ISL6307 Datasheet, PDF(24/34 Page) Intersil Corporation – 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current

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ISL6307 Datasheet, PDF (24/34 Pages) Intersil Corporation – 6-Phase PWM Controller with 8 Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current

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ISL6307

voltage on EN_PWR, EN_VTT or VCC below the POR-

falling threshold will reset the controller. Cycling the VID

codes will not reset the controller.

Overcurrent Protection

ISL6307 has two levels of overcurrent protection. Each

phase is protected from a sustained overcurrent condition on

a delayed basis, while the combined phase currents are

protected on an instantaneous basis.

In instantaneous protection mode, the ISL6307 takes

advantage of the proportionality between the load current

and the average current, IAVG, to detect an overcurrent

condition. See the Channel-Current Balance section for

more detail on how the average current is measured. The

average current is continually compared with a constant

100ÂµA reference current as shown in Figure 12. Once the

average current exceeds the reference current, a

comparator triggers the converter to shutdown.

In individual overcurrent protection mode, the ISL6307

continuously compares the current of each channel with the

same 100ÂµA reference current. If any channel current

exceeds the reference current continuously for eight

consecutive cycles, the comparator triggers the converter to

shutdown.

The overcurrent protection level for the above two OCP

modes can be adjusted by changing the value of current

sensing resistors. In addition, ISL6307 can also adjust the

average OCP threshold level by adjusting the value of the

resistor from IOUT to GND. This provides additional safety

for the voltage regulator.

The following equation can be used to calculate the value of

the resistor RIOUT based on the desired OCP level IAVG,

OCP2.

RIOUT

---------------2----------------

IAVG, OCP2

(EQ. 17)

OUTPUT CURRENT, 50A/DIV

OUTPUT VOLTAGE,

500mV/DIV

2ms/DIV

FIGURE 13. OVERCURRENT BEHAVIOR IN HICCUP MODE.

FSW = 500kHz

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 13) 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, there is no thermal hazard

during this kind of operation.

Current Sense Output

The ISL6307 has 2 current sense output pins IDROOP and

IOUT; They are identical. In typical application, IDROOP pin

is connected to FB pin for the application where load line is

required. IOUT pin was designed for load current

measurement. As shown in typical application schematics

on pages 4 to 7, load current information can be obtained by

measuring the voltage at IOUT pin with a resistor connecting

IOUT PIN to ground. When the programmable temperature

compensation function of ISL6307 is properly used, the

output current at IOUT pin is proportional to load current as

shown in Figure 14.

FN9224.0

March 9, 2006

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