IR3623MPBF_1 IRF [International Rectifier], IR3623MPBF_1 Datasheet - Page 11

• Manufacturer Part Number: IR3623MPBF_1
• Description: HIGH FREQUENCY 2-PHASE, SINGLE OR DUAL OUTPUT SYNCHRONOUS STEP DOWN CONTROLLER WITH OUTPUT TRACKING AND SEQUENCING
• Manufacturer: IRF [International Rectifier]

Current Share Mode
This feature allows to connect both outputs
together to increase current handling capability of
the converter to support a common load. In
current sharing mode, error amplifier 1 becomes
the master which regulates the common output
voltage and the error amplifier 2 performs the
current sharing function, figure 6 shows the
configuration of error amplifiers.
In this mode IR3623 make sure the master
channel starts first followed by slave channel to
prevent any glitch during start up. This is done by
clamping the output of slave’s error amplifier until
the master channel generates the first PWM
signal.
At no load condition the slave channel may be
kept off depends on the offset of error amplifier.
Lossless Inductor Current Sensing
The IR3623 uses a lossless current sensing for
current share purposes. The inductor current is
sensed by connecting a series resistor and a
capacitor network in parallel with inductor and
measuring the voltage across the capacitor, this
voltage is proportional to the inductor current. As
shown in figure 6 the voltage across the
inductor’s DCR can be expressed by:
The voltage across the C
Combining equations (1),(2) and (3) result to the
following expression for V
Usually the resistor R
the time constant of R
constant of the inductor which is the inductance
L
constants match, the voltage across C
proportional to the current through L
www.irf.com
1
V
V
RL
C
over the inductor’s DCR (R
1
V
1
(
(
s
C
s
1
)
)
(
=
s
V
=
)
RL
(
(
V
=
V
1
in
(
in
I
s
L
−
1
−
)
V
*
=
V
out
1
out
I
R
L
+
1
* )
* )
1
L
*
sR
1
and C
1
R
R
+
R
1
and C
1
1
L
C1
sL
L
1
can expressed by:
1
*
1
*
R
:
C
sC
*
1
L
1
1
1
sL
1
are chosen so that
L1
sC
1
1
-
). If the two time
1
- -
equals the time
1
-
1
( -
, and
- -
- -
2
-
)
( -
- -
- -
4
1 (
( -
)
1
3
)
is
)
the sense circuit can be treated as if only a
sense resistor with the value R
The mismatch of the time constant does not
affect the measurements of inductor DC current,
but affects the AC component of the inductor
current.
Soft-Start
The IR3623 has programmable soft-start to
control the output voltage rise and limit the inrush
current during start-up. It provides a separate
Soft-start function for each outputs. This will
enable to sequence the outputs by controlling the
rise time of each outputs through selection of
different value soft-start capacitors.
To
sequence initiates when the Vcc, Enable and
5V_sns rise above their threshold and generate
the Power On Reset (POR) signal. Soft-start
function operates by sourcing an internal current
to charge an external capacitor to about 3V.
Initially, the soft-start function clamps the error
amplifier’s output of the PWM converter.
Fig. 6: Loss Less inductor current sensing
ensure
and current sharing
V
V
in
in
Q3
Q2
Q4
correct
V
If
Master Phase
C
:
(
+
Slave Phase
s
R
R1
R2
L2
L1
IL1
)
1
FB2
V
VP2
≈
*
IR3623MPbF
L1
C
I
(s) -
start-up,
L
+ V
1
1
R
C2
R
C1
*
C1
=
L1
L2
(s)
R
R
L
-
L
1
L1
1
L
1
was used.
V
OUT
the
soft-start
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