ISL6567_07 Datasheet, PDF(12/26 Page) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

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ISL6567_07 Datasheet, PDF (12/26 Pages) Intersil Corporation – Multipurpose Two-Phase Buck PWM Controller with Integrated MOSFET Drivers

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ISL6567

OVERCURRENT PROTECTION

The individual channel currents, as sensed via the PHASE

pins and scaled via the ISEN resistors, as well as their

combined average are continuously monitored and

compared with an internal overcurrent (OC) reference. If the

combined channel current average exceeds the reference

current, the overcurrent comparator triggers an overcurrent

event. Similarly, an OC event is also triggered if either

channelâs current exceeds the OC reference for 7

consecutive switching cycles.

OUTPUT CURRENT

GGNNDD>>

OUTPUT CURRENT

GND>

OUTPUT VOLTAGE

FIGURE 6. OVERCURRENT BEHAVIOR WHILE IN INTERNAL

REFERENCE MODE

As a result of an OC event, output drives turn off both upper

and lower MOSFETs, and the SS capacitor is discharged via

a 20Î¼A current source. The behavior following this standard

response varies depending whether the controller is

operating in internal (using internal reference; MON > 3.5V)

or external reference mode (using external reference; MON

< 3.5V). As shown in Figure 6, the soft-start capacitor

discharge prompted by the OC event is followed by two SS

cycles, during which the ISL6567 stays off. Following the

dormant SS cycles, the controller attempts to re-establish

the output. Should the OC condition been removed, the

output voltage is ramped up and operation resumes as

normal. Should the OC condition still be present and result in

another OC event, the entire behavior repeats until the OC

condition is removed or the IC is disabled. Figure 7 details

the OC behavior while in external reference mode. Following

the OC event, the output drives are turned off, the ISL6567

latches off, and the SS capacitor is discharged to ground.

Resetting the OC latch involves removal of bias power or

cycling of the EN pin (pictured in Figure 7). Should the OC

event been removed, the controller initiates a new SS cycle

and restores the output voltage.

GND>

OUTPUT VOLTAGE

FIGURE 7. OVERCURRENT BEHAVIOR WHILE IN EXTERNAL

REFERENCE MODE

SETTING THE OUTPUT VOLTAGE

The ISL6567 uses a precision internal reference voltage to

set the output voltage. Based on this internal reference, the

output voltage can thus be set from 0.6V up to a level deter-

mined by the input voltage, the maximum duty cycle, and the

conversion efficiency of the circuit; the following equation

estimates this maximum amplitude the output voltage can be

regulated to. Obviously, insure that the input voltage and all

VOUTMAX = dMAX â VIN â Efficiency

the voltages sampled by the ISL6567 do not exceed the con-

trollerâs absolute maximum limits, or any other limits specified

in this document.

ISL6567

VREF

ERROR -

AMPLIFIER

EXTERNAL CIRCUIT

VDIFF

DIFFERENTIAL

AMPLIFIER

VSEN

RGND

To VOUT

FIGURE 8. SETTING THE OUTPUT VOLTAGE AT THE INPUT

OF THE DIFFERENTIAL AMPLIFIER

FN9243.2

March 20, 2007

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