ISL62882 Datasheet, PDF (19/42 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6.5 Mobile CPUs and GPUs

ISL62882, ISL62882B
Protections
The ISL62882 provides overcurrent, current-balance,
undervoltage, overvoltage, and over-temperature
protections.
The ISL62882 determines overcurrent protection (OCP)
by comparing the average value of the droop current
I_droop with an internal current source threshold. It
declares OCP when I_droop is above the threshold for
120µs. A resistor R_comp from the COMP pin to GND
programs the OCP current source threshold, as well 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
MIN
(kΩ)
R_comp
NOMINAL
(kΩ)
MAX
(kΩ)
2-PHASE
CONFIG.
1-PHASE CONFIG.
OCP THRESHOLD
(µA)
OVERSHOOT
REDUCTION
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)
Overvoltage
+200mV
120µs
<2µs
1ms
PWM tri-state, VR_ON
PGOOD
toggle or
latched low VDD
toggle
Undervoltage -
300mV
Phase Current
Unbalance
Overvoltage 1.55V
Over-Temperature
Immediately
Low-side
VDD
MOSFET on toggle
until _Vcore
<0.85V, then
PWM tri-state,
PGOOD
latched low.
1ms
N/A
19
FN6890.2
April 29, 2010