isl6334d Intersil Corporation, isl6334d Datasheet - Page 19

• Manufacturer Part Number: isl6334d
• Description: Vr11.1, 4-phase Pwm Controller With Phase Dropping, Droop Disabled And Load Current Monitoring Features
• Manufacturer: Intersil Corporation

Overcurrent Protection
ISL6334D 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, ISL6334D utilizes the
sensed average current I
condition. See “Voltage Regulation” on page 13 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 ISL6334D 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
11.8k
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
Ω
FIGURE 10. VR_RDY AND PROTECTION CIRCUITRY
DAC
50%
resistor from IMON to GND.
AVG
VID + 0.175V
UV
. With a resistor from IMON to GND, the voltage
+
-
AND CONTROL LOGIC
OV
SOFT-START, FAULT
AVG
AVG
19
to detect an overcurrent
can be set to 95µA by using a
OC
+
-
OC
1.11V
+
-
VR_RDY
IMON
105µA
I
AVG
ISL6334D
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, ISL6334D
continuously compares the sensed current signal of each
channel with the 129µA reference current. If one channel
current exceeds the reference current, ISL6334D 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.
FIGURE 11. OVERCURRENT BEHAVIOR IN HICCUP MODE.
0A
0V
F
SW
OUTPUT CURRENT
OUTPUT VOLTAGE
= 500kHz
2ms/DIV
October 29, 2008
FN6802.0