ISL62881HRTZ-T Intersil, ISL62881HRTZ-T Datasheet - Page 16

• Manufacturer Part Number: ISL62881HRTZ-T
• Description: IC REG PWM SGL PHASE 28TQFN
• Manufacturer: Intersil

Specifications of ISL62881HRTZ-T

• Applications: Controller, Intel IMVP-6.5™
• Voltage - Input: 5 V ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.0125 V ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Protections
The ISL62881 provides overcurrent, undervoltage, and
overvoltage protections.
The ISL62881 determines overcurrent protection (OCP)
by comparing the average value of the droop current
I
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
R
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 ISL62881 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 ISL62881 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
ISL62881 will declare a fault and de-assert PGOOD.
The ISL62881 takes the same actions for all of the above
fault protections: deassertion 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
droop
(kΩ)
MIN
comp
comp
TABLE 3. ISL62881 OCP THRESHOLD AND
305
205
155
104
78
62
45
with an internal current source threshold. It
value at the beginning of start-up, and sets the
value until the VR_ON signal drops below the
NOMINAL
droop
R
(kΩ)
none
comp
400
235
165
120
OVERSHOOT REDUCTION FUNCTION
85
66
50
such that the default OCP threshold gives
comp
comp
MAX
(kΩ)
none
droop
410
240
170
130
90
68
55
value. The ISL62881 detects the
from the COMP pin to GND
16
is above the threshold for
THRESHOLD
22.67
20.67
22.67
20.67
(µA)
OCP
20
18
20
18
ISL62881, ISL62881B
OVERSHOOT
REDUCTION
FUNCTION
Disabled
Enabled
comp
comp
is
to
Overcurrent
Way-Overcurrent
(2.5xOC)
Overvoltage +200mV 1ms
Undervoltage -300mV
Overvoltage 1.55V
VR_ON low or by bringing V
When VR_ON and V
levels, a soft-start will occur.
The second level of overvoltage protection is different. If
the output voltage exceeds 1.55V, the ISL62881 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 ISL62881 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.
As Figures 1 and 2 show, a resistor R
the IMON pin to convert the IMON pin current to voltage.
A capacitor can be paralleled with R
voltage information. The IMVP-6.5
requires that the IMON voltage information be referenced
to VSS
The IMON pin voltage range is 0V to 1.1V. A clamp circuit
prevents the IMON pin voltage from going above 1.1V.
I
IMON
FAULT TYPE
=
SENSE
TABLE 4. FAULT PROTECTION SUMMARY
3
×
I
droop
.
DD
120µs
<2µs
Immediately
PROTECTION
DURATION
BEFORE
return to their high operating
FAULT
DD
DD
below the POR threshold.
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.
imon
PROTECTI
imon
specification
ACTION
ON
to filter the
core
is connected to
March 9, 2011
VR_ON
toggle or
VDD
toggle
VDD
toggle
FAULT
RESET
FN6924.2
(EQ. 6)