DC1400A Linear Technology, DC1400A Datasheet - Page 16

• Manufacturer Part Number: DC1400A
• Description: BOARD EVAL LTM4608
• Manufacturer: Linear Technology
• Series: LTM®r

Specifications of DC1400A

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 1.2V, 1.5V, 1.8V, 2.5V, 3.3V
• Current - Output: 8A
• Voltage - Input: 2.5 ~ 5.5 V
• Regulator Topology: Buck
• Frequency - Switching: 1.5MHz
• Board Type: Fully Populated
• Utilized Ic / Part: LTM4608
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

LTM4608A
The track pin of the master can be controlled by an external
ramp or by R
RC ramp time can be programmed using equation:
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the mas-
ter’s track pin. As mentioned above, the TRACK pin has
a control range from 0V to 0.596V. The master’s TRACK
pin slew rate is directly equal to the master’s output slew
rate in Volts/Time:
where MR is the master’s output slew rate and SR is the
slave’s output slew rate in Volts/Time. When coincident
tracking is desired, then MR and SR are equal, thus R
is equal the 10k. R
where V
and V
feedback resistor of the slave regulator in equal slew rate
or coincident tracking, then R
V
In ratiometric tracking, a different slew rate maybe desired
for the slave regulator. R
is slower than MR. Make sure that the slave supply slew
rate is chosen to be fast enough so that the slave output
voltage will reach it final value before the master output.
16
APPLICATIONS INFORMATION
TRACK
R
t = – ln 1–
MR
SR
FB4
TRACK
. Therefore R
• 10k = R
FB

 

=
is the feedback voltage reference of the regulator
10k
V



is 0.596V. Since R
FB
SR
+
and C
0.596V
FB3
R
0.596V
V
V
FB4
FB2
FB
IN
FB3
SR
is derived from equation:
–
= 10k and R
in Figure 5 referenced to V

 • R

FB3
V
R
TRACK
FB3
FB4
SR
can be solved for when SR
FB3
is equal to R
• C
is equal to the 10k top
FB4
SR

 

= 6.65k in Figure 5.
FB2
with V
IN
. The
FB
FB3
=
For example: MR = 3.3V/ms and SR = 1.5V/ms. Then
R
For applications that do not require tracking or sequencing,
simply tie the TRACK pin to SV
turn on/off. Connecting TRACK to SV
~100µs of internal soft-start during start-up. Load current
needs to be present during track down.
Power Good
The PGOOD pin is an open-drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a ±10% window around the regulation point. As shown
in Figure 20, the sequencing function can be realized in a
dual output application by controlling the RUN pins and the
PGOOD signals from each other. The 1.5V output begins
its soft starting after the PGOOD signal of 3.3V output
becomes high, and 3.3V output starts its shut down after
the PGOOD signal of 1.5V output becomes low. This can
be applied to systems that require voltage sequencing
between the core and sub-power supplies.
FB3
= 22.1k. Solve for R
Figure 6. Output Voltage Coincident Tracking
FB4
TIME
to equal to 4.87k.
IN
MASTER OUTPUT
SLAVE OUTPUT
to let RUN control the
IN
4608A F06
also enables the
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