ISL6336D Datasheet, PDF(22/30 Page) Intersil Corporation – VR11.1, 6-Phase PWM Controller with Phase Dropping,Droop Disabled and Load Current Monitoring Features

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ISL6336D Datasheet, PDF (22/30 Pages) Intersil Corporation – VR11.1, 6-Phase PWM Controller with Phase Dropping,Droop Disabled and Load Current Monitoring Features

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ISL6336D

reset the controller. Cycling the VID codes will not reset the

controller.

VR_RDY

full-load operation, so there is no thermal hazard during this kind

of operation.

OUTPUT CURRENT

50%

DAC

SOFT-START, FAULT

AND CONTROL LOGIC

105ÂµA

IAVG

OUTPUT VOLTAGE

VDIFF

1.11V

IMON

VID + 0.175V

FIGURE 15. VR_RDY AND PROTECTION CIRCUITRY

Overcurrent Protection

The ISL6336D 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, ISL6336D utilizes the sensed

average current IAVG to detect an overcurrent condition. See

âVoltage Regulationâ on page 16 for more details on how the

average current is measured. The average current is continually

compared with a constant 105ÂµA reference current, as shown in

Figure 15. 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 IAVG. With a resistor from IMON to GND, the voltage at

IMON will be proportional to the sensed average current and the

resistor value. The ISL6336D 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 105ÂµA. For example,

the overcurrent threshold for the sensed average current IAVG

can be set to 95ÂµA by using a 11.8kÎ© 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 (see Figure 16) until

either controller is disabled or the fault is cleared. Note that the

energy delivered during trip-retry cycling is much less than during

2ms/DIV

FIGURE 16. OVERCURRENT BEHAVIOR IN HICCUP MODE

fSW = 500kHz

For the individual channel overcurrent protection, ISL6336D

continuously compares the sensed current signal of each

channel with the 129ÂµA reference current. If one channel current

exceeds the reference current, ISL6336D will pull the 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 129ÂµA reference current. The

peak current limit of an 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 CPUâs

PROC_HOT signal.

The diagram of thermal monitoring function block is shown in

Figure 17. 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 18 shows the TM

voltage over the temperature for a typical design with a

resistors for the accurate temperature compensation.

There are two comparators with hysteresis to compare the TM

pin voltage to the fixed thresholds for VR_FAN and VR_HOT

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FN8320.0

October 6, 2014

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