RT9641BGS datasheet(8/11 Pages) RICHTEK

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RT9641A/B

DS9641A/B-11 March 2007

www.richtek.com

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.

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.

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.

RSEL S5 S3

2.5V/3.3V

Comments

1kΩ

2.5V/2.6V

S0, S1 States(Active)

1kΩ

2.5V

1kΩ

Note

Maintains Previous State

1KΩ

S4/S5

10kΩ

3.3V/3.43V S0, S1 States(Active)

10kΩ

3.3V

10kΩ

Note

Maintains Previous State

10kΩ

S4/S5

Table 3. 2.5V/3.3V(2.6V/3.43V) VMEM Output (VOUT2)

Truth Table

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