10

LTC1433/LTC1434

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

70

80

0.01

0.1

1

1433/34 • F05

50

40

100

90

ONE 22

µH INDUCTOR

ON SSW AND BSW

100

µH ON SSW

22

µH ON BSW

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

The LTC1433/LTC1434 family also has remote output

voltage sense capability. The top of the internal resistive

output voltage as shown in Figure 6. When using an

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

SGND

LTC1433/

LTC1434

R2

R1

()

Figure 7. LTC1433/LTC1434 Adjustable Applications

SGND

LTC1433/

LTC1434

1433/34 F06

+

Figure 6. LTC1433/LTC1434 Fixed Output Applications