RT9641AGS RICHTEK [Richtek Technology Corporation], RT9641AGS Datasheet - Page 10

• Manufacturer Part Number: RT9641AGS
• Description: Triple Linear Regulator Controller Support ACPI Control Interface
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9641A/B
Transistor Selection/Considerations
The RT9641A/B typically requires one P-channel or PNP
transistor and two N-Channel power MOSFETs and two
bipolar NPN transistors.
One general requirement for selection of transistors for all
the linear regulators/switching elements is package
selection for efficient removal of heat. The power dissipated
in a linear regulator/switching element is:
P
Select a package and heatsink that maintains the junction
temperature below the rating with the maximum expected
ambient temperature.
Q1
The active element on the 2.5V/3.3V (2.6V/3.43V) V
output has different requirements for each the two voltage
settings. In 2.5V systems utilizing RDRAM (or voltage-
compatible) memory, Q1 had better to be a bipolar NPN
capable of conducting the maximum required output
current and it must have a minimum current gain (h
100~150 at this current and 0.7V V
the 2.5V(2.6V) output is regulated from the ATX 3.3V output
while in an active state. In 3.3V systems (SDRAM or
compatible) Q1 is suggested to use an N-channel
MOSFET, then the MOSFET serves like a switch when it
is connected to ATX3.3V during active states (S0, S1).
The main criteria for the selection of this transistor is output
voltage budgeting. The maximum R
highest junction temperature can be expressed with the
following equation:
R
V
V
I
The gate bias available for this MOEFET is approximately
6V, so the logic level MOSFET is prefered. The
3.3V(3.43V) V
5V in order to have high quality V
configuration, either MOSFET or NPN transistors can be
used. While the heat dissipation should be carefully
handled.
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10
OUT(MAX)
LINEAR
IN(MIN)
OUT(MIN)
DS(ON) MAX
: minimum input voltage
= I
: maximum output current
: minimum output voltage allowed.
O
= (V
x (V
(MEM)
IN(MIN)
IN
- V
power also can be regulated from ATX
−V
OUT
OUT (MIN)
)
)/ I
OUT( MAX)
CE
. In such systems,
DS(ON)
(MEM)
, where
, in such a
allowed at
(MEM)
fe
) of
Q4
If a P-Chanel MOSFET is used to switch the 5VSB output
of the ATX supply into the 5V
S4/S5 states (as dictated by EN5VDL status), then, similar
to the situation where Q1 is a MOSFET, the selection
criteria of this device is also proper voltage budgeting.
The maximum r
only 4.5V of V
selected. If a PNP device is chosen to perform this function,
it has to have a low saturation voltage while providing the
maximum sleep-state current and have current gain
sufficiently high to be saturated using the minimum drive
current (typically 20mA). A 100Ω ~ 200Ω resistor is
recommended to be inserted between the 5VDLSB pin
and Base node of the PNP transistor for limiting the base
current.
Q3, Q5
The two N-Channel MOSFETs are used to switch the 3.3V
and 5V inputs provided by the ATX supply into the 3.3V
and 5V
state. Similar R
unlike the PMOS, however, these NMOS transistors get
the benefit of an increased V
and 7V respectively).
Q2
The NPN transistor used as sleep-state pass element on
the 3.3V
100 at V
circuit operating temperature range.
DUAL
DUAL
CE
outputs, respectively, while in active (S0, S1)
= 1.5V and I
output must have a minimum current gain of
GS
DS(ON)
DS (ON)
, so a logic level MOSFET needs to be
criteria apply in these cases as well,
, however, has to be achieved with
CE
= 500mA throughout the in-
GS
DS9641A/B-11 March 2007
DUAL
drive (approximately 8V
output during S3 and
DUAL