ISL62881CHRTZ-T Intersil, ISL62881CHRTZ-T Datasheet - Page 17

• Manufacturer Part Number: ISL62881CHRTZ-T
• Description: IC REG PWM SGL PHASE 28TQFN
• Manufacturer: Intersil

Specifications of ISL62881CHRTZ-T

• Applications: Controller, Intel IMVP-6.5™
• Voltage - Input: 4.5 ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.0125 ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 28-VQFN
• For Use With: ISL62881CCPUEVAL2Z - EVAL BOARD ISL62881CCPU 28QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ISL62881C monitors the VSEN pin voltage and compares
it to 100ns filtered version. When the unfiltered version is
20mV below the filtered version, the controller knows
there is a fast voltage dip due to load insertion, hence
issues an additional master clock signal to deliver a PWM
pulse immediately.
The R
forward. The output voltage is insensitive to a fast slew
rate input voltage change.
Protections
The ISL62881C provides overcurrent, undervoltage,
and overvoltage protections.
The ISL62881C determines overcurrent protection
(OCP) by comparing the average value of the droop
current I
It declares OCP when I
120µs. A resistor R
programs the OCP current source threshold, as well as
the overshoot reduction function (to be discussed in
later sections), as Table 3 shows. It is recommended to
use the nominal R
the R
the internal OCP threshold accordingly. It remembers
the R
POR threshold.
The default OCP threshold is the value when R
not populated. It is recommended to scale the droop
current I
approximately the desired OCP level, then use R
fine tune the OCP level if necessary.
For overcurrent condition above 2.5x the OCP level, the
PWM output 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 ISL62881C 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
output and de-assert PGOOD.
The ISL62881C has two levels of overvoltage
protections. The first level of overvoltage protection is
(kΩ)
MIN
TABLE 3. ISL62881C OCP THRESHOLD AND
305
205
155
104
78
62
45
comp
comp
3™
NOMINAL
droop
droop
modulator intrinsically has voltage feed
R
(kΩ)
none
value until the VR_ON signal drops below the
value at the beginning of start-up, and sets
comp
400
235
165
120
OVERSHOOT REDUCTION FUNCTION
85
66
50
with an internal current source threshold.
such that the default OCP threshold gives
comp
comp
MAX
(kΩ)
none
410
240
170
130
90
68
55
droop
value. The ISL62881C detects
from the COMP pin to GND
17
THRESHOLD
is above the threshold for
(µA)
OCP
60
68
62
54
60
68
62
54
ISL62881C, ISL62881D
ISL62881C, ISL62881D
OVERSHOOT
REDUCTION
FUNCTION
Disabled
Enabled
comp
comp
is
to
referred to as PGOOD overvoltage protection. If the
output voltage exceeds the VID set value by +200mV for
1ms, the ISL62881C will declare a fault and de-assert
PGOOD.
The ISL62881C 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
POR threshold. When VR_ON and V
high operating levels, a soft-start will occur.
The second level of overvoltage protection is different. If
the output voltage exceeds 1.55V, the ISL62881C 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
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.
Table 4 summarizes the fault protections.
Current Monitor
The ISL62881C provides the current monitor function.
The IMON pin outputs a high-speed analog current
source that is 3 times of the droop current flowing out of
the FB pin. Thus as shown by Equation 6.
Overcurrent
Way-Overcurrent
(2.5xOC)
Overvoltage
+200mV
Undervoltage -
300mV
Overvoltage 1.55V Immediately
I
IMON
FAULT TYPE
=
TABLE 4. FAULT PROTECTION SUMMARY
3
×
I
droop
PROTECTION
120µs
<2µs
1ms
DURATION
BEFORE
FAULT
DD
will clear it. The 1.55V
PWM tri-state,
PGOOD latched
low
Low-side
MOSFET on
until V
<0.85V, then
PWM tri-state,
PGOOD latched
low.
PROTECTION
DD
ACTION
return to their
DD
core
below the
March 8, 2010
VR_ON
toggle or
VDD
toggle
VDD
toggle
FAULT
RESET
FN7596.0
(EQ. 6)