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ISL6532C

ACPI Regulator/Controller for Dual Channel DDR Memory Systems

Renesas Electronics 

ISL6532C

Had the cause of the over current still been present after the

delay interval, the over current condition would be sensed and

the regulator would be shut down again for another delay

interval of three soft start cycles. The resulting hiccup mode

style of protection would continue to repeat indefinitely.

VDDQ

VAGP

VTT

500mV/DIV

INTERNAL SOFT-START FUNCTION

DELAY INTERVAL

T0

T1

T2

TIME

FIGURE 3. VDDQ and VTT OVER CURRENT PROTECTION

AND VTT/VAGP LDO UNDER VOLTAGE

PROTECTION RESPONSES

The over-current function will trip at a peak inductor current

(IPEAK) determined by:

IPEAK = I--O-----C----S----E-r--D-T---S--x----O-R----N-O----C-----S----E---T--

where IOCSET is the internal OCSET current source (20A

typical). The OC trip point varies mainly due to the MOSFET

rDS(ON) variations. To avoid over-current tripping in the normal

operating load range, find the ROCSET resistor from the

equation above with:

1. The maximum rDS(ON) at the highest junction temperature.

2. The minimum IOCSET from the specification table.

3. Determine IPEAK for:

IPEAK > IOUTMAX + ----2---I--- , whereI is

the output inductor ripple current.

For an equation for the ripple current see the section under

component guidelines titled ‘Output Inductor Selection’.

A small ceramic capacitor should be placed in parallel with

ROCSET to smooth the voltage across ROCSET in the

presence of switching noise on the input voltage.

VTT Over Current Protection

FN9121 Rev 2.00

Jul 2004

The internal VTT LDO is protected from fault conditions

through a 3.3A current limit. This current limit protects the

ISL6532C if the LDO is sinking or sourcing current. During an

overcurrent event on the VTT LDO, only the VTT LDO is

disabled. Once the over current condition on the VTT rail is

removed, VTT will recover.

Over/Under Voltage Protection

All three regulators are protected from faults through internal

Over/Under voltage detection circuitry. If the any rail falls below

85% of the targeted voltage, then an undervoltage event is

tripped. An under voltage will disable all three regulators for a

period of 3 soft-start cycles, after which a normal soft-start is

initiated. If the output is still under 85% of target, the regulators

will continue to be disabled and soft-started in a hiccup mode

until the fault is cleared. This protection feature works much the

same as the VDDQ PWM over current protection works. See

Figure 3.

If the any rail exceeds 115% of the targeted voltage, then all

three outputs are immediately disabled. The ISL6532C will not

re-enable the outputs until either the bias voltage is toggled in

order to initiate a POR or the S5 signal is forced LOW and then

back to HIGH.

Thermal Protection (S0/S3 State)

If the ISL6532C IC junction temperature reaches a nominal

temperature of 140oC, all regulators will be disabled. The

ISL6532C will not re-enable the outputs until the junction

temperature drops below 110oC and either the bias voltage is

toggled in order to initiate a POR or the SLP_S5 signal is

forced LOW and then back to HIGH.

Shoot-Through Protection

A shoot-through condition occurs when both the upper and

lower MOSFETs are turned on simultaneously, effectively

shorting the input voltage to ground. To protect from a shoot-

through condition, the ISL6532C incorporates specialized

circuitry which insures that complementary MOSFETs are not

ON simultaneously.

The adaptive shoot-through protection utilized by the VDDQ

regulator looks at the lower gate drive pin, LGATE, and the

upper gate drive pin, UGATE, to determine whether a

MOSFET is ON or OFF. If the voltage from UGATE or from

LGATE to GND is less than 0.8V, then the respective MOSFET

is defined as being OFF and the other MOSFET is allowed to

turned ON. This method allows the VDDQ regulator to both

source and sink current.

Since the voltage of the MOSFET gates are being measured to

determine the state of the MOSFET, the designer is

encouraged to consider the repercussions of introducing

external components between the gate drivers and their

respective MOSFET gates before actually implementing such

measures. Doing so may interfere with the shoot-through

protection.

Application Guidelines

Page 10 of 16

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