Datasheet

LTM4649
14
4649f
For more information www.linear.com/LTM4649
APPLICATIONS INFORMATION
Regardless of the mode selected by the MODE pin, the
regulator channels will always start in pulse-skipping
mode up to TRACK/SS = 0.5V. Between TRACK/SS = 0.5V
and 0.54V, it will operate in forced continuous mode and
revert to the selected mode once TRACK/SS > 0.54V. In
order to track with another channel once in steady state
operation, the LTM4649 is forced into continuous mode
operation as soon as V
FB
is below 0.54V regardless of the
setting on the MODE pin.
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK/SS pins. 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 LTM4649 uses an
accurate 10k 0.5% resistor internally for the top feedback
resistor for each channel. Figure 6 shows an example of
coincident tracking. Equations:
V
SLAVE
= 1+
10k
R
TA






• V
TRACK
V
TRACK
is the track ramp applied to the slave’s track pin.
V
TRACK
has a control range of 0V to 0.6V, or the internal
reference voltage. When the master’s output is divided
down with the same resistor values used to set the slave’s
output, then the slave will coincident track with the master
until it reaches its final value. The master will continue to
its final value from the slave’s regulation point. Voltage
tracking is disabled when V
TRACK
is more than 0.6V. RTA
in Figure 5 will be equal to the R
FB
for coincident tracking.
Figure 6 shows the coincident tracking waveforms.
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the master’s
COMP
TRACK/SS
RUN
FREQ
MODE
PGOOD
V
OUT
V
OUT_LCL
DIFFOUT
DIFFP
DIFFN
V
FB
LTM4649
V
IN
R2
10k
R
FB1
6.65k
C10
22µF
16V
C7
22µF
16V
C
SS
SOFT-START
CAPACITOR
V
OUT2
1.5V
10A
C11
100µF
6.3V
×2
INTV
CC
V
IN
GND
COMP
TRACK/SS
RUN
FREQ
MODE
PGOOD
V
OUT
V
OUT_LCL
DIFFOUT
DIFFP
DIFFN
V
FB
LTM4649
V
IN
R1
10k
R
FB
10k
C2
22µF
16V
C3
22µF
16V
C6
100µF
6.3V
×2
V
OUT1
1.2V
10A
INTV
CC
4649 F05
GND
R
TB
10k
R
TA
10k
MASTER RAMP
OR OUTPUT
V
IN
Figure 5. Dual Outputs (1.5V and 1.2V) with Tracking