isl62883c Intersil Corporation, isl62883c Datasheet - Page 26

• Manufacturer Part Number: isl62883c
• Description: Multiphase Pwm Regulator For Imvp-6.5? Mobile Cpus And Gpus
• Manufacturer: Intersil Corporation

For example, the OCP threshold is 60µA for 3-phase
solution. We will design I
so the OCP trip level is 1.5x of the full load current.
For inductor DCR sensing, Equation 28 gives the DC
relationship of V
Substitution of Equation 28 into Equation 1 gives
Equation 29:
Therefore:
Substitution of Equation 20 and application of the OCP
condition in Equation 30 gives Equation 31:
where I
corresponding droop current. For example, given N = 3,
R
DCR = 0.88mΩ, I
Equation 31 gives R
For resistor sensing, Equation 32 gives the DC
relationship of V
Substitution of Equation 32 into Equation 1 gives
Equation 33:
Therefore
Substitution of Equation 34 and application of the OCP
condition in Equation 30 gives Equation 35:
where I
corresponding droop current. For example, given N = 3,
R
Equation 35 gives R
A resistor from COMP to GND can adjust the internal OCP
threshold, providing another dimension of fine-tune
R
I
V
I
R
V
R
R
sum
sen
droop
droop
Cn
i
i
Cn
i
i
=
=
=
=
= 1mΩ, I
=
---------------------------------------------------------------------------------------------------------------------------- -
N
= 3.65kΩ, R
=
--------------------------------------------------------------------------------- -
N
2R
--------------------------- -
2R
---------------------------------------
N
N
=
=
⎛
⎜
⎜
⎜
⎝
×
×
omax
R
-------------
omax
×
×
------------------------------------------
R
sen
sen
2
⎛
⎜
⎝
sen
⎛
⎝
N
---- -
R
---- -
R
I
I
2
2
ntcnet
2R
(
----------------------------------------------------
droop
droopmax
R
×
i
R
R
i
ntcnet
×
×
R
×
×
(
----------------------------------------------------
ntcs
ntcs
ntcnet
×
R
R
R
-------------
ntcnet
------------------------------------------
R
is the full load current, I
I
I
is the full load current, I
o
omax
ntcs
ntcs
I
omax
sen
ntcnet
o
N
+
+
+
cn
cn
R
R
-------------- -
+
R
R
omax
p
ntcnet
+
+
×
×
sum
(s) and I
R
-------------- -
(s) and I
N
ntc
ntc
R
R
= 11kΩ, R
I
DCR
sum
o
= 51A and I
+
i
i
N
ntc
ntc
= 606Ω.
= 831Ω.
)
R
-------------- -
+
×
×
sum
= 51A and I
N
⎞
⎠
R
) R
+
DCR
-------------
R
×
×
×
p
droop
N
R
p
I
I
26
o
p
droop
×
+
o
o
p
⎞
⎟
⎟
⎟
⎠
(s).
DCR
-------------
R
-------------- -
(s).
×
×
ntcs
sum
N
N
DCR
I
to be 40.9µA at full load,
o
droopmax
⎞
⎟
⎠
×
= 2.61kΩ, R
×
I
×
o
droopmax
I
I
droopmax
omax
droopmax
droopmax
= 40.9µA,
= 40.9µA,
ntc
is the
is the
(EQ. 28)
= 10kΩ,
(EQ. 29)
(EQ. 30)
(EQ. 31)
(EQ. 32)
(EQ. 33)
(EQ. 34)
(EQ. 35)
ISL62883C
flexibility. Table 4 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 29
into Equation 2 gives the load line slope expression:
For resistor sensing, substitution of Equation 33 into
Equation 2 gives the load line slope expression:
Substitution of Equation 30 and rewriting Equation 36,
or substitution of Equation 34 and rewriting Equation 37
give the same result in Equation 38:
One can use the full load condition to calculate R
For example, given I
and LL = 1.9mΩ, Equation 38 gives R
It is recommended to start with the R
calculated by Equation 38, 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
Refer to Equation 18 for the IMON pin current
expression.
Refer to Figures 1 and 2, the IMON pin current flows
through R
Equation 39:
Rewriting Equation 38 gives Equation 40:
Substitution of Equation 40 into Equation 39 gives
Equation 41:
Rewriting Equation 41 and application of full load
condition gives Equation 42:
For example, given LL = 1.9mΩ, R
V
R
R
LL
LL
V
I
V
R
Rimon
imon
droop
droop
Rimon
Rimon
imon
=
=
V
------------------ -
V
------------------ -
= 8.14kΩ.
droop
=
=
droop
droop
= 999mV at I
=
I
I
=
=
o
o
------------------ -
R
V
----------------------------------------------
imon
----------------
I
3
droop
3I
--------------------- -
droop
Rimon
R
I
I
×
o
o
droop
such that the default OCP threshold gives
o
=
=
3I
I
×
droop
. The voltage across R
o
2R
------------------------------------------ -
LL
2R
---------------------- -
×
×
×
×
LL
LL
droop
sen
R
LL
R
×
×
droop
i
N
R
omax
R
imon
×
×
omax
imon
R
R
×
droop
i
------------------------------------------
R
ntcnet
= 51A, I
= 51A, Equation 42 gives
R
ntcnet
+
R
-------------- -
sum
droop
N
droopmax
imon
droop
droop
×
DCR
-------------
= 2.37kΩ,
N
is expressed in
= 2.37kΩ.
value
= 40.9µA
March 18, 2010
droop
comp
(EQ. 38)
(EQ. 36)
(EQ. 37)
(EQ. 39)
(EQ. 40)
(EQ. 41)
(EQ. 42)
FN7557.1
.
to