LTM4604 LINER [Linear Technology], LTM4604 Datasheet - Page 10

• Manufacturer Part Number: LTM4604
• Description: Low Voltage, 4A DC/DC ?ModuleTM with Tracking
• Manufacturer: LINER [Linear Technology]

LTM4604
Run Enable and Soft-Start
The RUN/SS pin provides dual functions of enable and
soft-start control. The RUN/SS pin is used to control
turn on of the LTM4604. While this pin is below 0.5V, the
LTM4604 will be in a 7μA low quiescent current state. A
0.8V threshold will enable the LTM4604. This pin can be
used to sequence LTM4604 devices. The soft-start control
is provided by a 1M pull-up resistor (R
capacitor (C
capacitor can be applied to the RUN/SS pin to increase the
soft-start time. A typical value is 0.01μF. The approximate
equation for soft-start is:
where R
Figure 1, 1.8V is the soft-start upper range, and C
is the additional capacitance for further soft-start contol.
The soft-start function can also be used to control the
output ramp-up time, so that another regulator can be
easily tracked. An independent ramp control signal can
be applied to the master ramp, otherwise, connect the
TRACK pin to V
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 same as the slave regulator’s feedback divider
to implement coincident tracking. The LTM4604 uses a
very accurate 4.99k resistor for the top feedback resistor.
Figure 2 shows an example of coincident tracking.
V
V
to the point of the programmed value at which V
proceeds beyond the 0.8V reference value. The V
pin must go beyond 0.8V to ensure the slave output has
reached its fi nal value. Load current must be present for
proper tracking.
APPLICATIONS INFORMATION
10
TRACK
TRACK
t
V
SOFTSTART
TRACK
is the track ramp applied to the slave’s TRACK pin.
applies the track reference for the slave output up
SS
=
and C
SS
4 99
) as drawn in the Block Diagram. An external
=
.
IN
ln
SS
R
to disable tracking.
k R
FB
⎛
⎝ ⎜
+
are shown in the Block Diagram of
V
2
IN
FB
V
– .
2
IN
1 8
•
V
V
MASTER
⎞
⎠ ⎟
•
R
SS
(
SS
C
SS
) and a 1000pF
+
C
SSE
TRACK
TRACK
X X T
SSEXT
)
C
SSEXT
X5R OR X7R
X5R OR X7R
10μF
10μF
6.3V
6.3V
C
C
IN1
IN2
PGOOD
COMP
RUN/SS
PGOOD
COMP
RUN/SS
LTM4604
LTM4604
GND
GND
V
V
V
V
5V
5V
IN
IN
IN
IN
TRACK
TRACK
V
V
OUT
OUT
FB
FB
Figure 2
Figure 3
R
5.76k
RAMP
CONTROL
OR V
FB2
TIME
IN
R
4.99k
FB1
MASTER OUTPUT
SLAVE OUTPUT
R
1.62k
R
5.76k
FB3
FB
4604 F03
C
22μF
6.3V ×3
X5R OR
X7R
C
22μF
6.3V ×3
X5R OR
X7R
OUT1
OUT2
4604 F02
V
3.3V
4A
V
1.5V
4A
MASTER
SLAVE
4604f