LTC3856 LINER [Linear Technology], LTC3856 Datasheet - Page 27

• Manufacturer Part Number: LTC3856
• Description: 2-Phase Synchronous Step-Down DC/DC Controller with Diffamp
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
is needed to supply the high transient currents required
by the MOSFET gate drivers and to prevent interaction
between the channels.
High input voltage applications in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3856 to be
exceeded. The INTV
gate charge current, may be supplied by either the 5V LDO
or EXTV
than 4.7V, the LDO is enabled. Power dissipation for the
IC in this case is highest and is equal to V
gate charge current is dependent on operating frequency
as discussed in the Efficiency Considerations section.
The junction temperature can be estimated by using the
equations given in Note 3 of the Electrical Characteristics
CC
. When the voltage on the EXTV
TK/SS2
V
OUT1
PIN
(11a) Coincident Tracking
CC
TO
(12a) Coincident Tracking Set-Up
current, which is dominated by the
TIME
R3
R4
R1
R2
Figure 12. Set-Up and Coincident and Ratiometric Tracking
Figure 11. Two Different Modes of Output Voltage Tracking
TO
V
PIN
FB1
3856 F11a
V
IN
PIN
V
V
FB2
TO
OUT1
OUT2
CC
• I
INTVCC
pin is less
R3
R4
. The
V
OUT2
table. For example, the LTC3856 INTV
to less than 42mA from a 38V supply in the UH package
and not using the EXTV
To prevent the maximum junction temperature from be-
ing exceeded, the input supply current must be checked
while operating in continuous conduction mode (MODE
= SGND) at maximum V
EXTV
and the EXTV
remains on as long as the voltage applied to EXTV
above 4.5V. Using the EXTV
and control power to be derived from one of switching
regulator outputs during normal operation and from the
INTV
T
V
TK/SS2
J
OUT1
CC
(12b) Ratiometric Tracking Set-Up
CC
= 70°C + (42mA)(38V)(34°C/W) = 125°C
PIN
TO
when the output is out of regulation (e.g., start-up,
rises above 4.7V, the INTV
R1
R2
CC
TO
V
PIN
is connected to the INTV
FB1
(11b) Ratiometric Tracking
V
PIN
FB2
TO
CC
IN
TIME
supply:
. When the voltage applied to
CC
R3
R4
allows the MOSFET driver
3856 F12
V
OUT2
CC
CC
LDO is turned off
LTC3856
3856 F11b
current is limited
CC
V
V
OUT1
OUT2
. The EXTV
CC
remains

3856f
CC