LTC3419 datasheet(13/16 Pages) LINER

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LTC3419

3419f

APPLICATIONS INFORMATION

Figure 2. LTC3419 Layout Diagram (See Board Layout Checklist)

Figure 3. LTC3419 Suggested Layout

VIN

RUN2

RUN1

LTC3419

VFB2

SW2

SW1

VFB1

CF2

CF1

GND

VIN

2.5V TO 5.5V

VOUT2

VOUT1

3419 F02

COUT2

COUT1

BOLD LINES INDICATE HIGH CURRENT PATHS

MODE

3419 F03

CIN

COUT1

COUT2

VOUT2

VOUT1

GND

CF1

CF2

VFB1

RUN1

MODE

SW1

VFB2

RUN2

SW2

VIN

VIA TO GND

VIA TO VIN

Design Example

As a design example, consider using the LTC3419 in a

portable application with a Li-Ion battery. The battery

provides a VIN ranging from 2.8V to 4.2V. The load on

each channel requires a maximum of 600mA in active

mode and 2mA in standby mode. The output voltages are

VOUT1 = 2.5V and VOUT2 = 1.8V.

Start with channel 1. First, calculate the inductor value

for about 40% ripple current (240mA in this example) at

maximum VIN. Using a derivation of Equation 1:

MHz

2 25

240

=−

⎛

⎝⎜

⎞

⎠⎟

.• (

)

•

μH

For the inductor, use the closest standard value of

2.2μH.

A 10μF ceramic capacitor should be more than sufﬁcient

for this output capacitor. As for the input capacitor, a

typical value of CIN = 10μF should sufﬁce, as the source

impedance of a Li-Ion battery is very low.

The feedback resistors program the output voltage. To

maintain high efﬁciency at light loads, the current in these

resistors should be kept small. Choosing 10μA with the

0.6V feedback voltage makes R1~60k. A close standard

1% resistor is 59k. Using Equation 2.

OUT

1 187

=−

⎛

⎝⎜

⎞

⎠⎟

•

An optional 22pF feedback capacitor (CF1) may be used

to improve transient response.

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