ISL6564 Datasheet, PDF(19/27 Page) Intersil Corporation – Multi-Phase PWM Controller with Linear 6-bit DAC Capable of Precision rDS(ON) or DCR Differential Current Sensing

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ISL6564 Datasheet, PDF (19/27 Pages) Intersil Corporation – Multi-Phase PWM Controller with Linear 6-bit DAC Capable of Precision rDS(ON) or DCR Differential Current Sensing

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ISL6564

PGOOD

75%

110ÂµA

REPEAT FOR

EACH CHANNEL

DAC

REFERENCE

SOFT START, FAULT

AND CONTROL LOGIC

110ÂµA

IAVG

VDIFF

OVP

VID + 0.2V

FIGURE 12. POWER GOOD AND PROTECTION CIRCUITRY

Undervoltage Detection

The undervoltage threshold is set at 75% of the VID code.

When the output voltage at VSEN is below the undervoltage

threshold, PGOOD gets pulled low.

Overvoltage Protection

When VCC is above 1.4V, but otherwise not valid as defined

under Power on Reset in Electrical Specifications, the

overvoltage trip circuit is active using auxiliary circuitry. In

this state, an overvoltage trip occurs if the voltage at VSEN

exceeds 1.8V.

With valid VCC, the overvoltage circuit is sensitive to the

voltage at VDIFF. In this state, the trip level is 1.7V prior to

valid enable conditions being met as described in Enable

and Disable. The only exception to this is when the IC has

been disabled by an overvoltage trip. In that case the

overvoltage trip point is VID plus 200mV. During soft-start,

the overvoltage trip level is the higher of 1.5V or VID plus

200mV. Upon successful soft-start, the overvoltage trip level

is 200mV above VID. Two actions are taken by the ISL6564

to protect the microprocessor load when an overvoltage

condition occurs.

At the inception of an overvoltage event, all PWM outputs

are commanded low instantly (less than 20ns) until the

voltage at VSEN falls below 0.6V with valid VCC or 1.5V

otherwise. This causes the Intersil drivers to turn on the

lower MOSFETs and pull the output voltage below a level

that might cause damage to the load. The PWM outputs

remain low until VDIFF falls to the programmed DAC level

when they enter a high-impedance state. The Intersil drivers

respond to the high-impedance input by turning off both

upper and lower MOSFETs. If the overvoltage condition

reoccurs, the ISL6564 will again command the lower

MOSFETs to turn on. The ISL6564 will continue to protect

the load in this fashion as long as the overvoltage condition

recurs.

Simultaneous to the protective action of the PWM outputs,

the OVP pin pulls to VCC delivering up to 100mA to the gate

of a crowbar MOSFET or SCR placed either on the input rail

or the output rail. Turning on the MOSFET or SCR collapses

the power rail and causes a fuse placed further up stream to

blow. The fuse must be sized such that the MOSFET or SCR

will not overheat before the fuse blows. The OVP pin is

tolerant to 12V (see Absolute Maximum Ratings), so an

external resistor pull up can be used to augment the driving

capability. If using a pull up resistor in conjunction with the

internal overvoltage protection function, care must be taken

to avoid nuisance trips that could occur when VCC is below

2V. In that case, the controller is incapable of holding OVP

low.

Once an overvoltage condition is detected, normal PWM

operation ceases until the ISL6564 is reset. Cycling the

voltage on EN or ENLL or VCC below the POR-falling

threshold will reset the controller. Cycling the VID codes will

not reset the controller.

Overcurrent Protection

ISL6564 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 ISL6564 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

110ÂµA reference current as shown in Figure 10. Once the

average current exceeds the reference current, a

comparator triggers the converter to shutdown.

In individual overcurrent protection mode, the ISL6564

continuously compares the current of each channel with the

same 110ÂµA reference current. If any channel current

exceeds the reference current continuously for eight

consecutive cycles, the comparator triggers the converter to

shutdown.

FN9156.2

December 27, 2004

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