Datasheet

10
LTC1433/LTC1434
APPLICATIONS INFORMATION
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Efficiency Considerations
Since there are two separate pins for the drain of the small
and large P-channel switch, we could utilize two induc-
tors to further enhance the efficiency of the regulator over
the low load current range. Figure 4 shows the circuit
connection.(Also refer to the Typical Applications sec-
tion.)
Figure 4. Using Two Inductors for Higher Low Current Efficiency
BSW
SSW
D1
D2
1433/34 F04
L2
L1
LTC1433/
LTC1434
To reduce core losses, the user can use a higher value
inductor on the small P-channel switch. Since this switch
only carries a small part of the overall current, the user can
still use a small physical size inductor without sacrificing
on copper losses. The Schottky diode can also be chosen
with a lower current rating. For the graph in Figure 5, a
Coilcraft DT1608C series inductor is used along with a
MBRS0520LT3 Schottky diode on the SSW pin. As can be
seen from Figure 5, the average efficiency gain over the
region where the small P-channel is on is about 3%.
LOAD CURRENT (A)
0.001
60
EFFICIENCY (%)
70
80
0.01 0.1 1
1433/34 • F05
50
40
100
90
V
IN
= 5V
V
IN
= 9V
ONE 22µH INDUCTOR
ON SSW AND BSW
100µH ON SSW
22µH ON BSW
V
OUT
= 3.3V
C
OSC
= 47pF
Figure 5. Efficiency Comparison Between Single Inductor
and Dual Inductor
Hence, the dual inductor configuration is good for the user
who requires as high an efficiency as possible at low load
while retaining constant frequency operation.
Output Voltage Programming
The LTC1433/LTC1434 family all have pin selectable out-
put voltage programming. The output voltage is selected
by the V
PROG
pin as follows:
V
PROG
= 0V V
OUT
= 3.3V
V
PROG =
V
IN
V
OUT
= 5V
V
PROG
= Open (DC) V
OUT
= Adjustable
The LTC1433/LTC1434 family also has remote output
voltage sense capability. The top of the internal resistive
divider is internally connected to V
OSENSE
. For fixed output
voltage applications, the V
OSENSE
pin is connected to the
output voltage as shown in Figure 6. When using an
external resistive divider, the V
PROG
pin is left open DC and
the V
OSENSE
pin is connected to the feedback resistors as
shown in Figure 7. To prevent stray pickup, a 100pF
capacitor is suggested across R1 located close to the
LTC1433/LTC1434.
R1
R2
OPEN (DC)
1433/34 F07
100pF
V
OUT
V
PROG

SGND
LTC1433/
LTC1434
V
OSENSE
V
OUT
= 1.19V 1 +
R2
R1
()
Figure 7. LTC1433/LTC1434 Adjustable Applications
V
PROG

SGND
LTC1433/
LTC1434
1433/34 F06
C
OUT
V
OUT
GND: V
OUT
= 3.3V
V
IN
: V
OUT
= 5V
+
V
OSENSE
Figure 6. LTC1433/LTC1434 Fixed Output Applications