LTC3890EGN-1#PBF Linear Technology, LTC3890EGN-1#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC3890EGN-1#PBF
• Description: IC BUCK SYNC ADJ 25A DUAL 28SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3890EGN-1#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 24 V
• Current - Output: 25A
• Frequency - Switching: 50kHz ~ 900kHz
• Voltage - Input: 4 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Primary Input Voltage: 12V
• No. Of Outputs: 2
• Output Voltage: 24V
• Output Current: 25A
• No. Of Pins: 32
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Supply Voltage Min: 4V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

LTC3890
The following list summarizes the four possible connec-
tions for EXTV
1. EXTV
2. EXTV
3. EXTV
4. EXTV
Topside MOSFET Driver Supply (C
External bootstrap capacitors, C
pins supply the gate drive voltages for the topside MOSFETs.
Capacitor C
external diode D
When one of the topside MOSFETs is to be turned on, the
driver places the C
APPLICATIONS INFORMATION
22
from the internal 5.1V regulator resulting in an efficiency
penalty of up to 10% at high input voltages.
connection for a 5V to 14V regulator and provides the
highest efficiency.
supply is available in the 5V to 14V range, it may be
used to power EXTV
MOSFET gate drive requirements. Ensure that EXTV
< V
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. This can be done with the capacitive charge
pump shown in Figure 9. Ensure that EXTV
IN
EXTV
.
CC
CC
CC
CC
1/2 LTC3890
Figure 9. Capacitive Charge Pump for EXTV
Grounded. This will cause INTV
Connected to an Output-Derived Boost Network.
CC
Connected Directly to V
Connected to an External Supply. If an external
B
in the Functional Diagram is charged though
PGND
CC
TG1
BG1
SW
V
C
IN
:
B
IN
B
MTOP
MBOT
from INTV
voltage across the gate-source of the
CC
providing it is compatible with the
BAT85
CC
B
L
when the SW pin is low.
, connected to the BOOST
OUT
NDS7002
B
R
, D
SENSE
. This is the normal
B
CC
)
3890 F09
to be powered
CC
CC
BAT85
BAT85
C
V
OUT
OUT
CC
< V
to an
IN
.
CC
desired MOSFET. This enhances the top MOSFET switch
and turns it on. The switch node voltage, SW, rises to V
and the BOOST pin follows. With the topside MOSFET
on, the boost voltage is above the input supply: V
V
to be 100 times that of the total input capacitance of the
topside MOSFET(s). The reverse breakdown of the external
Schottky diode must be greater than V
The external diode D
diode, but in either case it should have low-leakage and
fast recovery. Pay close attention to the reverse leakage
current specification for this diode, especially at high
temperatures where it generally increases substantially.
For applications with output voltages greater than ~5V
that are switching infrequently, a leaky diode D
discharge the bootstrap capacitor C
path from the output voltage to the BOOST pin to INTV
Not only does this increase the quiescent current of the
converter, but it can cause INTV
levels if the leakage exceeds the current consumption on
INTV
Particularly, this is a concern in Burst Mode operation at
no load or very light loads, where the part is switching
very infrequently and the current draw on INTV
low (typically about 35μA). Generally, pulse-skipping and
forced continuous modes are less sensitive to leakage,
since the more frequent switching keeps the bootstrap
capacitor C
output voltage to INTV
However, in cases where the converter has been operat-
ing (in any mode) and then is shut down, if the leakage
of diode D
before the output voltage discharges to below ~5V, then
the leakage current path can be created from the output
voltage to INTV
sink about 30μA. To accommodate diode leakage greater
than this amount in shutdown, INTV
with an external resistor or clamped with a Zener diode.
Alternatively, the PGOOD resistor can be used to sink the
current (assuming the resistor pulls up to INTV
PGOOD is pulled low when the converter is shut down.
Nonetheless, using a low-leakage diode is the best choice
to maintain low quiescent current under all conditions.
IN
+ V
CC
INTVCC
.
B
B
fully discharges the bootstrap capacitor C
charged, preventing a current path from the
. The value of the boost capacitor, C
CC
. In shutdown, the INTV
B
can be a Schottky diode or silicon
CC
.
CC
to rise to dangerous
B
, creating a current
CC
IN(MAX)
CC
can be loaded
pin is able to
.
B
CC
CC
can fully
B
BOOST
, needs
) since
is very
3890fa
CC
IN
=
B
.