LTM4606 LINER [Linear Technology], LTM4606 Datasheet - Page 12

• Manufacturer Part Number: LTM4606
• Description: Ultralow EMI 28VIN, 6A DC/DC ?Module
• Manufacturer: LINER [Linear Technology]

LTM4606
APPLICATIONS INFORMATION
Soft-Start and 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 this pin will program the ramp rate of the
output voltage. A 1.5μA current source will charge up the
external soft-start capacitor to 80% of the 0.6V internal
voltage reference minus any margin delta. This will control
the ramp of the internal reference and the output voltage.
The total soft-start time can be calculated as:
When the RUN pin falls below 2.5V, then the SS pin is reset
to allow for proper soft-start control when the regulator is
enabled again. Current foldback and force continuous mode
are disabled during the soft-start process. The soft-start
function can also be used to control the output ramp up time,
so that another regulator can be easily tracked to it.
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK/SS pin. The output can be tracked up and
12
t
SOFTSTART
≅
0 8 0 6
. • .
(
V V
Figure 3. Normalized Output Ripple Current vs Duty Cycle, Dlr = V
–
OUT MARGIN
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0.1 0.15 0.2 0.25
(
)
)
•
1 5
C
.
0.3
SS
µA
0.35
0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
DUTY CYCLE (V
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. Figure 4
shows an example of coincident tracking. Ratiometric
modes of tracking can be achieved by selecting different
resistor values to change the output tracking ratio. The
master output must be greater than the slave output for
the tracking to work. Figure 5 shows the coincident output
tracking characteristics.
CONTROL
MASTER
OUTPUT
TRACK
O
/V
IN
)
Figure 4. Output Voltage Coincident Tracking
V
C
IN
R2
60.4k
R1
19.1k
IN
100k
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
V
PGOOD
RUN
COMP
INTV
DRV
f
TRACK/SS
SET
D
CC
CC
O
4612 F05
T/L
SGND
LTM4606
V
IN
I
PLLIN
PGND
MARG0
MARG1
MPGM
V
FCB
OUT
V
FB
4606 F04
19.1k
C
OUT
SLAVE
OUTPUT
2.5V
4606f