Datasheet
LTM4608A
15
4608afd
applicaTions inForMaTion
CLKIN is tied to ground or if it’s driven by an external
frequency synchronization signal. A capacitor value of
0.01µF must be placed from the PLLLPF pin to ground to
control the slew rate of the spread spectrum frequency
change. Add a control ramp on the TRACK pin with R
SR
and C
SR
referenced to V
IN
. Figure 21 shows an example
for spread spectrum operation.
R
SR
≥
1
− ln 1−
0.592
V
IN
• 500 • C
SR
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK 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
Figure 5. Dual Outputs (3.3V and 1.5V) with Tracking
same as the slave regulator’s feedback divider to implement
coincident tracking. The LTM4608A uses an accurate 10k
resistor internally for the top feedback resistor. Figure 5
shows an example of coincident tracking:
Slave = 1+
10k
R
FB4
• V
TRACK
V
TRACK
is the track ramp applied to the slave’s track pin.
V
TRACK
has a control range of 0V to 0.596V, 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, this resistor divider is connected to the slave’s track
pin. The slave will then 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 0.596V.
V
IN
SV
IN
SW
RUN
PLLLPF
TRACK
MODE
PHMODE
V
OUT
FB
I
TH
I
THM
PGOOD
BSEL
MGN
CLKOUT GND
CLKIN
RUN
TRACK
TRACK
R
SR
C
SR
C2
100pF
C3
22pF
R
FB1
2.21k
100µF
MASTER
3.3V
7A
V
IN
5V
TIE TO V
IN
FOR DISABLE
AND DEFAULT
100µs SOFT-START
APPLY A CONTROL
RAMP WITH R
SR
AND
C
SR
TIED TO V
IN
WHERE
t = –(ln
(1 – 0.596/V
IN
) • R
SR
• C
SR
)
OR APPLY AN EXTERNAL TRACKING RAMP
LTM4608A
SGND
V
IN
SV
IN
SW
RUN
PLLLPF
TRACK
MODE
PHMODE
V
OUT
FB
I
TH
I
THM
PGOOD
BSEL
MGN
CLKOUT GND
CLKIN
RUN
MASTER
3.3V
R
FB2
6.65k
50k
50k
V
IN
R
FB3
10k
R
FB4
6.65k
4608A F05
C1
100µF
C4
100µF
SLAVE
1.5V
8A
LTM4608A
SGND
+