Datasheet

LTC3829
29
3829fa
For more information www.linear.com/LTC3829
4. EXTV
CC
connected to an output-derived boost network.
For 3.3V and other low voltage regulators, efficiency
gains can still be realized by connecting EXTV
CC
to an
output-derived voltage that has been boosted to greater
than 4.7V.
For applications where the main input power is 5V, tie
the V
IN
and INTV
CC
pins together and tie the combined
pins 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
CC
linear
regulator and will prevent INTV
CC
from dropping too low
due to the dropout voltage. Make sure the INTV
CC
voltage
is at or exceeds the R
DS(ON)
test voltage for the MOSFET
which is typically 4.5V for logic-level devices
Topside MOSFET Driver Supply (C
B
, D
B
)
External bootstrap capacitors, C
B
, connected to the BOOST
pins supply the gate drive voltages for the topside MOSFETs.
Capacitor C
B
in the Functional Diagram is charged though
external diode D
B
from INTV
CC
when the SW pin is low.
When one of the topside MOSFETs is to be turned on, the
driver places the C
B
voltage across 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
IN
and the BOOST pin follows. With the topside MOSFET
on, the boost voltage is above the input supply:
V
BOOST
= V
IN
+ V
INTVCC
The value of the boost capacitor, C
B
, needs 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
IN(MAX)
. When adjusting the gate
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.
Setting Output Voltage
The LTC3829 output voltage is set by an external feed-
back resistive divider carefully placed across the output,
as shown in Figure 14. The regulated output voltage is
determined by:
V
OUT
= 0.6V • 1+
R
B
R
A






To improve the frequency response, a feedforward ca-
pacitor, C
FF
, may be used. Great care should be taken to
route the V
FB
line away from noise sources, such as the
inductor or the SW line.
If diffamp is used, then the resistor, R
B
, should connect
to the output of the diffamp, DIFFOUT.
APPLICATIONS INFORMATION
R
VIN
1Ω
C
IN
3829 F13
5V
C
INTVCC
4.7µF
+
INTV
CC
LTC3829
V
IN
Figure 13. Setup for a 5V Input
Figure 14. Setting Output Voltage
LTC3829
V
FB
V
OUT
R
B
C
FF
R
A
3829 F14