RT9641A datasheet(8/14 Pages) RICHTEK

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RT9641A/B

www.richtek-ic.com.tw

DS9641A/B-03 March 2002

Table 2. 5VDUAL Output (VOUT3) Truth Table

EN5VDL S5 S3 5VDL

Comments

S0, S1 States(Active)

Note Maintains Previous State

S4/S5

S0, S1 States(Active)

Note Maintains Previous State

S4/S5

Note: Combination not allowed.

Very similarly, Table 2 details the fact that EN5VDL

status controls whether the 5VDUAL plane supports

sleeps states.

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

Truth Table

RSEL S5 S3

2.5V/3.3V

Comments

Ω

2.5V/2.6V

S0, S1 States(Active)

Ω

2.5V

Ω

Note

Maintains Previous State

Ω

S4/S5

10K

Ω 1 1

3.3V/3.43V

S0, S1 States(Active)

10K

Ω 1 0

3.3V

10K

Ω 0 1

Note

Maintains Previous State

10K

Ω 00

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

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.

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