ISL62881CHRTZ-T Intersil, ISL62881CHRTZ-T Datasheet - Page 21

• 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

Transfer function A
Current-sensing resistor R
significant variation over-temperature, so there is no
need for the NTC network.
The recommended values are R
C
Overcurrent Protection
Referring to Equation 1 and Figures 12, 13 and 19,
resistor R
the internal OCP threshold. It is recommended to design
I
For example, the OCP threshold is 60µA. We will design
I
of the full load current.
For inductor DCR sensing, Equation 16 gives the DC
relationship of V
Substitution of Equation 16 into Equation 1 gives:
Therefore:
Substitution of Equation 8 and application of the OCP
condition in Equation 18 gives:
where I
corresponding droop current. For example, given
R
DCR = 1.3mΩ, I
Equation 19 gives R
For resistor sensing, Equation 20 gives the DC
relationship of V
Substitution of Equation 20 into Equation 1 gives
Equation 21:
Therefore:
Substitution of Equation 22 and application of the OCP
condition in Equation 18 gives:
I
V
R
V
R
droop
R
I
droop
droop
droop
n
sum
Cn
Cn
i
i
i
=
= 5600pF.
=
=
=
=
----------------------------------------------------------------------------------------------------------------- -
⎛
⎜
⎝
2R
--------------------------- -
--------------------------------------------------------------------- -
(
= 1.82kΩ, R
(
----------------------------------------------------
R
=
2
to be 50µA at full load, so the OCP trip level is 1.2x
R
R
R
without using the R
⎛
⎜
⎝
=
I
----------------------------------------- -
R
ntcnet
droop
2R
omax
sen
×
ntcs
ntcs
sen
---- -
R
2
---- -
R
ntcnet
2
i
(
----------------------------------------------------
i
R
R
i
ntcnet
×
sets the droop current I
R
×
×
×
ntcs
ntcs
+
+
----------------------------------------- -
R
ntcnet
R
I
I
+
o
R
R
is the full load current, I
ntcnet
o
sen
+
R
ntc
ntc
+
+
R
×
R
sum
omax
cn
cn
ntcnet
R
R
DCR
)
×
sum
+
p
ntc
ntc
(s) and I
×
(s) and I
I
Rsen
+
R
)
o
= 11kΩ, R
R
i
R
×
p
)
×
+
= 873Ω.
p
= 22A and I
sum
×
I
×
droop
DCR
R
+
(s) always has unity gain at DC.
I
R
o
p
R
p
sum
×
21
×
sen
comp
⎞
⎟
⎠
o
DCR
o
DCR
(s).
×
(s).
⎞
⎟
⎠
ntcs
I
value will not have
×
o
I
sum
resistor.
×
droopmax
×
I
= 2.61kΩ, R
I
o
droopmax
omax
droop
= 1kΩ and
droopmax
. Table 3 shows
ISL62881C, ISL62881D
ISL62881C, ISL62881D
= 50µA,
ntc
is the
= 10kΩ,
(EQ. 16)
(EQ. 17)
(EQ. 18)
(EQ. 19)
(EQ. 20)
(EQ. 21)
(EQ. 22)
where I
corresponding droop current. For example, given
R
Equation 23 gives R
A resistor from COMP to GND can adjust the internal OCP
threshold, providing another dimension of fine-tune
flexibility. Table 3 shows the detail. It is recommended to
scale I
approximately the desired OCP level, then use R
fine tune the OCP level if necessary.
Load Line Slope
Refer to Figure 12.
For inductor DCR sensing, substitution of Equation 17
into Equation 2 gives the load line slope expression in
Equation 24.
For resistor sensing, substitution of Equation 21 into
Equation 2 gives the load line slope expression in
Equation 25:
Substitution of Equation 18 and rewriting Equation 24,
or substitution of Equation 22 and rewriting Equation 25
gives the same result in Equation 26:
One can use the full load condition to calculate R
For example, given I
LL = 7mΩ, Equation 26 gives R
It is recommended to start with the R
calculated by Equation 26, and fine tune it on the actual
board to get accurate load line slope. One should record
the output voltage readings at no load and at full load for
load line slope calculation. Reading the output voltage at
lighter load instead of full load will increase the
measurement error.
Current Monitor
Referring to Equation 6 for the IMON pin current
expression.
Refer to Figures 1 and 2, the IMON pin current flows
through R
Equation 27:
Rewriting Equation 26 gives Equation 28:
V
R
LL
LL
I
R
droop
sen
Rimon
droop
i
=
=
=
= 1mΩ, I
2R
---------------------------------------
V
------------------ -
V
------------------ -
droop
=
droop
droop
I
=
=
omax
droopmax
sen
I
I
o
o
------------------ -
R
----------------
I
3
droop
imon
droop
×
I
×
I
o
o
I
such that the default OCP threshold gives
=
=
I
droop
omax
is the full load current, I
omax
. The voltage across R
2R
---------------------- -
2R
------------------------------------------ -
×
×
LL
LL
droop
sen
R
×
i
R
= 22A and I
i
R
×
omax
imon
= 880Ω.
i
R
×
droop
----------------------------------------- -
R
ntcnet
= 22A, I
R
ntcnet
+
droop
droopmax
R
sum
droopmax
imon
= 3.08kΩ.
×
droopmax
droop
DCR
= 50µA,
is shown in
value
= 50µA and
March 8, 2010
is the
droop
comp
(EQ. 23)
(EQ. 24)
(EQ. 25)
(EQ. 26)
(EQ. 27)
(EQ. 28)
FN7596.0
.
to