
, however, has to be achieved with only
I
OUTmax
)
–
V
OUTmin
DS(ON)
, where
www.DataSheet4U.com
allowed at highest
DUAL
output during
SB
AUX