LTC3126 datasheet(13/30 Pages) LINER

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LTC3126

3126f

For more information www.linear.com/LTC3126

Quick reFerence

LTC3126

RBOT

3126 F01

RTOP

RFF

CFF

VOUT

GND

Figure 1. FB Resistor Divider

Table 2. Recommended Minimum Inductor Values

fSW = 750kHz

VOUT

MINIMUM INDUCTOR VALUE

12V

8.0µH

3.3µH

3.3V

2.2µH

1.8V

1.2µH

fSW = 1MHz

VOUT

MINIMUM INDUCTOR VALUE

12V

6.0µH

2.5µH

3.3V

1.8µH

1.8V

1.0µH

fSW = 2MHz

VOUT

MINIMUM INDUCTOR VALUE

12V

3.3µH

1.5µH

3.3V

1.0µH

1.8V

1.0µH

The peak-to-peak inductor ripple, ΔIL, is given by the fol-

lowing equation.

∆IL =

VOUT

fSW •L

1–

VOUT

VIN









Output Capacitor

The recommended minimum output capacitor, CMIN, is

given below as a function of output voltage:

CMIN =

VOUT

150µF

Table 3. Minimum Output Capacitor vs VOUT

VOUT

MINIMUM COUT

24V

10µF

12V

22µF

33µF

3.3V

47µF

1.8V

100µF

1.2V

150µF

Output Voltage

The buck converter output voltage is set via a resistor

divider connected to the FB pin as shown in Figure 1.

In most applications, choosing RTOP equal to 1MΩ rep-

resents a good trade-off between quiescent current and

robustness against PCB leakage. RBOT can be determined

by the following equation where VOUTisthedesiredoutput

voltage:

RBOT =

RTOP

VOUT

0.818V

–1









Inductor Value

If the buck converter will be operated at duty cycles greater

than 50% (i.e., VIN < 2VOUT) then the inductor value must

be equal or greater than LMIN as defined by the following

equation:

LMIN =

MHz

fSW

•

VOUT

µH

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