ISL62882_14 Datasheet, PDF (19/42 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5™ Mobile CPUs and GPUs

ISL62882, ISL62882B
as the overshoot reduction function in 1-phase configuration, as
Table 4 shows. It is recommended to use the nominal R_comp
value. The ISL62882 detects the R_comp value at the beginning of
start-up, and sets the internal OCP threshold accordingly. It
remembers the R_comp value until the VR_ON signal drops below
the POR threshold.
TABLE 4. ISL62882 R_comp PROGRAMABILITY
R_comp
2-PHASE
CONFIG.
1-PHASE CONFIG.
OVERSHOOT
MIN NOMINAL MAX
REDUCTION
(kΩ)
(kΩ)
(kΩ) OCP THRESHOLD (µA) FUNCTION
none
none
40
20
Disabled
320
400
480 45.3
22.7
210
235
260 41.3
20.7
155
165
175
36
18
104
120
136 37.33
20
Enabled
78
85
92
38.7
22.7
62
66
70
42.7
20.7
45
50
55
44
18
The default OCP threshold is the value when R_comp is not populated.
It is recommended to scale the droop current I_droop such that the
default OCP threshold gives approximately the desired OCP level,
then use R_comp to fine tune the OCP level if necessary.
For overcurrent conditions above 2.5x the OCP level, the PWM
outputs will immediately shut off and PGOOD will go low to
maximize protection. This protection is also referred to as way-
overcurrent protection or fast-overcurrent protection, for short-
circuit protections.
The ISL62882 monitors the ISEN pin voltages to determine
current-balance protection. If the ISEN pin voltage difference is
greater than 9mV for 1ms, the controller will declare a fault and
latch off.
The ISL62882 will declare undervoltage (UV) fault and latch off if
the output voltage is less than the VID set value by 300mV or
more for 1ms. It’ll turn off the PWM outputs and de-assert
PGOOD.
The ISL62882 has two levels of overvoltage protections. The first
level of overvoltage protection is referred to as PGOOD
overvoltage protection. If the output voltage exceeds the VID set
value by +200mV for 1ms, the ISL62882 will declare a fault and
de-assert PGOOD.
The ISL62882 takes the same actions for all of the above fault
protections: de-assertion of PGOOD and turn-off of the high-side
and low-side power MOSFETs. Any residual inductor current will
decay through the MOSFET body diodes. These fault conditions
can be reset by bringing VR_ON low or by bringing V_DD below the
POR threshold. When VR_ON and V_DD return to their high
operating levels, a soft-start will occur.
The second level of overvoltage protection is different. If the output
voltage exceeds 1.55V, the ISL62882 will immediately declare an
OV fault, de-assert PGOOD, and turn on the low-side power
MOSFETs. The low-side power MOSFETs remain on until the output
voltage is pulled down below 0.85V when all power MOSFETs are
turned off. If the output voltage rises above 1.55V again, the
protection process is repeated. This behavior provides the
maximum amount of protection against shorted high-side power
MOSFETs while preventing output ringing below ground. Resetting
VR_ON cannot clear the 1.55V OVP. Only resetting V_DD will clear it.
The 1.55V OVP is active all the time when the controller is enabled,
even if one of the other faults have been declared. This ensures
that the processor is protected against high-side power MOSFET
leakage while the MOSFETs are commanded off.
The ISL62882 has a thermal throttling feature. If the voltage on
the NTC pin goes below the 1.18V OT threshold, the VR_TT# pin is
pulled low indicating the need for thermal throttling to the
system. No other action is taken within the ISL62882 in response
to NTC pin voltage.
Table 5 summarizes the fault protections.
TABLE 5. FAULT PROTECTION SUMMARY
FAULT TYPE
FAULT DURATION
BEFORE
PROTECTION
PROTECTION
ACTION
FAULT
RESET
Overcurrent
Way-Overcurrent
(2.5xOC)
120µs
<2µs
PWM tri-state,
PGOOD latched
low
VR_ON
toggle or
VDD toggle
Overvoltage +200mV
1ms
Undervoltage -300mV
Phase Current
Unbalance
Overvoltage 1.55V
Immediately
Low-side MOSFET VDD toggle
on until V_CORE
<0.85V, then
PWM tri-state,
PGOOD latched
low.
Over-Temperature
1ms
N/A
19
FN6890.4
June 21, 2011