LTC3856IFE#TRPBF Linear Technology, LTC3856IFE#TRPBF Datasheet - Page 28

• Manufacturer Part Number: LTC3856IFE#TRPBF
• Description: IC REG CTLR 2CHAN SYNC 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3856IFE#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 125°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: -

LTC3856
applicaTions inForMaTion
short circuit). If more current is required through the
EXTV
be added between the EXTV
apply more than 6V to the EXTV
EXTV
Significant efficiency and thermal gains can be realized
by powering INTV
rent resulting from the driver and control currents will be
scaled by a factor of (duty cycle)/(switcher efficiency).
Tying the EXTV
temperature in the previous example from 125°C to:
However, for low voltage outputs, additional circuitry is
required to derive INTV
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 LDO resulting
in an efficiency penalty of up to 10% at high input
voltages.
connection for a 5V regulator and provides the highest
efficiency.
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, efficiency
gains can still be realized by connecting EXTV
output-derived voltage that has been boosted to greater
than 4.7V.
J
CC
CC
= 70°C + (42mA)(5V)(34°C/W) = 77°C
CC
CC
CC
than is specified, an external Schottky diode can
CC
< V
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
IN
.
CC
CC
:
pin to a 5V supply reduces the junction
CC
from the output, since the V
CC
power from the output.
CC
CC
and INTV
OUT
pin and make sure that
. This is the normal
CC
pins. Do not
LTC3856
Figure 13. Set-Up for a 5V Input
CC
INTV
IN
V
to an
CC
IN
cur-
CC
CC
C
4.7µF
INTVCC
For applications where the main input power is 5V, tie the
V
to the 5V input with a 1Ω or 2.2Ω resistor (as shown in
Figure 13) to minimize the voltage drop caused by the
gate charge current. This will override the INTV
regulator and will prevent INTV
due to the dropout voltage. Make sure the INTV
is at or exceeds the R
which is typically 4.5V for logic-level devices.
Topside MOSFET Driver Supply (C
External bootstrap capacitors, C
BOOST pins supply the gate drive voltages for the top-
side MOSFETs. Capacitor C
is charged though external diode D
the SW pin is low. When one of the topside MOSFETs is
to be turned on, the driver places the C
the gate source of the desired MOSFET. This enhances
the MOSFET and turns on the topside switch. The switch
node voltage, SW, rises to V
With the topside MOSFET on, the boost voltage is above
the input supply:
The value of the boost capacitor, C
that of the total input capacitance of the topside MOSFET(s).
The reverse breakdown of the external Schottky diode
must be greater than V
drive level, the final arbiter is the total input current for
the regulator. If a change is made and the input current
decreases, then the efficiency has improved. If there is
no change in input current, then there is no change in
efficiency.
IN
V
and INTV
BOOST
R
1Ω
VIN
+
= V
3856 F13
C
CC
5V
IN
IN
pins together and tie the combined pins
+ V
INTVCC
DS(ON)
IN(MAX)
IN
B
test voltage for the MOSFET,
and the BOOST pin follows.
in the Functional Diagram
. When adjusting the gate
CC
B
from dropping too low
, needs to be 100 times
B
B
B
, connected to the
, D
from INTV
B
B
)
voltage across
CC
CC
CC
voltage
linear
when
3856f