9
FN4882.5
July 21, 2005
rather awaits until the main ATX outputs are well within
regulation limits.
SOFT-START INTO ACTIVE STATES (S0, S1)
If both S3 and S5 are logic high at the time the 5VSB is
applied, the HIP6503 will assume active state wake-up and
keep off the required outputs until some time (typically 25ms)
after the ATX’s main outputs used by the application (3.3V,
5V, and 12V) exceed the set thresholds. This time-out
feature is necessary in order to insure the main ATX outputs
are stabilized. The time-out also assures smooth transitions
from sleep into active when sleep states are being
supported. 3.3V
DUAL
/3.3V
SB
and 1.8V
SB
outputs, whose
operation is only dependent on 5V
SB
presence, will come up
right after bias voltage surpasses POR level.
During sleep to active state transitions from conditions
where the outputs are initially 0V (such as S5 to S0 transition
on the 5V
DUAL
output with EN5VDL = 0, or simple power-up
sequence directly into active state), the memory (in 3.3V
setting) and 5V
DUAL
outputs go through a quasi soft-start by
being pulled high through the body diodes of the N-Channel
MOSFETs connected between these outputs and the 3.3V
and 5V ATX outputs. Figure 8 shows this start-up case,
exemplifying the 5V
DUAL
output.
5VSB is already present when the main ATX outputs are
turned on, at time T0. As a result of +5V
IN
ramping up, the
5V
DUAL
output capacitors charge up through the body diode
of Q5 (see Figure 3). At time T1, all main ATX outputs
exceed the HIP6503’s undervoltage thresholds, and the
internal 25ms (typical) timer is initiated. At T2 the time-out
initiates a soft-start, and the 2.5V memory and clock outputs
are ramped-up, reaching regulation limits at time T3.
Simultaneous with the beginning of the memory and clock
voltage ramp-up, at time T2, the DLA pin is pulled high,
turning on Q3 and Q5 in the process, and bringing the
5V
DUAL
output in regulation. Shortly after time T3, as the SS
voltage reaches 2.75V, the soft-start capacitor is quickly
discharged down to approximately 2.45V, where it remains
until a valid sleep state request is received from the system.
Fault Protection
All the outputs are monitored against undervoltage events. A
severe overcurrent 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 drops below
80% (typical) of their set value, such event is reported by
having the FAULT/MSEL pin pulled to 5V. Additionally,
exceeding the maximum current rating of an integrated
regulator (output with pass regulator on chip) 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.
A FAULT condition occurring on an output when controlled
through an external pass transistor will only set off the
FAULT flag, and it will not shut off or latch off any part of the
circuit. A FAULT condition occurring on an output when
controlled through an internal pass transistor, will set off the
FAULT flag, and it will shut off the respective faulting
regulator only. If shutdown or latch off of the entire circuit is
desired in case of a fault, regardless of the cause, 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
and reset any internally latched-off output.
Special consideration is given to the initial start-up
sequence. If, following a 5VSB POR event, any of the
1.8V
SB
or 3.3V
DUAL
/3.3V
SB
outputs is ramped up and is
subject to an undervoltage event before the remainder of the
controlled voltages have been brought up, then the FAULT
output goes high and the entire IC latches off. Latch-off
condition can be reset by cycling the bias power (5V
SB
).
Undervoltage events on the 1.8V
SB
and the
3.3V
DUAL
/3.3V
SB
outputs at any other times are handled
according to the description found in the second paragraph
under the current heading.
Another condition that could set off the FAULT flag is chip
over-temperature. If the HIP6503 reaches an internal
temperature of 140°C (typical), the FAULT flag is set off, but
the chip continues to operate until the temperature reaches
155°C (typical), when unconditional shutdown of all outputs
takes place. Operation resumes at 140°C and the
temperature cycling occurs until the fault-causing condition
is removed.
FIGURE 8. SOFT-START INTERVAL IN ACTIVE STATE
(2.5/3.3V
MEM
OUTPUT SHOWN IN 2.5V SETTING)
0V
0V
TIME
OUTPUT
(1V/DIV)
VOLTAGES
T1 T2
T3
T0
INPUT VOLTAGES
(2V/DIV)
+5V
IN
+12V
IN
+5VSB
V
OUT1
(1.8V
SB
)
V
OUT3
(
3.3V
DUAL
/3.3V
SB
)
V
OUT5
(5V
DUAL
)
DLA PIN
(2V/DIV)
SOFT-START
(1V/DIV)
+3.3V
IN
V
OUT2, 4
(2.5V
MEM
, 2.5V
CLK
)
HIP6503
