LTC3834 Linear Technology, LTC3834 Datasheet - Page 16

• Manufacturer Part Number: LTC3834
• Description: Synchronous Step-Down Controller
• Manufacturer: Linear Technology

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LTC3834
Tracking and Soft-Start (TRACK/SS Pin)
The start-up of V
TRACK/SS pin. When the voltage on the TRACK/SS pin is
less than the internal 0.8V reference, the LTC3834 regulates
the V
instead of 0.8V. The TRACK/SS pin can be used to program
an external soft-start function or to allow V
another supply during start-up.
Soft-start is enabled by simply connecting a capacitor
from the TRACK/SS pin to ground, as shown in Figure 3.
An internal 1μA current source charges up the capacitor,
providing a linear ramping voltage at the TRACK/SS pin.
The LTC3834 will regulate the V
APPLICATIONS INFORMATION
16
Figure 3. Using the TRACK/SS Pin to Program Soft-Start
FB
pin voltage to the voltage on the TRACK/SS pin
OUT
(4a) Coincident Tracking
is controlled by the voltage on the
C
SS
TIME
TRACK/SS
SGND
LTC3834
FB
3834 F03
Figure 4. Two Different Modes of Output Voltage Tracking
pin (and hence V
Figure 5. Using the TRACK/SS Pin for Tracking
3834 F04A
V
V
X
OUT
OUT
(MASTER)
(SLAVE)
V
x
to “track”
R
R
TRACKB
TRACKA
OUT
V
OUT
)
RB
RA
according to the voltage on the TRACK/SS pin, allowing
V
The total soft-start time will be approximately:
Alternatively, the TRACK/SS pin can be used to track two
(or more) supplies during start-up, as shown qualitatively
in Figures 4a and 4b. To do this, a resistor divider should
be connected from the master supply (V
SS pin of the slave supply (V
During start-up V
set by the resistor divider:
For coincident tracking (V
V
TRACK/SS
OUT
FB
R
R
LTC3834
t
V
SS
A
B
V
OUT
to rise smoothly from 0V to its fi nal regulated value.
X
= R
= R
=
3834 F05
C
=
TRACKA
TRACKB
SS
R
TRACKA
•
(4b) Ratiometric Tracking
R
. 0 8
1
A
μA
OUT
V
•
TIME
will track V
R
TRACKA
OUT
R
OUT
A
= V
+
+
), as shown in Figure 5.
X
R
R
X
according to the ratio
3834 F04B
B
TRACKB
during start-up),
V
V
X
OUT
(MASTER)
X
(SLAVE)
) to the TRACK/
3834fb