RT9641A_07 Datasheet, PDF (8/11 Pages) Richtek Technology Corporation – Triple Linear Regulator Controller Support ACPI Control Interface

RT9641A/B
Table 3. 2.5V/3.3V(2.6V/3.43V) VMEM Output (V_OUT2)
Truth Table
RSEL S5 S3 2.5V/3.3V
Comments
1kΩ 1
1kΩ 1
1kΩ 0
1KΩ 0
10kΩ 1
10kΩ 1
10kΩ 0
10kΩ 0
1 2.5V/2.6V S0, S1 States(Active)
0 2.5V S3
1 Note Maintains Previous State
0
0V
S4/S5
1 3.3V/3.43V S0, S1 States(Active)
0 3.3V S3
1 Note Maintains Previous State
0
0V
S4/S5
Note: Combination not allowed.
As seen in Table 3, 2.5V/3.3V(2.6V/3.43V) VMEM output
is maintained in S3 (Suspend-To-RAM), but not in S4/S5
state. The dual-voltage support accommodates both
SDRAM as well as RDRAM type memories.
Fault Protection
All the outputs are monitored against under-voltage events.
A serve over-current caused by a failed load on any of the
outputs, would, in turn, cause that specific output to
suddenly drop. If any of the output voltages drop below
68% of their set value, such event is reported by having
the FAULT/MSEL pin pulled to 5V. Additionally, the 2.5V/
3.3V(2.6V/3.43V) memory regulator is internally current
limited while in a sleep state. Exceeding the maximum
current rating of this output in a sleep state can lead to
output voltage drooping. If excessive, this droop can
ultimately trip the under-voltage detector and send a
FAULT signal to the computer system. However, a FAULT
condition will only set off the FAULT flag, and it will not
shut off or latch off any part of the circuit. If shutdown or
latch off the circuit is desired, this can be achieved by
externally pulling or latching the SS pin low. Pulling the
SS pin low will also force the FAULT pin to go low.
Under-voltage sensing is disabled on all disabled outputs
and during soft-start ramp-up intervals.
Another condition that could set off the FAULT flag is chip
over-temperature. If the RT9641A/B reaches an internal
temperature of 145°C (typical), the FAULT flag is set
(FAULT/MSEL pulled high), but the chip continues to
operate until the temperature reaches 155°C (typical),
when unconditional shutdown of all outputs takes place.
The thermal shutdown can be released with a re-soft-start
when the chip cools down.
Shutdown
In case of a FAULT condition that might endanger the
computer system, or at any other time, the RT9641A/B
can be shut down by pulling the SS pin below the specified
shutdown level (typically 0.8V) with an open drain or open
collector device capable of sinking a minimum of 2mA.
Pulling the SS pin low effectively shuts down all the pass
elements. Upon release of the SS pin, the RT9641A/B
undergoes a new soft-start cycle and resumes normal
operation in accordance to the ATX supply and control
pins status.
Layout Considerations
The typical application employing a RT9641A/B is a fairly
straight-forward implementation. Similar to any other linear
regulators, attention has to be paid to a few potentially
sensitive small signal components, such as those
connected to high-impedance nodes or those supplying
critical by-pass currents.
The power components (pass transistors) and the controller
IC should be placed first. The controller should be placed
in a central position on the motherboard, closer to the
memory load if possible. Ensure the VSEN2 connection
is properly sized to carry 300mA without significant
resistive losses. The pass transistors should be placed
on pads capable of heatsinking, matching the device's
power dissipation. Where applicable, multiple via
corrections to a large internal plane can significantly lower
localized device temperature rise.
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DS9641A/B-11 March 2007