LTC3890EGN-1 LINER [Linear Technology], LTC3890EGN-1 Datasheet - Page 20

• Manufacturer Part Number: LTC3890EGN-1
• Description: 60V Low IQ, Dual, 2-Phase Synchronous Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LTC3890-1
Tracking and Soft-Start (TRACK/SS Pins)
The start-up of each V
the respective TRACK/SS pin. When the voltage on the
TRACK/SS pin is less than the internal 0.8V reference, the
LTC3890-1 regulates the V
the TRACK/SS pin instead of 0.8V. The TRACK/SS pin can
be used to program an external soft-start function or to
allow V
Soft-start is enabled by simply connecting a capacitor
from the TRACK/SS pin to ground, as shown in Figure 6.
An internal 1μA current source charges the capacitor,
providing a linear ramping voltage at the TRACK/SS pin.
The LTC3890-1 will regulate the V
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 7a and 7b. 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
APPLICATIONS INFORMATION
20
OUT
R
R
t
V
SS
Figure 6. Using the TRACK/SS Pin to Program Soft-Start
A
B
V
OUT
to rise smoothly from 0V to its fi nal regulated value.
X
= R
= R
= C
OUT
=
TRACKA
TRACKB
SS
to track another supply during start-up.
R
TRACKA
•
R
0.8V
1μA
A
OUT
•
will track V
OUT
C
R
SS
TRACKA
OUT
FB
TRACK/SS
SGND
is controlled by the voltage on
1/2 LTC3890-1
pin voltage to the voltage on
R
OUT
= V
A
+
+
), as shown in Figure 8.
FB
38901 F06
X
X
R
R
according to the ratio
during start-up):
pin (and hence V
B
TRACKB
X
) to the TRACK/
OUT
)
INTV
The LTC3890-1 features two separate internal P-channel
low dropout linear regulators (LDO) that supply power
at the INTV
EXTV
pin. INTV
LTC3890-1’s internal circuitry. The V
Figure 7. Two Different Modes of Output Voltage Tracking
CC
CC
Regulators
Figure 8. Using the TRACK/SS Pin for Tracking
pin depending on the connection of the EXTV
CC
CC
powers the gate drivers and much of the
pin from either the V
R
R
TRACKB
TRACKA
(7b) Ratiometric Tracking
(7a) Coincident Tracking
V
x
V
TIME
TIME
OUT
R
R
B
A
1/2 LTC3890-1
V
TRACK/SS
FB
IN
38901 F07b
38901 F07a
IN
LDO and the EXTV
38901 F08
supply pin or the
V
V
V
V
X(MASTER)
OUT(SLAVE)
X(MASTER)
OUT(SLAVE)
38901f
CC
CC