ISL6277A Datasheet, PDF (28/38 Pages) Intersil Corporation – Multiphase PWM Regulator for AMD Fusion Mobile CPUs Using SVI 2.0

ISL6277A
Current-Balance
The controller monitors the ISENx pin voltages to determine current-
balance protection. If the ISENx pin voltage difference is greater
than 9mV for 1ms, the controller will declare a fault and latch off.
Undervoltage
If the VSEN voltage falls below the output voltage VID value plus
any programmed offsets by -325mV, the controller declares an
undervoltage fault. The controller de-asserts PGOOD and
tri-states the power MOSFETs.
Overvoltage
If the VSEN voltage exceeds the output voltage VID value plus any
programmed offsets by +325mV, the controller declares an
overvoltage fault. The controller de-asserts PGOOD and turns on the
low-side power MOSFETs. The low-side power MOSFETs remain on
until the output voltage is pulled down below the VID set value. Once
the output voltage is below this level, the lower gate is tri-stated. If
the output voltage rises above the overvoltage threshold again, the
protection process is repeated. when all power MOSFETs are turned
off. This behavior provides the maximum amount of protection
against shorted high-side power MOSFETs while preventing output
ringing below ground.
Thermal Monitor [NTC, NTC_NB]
The ISL6277A 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.
NTC
R_p
+
V_{NTC RNTC}
-
R_s
INTERNAL TO
ISL6277A
30µA
VR_HOT_L
+V
R
MONITOR
WARNING SHUTDOWN
640mV 580mV
FIGURE 20. CIRCUITRY ASSOCIATED WITH THE THERMAL MONITOR
FEATURE OF THE ISL6277A
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.
TABLE 13. FAULT PROTECTION SUMMARY
FAULT TYPE
FAULT DURATION
BEFORE
PROTECTION PROTECTION ACTION
FAULT
RESET
Overcurrent
7.5µs to 11.5µs
Phase Current
Unbalance
Way-Overcurrent
(1.5xOC)
1ms
PWM tri-state, PGOOD
latched low
Undervoltage
-325mV
Overvoltage
+325mV
Immediately
PGOOD latched low.
PWM tri-state.
PGOOD latched low.
Actively pulls the
output voltage to
below VID value, then
tri-state.
ENABLE
toggle or
VDD toggle
NTC Thermal
100µs min.
PGOOD latched low.
PWM tri-state.
28
FN8322.0
December 19, 2012