LTC1929-PG LINER [Linear Technology], LTC1929-PG Datasheet - Page 16

• Manufacturer Part Number: LTC1929-PG
• Description: 2-Phase, High Efficiency,Synchronous Step-Down Switching Regulators
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC1929/LTC1929-PG
EXTV
The LTC1929 contains an internal P-channel MOSFET
switch connected between the EXTV
When the voltage applied to EXTV
internal regulator is turned off and the switch closes,
connecting the EXTV
supplying internal and MOSFET gate driving power. The
switch remains closed as long as the voltage applied to
EXTV
driver and control power to be derived from the output
during normal operation (4.7V < V
the internal regulator when the output is out of regulation
(start-up, short-circuit). Do not apply greater than 7V to
the EXTV
using the application circuits shown. If an external voltage
source is applied to the EXTV
not present, a diode can be placed in series with the
LTC1929’s V
EXTV
V
Significant efficiency gains can be realized by powering
INTV
from the driver and control currents will be scaled by the
ratio: (Duty Factor)/(Efficiency). For 5V regulators this
means connecting the EXTV
ever, for 3.3V and other lower voltage regulators, addi-
tional circuitry is required to derive INTV
output.
The following list summarizes the four possible connec-
tions for EXTV
16
IN
Figure 5a. Secondary Output Loop with EXTV
.
CC
CC
CC
CC
OPTIONAL EXTV
5V < V
EXTV
and the V
from the output, since the V
Connection
remains above 4.5V. This allows the MOSFET
CC
CC
SEC
LTC1929
pin and ensure that EXTV
< 7V
IN
CC:
pin and a Schottky diode between the
CC
IN
PGND
CONNECTION
pin, to prevent current from backfeeding
SW1
TG1
BG1
U
V
IN
CC
C
IN
N-CH
N-CH
pin to the INTV
U
+
CC
CC
pin directly to V
pin when the V
CC
1N4148
V
EXTVCC
IN
W
T1
rises above 4.7V, the
CC
CC
IN
< V
CC
and INTV
current resulting
< 7V) and from
CC
power from the
CC
IN
R
SENSE
Connection
V
+ 0.3V when
pin thereby
SEC
IN
OUT
+
+
U
supply is
CC
1929 F05a
. How-
1 F
C
V
OUT
OUT
pins.
1. EXTV
to be powered from the internal 5V regulator resulting in
a significant efficiency penalty at high input voltages.
2. EXTV
connection for a 5V regulator and provides the highest
efficiency.
3. EXTV
supply is available in the 5V to 7V range, it may be used to
power EXTV
gate drive requirements.
4. EXTV
For 3.3V and other low voltage regulators, efficiency gains
can still be realized by connecting EXTV
derived voltage which has been boosted to greater than
4.7V but less than 7V. This can be done with either the
inductive boost winding as shown in Figure 5a or the
capacitive charge pump shown in Figure 5b. The charge
pump has the advantage of simple magnetics.
Topside MOSFET Driver Supply (C
Functional Diagram)
External bootstrap capacitors C
the BOOST1 and BOOST2 pins supply the gate drive
voltages for the topside MOSFETs. Capacitor C
Functional Diagram is charged though diode D
INTV
turns on, the driver places the C
source of the desired MOSFET. This enhances the MOSFET
and turns on the topside switch. The switch node voltage,
CC
EXTV
when the SW pin is low. When the topside MOSFET
CC
CC
CC
CC
Figure 5b. Capacitive Charge Pump for EXTV
CC
left open (or grounded). This will cause INTV
connected to an output-derived boost network.
LTC1929
connected to an external supply. If an external
connected directly to V
CC
providing it is compatible with the MOSFET
PGND
SW1
BG1
TG1
V
IN
C
IN
N-CH
N-CH
+
B
B1
BAT85
voltage across the gate-
V
OUT
IN
and C
L1
B
,D
. This is the normal
VN2222LL
B
) (Refer to
0.22 F
CC
B2
R
SENSE
to an output-
connected to
+
+
CC
B
1929 F05b
BAT85
B
BAT85
C
V
in the
OUT
OUT
from
CC