LTM4622A
12
Rev B
For more information
The LTM4622A device is an inherently current mode
controlled device, so parallel modules will have very
good current sharing. This will balance the thermals on
the design. Please tie RUN, TRACK/SS, FB and COMP pin
of each paralleling channel together. Figure 31 shows an
example of parallel operation and pin connection.
INPUT RMS Ripple Current Cancellation
provides a detailed explanation of
multiphase operation. The input RMS ripple current can-
cellation mathematical derivations are presented, and a
graph is displayed representing the RMS ripple current
reduction as a function of the number of interleaved phases.
Soft-Start and Output Voltage Tracking
The TRACK/SS pin provides a means to either soft-start
the regulator or track it to a different power supply. A
capacitor on the TRACK/SS pin will program the ramp rate
of the output voltage. An internal 1.4µA current source
will charge up the external soft-start capacitor towards
INTV
CC
voltage. When the TRACK/SS voltage is below
0.6V, it will take over the internal 0.6V reference voltage
to control the output voltage. The total soft-start time
can be calculated as:
t
SS
= 0.6 •
C
SS
1.4µA
where C
SS
is the capacitance on the TRACK/SS pin. Current
foldback and force continuous mode are disabled during
the soft-start process.
The LTM4622A has internal 400μs soft-start time when
TRACK/SS leave floating.
APPLICATIONS INFORMATION
Figure 3. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle
Figure 2. Example of Clock Phasing for 4-Phase
Operation with LTC6902
4622A F02
V
+
3.3V INTV
CC
PH
SET
LTC6902
200k
0°
SYNC/MODE V
OUT1
8A
180°
V
OUT2
DIV
GND
90°
SYNC/MODE V
OUT1
270°
0°
90°
V
OUT2
MOD
OUT1
OUT2
0.75 0.8
4622A F03
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.85 0.9
DUTY FACTOR (V
OUT
/V
IN
)
0
DC LOAD CURRENT
RMS INPUT RIPPLE CURRENT
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
