ISL6326BIRZ-T Intersil, ISL6326BIRZ-T Datasheet - Page 12

• Manufacturer Part Number: ISL6326BIRZ-T
• Description: IC CTRLR PWM 4PHASE BUCK 40-QFN
• Manufacturer: Intersil

Specifications of ISL6326BIRZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 25%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

pages 4 and 5). Equation 3 is provided to assist in selecting
the correct resistor value.
R
where F
Current Sensing
ISL6326B senses the current continuously for fast response.
ISL6326B supports inductor DCR sensing, or resistive
sensing techniques. The associated channel current sense
amplifier uses the ISEN inputs to reproduce a signal
proportional to the inductor current, I
I
current is used for current balance, load-line regulation, and
overcurrent protection.
The internal circuitry, shown in Figures 3, and 4, represents
one channel of an N-channel converter. This circuitry is
repeated for each channel in the converter, but may not be
active depending on the status of the PWM3 and PWM4
pins, as described in the PWM Operation section.
INDUCTOR DCR SENSING
An inductor’s winding is characteristic of a distributed
resistance as measured by the DCR (Direct Current
Resistance) parameter. Consider the inductor DCR as a
separate lumped quantity, as shown in Figure 3. The
channel current I
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 3.
The voltage on the capacitor V
proportional to the channel current I
If the R-C network components are selected such that the
RC time constant (= R*C) matches the inductor time
constant (= L/DCR), the voltage across the capacitor V
equal to the voltage drop across the DCR, i.e., proportional
to the channel current.
V
SEN
V
T
C
L
=
=
=
, is proportional to the inductor current. The sensed
2.5X10
------------------------- -
⎛
⎝
-------------------------------------------------------------------- -
I
L
s
F
SW
⋅
⋅
SW
(
-------------
DCR
s L
L
is the switching frequency of each phase.
⋅
10
(
s RC
+
+
⋅
DCR
1
L
⎞
⎠
, flowing through the inductor, will also
⋅
+
(
DCR I
)
1
)
⋅
L
12
)
C
, can be shown to be
L
L
, see Equation 5.
. The sense current,
L
.
(EQ. 4)
(EQ. 5)
(EQ. 3)
C
is
ISL6326B
With the internal low-offset current amplifier, the capacitor
voltage V
Therefore, the current out of ISEN+ pin, I
to the inductor current.
Because of the internal filter at ISEN- pin, one capacitor, C
is needed to match the time delay between the ISEN- and
ISEN+ signals. Select the proper C
constant of R
Equation 6 shows that the ratio of the channel current to the
sensed current, I
resistor and the DCR of the inductor.
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense
resistor R
serve as the current sense element (see Figure 4). This
technique is more accurate, but reduces overall converter
efficiency due to the additional power loss on the current
sense element R
The same capacitor C
between ISEN- and ISEN+ signals. Select the proper C
keep the time constant of R
to 27ns.
I
SEN
ISL6326B INTERNAL CIRCUIT
CURRENT
=
SENSE
I
FIGURE 3. DCR SENSING CONFIGURATION
L
C
SENSE
I
n
I
⋅
SEN
----------------- -
R
is replicated across the sense resistor R
DCR
ISL6605
ISEN
ISEN
=
SEN
SENSE
in series with each output inductor can
PWM(n)
I
L
and C
----------------- -
R
DCR
, is driven by the value of the sense
ISEN
T
.
is needed to match the time delay
+
-
T
(R
V
ISEN
IN
ISEN
ISEN-(n)
ISEN+(n)
and C
x C
INDUCTOR
R
T
L
to keep the time
I
T
L
T
s ( )
V
) close to 27ns.
L
SEN
(R
V
DCR
C
-
C
ISEN
(s)
, is proportional
-
R
(PTC)
C
ISEN(n)
T
x C
C
April 21, 2006
V
T
OUT
ISEN
OUT
) close
(EQ. 6)
FN9286.0
T
.
to
T
,