ISL6277HRZ datasheet(27/37 Pages) RENESAS

27 / 37 page

ISL6277

FN8270 Rev 1.00

Page 27 of 37

Mar 8, 2012

Thermal Monitor [NTC, NTC_NB]

The ISL6277 features two thermal monitors which use an

external resistor network which includes an NTC thermistor to

monitor motherboard temperature and alert the AMD CPU of a

thermal issue. Figure 20 shows the basic thermal monitor circuit

on the Core VR NTC pin. The Northbridge VR features the same

thermal monitor. The controller drives a 30µA current out of the

NTC pin and monitors the voltage at the pin. The current flowing

out of the NTC pin creates a voltage that is compared to a

warning threshold of 640mV. When the voltage at the NTC pin

falls to this warning threshold or below, the controller asserts

VR_HOT_L to alert the AMD CPU to throttle back load current to

stabilize the motherboard temperature. A thermal fault counter

begins counting toward a minimum shutdown time of 100µs.

The thermal fault counter is an up/down counter, so if the

voltage at the NTC pin rises above the warning threshold, it will

count down and extend the time for a thermal fault to occur. The

warning threshold does have 20mV of hysteresis.

If the voltage at the NTC pin continues to fall down to the

shutdown threshold of 580mV or below, the controller goes into

shutdown and triggers a thermal fault. The PGOOD pin is pulled

low and tri-states the power MOSFETs. A fault on either side will

shutdown both VRs.

As the board temperature rises, the NTC thermistor resistance

decreases and the voltage at the NTC pin drops. When the

voltage on the NTC pin drops below the over-temperature trip

threshold, then VR_HOT is pulled low. The VR_HOT signal is used

to change the CPU operation and decrease power consumption.

With the reduction in power consumption by the CPU, the board

temperature decreases and the NTC thermistor voltage rises.

Once the over-temperature threshold is tripped and VR_HOT is

taken low, the over-temperature threshold changes to the reset

level. The addition of hysteresis to the over-temperature

threshold prevents nuisance trips. Once both pin voltages exceed

the over-temperature reset threshold, the pull-down on VR_HOT

is released. The signal changes state and the CPU resumes

normal operation. The over-temperature threshold returns to the

trip level.

Table 13 summarizes the fault protections.

Fault Recovery

All of the previously described fault conditions can be reset by

bringing ENABLE low or by bringing VDD below the POR

threshold. When ENABLE and VDD return to their high operating

levels, the controller resets the faults and soft-start occurs.

Interface Pin Protection

The SVC and SVD pins feature protection diodes which must be

considered when removing power to VDD and VDDIO, but leaving

it applied to these pins. Figure 21 shows the basic protection on

the pins. If SVC and/or SVD are powered but VDD is not, leakage

current will flow from these pins to VDD.

NTC

RNTC

VNTC

30µA

INTERNAL TO

ISL6277

FIGURE 20. CIRCUITRY ASSOCIATED WITH THE THERMAL MONITOR

FEATURE OF THE ISL6277

MONITOR

WARNING

640mV

SHUTDOWN

580mV

VR_HOT_L

TABLE 13. FAULT PROTECTION SUMMARY

FAULT TYPE

FAULT DURATION

BEFORE

PROTECTION

ACTION

FAULT

RESET

Overcurrent

7.5µs to 11.5µs

PWM tri-state,

PGOOD latched

low

ENABLE

toggle or

VDD toggle

Phase Current

Unbalance

1ms

Way-Overcurrent

(1.5xOC)

Immediately

Undervoltage

-325mV

PGOOD latched

low.

PWM tri-state.

Overvoltage

+325mV

PGOOD latched

low.

Actively pulls the

output voltage to

below VID value,

then tri-state.

NTC Thermal

100µs min

PGOOD latched

low.

PWM tri-state.

SVC, SVD

INTERNAL TO

ISL6277

FIGURE 21. PROTECTION DEVICES ON THE SVC AND SVD PINS

GND

VDD

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