ISL6364 Datasheet, PDF (29/44 Pages) Intersil Corporation – Dual 4-Phase + 1-Phase PWM Controller for VR12/IMVP7 Applications

ISL6364
OVP threshold is 2.3V. Once the VR output voltage reaches above
the DAC, fires the first PWM and completes the soft-start, the OVP
trip point will change to a tacking level of DAC+179mV.
Two actions are taken by ISL6364 to protect the microprocessor
load when an overvoltage condition occurs.
At the inception of an overvoltage event, all PWM outputs are
commanded low instantly. This causes the Intersil drivers to turn on
the lower MOSFETs and pull the output voltage below a level to avoid
damaging the load. When the output voltage falls below the DAC
plus 107mV, PWM signals enter a high-impedance state (or pulled
to 40% of VCC). The Intersil drivers respond to the high-impedance
input by turning off both upper and lower MOSFETs. If the
overvoltage condition reoccurs, ISL6364 will again command the
lower MOSFETs to turn on. ISL6364 will continue to protect the load
in this fashion as long as the overvoltage condition occurs.
Once an overvoltage condition is detected, the respective VR#
ceases the normal PWM operation and pulls its VR_Ready low
until ISL6364 is reset. Cycling the voltage VCC below the
POR-falling threshold will reset the controller. Cycling the EN_VTT,
or EN_PWR will also reset the controller in ISL6364, but not in
ISL6364A.
VR_RDY
In instantaneous protection mode, ISL6364 utilizes the sensed
average current I_AVG to detect an overcurrent condition. See
“Current Sensing” on page 16 for more details on how the
average current is measured. The average current is continually
compared with a constant 100µA reference current, as shown in
Figure 17. Once the average current exceeds the reference
current, a comparator triggers the converter to shutdown. In
addition, the current out of the IMON pin is equal to the sensed
average current I_AVG. With a resistor from IMON to GND, the
voltage at the IMON will be proportional to the sensed average
current and the resistor value. The ISL6364 continuously monitors
the voltage at IMON pin. If the voltage at the IMON pin is higher
than 1.12V, a precision comparator triggers the overcurrent
shutdown. Since the internal current comparator has wider
tolerance than the voltage comparator, the IMON voltage
comparator is the preferred one for OCP trip. Hence, the resistor
between IMON and GND can be scaled such that the overcurrent
protection threshold is tripping lower than 100µA. For example,
the overcurrent threshold for the sensed average current I_AVG can
be set to 95µA by using a 11.8kΩ resistor from IMON to GND.
Thus, the internal 100µA comparator might only be triggered at its
lower corner. However, IMON OCP trip should NOT be too far away
from 140µA, which is used for cycle-by-cycle protection and
inductor saturation.
DAC
+
OC
-
100µA
I_AVG
SOFT-START, FAULT
AND CONTROL LOGIC
VSEN
+
OV
-
VID + 0.179V
ISL6364
+
OC
-
1.12V
IMON
FIGURE 17. VR_RDY AND PROTECTION CIRCUITRY
Overcurrent Protection
ISL6364 has two levels of overcurrent protection. Each phase is
protected from a sustained overcurrent condition by limiting its
peak current, while the combined phase currents are protected on
an instantaneous basis.
For the individual channel overcurrent protection, ISL6364
continuously compares the sensed peak current (~50ns filter) signal
of each channel with the 140µA reference current. If one channel
current exceeds the reference current, ISL6364 will pull PWM signal
of this channel to low for the rest of the switching cycle. This PWM
signal can be turned on next cycle if the sensed channel current is
less than the 140µA reference current. The peak current limit of
individual channel will only use for cycle-by-cycle current limiting and
will not trigger the converter to shutdown.
OUTPUT CURRENT
0A
OUTPUT VOLTAGE
0V
2ms/DIV
FIGURE 18. OVERCURRENT BEHAVIOR IN HICCUP MODE. F_SW =
500kHz
At the beginning of overcurrent shutdown, the controller places
all PWM signals in a high-impedance state (or pulled to 40% of
VCC), commanding the Intersil MOSFET driver ICs to turn off both
upper and lower MOSFETs. The system remains in this state a
period of 8ms. 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 (as shown in Figure 18)
until either 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 during
this kind of operation
Thermal Monitoring (VR_HOT#)
VR_HOT# indicates the temperature status of the voltage
regulator. VR_HOT# is an open-drain output, and an external
pull-up resistor is required. This signal is valid only after the
controller is enabled.
29
FN6861.0
December 22, 2010