ISL6262AIRZ Intersil, ISL6262AIRZ Datasheet - Page 26

• Manufacturer Part Number: ISL6262AIRZ
• Description: IC CORE CTRLR 2PHASE 48-QFN
• Manufacturer: Intersil

Specifications of ISL6262AIRZ

• Applications: Controller, Intel IMVP-6
• Voltage - Input: 5 ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.3 ~ 1.5 V
• Operating Temperature: -40°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 48-VQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In the previous example, the two errors add to 4A. For the
two phase DC/DC, the currents would be 22A in one phase
and 18A in the other phase. In the above analysis, the
current balance can be calculated with 2A/20A = 10%. This
is the worst case calculation. For example, the actual
tolerance of two 10% DCRs is 10%*sqrt(2) = 7%.
There are provisions to correct the current imbalance due to
layout or to purposely divert current to certain phase for
better thermal management. Customer can put a resistor in
parallel with the current sensing capacitor on the phase of
interest in order to purposely increase the current in that
phase.
If the PC board trace resistance from the inductor to the
microprocessor are significantly different between two
phases, the current will not be balanced perfectly. Intersil
has a proprietary method to achieve the perfect current
sharing in case of severe unbalanced layout.
When choosing the current sense resistor, both the
tolerance of the resistance and the TCR are important. Also,
the current sense resistor’s combined tolerance at a wide
temperature range should be calculated.
Droop Using Discrete Resistor Sensing - Static/
Dynamic Mode of Operation
Figure 42 shows the equivalent circuit of a discrete current
sense approach. Figure 33 shows a more detailed
schematic of this approach. Droop is solved the same way
as the DCR sensing approach with a few slight
modifications.
First, because there is no NTC required for thermal
compensation, the R
section is not required. Second, because there is no time
constant matching required, the C
matched to the L/DCR time constant. This component does
indeed provide noise immunity and therefore is populated
with a 39pF capacitor.
The R
sufficient for this approach.
Now the input to the droop amplifier is essentially the
Vrsense voltage. This voltage is given by Equation 30.
The gain of the droop amplifier, K
for the ratio of the R
use the Equation 31.
Vrsense
K
droopamp
current balance circuit. The error current that results is
given by 2mV/DCR. If DCR = 1mΩ then the error is 2A.
S
values in the previous section, R
EQV
=
=
------------------- - 2
R
R
droop
sense
R
------------------- - I
sense
2
sense
n
•
resistor network in the previous
•
OUT
to droop impedance, R
26
droopamp
n
component is not
S
, must be adjusted
= 1.5k_1%, are
droop
(EQ. 30)
(EQ. 31)
. We
ISL6262A
Solving for the R
Intel IMVP-6+ specification, R
R
These values are extremely sensitive to layout. Once the
board has been laid out, some tweaking may be required to
adjust the full load droop. This is fairly easy and can be
accomplished by allowing the system to achieve thermal
equilibrium at full load, and then adjusting R
desired droop value.
Fault Protection - Overcurrent Fault Setting
As previously described, the overcurrent protection of the
ISL6262A is related to the droop voltage. Previously we
have calculated that the droop voltage = ILoad*R
where R
in the Intel IMVP-6+ specification. Knowing this relationship,
the overcurrent protection threshold can be set up as a
voltage droop level. Knowing this voltage droop level, one
can program in the appropriate drop across the R
resistor. This voltage drop will be referred to as Voc. Once
the droop voltage is greater than Voc, the PWM drives will
turn off and PGOOD will go low.
The selection of R
desire an overcurrent trip level, I
from the Intel Specification that the load line slope, R
0.0021 (V/A), we can then calculate for R
Equation 33.
Note: If the droop load line slope is not -0.0021 (V/A) in the
application, the overcurrent setpoint will differ from
predicted.
R
R
drp1
drp2
OC
=
=1kΩ, we obtain in Equation 32.
=
I
---------------------------------- -
droop
OC
(
K
droopamp
10μA
•
R
is the load line slope specified as 0.0021 (V/A)
droop
drp2
OC
–
=
value, R
1
is given in Equation 33. Assuming we
55 0.0021
------------------------------
) R
10 10
•
•
•
drp1
droop
sense
–
6
=
OC
3.2kΩ
=
= 0.0021(V/A) as per the
, of 55A, and knowing
= 0.001Ω and
11.5kΩ
OC
drp2
as shown in
December 23, 2008
to obtain the
droop
OC
droop
(EQ. 32)
(EQ. 33)
FN6343.1
,
is