AS1324 datasheet(15/21 Pages) AMSCO

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AS1324

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

9.9 Design Example

Figure 28 shows the AS1324 used in a single lithium-ion (3.7V typ) battery-powered mobile phone application. The load current requirement is

600mA (max) but most of the time the device will require only 2mA (standby mode current).

Figure 28. Design Example

For the circuit shown in Figure 28, efficiency at low- and high-load currents is an important consideration when selecting the value for the

external inductor, which is calculated as:

From (EQ 14), substituting VOUT = 2.2V, VIN = 3.7V,

∆IL = 240mA and f = 1.5MHz gives:

Therefore, a standard 2.2µH inductor should be used for this design.

For best overall efficiency use an inductor with a rating of 720mA or greater and less than 0.2

Ω series resistance. CIN will require an RMS

current rating of at least 0.3A

≅ ILOAD(MAX)/2, whereas COUT will require an ESR of less than 0.25Ω. In most cases, a ceramic capacitor will

satisfy this requirement.

For the feedback resistors, select the value for R1 = 375k

Ω. R2 can then be calculated from (EQ 7) to be:

R2 = (VOUT/0.6 - 1)375k = 1000k

Ω

COUT

10µF

CER

CIN

4.7µF

CER

VIN

3.7V

VOUT

2.2V

2.2µH

375k

Ω

22pF

Ω

AS1324

VIN

VFB

GND

(EQ 14)

OUT

∆I

--------------

OUT

--------------

–









(EQ 15)

2,2V

1,5MHz

240mA

(

)

----------------------------------------------------

2,2V

3 7V

------------

–









2,48

µH

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