Linear Technology Analog Devices LTM4636-1, Manual, Page: 14 / 36

LTM4636
14
4636f
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The relationship of FREQV voltage to switching frequency
is shown in Figure 3. For low output voltages from 0.6V
to 1.2V, 350kHz operation is an optimal frequency for the
best power conversion efficiency while maintaining the
inductor current to about 45% of maximum load current.
For output voltages from 1.5V to 1.8V, 500kHz is optimal.
For output voltages from 2.5V to 3.3V, 700kHz is optimal.
See efficiency graphs for optimal frequency set point. Limit
the 2.5V and 3.3V outputs to 35A.
The LTM4636 can be synchronized from 200kHz to
1200kHz with an input clock that has a high level above
2V and a low level below 1.2V. See the Typical Applica-
tions section for synchronization examples. The LTM4636
minimum on-time is limited to approximately 100ns. The
on-time can be calculated as:
t
ON(MIN)
=
1
FREQ
•
V
OUT
V
IN

 

applicaTions inForMaTion
The LTM4636's CLKOUT pin phase difference from V
OUT
can be programmed by applying a voltage to the PHMODE
pin. This voltage can be programmed using the 5.5V INTV
CC
pin. Most of the phase selections can be programmed by
either grounding, floating, or tying this pin to INTV
CC
. The
60 degree phase shift will require 3/4 INTV
CC
and can be
programmed with a voltage divider from the INTV
CC
pin.
See Figure 4 for phase programming and the 2 to 6 phase
connections. See Figure 27 for example design.
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK/SS pin. The output can be tracked up
and down with another regulator. The master regulator’s
output is divided down with an external resistor divider
that is the same as the slave regulator’s feedback divider
to implement coincident tracking. The LTM4636 uses an
Figure 3. FREQ Voltage to Switching Frequency
V
FREQ
(V)
0.4
FREQUENCY (kHz)
900
1100
1300
1.0 1.4
4636 F03
700
500
0.6 0.8 1.2 1.6 1.8
300
100