ISL6261CRZ-T Intersil, ISL6261CRZ-T Datasheet - Page 19

• Manufacturer Part Number: ISL6261CRZ-T
• Description: IC CTRLR BUCK 1PHASE 40-MLFP
• Manufacturer: Intersil

Specifications of ISL6261CRZ-T

• Applications: Converter, Intel IMVP-6
• Voltage - Input: 5 ~ 21 V
• Number Of Outputs: 1
• Voltage - Output: 0.3 ~ 1.5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 40-VFQFN, 40-VFQFPN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Static Mode of Operation - Static Droop Using DCR
Sensing
The ISL6261 has an internal differential amplifier to
accurately regulate the voltage at the processor die.
For DCR sensing, the process to compensate the DCR
resistance variation takes several iterative steps. Figure 2
shows the DCR sensing method. Figure 9 shows the
simplified model of the droop circuitry. The inductor DC
current generates a DC voltage drop on the inductor DCR.
Equation 15 gives this relationship.
An R-C network senses the voltage across the inductor to
get the inductor current information. R
network consisting of R
will be discussed in the next section.
The first step in droop load line compensation is to choose
R
at light loads between the VSUM and VO nodes. As a rule of
thumb, the voltage drop across the R
be 0.5-0.8 times V
fairly reasonable amount of light load signal from which to
derive the droop voltage.
The NTC network resistor value is dependent on the
temperature and is given by:
V
R
n
DCR
n
and R
(
T
=
)
OC
Internal to
=
I
ISL6261
s
o
(
such that the correct droop voltage appears even
R
×
R
series
series
DCR
+
DCR
+
R
R
ntc
. This gain, defined as G1, provides a
ntc
ntc
1
)
+
, R
⋅
R
R
FIGURE 9. EQUIVALENT MODEL FOR DROOP CIRCUIT USING DCR SENSING
series
19
par
par
10uA
and R
DROOP
n
n
network, V
represents the NTC
par
. The choice of R
DROOP
OCSET
VSUM
DFB
n
VO
, is set to
(EQ. 15)
(EQ. 16)
s
ISL6261
R
ocset
G1, the gain of V
temperature of the NTC thermistor:
The inductor DCR is a function of the temperature and is
approximately given by
in which 0.00393 is the temperature coefficient of the copper.
The droop amplifier output voltage divided by the total load
current is given by:
R
independent of the inductor temperature, it is desired to
have:
where G
temperature characteristics G
For different G1 and NTC thermistor preference, Intersil
provides a design spreadsheet to generate the proper value
of R
G
G
G
DCR
R
droop
1
1
droop
1
(
(
(
T
ntc
T
) T
(
)
VO
)
, R
T
is the actual load line slope. To make R
⋅
=
=
=
Δ
1 (
1target
)
series
G
1 (
R
=
+
R
n
1
+
DCR
. 0
(T)
R
par
(
. 0
T
, R
00393
is the desired ratio of V
n
(
00393
)
⋅
n
T
par
G
+
DCR
25
to V
)
t 1
.
C
R
arg
⋅
( *
s
DCR
1 (
*
et
R
R
(
T
T (
T
+
series
ntc
, is also dependent on the
−
)
. 0
−
⋅
25
00393
25
k
1
droopamp
))
is described by:
R
)
n
≅
G
( *
(R
R +R
n
1
ntc
ntc
t
/V
T
R
arg
V
+R
DCR
s
−
dcr
et
series
series
25
. Therefore, the
))
droop
September 27, 2006
I
o
+R
)
R
DCR
par
par
(EQ. 17)
(EQ. 18)
(EQ. 19)
(EQ. 20)
(EQ. 21)
FN9251.1