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LTC3405

3405fa

APPLICATIO S I FOR ATIO

Figure 11a

Figure 11b

VIN

CIN

†

2.2µF

CER

VIN

2.7V

TO 4.2V

LTC3405

RUN

MODE

6.8µH*

22pF

887k

412k

3405 F11a

VFB

GND

COUT**

33µF

TANT

VOUT

2.5V

* SUMIDA CMD4D11-6R8MC

** AVX TPSB336K006R0600

† TAIYO YUDEN LMK212BJ225MG

TYPICAL APPLICATIO S

4.7µH*

22pF

200k

COUT

†

4.7µF

CER

332k

VIN

CIN**

1µF

CER

†

MURATA LQH3C4R7M34

TAIYO YUDEN CERAMIC JMK107BJ105MA

TAIYO YUDEN CERAMIC JMK212BJ475MG

VIN

2.7V

TO 4.2V

LTC3405

RUN

MODE

3405 TA01a

VFB

GND

VOUT

1.8V

Single Li-Ion to 1.8V/300mA Regulator

Optimized for Small Footprint and High Efficiency

Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 100mA and

f = 1.5MHz in equation (3) gives:

MHz

−

⎛

⎝

⎜

⎞

⎠

⎟ ≅

1 5

100

)

For best efficiency choose a 300mA or greater inductor

with less than 0.3Ω series resistance.

CIN will require an RMS current rating of at least 0.125A ≅

ILOAD(MAX)/2 at temperature and COUT will require an ESR

of less than 0.6Ω and greater than 0.1Ω. In most cases,

a tantalum capacitor will satisfy this requirement.

OUTPUT CURRENT (mA)

0.1

1000

100

3405 F11b

100

VIN = 2.7V

VIN = 4.2V

VIN = 3.6V

OUTPUT CURRENT (mA)

0.1

1000

100

3405 TA01b

100

VIN = 2.7V

VIN = 4.2V

VIN = 3.6V

3405 TA01c

40µs/DIV

VIN = 3.6V

ILOAD = 100mA TO 250mA

VOUT

100mV/DIV

AC COUPLED

ILOAD

200mA/DIV

For the feedback resistors, choose R1 = 412k. R2 can

then be calculated from equation (2) to be:

k use

OUT

1 1 875 5

−

⎛

⎝

⎜

⎞

⎠

⎟

. ;

87k

Figure 11 shows the complete circuit along with its

efficiency curve.

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