ISL8103CRZ Intersil, ISL8103CRZ Datasheet - Page 20

• Manufacturer Part Number: ISL8103CRZ
• Description: IC PWM CTRLR BUCK 2PHASE 40-QFN
• Manufacturer: Intersil

Specifications of ISL8103CRZ

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 1.5MHz
• Duty Cycle: 66.6%
• Voltage - Supply: 4.75 V ~ 12.6 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 1.5MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Current Balancing Component Selection
The ISL8103 senses the channel load current by sampling
the voltage across the lower MOSFET r
Figure 17. The ISEN pins are denoted ISEN1, ISEN2, and
ISEN3. The resistors connected between these pins and the
respective phase nodes determine the gains in the channel
current balance loop.
Select values for these resistors based on the room
temperature r
operating current, I
Equation 23.
In certain circumstances, it may be necessary to adjust the
value of one or more ISEN resistors. When the components
of one or more channels are inhibited from effectively
dissipating their heat so that the affected channels run hotter
than desired, choose new, smaller values of R
affected phases (see the section entitled Channel Current
Balance). Choose R
decrease in temperature rise in order to cause proportionally
less current to flow in the hotter phase.
In Equation 24, make sure that ΔT
temperature rise above the ambient temperature, and ΔT
the measured temperature rise above the ambient
temperature. While a single adjustment according to
Equation 24 is usually sufficient, it may occasionally be
necessary to adjust R
optimal thermal balance between all channels.
Load Line Regulation Component Selection (DCR
Current Sensing)
For accurate load line regulation, the ISL8103 senses the
total output current by detecting the voltage across the
R
R
FIGURE 17. ISL8103 INTERNAL AND EXTERNAL CURRENT-
ISEN
ISEN 2 ,
ISL8103
=
=
-----------------------
50 10
r
DS ON
R
⋅
ISEN
SENSING CIRCUITRY
(
DS(ON)
–
6
)
⋅
⋅
FL
ΔT
----------
ΔT
I
------- -
ISEN,2
FL
N
ISEN(n)
of the lower MOSFETs; the full load
; and the number of phases, N using
ISEN
2
1
CHANNEL N
LOWER MOSFET
two or more times to achieve
in proportion to the desired
R
ISEN
20
2
V
is the desired
IN
+
CHANNEL N
UPPER MOSFET
DS(ON)
-
I
L
x
r
DS ON
I
L
ISEN
, as shown in
(
for the
)
(EQ. 23)
(EQ. 24)
1
is
ISL8103
output inductor DCR of each channel (As described in
“Load-Line (Droop) Regulation” on page 12” ). As Figure 7
illustrates, an R-C network is required to accurately sense
the inductor DCR voltage and convert this information into a
droop voltage, which is proportional to the total output
current.
Choosing the components for this current sense network is a
two step process. First, R
chosen so that the time constant of this R
network matches the time constant of the inductor L/DCR.
Then the resistor R
sense network gain, obtaining the desired full load droop
voltage. Follow the steps below to choose the component
values for this R-C network.
Due to errors in the inductance or DCR it may be necessary
to adjust the value of R
correctly. The effects of time constant mismatch can be seen
in the form of droop overshoot or undershoot during the
initial load transient spike, as shown in Figure 18. Follow the
steps below to ensure the R-C and inductor L/DCR time
constants are matched accurately.
After choosing a new value for R
necessary to adjust the value of R
load droop voltage. Use Equation 26 to obtain the new value
for R
1. Choose an arbitrary value for C
2. Plug the inductor L and DCR component values, and the
3. Use the new value for R
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 18.
3. Select a new value, R
4. Replace R
value is 0.01µF.
values for C
calculate the value for R
as well as the desired full load current, I
voltage, V
calculate the value for R
about L/DCR/2 (sec/div). For example, with L = 1µH and
DCR = 1mΩ, set the oscilloscope to 500µs/div.
resistor based on the original value, R
following equation.
the error is corrected. Repeat the procedure if necessary.
R
R
R
S.
COMP
S
COMP 2
=
------------------------ - R
V
DROOP
,
=
I
FL
DROOP
=
COMP
---------------------------------------
DCR C
COMP
R
COMP 1
⋅
S
⋅
L
with the new value and check to see that
must be chosen to set the current
, and inductor DCR in Equation 26 to
COMP
COMP
chosen in steps 1, into Equation 25 to
COMP
,
COMP
COMP,2
⋅
COMP
Δ
----------
Δ
⋅
COMP
S
V
V
DCR
.
1
2
to match the time constants
and C
COMP
, for the time constant
obtained from Equation 25,
S
COMP
.
to obtain the desired full
COMP
, it will most likely be
. The recommended
COMP
COMP,1
FL
, full load droop
must be
-C
, using the
COMP
July 21, 2008
(EQ. 25)
(EQ. 26)
(EQ. 27)
FN9246.1