LTC3865EFE#TRPBF Linear Technology, LTC3865EFE#TRPBF Datasheet - Page 21

• Manufacturer Part Number: LTC3865EFE#TRPBF
• Description: IC BUCK SYNC ADJ DUAL 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3865EFE#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

APPLICATIONS INFORMATION
When the master channel’s output experiences dynamic
excursion (under load transient, for example), the slave
channel output will be affected as well. For better output
regulation, use the coincident tracking mode instead of
ratiometric.
INTV
The LTC3865 features a true PMOS LDO that supplies
power to INTV
gate drivers and much of the LTC3865/LTC3865-1’s internal
circuitry. The linear regulator regulates the voltage at the
INTV
connects to INTV
supply the needed power when its voltage is higher than
4.7V. Each of these can supply a peak current of 80mA
and must be bypassed to ground with a minimum of 4.7μF
ceramic capacitor or low ESR electrolytic capacitor. No mat-
ter what type of bulk capacitor is used, an additional 0.1μF
ceramic capacitor placed directly adjacent to the INTV
and PGND pins is highly recommended. Good bypassing
is needed to supply the high transient currents required
by the MOSFET gate drivers and to prevent interaction
between channels.
High input voltage applications in which large MOSFETs are
being driven at high frequencies may cause the maximum
junction temperature rating for the LTC3865/LTC3865-1
to be exceeded. The INTV
by the gate charge current, may be supplied by either the
5V linear regulator or EXTV
EXTV
Power dissipation for the IC in this case is highest and is
equal to V
dent on operating frequency as discussed in the Effi ciency
Considerations section. The junction temperature can be
estimated by using the equations given in Note 3 of the
Electrical Characteristics. For example, the LTC3865 INTV
current is limited to less than 42mA from a 38V supply in
the UH package and not using the EXTV
To prevent the maximum junction temperature from being
exceeded, the input supply current must be checked while
operating in continuous conduction mode (MODE/PLLIN
= SGND) at maximum V
T
J
CC
CC
CC
= 70°C + (42mA)(38V)(34°C/W) = 125°C
Regulators and EXTV
pin to 5V when V
pin is less than 4.7V, the linear regulator is enabled.
IN
• I
CC
INTVCC
CC
from the V
through a P-channel MOSFET and can
. The gate charge current is depen-
IN
IN
CC
. When the voltage applied to
IN
CC
is greater than 5.5V. EXTV
current, which is dominated
CC
supply. INTV
. When the voltage on the
CC
CC
supply:
powers the
CC
CC
CC
EXTV
turned off and the EXTV
The EXTV
EXTV
MOSFET driver and control power to be derived from one
of the LTC3865/LTC3865-1’s switching regulator outputs
during normal operation and from the INTV
output is out of regulation (e.g., start-up, short-circuit). If
more current is required through the EXTV
fi ed, an external Schottky diode can be added between the
EXTV
the EXTV
Signifi cant effi ciency and thermal gains can be realized by
powering INTV
resulting from the driver and control currents will be scaled
by a factor of (Duty Cycle)/(Switcher Effi ciency).
Tying the EXTV
temperature in the previous example from 125°C to:
However, for 3.3V and other low voltage outputs, addi-
tional circuitry is required to derive INTV
the output.
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
2. EXTV
3. EXTV
4. EXTV
T
to be powered from the internal 5V regulator result-
ing in an effi ciency penalty of up to 10% at high input
voltages.
connection for a 5V regulator and provides the highest
effi ciency.
supply is available, it may be used to power EXTV
providing it is compatible with the MOSFET gate drive
requirements.
For 3.3V and other low voltage regulators, effi ciency
gains can still be realized by connecting EXTV
output-derived voltage that has been boosted to greater
than 4.7V.
J
CC
CC
CC
= 70°C + (42mA)(5V)(34°C/W) = 77°C
remains above 4.5V. Using the EXTV
and INTV
rises above 4.7V, the INTV
CC
CC
CC
CC
CC
CC
connected to an external supply. If a 5V external
connected to an output-derived boost network.
left open (or grounded). This will cause INTV
connected directly to V
pin and make sure that EXTV
remains on as long as the voltage applied to
CC
CC
CC
LTC3865/LTC3865-1
:
CC
pin to a 5V supply reduces the junction
from the output, since the V
pins. Do not apply more than 6V to
CC
is connected to the INTV
OUT
CC
. This is the normal
linear regulator is
CC
CC
CC
than is speci-
CC
< V
CC
power from
allows the
IN
when the
IN
CC
.
21
current
to an
3865fb
CC
CC
CC
.