ISL6323EVAL1Z Intersil, ISL6323EVAL1Z Datasheet - Page 13

• Manufacturer Part Number: ISL6323EVAL1Z
• Description: EVAL BOARD 1 FOR ISL6323
• Manufacturer: Intersil

Specifications of ISL6323EVAL1Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ground. The PWM signals command the MOSFET driver to
turn on/off the channel MOSFETs.
For 4-channel operation, the channel firing order is 4-3-2-1:
PWM3 pulse happens 1/4 of a cycle after PWM4, PWM2
output follows another 1/4 of a cycle after PWM3, and
PWM1 delays another 1/4 of a cycle after PWM2. For
3-channel operation, the channel firing order is 3-2-1.
Connecting ISEN4- to VCC selects 3-channel operation and
the pulse times are spaced in 1/3 cycle increments. If ISEN3- is
connected to VCC, 2-channel operation is selected and the
PWM2 pulse happens 1/2 of a cycle after PWM1 pulse.
Continuous Current Sampling
In order to realize proper current-balance, the currents in
each channel are sampled continuously every switching
cycle. During this time, the current-sense amplifier uses the
ISEN inputs to reproduce a signal proportional to the
inductor current, I
scaled version of the inductor current.
The ISL6323 supports Inductor DCR current sensing to
continuously sample each channel’s current for channel-current
balance. The internal circuitry, shown in Figure 6 represents
Channel N of an N-Channel converter. This circuitry is repeated
for each channel in the converter, but may not be active
depending on how many channels are operating.
Inductor windings have a characteristic distributed
resistance or DCR (Direct Current Resistance). For
simplicity, the inductor DCR is considered as a separate
lumped quantity, as shown in Figure 6. The channel current
I
Equation 5 shows the S-domain equivalent voltage, V
across the inductor.
A simple R-C network across the inductor (R
extracts the DCR voltage, as shown in Figure 6. The voltage
Ln
V
L
, flowing through the inductor, passes through the DCR.
s ( )
=
FIGURE 4. CONTINUOUS CURRENT SAMPLING
I
L
n
⋅
(
s L
⋅
L
+
. This sensed current, I
DCR
PWM
)
SWITCHING PERIOD
13
TIME
I
I
SEN
L
SEN
1
, R
, is simply a
2
and C)
L
(EQ. 5)
,
ISL6323
across the sense capacitor, V
proportional to the channel current I
Where:
If the R-C network components are selected such that the
RC time constant matches the inductor L/DCR time constant
(see Equation 8), then V
the DCR multiplied by the ratio of the resistor divider, K. If a
resistor divider is not being used, the value for K is 1.
The capacitor voltage V
internal sense resistor, R
R
current, I
controller for load-line regulation, channel-current balancing,
and overcurrent detection and limiting. Equation 9 shows that
the proportion between the channel current, I
current, I
resistance, R
-------------
DCR
K
V
ISEN
L
C
=
FIGURE 5. INDUCTOR DCR CURRENT SENSING
s ( )
MOSFET
DRIVER
-------------------- -
R
TO NORTH BRIDGE
TO ACTIVE
CORE CHANNELS
=
ISL6323 INTERNAL CIRCUIT
2
which is proportional to the inductor current. This
=
R
SAMPLE
+
-------------------- - C
R
R
SEN
SEN
2
------------------------------------------------------- - K DCR I
⎛
⎜
⎝
1
R
1
s
I
n
+
1
⋅
⋅
R
, is continuously sensed and is then used by the
, is driven by the value of the effective sense
R
(
----------------------- - C
ISEN
R
R
CONFIGURATION
⎛
⎝
2
2
-------------
DCR
1
1
s L
⋅
+
⋅
UGATE(n)
LGATE(n)
⋅
I
R
SEN
, and the DCR of the inductor.
R
2
2
+
)
{
⋅
1
+
C
-
⎞
⎠
ISEN
, is then replicated across the effective
C
+
is equal to the voltage drop across
1
⎞
⎟
⎠
. This develops a current through
⋅
V
R
V
C
IN
ISEN
C
, can be shown to be
(s)
⋅
-
Ln
R
INDUCTOR
⋅
, shown in Equation 6.
1
L
V
ISENn-
ISENn+
L
VCC
RSET
I
L
L
n
(s)
n
V
C
L
DCR
R
-
(s)
C
, and the sensed
2
-
R
C
October 21, 2008
SET
SET
C
V
(EQ. 6)
(EQ. 7)
OUT
FN9278.4
(EQ. 8)
OUT