LTM4632
11
4632fb
For more information www.linear.com/LTM4632
APPLICATIONS INFORMATION
Force Continuous Current Mode (CCM) Operation
In applications where fixed frequency operation is more
critical than low current efficiency, and where the lowest
output ripple is desired, forced continuous operation
should be used. Forced continuous operation can be
enabled by tying the SYNC/MODE pin to GND. In this
mode, inductor current is allowed to reverse during low
output loads, the COMP voltage is in control of the current
comparator threshold throughout, and the top MOSFET
always turns on with each oscillator pulse. During start-up,
forced continuous mode is disabled and inductor current
is prevented from reversing until the LTM4632’s output
voltage is in regulation.
Operating Frequency
The operating frequency of the LTM4632 is optimized to
achieve the compact package size and the minimum output
ripple voltage while still keeping high efficiency. The default
operating frequency is internally set to 1MHz. In most ap
-
plications, no additional frequency adjusting is required.
Frequency Synchronization
The power module has a phase-locked loop comprised
of an internal voltage controlled oscillator and a phase
detector. This allows the internal top MOSFET turn-on
to be locked to the rising edge of the external clock. The
external clock frequency range must be within ±30%
around the set operating frequency. A pulse detection
circuit is used to detect a clock on the SYNC/MODE pin
to turn on the phase locked loop. The pulse width of the
clock has to be at least 100ns. The clock high level must
be above 2V and clock low level below 0.3V. The presence
of an external clock will place both regulator channels into
forced continuous mode operation. During the start-up of
the regulator, the phase-locked loop function is disabled.
Multiphase Operation (Configured as Multiphase
Single Output VTT)
For VTT termination output loads that demand more than
3A of current, two outputs in the LTM4632 or even multiple
LTM4632s can be paralleled to run out of phase to provide
a multiphase single output VTT termination supply capable
of souring and sinking higher current.
33.2k
3.3
INTV
CC
V
+
PH MOD
V
OUT1
V
OUT2
OUT1
0°
0°
90°
270°
4632 F02
180°
V
TT
12A
90°
OUT2
SET
SYNC/
MODE
V
OUT1
V
OUT2
SYNC/
MODE
DIV
GND
LTC6902
LTM4632
LTM4632
Figure 2. Example of Clock Phasing for 4-Phase
Single Output VTT Operation with LTC6902
The two switching mode regulator channels inside the
LTM4632 are internally set to operate 180° out of phase.
Multiple LTM4632s could easily operate 90 degrees, 60
degrees or 45 degrees shift which corresponds to 4-phase,
6-phase or 8-phase operation by letting SYNC/MODE of the
LTM4632 synchronize to an external multiphase oscillator
like LTC6902. Figure 2 shows a 4-phase single output VTT
termination supply design example for clock phasing.
Tie FB1 pin of the LTM4632 to its INTV
CC
pin to put the
module into two phase single VTT output operation mode.
This will internally switch the Channel 1 error amplifier
reference voltage from 0.6V to VTTR voltage, which is the
same as Channel 2. Repeat this for each LTM4632 module
in multiple LTM4632s paralleling application.
Also tie RUN, TRACK/SS and COMP pin of each paralleling
channel together. Figure 20 shows an example of paralleled
multiphase single output VTT termination supply operation
and pin connection.
The LTM4632 device is an inherently current mode con
-
trolled device, so parallel modules will have very good cur-
rent sharing. This will balance the thermals on the design.
Multiphase Operation
(Configured as VDDQ+VTT)
For application which both VDDQ and VTT termination
output loads demand more than 3A of current, two or
multiple Channel 1 outputs from different LTM4632
modules can be easily paralleled to provide a multiphase
single VDDQ output while Channel 2 outputs from different
LTM4632 modules can paralleled to provide a multiphase
single VTT output.
