ISL6334AIRZR5368 Intersil, ISL6334AIRZR5368 Datasheet - Page 22

• Manufacturer Part Number: ISL6334AIRZR5368
• Description: IC CTRLR PWM 4PHASE BUCK 40QFN
• Manufacturer: Intersil

Specifications of ISL6334AIRZR5368

• Applications: Controller, Intel VR11.1
• Voltage - Input: 3 V ~ 12 V
• Number Of Outputs: 1
• Voltage - Output: 0.5 V ~ 1.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Overcurrent Protection
ISL6334AR5368 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.
In instantaneous protection mode, ISL6334AR5368 utilizes
the sensed average current I
condition. See “Channel-Current Balance” on page 15 for
more details on how the average current is measured. The
average current is continually compared with a constant
105µA reference current, as shown in Figure 10. Once the
average current exceeds the reference current, a
comparator triggers the converter to shutdown.
The current out of IMON pin is equal to the sensed average
current I
at IMON will be proportional to the sensed average current
and the resistor value. The ISL6334AR5368 continuously
monitors the voltage at IMON pin. If the voltage at IMON pin is
higher than 1.11V, a comparator triggers the overcurrent
shutdown. By increasing the resistor between IMON and
GND, the overcurrent protection threshold can be adjusted to
be less than 105µA. For example, the overcurrent threshold
for the sensed average current I
using a 11.8kΩ resistor from IMON to GND.
At the beginning of overcurrent shutdown, the controller
places all PWM signals in a high-impedance state within
20ns, commanding the Intersil MOSFET driver ICs to turn off
both upper and lower MOSFETs. The system remains in this
state a period of 4096 switching cycles. 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 11) until either
controller is disabled or the fault is cleared. Note that the
VDIFF
FIGURE 10. VR_RDY AND PROTECTION CIRCUITRY
DAC
50%
AVG
VID + 0.175V
UV
. With a resistor from IMON to GND, the voltage
+
-
AND CONTROL LOGIC
OV
SOFT-START, FAULT
22
AVG
AVG
to detect an overcurrent
can be set to 95µA by
OC
+
-
OC
1.11V
+
-
VR_RDY
IMON
ISL6334AR5368
105µA
I
AVG
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.
For the individual channel overcurrent protection,
ISL6334AR5368 continuously compares the sensed current
signal of each channel with the 129µA reference current. If
one channel current exceeds the reference current,
ISL6334AR5368 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 129µA reference current. The peak current limit of
individual channel will not trigger the converter to shutdown.
Thermal Monitoring (VR_HOT/VR_FAN)
There are two thermal signals to indicate the temperature
status of the voltage regulator: VR_HOT and VR_FAN. Both
VR_FAN and VR_HOT pins are open-drain outputs, and
external pull-up resistors are required. Those signals are
valid only after the controller is enabled.
The VR_FAN signal indicates that the temperature of the
voltage regulator is high and more cooling airflow is needed.
The VR_HOT signal can be used to inform the system that
the temperature of the voltage regulator is too high and the
CPU should reduce its power consumption. The VR_HOT
signal may be tied to the CPU’s PROC_HOT signal.
The diagram of thermal monitoring function block is shown in
Figure 12. One NTC resistor should be placed close to the
power stage of the voltage regulator to sense the operational
temperature, and one pull-up resistor is needed to form the
voltage divider for the TM pin. As the temperature of the power
stage increases, the resistance of the NTC will reduce, resulting
in the reduced voltage at the TM pin. Figure 13 shows the TM
voltage over the temperature for a typical design with a
recommended 6.8kΩ NTC (P/N: NTHS0805N02N6801 from
Vishay) and 1kΩ resistor RTM1. We recommend using those
resistors for the accurate temperature compensation.
FIGURE 11. OVERCURRENT BEHAVIOR IN HICCUP MODE.
0A
0V
F
SW
OUTPUT CURRENT
OUTPUT VOLTAGE
= 500kHz
2ms/DIV
September 7, 2010
FN6839.2