LTC1430 LINER [Linear Technology], LTC1430 Datasheet - Page 7

• Manufacturer Part Number: LTC1430
• Description: High Power Step-Down Switching Regulator Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
MOSFET Gate Drive
Gate drive for the top N-channel MOSFET M1 is supplied
from PV
power supply input) by at least one power MOSFET
V
allows PV
up to 13V maximum. This higher voltage can be supplied
with a separate supply, or it can be generated using a
simple charge pump as shown in Figure 4. When using a
separate PV
inrush current if PV
90% maximum duty cycle ensures that the charge pump
will always provide sufficient gate drive to M1. Gate drive
for the bottom MOSFET M2 is provided through PV
16-lead devices or V
can usually be driven directly from PV
parts, although it can also be charge pumped or connected
to an alternate supply if desired. The 8-lead parts require
an RC filter from PV
Input Supply Considerations.
EXTERNAL COMPONENT SELECTION
Power MOSFETs
Two N-channel power MOSFETs are required for most
LTC1430 circuits. These should be selected based prima-
rily on threshold and on-resistance considerations; ther-
mal dissipation is often a secondary concern in high
USE FOR PV
GS(ON)
OPTIONAL
D
12V
1N5242
Z
CC1
CC
for efficient operation. An internal level shifter
CC1
. This supply must be above PV
CC1
7V
LTC1430
to operate at voltages above V
Figure 4. Doubling Charge Pump
supply, the PV
PV
CC2
U
CC1
CC
CC
PV
/PV
is present during power up. The
to ensure proper operation; see
CC1
U
CC2
G1
G2
CC
1N4148
for 8-lead devices. PV
0.1 F
input may exhibit a large
PV
W
CC
M1
M2
CC
L1
CC
CC
with 16-lead
+
( the main
and PV
U
CC2
C
LTC1430 • F04
OUT
V
CC2
OUT
CC
for
,
efficiency designs. Required MOSFET threshold should be
determined based on the available power supply voltages
and/or the complexity of the gate drive charge pump
scheme. In 5V input designs where an auxiliary 12V supply
is available to power PV
with R
good results. The current drawn from this supply varies
with the MOSFETs used and the LTC1430’s operating
frequency, but is generally less than 50mA.
LTC1430 designs that use a doubler charge pump to
generate gate drive for M1 and run from PV
below 7V cannot provide enough gate drive voltage to fully
enhance standard power MOSFETs. When run from 5V, a
doubler circuit may work with standard MOSFETs, but the
MOSFET R
the FETs and costing efficiency. Logic level FETs are a
better choice for 5V PV
enhanced with a doubler charge pump and will operate at
maximum efficiency. Doubler designs running from PV
voltages near 4V will begin to run into efficiency problems
even with logic level FETs; such designs should be built
with tripler charge pumps (see Figure 5) or with newer,
super low threshold MOSFETs. Note that doubler charge
pump designs running from more than 7V and all tripler
charge pump designs should include a zener clamp diode
D
absolute maximum rating at that pin.
Z
at PV
D
12V
1N5242
10 F
Z
DS(ON)
LTC1430
CC1
PV
ON
1N5817
CC2
specified at V
may be quite high, raising the dissipation in
to prevent transients from exceeding the
Figure 5. Tripling Charge Pump
PV
1N5817
CC1
G1
G2
CC1
CC
GS
and PV
0.1 F
systems; they can be fully
= 5V or 6V can be used with
1N5817
0.1 F
CC2
PV
, standard MOSFETs
CC
M1
M2
LTC1430
L1
CC
+
voltages
C
LTC1430 • F05
OUT
7
V
OUT
CC