ISL6532B Datasheet, PDF (8/15 Pages) Intersil Corporation – ACPI Regulator/Controller for Dual Channel DDR Memory Systems

ISL6532B
ACPI State Transitions
Cold Start (S5/S4 to S0 Transition)
At the onset of a mechanical start, the ISL6532B receives it’s
bias voltage from the 5V Standby bus (5VSBY). As soon as
the SLP_S3 and SLP_S5 signals have transitioned HIGH,
the ISL6532B starts an internal counter. Following a cold
start or any subsequent S5 state, state transitions are
ignored until the system enters S0/S1. None of the
regulators will begin the soft start procedure until the 5V
Standby bus has exceeded POR, the 12V bus has exceeded
POR and V_NCH has exceeded the trip level.
Once all of these conditions are met, the PWM error
amplifier will first be reset by internally shorting the COMP
pin to the FB pin. This reset lasts for 2048 clock cycles which
is typically 8.2ms (one clock cycle = 1/f_OSC). The digital soft
start sequence will then begin.
The PWM error amplifier reference input is clamped to a level
proportional to the soft-start voltage. As the soft-start voltage
slews up, the PWM comparator generates PHASE pulses of
increasing width that charge the output capacitor(s). The
internal V_TT LDO will also soft start through the reference
that tracks the output of the PWM regulator. The soft start
lasts for 2048 clock cycles, which is typically 8.2ms. This
method provides a rapid and controlled output voltage rise.
Figure 1 shows the soft start sequence for a typical cold
start. Due to the soft start capacitance, C_SS, on the
VREF_IN pin, the S5 to S0 transition profile of the V_TT rail
will have a more rounded features at the start and end of the
soft start whereas the V_DDQ profile has distinct starting and
ending points to the ramp up.
S3
S5
12VATX 2V/DIV
5VSBY
1V/DIV
V_DDQ
500mV/DIV
V_TT
500mV/DIV
PGOOD
5V/DIV
2048 CLOCK 2048 CLOCK
CYCLES
CYCLES
12V POR
SOFT START SOFT START ENDS
INITIATES PGOOD COMPARATOR
ENABLED
FIGURE 1. TYPICAL COLD START
By directly monitoring 12VATX and the SLP_S3 and SLP_S5
signals, the ISL6532B can achieve PGOOD status
significantly faster than other devices that depend on the
Latched_Backfeed_Cut signal for timing.
Active to Sleep (S0 to S3 Transition)
When SLP_S3 goes LOW with SLP_S5 still HIGH, the
ISL6532B will disable the V_TT linear regulator. The V_DDQ
standby regulator will be enabled and the V_DDQ switching
regulator will be disabled. NCH is pulled low to disable the
backfeed blocking MOSFET. PGOOD will also transition
LOW. When V_TT is disabled, the internal reference for the
V_TT regulator is internally shorted to the V_TT rail. This allows
the V_TT rail to float. When floating, the voltage on the V_TT
rail will depend on the leakage characteristics of the memory
and MCH I/O pins. It is important to note that the V_TT rail
may not bleed down to 0V.
The V_DDQ rail will be supported in the S3 state through the
standby V_DDQ LDO. When S3 transitions LOW, the Standby
regulator is immediately enabled. The switching regulator is
disabled synchronous to the switching waveform. The shut
off time will range between 4 and 8µs. The standby LDO is
capable of supporting up to 650mA of load with P5VSBY tied
to the 5V Standby Rail. The standby LDO may receive input
from either the 3.3V Standby rail or the 5V Standby rail
through the P5VSBY pin. It is recommended that the 5V
Standby rail be used as the current delivery capability of the
LDO is greater.
Sleep to Active (S3 to S0 Transition)
When SLP_S3 transitions from LOW to HIGH with SLP_S5
held HIGH and after the 12V rail exceeds POR, the
ISL6532B will enable the V_DDQ switching regulator, disable
the V_DDQ standby regulator, enable the V_TT LDO and force
the NCH pin to a high impedance state turning on the
blocking MOSFET. The internal short between the V_TT
reference and the V_TT rail is released. Upon release of the
short, the capacitor on VREF_IN is then charged up through
the internal resistor divider network. The V_TT output will
follow this capacitor charge-up, acting as the S3 to S0
transition soft start for the V_TT rail. The PGOOD comparator
is enabled only after 2048 clock cycles, or typically 8.2ms,
have passed following the S3 transition to a HIGH state.
Figure 2 illustrates a typical state transition from S3 to S0. It
should be noted that the soft start profile of the V_TT LDO
output will vary according to the value of the capacitor on the
VREF_IN pin.
Active to Shutdown (S0 to S4/S5 Transition)
When the system transitions from active, S0, state to
shutdown, S4/S5, state, the ISL6532B IC disables all
regulators and forces the PGOOD pin and the NCH pin
LOW.
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