ISL6322_07 Datasheet, PDF (26/41 Pages) Intersil Corporation – Four-Phase Buck PWM Controller with Integrated MOSFET Drivers and I2C Interface for Intel VR10, VR11, and AMD Applications

ISL6322
a level that might cause damage to the load. The LGATE
outputs remain high and PWM4 remains low until VDIFF falls
100mV below the OVP threshold that tripped the overvoltage
protection circuitry. The ISL6322 will continue to protect the
load in this fashion as long as the overvoltage condition
recurs.
Once an overvoltage condition ends, the ISL6322 latches off
and must be reset by toggling EN, or through POR, before a
soft-start can be re-initiated.
TABLE 6. INTEL VR10 AND VR11 OVP THRESHOLDS
MODE OF
OPERATION
DEFAULT
ALTERNATE
Soft-Start
(TD1 and TD2)
1.280V and
VDAC+250mV
(higher of the two)
1.280V and
VDAC+175mV
(higher of the two)
Soft-Start
(TD3 and TD4)
VDAC+250mV
VDAC+175mV
Normal Operation
VDAC+250mV
VDAC+175mV
TABLE 7. AMD OVP THRESHOLDS
MODE OF
OPERATION
DEFAULT
ALTERNATE
Soft-Start
2.200V and
VDAC+250mV
(higher of the two)
2.200V and
VDAC+175mV
(higher of the two)
Normal Operation
VDAC+250mV
VDAC+175mV
One exception that overrides the overvoltage protection
circuitry is a dynamic VID transition in AMD modes of
operation. If a new VID code is detected during normal
operation, the OVP protection circuitry is disabled from the
beginning of the dynamic VID transition, until 50μs after the
internal DAC reaches the final VID setting. This is the only
time during operation of the ISL6322 that the OVP circuitry is
not active.
Pre-POR Overvoltage Protection
Prior to PVCC and VCC exceeding their POR levels, the
ISL6322 is designed to protect the load from any overvoltage
events that may occur. This is accomplished by means of an
internal 10kΩ resistor tied from PHASE to LGATE, which
turns on the lower MOSFET to control the output voltage
until the overvoltage event ceases or the input power supply
cuts off. For complete protection, the low side MOSFET
should have a gate threshold well below the maximum
voltage rating of the load/microprocessor.
In the event that during normal operation the PVCC or VCC
voltage falls back below the POR threshold, the pre-POR
overvoltage protection circuitry reactivates to protect from
any more pre-POR overvoltage events.
Open Sense Line Prevention
In the case that either of the remote sense lines, VSEN or
GND, become open, the ISL6322 is designed to prevent the
controller from regulating. This is accomplished by means of
a small 5μA pull-up current on VSEN, and a pull-down
current on RGND. If the sense lines are opened at any time,
the voltage difference between VSEN and RGND will
increase until an overvoltage event occurs, at which point
overvoltage protection activates and the controller stops
regulating. The ISL6322 will be latched off and cannot be
restarted until the controller is reset.
Overcurrent Protection
The ISL6322 takes advantage of the proportionality between
the load current and the average current, I_AVG, to detect an
overcurrent condition. See “Continuous Current Sampling”
on page 13 for more detail on how the average current is
measured. The average current is continually compared with
a constant 125μA OCP reference current as shown in
Figure 14. Once the average current exceeds the OCP
reference current, a comparator triggers the converter to
begin overcurrent protection procedures.
This method for detecting overcurrent events limits the
minimum overcurrent trip threshold because of the fact the
ISL6322 uses set internal R_ISEN current sense resistors.
The minimum overcurrent trip threshold is dictated by the
DCR of the inductors and the number of active channels. To
calculate the minimum overcurrent trip level, I_OCP,min, use
Equation 21, where N is the number of active channels, DCR
is the individual inductor’s DCR, and R_ISEN is the 300Ω
internal current sense resistor.
I_{OCP, min}
=
1_----2_---5_-----⋅_---1_---0_----^–_---⁶_----⋅_---R_{-----I--S----E---N------}⋅_---N_--
DCR
(EQ. 21)
If the desired overcurrent trip level is greater then the
minimum overcurrent trip level, I_OCP,min, then the resistor
divider R-C circuit around the inductor shown in Figure 5
should be used to set the desired trip level.
I_OCP
=
⎛
⎜
⎝
1_----2_---5_-----⋅_---1_---0_----^–_-D--⁶_---C-⋅_---RR_{-----I--S----E---N------}⋅_---N_{-- ⎠⎟⎞}
⋅
⎛
⎜
⎝
-^R----¹--_R--+---₂--^R-----²-_{⎠⎟⎞}
(EQ. 22)
I_OCP > I_{OCP, min}
The overcurrent trip level of the ISL6322 cannot be set any
lower than the I_OCP,min level calculated above.
At the beginning of overcurrent shutdown, the controller sets
all of the UGATE and LGATE signals low, puts PWM4 in a
high-impedance state, and forces PGOOD low. This turns off
all of the upper and lower MOSFETs. The system remains in
this state for a fixed period of 12ms. If the controller is still
enabled at the end of this wait period, it will attempt a
soft-start. If the fault remains, the trip-retry cycles will
continue indefinitely until either the controller is disabled or
the fault is cleared. Note that the energy delivered during
trip-retry cycling is much less than during full-load operation,
so there is no thermal hazard.
26
FN6328.1
February 15, 2007